Proceedings of ACCUSIM Summer School Conference · ACCUSIM Summer School Conference thLjubljana, 25...

Accurate Simulations in Hydro-Machinery

and Marine Propellers

Proceedings

of ACCUSIM Summer School Conference

25th – 27

th September 2017

Kolektor Turboinštitut, Rovšnikova 7, Ljubljana

Proceedings of

ACCUSIM Summer School Conference

Accurate Simulations in Hydro-Machinery and Marine Propellers

Published by:

Kolektor Turboinštitut, d. o. o.

Rovšnikova 7, 1210 Ljubljana, Slovenia

www.kolektorturboinstitut.com

Editors:

Dragica Jošt

Aljaž Škerlavaj

Kolektor Turboinštitut, d. o. o.

Rovšnikova 7, 1210 Ljubljana, Slovenia

[email protected]

[email protected]

Published:

Ljubljana, 2017

Internal publisher classification

No. 3189

Number of copies: 55

__________________________________________________________________________________

CIP - Kataložni zapis o publikaciji

Narodna in univerzitetna knjižnica, Ljubljana

004.94:532.5:621.224(082)

ACCUSIM Summer School Conference (2017 ; Ljubljana)

Accurate simulations in hydro-machinery and marine propellers : proceedings of ACCUSIM

Summer School Conference 25th - 27th September 2017, Ljubljana / [editors Dragica Jošt, Aljaž

Škerlavaj]. - Ljubljana : Kolektor Turboinštitut, 2017

ISBN 978-961-285-877-3

1. Gl. stv. nasl. 2. Jošt, Dragica

291795200

___________________________________________________________________________

http://www.kolektorturboinstitut.com/

mailto:[email protected]


Dragica Jošt

Aljaž Škerlavaj (Eds.)

Accurate Simulations in Hydro-Machinery

and Marine Propellers

Proceedings of

ACCUSIM Summer School Conference

25th – 27

th September 2017

Kolektor Turboinštitut, Ljubljana

ACCUSIM Summer School Conference Ljubljana, 25th – 27th September 2017

2

Contents

ACCUSIM Project

5

Kolektor Turboinštitut

5

Enrico Nobile

A brief overview of research activities at Fisica Tecnica (Thermal Fluids) at the Dept. of

Architecture and Engineering of the University of Trieste

6

Jure Ravnik

Turbulence modelling

8

Dragica Jošt

Improvement of efficiency prediction for axial water turbines with advanced turbulence

models

9

Aljaž Škerlavaj

Numerical simulation of flow in a high head Francis turbine with prediction of

efficiency, rotor stator interaction and vortex structures in the draft tube

11

Maja Ondračka

OpenFOAM in turbomachinery

12

Dragica Jošt

Comparison of results obtained with OpenFOAM and Ansys-CFX

14

Matevž Dular

Advanced experimental and numerical techniques for cavitation erosion prediction

15

Mitja Morgut

Calibration of mass transfer models for the numerical prediction of sheet cavitation

around a hydrofoil

16

Dragica Jošt

Cavitation prediction for water turbines

17

Mitja Morgut

Numerical predictions of the cavitating flow around model scale propellers working in

uniform and non-uniform inflow

19

Aljaž Škerlavaj

Sheet and cloud cavitation prediction in double suction centrifugal pump

20

Dragica Jošt

Simulation of cavitating vortex rope in the draft tube of a Francis turbine

22

Carlo Poloni

No-free lunch theorem from an engineering perspective

23

Aljaž Škerlavaj

Optimization of a double-sided centrifugal pump

24

Roberto Renato Stopar

Multi-objective optimization of the Francis turbine runner cone

26


3

Authors:

Prof. Enrico Nobile

Dept. of Engineering and Architecture

University of Trieste

[email protected]

Prof. Jure Ravnik

Faculty of Mechanical Engineering

University of Maribor

[email protected]

Maja Ondračka

Maja Ondračka s.p.

[email protected]

Prof. Matevž Dular


University of Ljubljana

[email protected]

Prof. Carlo Poloni

University of Trieste & ESTECO Spa

[email protected]

Dr. Mitja Morgut

Dept. of Engineering and Architecture


[email protected]

Dr. Dragica Jošt


[email protected]

Dr. Aljaž Škerlavaj


[email protected]

Renato Roberto Stopar


[email protected]


4

Kolektor Turboinštitut and Dept. of Engineering and Architecture of the University of Trieste are

pleased to share their knowledge and expertise, gained during the Marie-Curie European project

ACCUSIM, about the application of:


OpenFOAM

Cavitation

Design optimization.

For each of these topics the invited speakers will have introductory lectures, followed by the

presentations of the results achieved during the ACCUSIM project.

The research leading to the results presented in the following presentations has received funding

from the People Programme (Marie Curie Action) of the European Union’s Seventh Framework

Programme FPT/2007-2013/ under REA grant agreement n°612279:

Dragica Jošt, Improvement of efficiency prediction for axial water turbines with advanced

turbulence models,

Aljaž Škerlavaj, Numerical simulation of flow in a high head Francis turbine with prediction

of efficiency, rotor stator interaction and vortex structures in the draft tube,

Dragica Jošt, Comparison of results obtained with OpenFOAM and Ansys-CFX,

Mitja Morgut, Calibration of mass transfer models for the numerical prediction of sheet

cavitation around a hydrofoil,

Dragica Jošt, Cavitation prediction for water turbines,

Mitja Morgut, Numerical predictions of the cavitating flow around model scale propellers

working in uniform and non-uniform inflow,

Aljaž Škerlavaj, Sheet and cloud cavitation prediction in double suction centrifugal pump,

Dragica Jošt, Simulation of cavitating vortex rope in the draft tube of a Francis turbine,

Aljaž Škerlavaj, Optimization of a double-sided centrifugal pump,

Roberto Renato Stopar, Multi-objective optimization of the Francis turbine runner cone.

We would like to express special thanks to the invited lecturers. They were not included in the

ACCUSIM project, but they kindly agreed to contribute to the quality of the ACCUSIM Summer School

with the following presentations:

Jure Ravnik, Turbulence modelling,

Maja Ondračka, OpenFOAM in turbomachinery,

Matevž Dular, Advanced experimental and numerical techniques for cavitation erosion

prediction,

Carlo Poloni, No-free lunch theorem from an engineering perspective.

Organizing committee:

Dragica Jošt

Aljaž Škerlavaj


Mitja Morgut

Enrico Nobile


5

ACCUSIM Project

The design of hydro-machinery is typically based on qualitative, rather than quantitative, assessment of

numerical simulations, since the values of the numerically predicted characteristics are frequently far

from the measured ones.

Therefore, University of Trieste and Kolektor Turboinštitut joined in the ACCUSIM (Accurate

Simulations in Hydro-Machinery and Marine Propellers) project with the primary aim to develop

reliable, high fidelity methods for the accurate prediction, and optimisation, of the performance of

hydro-machinery and marine propellers. For this purpose, the participating partners shared their

knowledge, and worked collaboratively, in CFD (Computational Fluid Dynamics) and particularly in

SRS (Scale Resolving Simulations) for turbulent flows, modelling of cavitation, exploitation of HPC

and cloud computing, open source CFD tools, and optimisation.

The success of the proposed project was foreseen in the synergistic effects of highly complementary

expertise of two leading edge cross-sectoral European partners: the Applied Physics (Fisica Tecnica)

group of the University of Trieste, Italy, and Kolektor Turboinštitut, a Slovenian enterprise for hydro-

machinery design, for production of small hydro turbines, as well as an independent performer of on-

site and model acceptance tests for hydro machinery.

Approaching the end of the ACCUSIM project, the summer school is being organized to share the results,

obtained during the project, to general public, enterprises and scientific community. The school also

aims to familiarize the participants with CFD technologies and their specific application to the hydraulic

machine design.


Kolektor Turboinštitut is a company with nearly 70 years of tradition in research and development of

hydraulic machines. It is one of only two independent laboratories in the world for model testing of

water turbines and pumps capable to perform model acceptance tests in accordance with international

IEC standard 60193. The main activities of the company are: research and development of water turbines

and pumps, model and site testing and design, manufacturing and engineering of equipment for small

hydropower plants. On average more than 90% of income is realised on foreign markets.

Kolektor Turboinštitut has 30 years of experience in Computational Fluid Dynamics - CFD. It is one of

the internationally recognized industrial users of intensive computational methods for engineering and

research of water turbines and pumps. Following its research orientation Turboinštitut in 2008

established supercomputer center LSC Adria with for that time one of the most powerful computers in

the region. Numerical flow analysis is in Kolektor Turboinštitut indispensable tool in design process.

Prediction of energetic and cavitation characteristics is supported by experimental work. With the

ACCUSIM project Turboinštitut did a step forward in accuracy of numerical results.


6

A brief overview of research activities at Fisica Tecnica (Thermal

Fluids) at the Dept. of Architecture and Engineering of the


Enrico Nobile

[email protected]


Summary

In this presentation, after a brief overview of the University of Trieste and its Dipartimento di Ingegneria

e Architettura (Dept. of Engineering and Architecture), some recent and ongoing research activities

within the Fisica Tecnica (thermodynamics and thermal-fluids) group will be illustrated.

The selected topics are:

- Multiobjective optimization of heat exchangers.

As an example, a CFD-based shape optimization of a tube bundle in crossflow is presented,

where also the flow inside the tubes has been computed, and the coupled simulation of the

external flow and thermal field is performed on a periodic domain [1]. The results demonstrate

how the search for efficient geometric configurations should also take into account the internal

flow field.

- X-ray microtomography-based CFD characterization of flow permeability and effective thermal

conductivity of aluminum metal foams.

Metal foams are gaining attention in view of their potential for increasing the thermal efficiency

of heat transfer devices, while allowing the use of smaller and lighter equipment. The main

results of high-resolution X-ray microtomography-based CFD simulations, performed on open-

cell aluminum foams samples, will be illustrated [2, 3]. The computed values of permeability

and effective thermal conductivity are reported and compared to the corresponding experimental

values available in the literature. The following figure depicts the velocity contours inside a 30

PPI (Pore Per Inch) aluminum foam at three different sections.

- Development of advanced meshless methods for numerical simulation of fluid flow and heat transfer

problems.

When dealing with mesh-based simulations on complex bodies, the effort put in meshing can be

considerable, affecting both the time consumption and the accuracy of the simulation. Meshless

methods need only a distribution of nodes within the domain to discretize the field equations: this

is a clear advantage since the node generation process can be easier and more efficient than a

meshing process. The employed meshless method is based on local Radial Basis Functions (RBF)



7

interpolation and direct collocation [4, 5], which has been shown to be an effective and reliable

numerical approach. A novel node generation technique based on Quadtree/Octree and node

refinement have been proposed for 2D and 3D cases; an example of 3D node distribution

generated by this technique is reported for a test geometry, together with the corresponding

temperature distribution.

References

[1] P. Ranut, G. Janiga, E. Nobile, D. Thévenin, Multi-objective shape optimization of a tube bundle in cross-flow,

Int. J. Heat and Mass Transfer, 68 (2014) 585–598.

[2] P. Ranut, E. Nobile, L. Mancini, High resolution microtomography-based CFD simulation of flow and heat

transfer in aluminum metal foams, Applied Thermal Engineering, 69 (2014) 230-240.

[3] P. Ranut, E. Nobile, L. Mancini, High resolution X-ray microtomography-based CFD simulation for the

characterization of flow permeability and effective thermal conductivity of aluminum metal foams,

Experimental Thermal and Fluid Science, 67 (2015) 30–36.

[4] B. Šarler, R. Vertnik: Meshfree Explicit Local Radial Basis Function Collocation Method for Diffusion

Problems, Computers & Mathematics with Applications, 51(8) 1269-1282, (2006).

[5] R. Zamolo and E. Nobile, Numerical analysis of heat conduction problems on irregular domains by means of

a collocation meshless method, IOP Conf. Series: Journal of Physics: Conf. Series 796 (2017) 012006.


8


Jure Ravnik

Faculty of Mechanical Engineering, University of Maribor

Summary

In this lecture, we will discuss the different approaches to turbulence modelling. We will start by

describing the difference between a natural phenomenon and a mathematical-physical model. We will

highlight the important distinction and discuss how these differences must be taken into account in the

modelling process. We will explain the processes in turbulent flows, the variables and parameters. Based

on the Reynolds experiment and the description of the nature of turbulence, we will present the nonlinear

properties of fluid flows. Kolmogorov time and length scales will presented and an estimate for a

physically appropriate times step and grid resolution will be given. Wall bounded flows will be discusses

and properties boundary layers presented. An overview of numerical methods for the solution of partial

differential equations will be given. The importance of boundary and initial conditions will be described.

Numerical diffusion and dispersion with be discussed and explained. Our inability to avoid numerical

diffusion in second-order and first order CFD codes will be shown and the effect of this fact on direct

numerical and large eddy simulations will be given. Prandtl mixing length concept will be explained in

order to gain insight into basic ideas of turbulence modelling. Finally, direct numerical simulation, large

eddy simulation and Reynolds average turbulence modelling approached will be discussed.

Suggested reading, references:

[1] Stephen B. Pope: Turbulent flows, Cambridge university press, 2000

[2] P. Sagaut, Large Eddy Simulation for Incompressible Flows: An Introduction (Scientific

Computation), Springer, 2005

[3] J. H. Ferziger and M. Perič, Computational Methods for Fluid Dynamics, Springer, 2002


9

Improvement of efficiency prediction for axial water turbines with

advanced turbulence models

Dragica Jošt


Summary

A comparison between numerical results and measurements for a six-blade Kaplan turbine for middle

head and a three-blade bulb turbine for extremely low head was done in order to determine an

appropriate numerical setup for accurate and reliable simulations of flow in axial turbines. Values of

discharge, torque and losses obtained by different turbulence models were compared to each other and

to the measurements. Steady state simulations were performed with various turbulence models. The

effect of curvature correction (CC) and Kato-Launder (KL) limiter of turbulence production were tested.

Transient simulations were performed with shear-stress-transport (SST) turbulence model, the scale-

adaptive-simulation (SAS SST) model, and with zonal large-eddy-simulation (ZLES). Details about

turbulent structures in the draft tube were illustrated in order to explain the reasons for differences in

flow energy losses obtained by different turbulence models. Also the effects of different advection

schemes (high resolution scheme – HRS and bounded central differential scheme – BCDS) and mesh

refinement were tested.

On the basis of a detailed analysis of flow in a Kaplan turbine and in a bulb turbine with different

turbulence models and at different operating regimes it can be concluded:

Results of steady state simulations in the Kaplan turbine were improved by using the Kato

Launder limiter of production term (KL) and the curvature correction (CC) therefore KL and

CC were used also in simulation of flow in the bulb turbine.

In both cases it was found out that steady state analysis is not suitable for all operating regimes.

While for Kaplan turbine the prediction of efficiency by RANS two-equation models and by

SSG RSM was quite accurate for small and optimal runner blade angles and only at full rate the

predicted efficiency was significantly too small, for the bulb turbine steady state simulations

entirely failed. In both cases the main reasons for discrepancy between measured and calculated

efficiency were underestimated torque on the shaft and overestimated flow energy losses in the

draft tube.

Transient simulations by the SST, SAS SST and SAS SST ZLES were performed at one

operating point for maximal runner blade angle. The results were significantly improved. The

largest improvement was achieved by SAS SST ZLES.

Comparing transient results of SST HRS, SAS HRS and SAS BCDS, it can be concluded that

the improvement due to the use of BCDS instead of HRS, was even larger than the improvement

due to the use of SAS instead of SST. With BCDS, the agreement with measurements was

improved mostly because of smaller losses in the runner and better prediction of torque on the

shaft.

For bulb turbine meshes of different density were used. The results of the SAS SST ZLES model

were better than the results of the SAS SST model on all meshes. Positive effect of mesh

refinement in the draft tube was clearly seen. While with mesh refinement in the runner only,

no improvement was obtained, the best results were obtained when both meshes, in the runner

and in the draft tube were refined.

Finally, in both cases the simulations by SAS SST ZLES were performed at several operating

points for three runner blade angles. Comparing the results of the steady state analysis to the

results of the SAS SST ZLES the agreement of the former ones with measurements was

improved at all operating regimes. For Kaplan turbine the discrepancy was everywhere smaller

than 0.8 %. For bulb turbine in spite of large improvement the discrepancy with measurements

was even on finest mesh still about 2.1 %.

Too long CPU time is main disadvantage of transient simulations and the reason for their limited

use in design process. It can be expected that with future development of hardware and software

the problem will be overcome.


10

Fig. 1: Computational mesh for the Kaplan turbine Fig. 2: Predicted and measured efficiency for the

Kaplan turbine

Fig. 3: Results for the bulb turbine: Flow in the draft tube (top) and contours of viscosity ratio (bottom). Steady

state results with SSTon the basic mesh - left, transient results with ZLES on the fine mesh - right

References:

[1] JOŠT, D., ŠKERLAVAJ, A., LIPEJ, A. Numerical flow simulation and efficiency prediction for axial turbines

by advanced turbulence models. V: Proceedings of the 26th IAHR Symposium on Hydraulic Machinery and

Systems, 19-23 August 2012, Beijing, China, (IOP conference series. Earth and environmental science (Online),

ISSN 1755-1315, vol. 15, part 2, 2012). London: Institute of Physics. 2012, vol. 15, prt. 6, str. 062016-1-

062016-9, doi: 10.1088/1755-1315/15/6/062016.

[2] JOŠT, D., ŠKERLAVAJ, A., LIPEJ, A. Improvement of efficiency prediction for a Kaplan turbine with

advanced turbulence models. Journal of Mechanical Engineering - Strojniški vestnik, ISSN 0039-2480, Feb.

2014, vol. 60, no. 2, str. 124-134, SI 25, ilustr., doi: 10.5545/sv-jme.2013.1222.

[3] JOŠT, D., ŠKERLAVAJ, A. Efficiency prediction for a low head bulb turbine with SAS SST and zonal LES

turbulence models. V: 27th IAHR Symposium on Hydraulic Machinery and Systems 2014, Montreal, (IOP

conference series. Earth and environmental science (Print), ISSN 1755-1307, Vol. 22). Bristol: Institute of

Physics; Red Hook (NY): Curran Associates. cop. 2015, str. 396-405. http://dx.doi.org/10.1088/1755-

1315/22/2/022007.

[4] JOŠT, D., ŠKERLAVAJ, A., MEŽNAR, P., MORGUT, M. Napoved izkoristka nizkotlačne cevne turbine z

numerično analizo toka = Efficiency prediction for a low head bulb turbine with numerical flow analysis. V:

HRIBERŠEK, Matjaž (ur.), RAVNIK, Jure (ur.). Zbornik del, Kuhljevi dnevi 2014, Maribor, 24.-25. september,

2014. Ljubljana: Slovensko društvo za mehaniko. 2014, str. 79-86.

http://www.drustvozamehaniko.si/zbornik/ZbornikKD2014.pdf.

[5] JOŠT, D., ŠKERLAVAJ, A., MORGUT, M., NOBILE, E.. Effects of turbulence model and mesh resolution

on the performance prediction of a bulb turbine. V: NAFEMS World Congress 2015 incorporating the 2nd

International SPDM Conference : proceedings. San Diego: [s. n.]. 2015.

[6] JOŠT, D., ŠKERLAVAJ, A., MEŽNAR, P., MORGUT, M., NOBILE, E., Simulation Conference in Vienna -

ANSYS Conference & 10th CADFEM Austria Users' Meeting , Vienna, April 29-30, 2015. Improvement of

efficiency prediction for axial turbines with advanced turbulence models : [Vienna, 29. 4. 2015].

https://doi.org/10.1088/1755-1315/15/6/062016

https://doi.org/10.5545/sv-jme.2013.1222

http://dx.doi.org/10.1088/1755-1315/22/2/022007

http://dx.doi.org/10.1088/1755-1315/22/2/022007

http://www.drustvozamehaniko.si/zbornik/ZbornikKD2014.pdf


11

Numerical simulation of flow in a high head Francis turbine with prediction

of efficiency, rotor stator interaction and vortex structures in the draft tube

Aljaž Škerlavaj


Summary

Flow in a high-head Francis turbine was analysed by two CFD codes, CFX and OpenFOAM, using three

turbulence models (k-ɛ, SST and ZLES) and three computational grids. Numerical results were

compared with available experimental data. The following conclusions can be drawn:

- Predicted axial and circumferential velocity components on Line 1 and Line 2 in the conical part

of the draft tube agree satisfactorily with the experimental data, but no numerical setup was the best at

all three operating points. ZLES model agreed much better with experimental data than steady-state

simulations at high load and at the best efficiency point.

- Axial and circumferential velocity components on two planes in the conical part of the draft

tube, predicted with ZLES CC KL generally agree well with the experimental data, but wakes behind

runner blades on Plane 1 are in comparison with experiment less distinct.

- Numerically predicted pressure pulsations at five locations were compared to the measured

results. CFD predicted frequency of pressure pulsations correctly, but did not detect some pressure peaks

in the runner.

- Torque losses in labyrinth seals have to be taken into account to get proper values of torque on

the shaft. Volumetric losses are much smaller and except at part load can be neglected.

- Proper grid refinement near stay and guide vanes and especially near runner blades is crucial for

accurate prediction of torque on the shaft, head and efficiency. With too coarse grid near runner blades

significantly overestimated values of head and torque were obtained. With proper grid refinement in

distributor and runner and taking into account losses in labyrinth seals very accurate prediction of torque

on the shaft, head and efficiency was obtained.

- Steady-state simulations with k-ε and SST turbulence models on basic grid (BG2) were

performed with open source code OpenFOAM. The values of efficiency as well as local field details

(velocity components) obtained with OpenFOAM were in line with those predicted with CFX.

Basic

grid

BG

Fine

Grid

FG

Figure 1: Velocity distribution on

mid cross section at the best

efficiency point obtained with

CFX using SST CC KL model

Figure 2: Turbine efficiency, numerical and experimental results. Torque

losses in labyrinth seals are taken into account

References JOŠT, D., ŠKERLAVAJ, A. MORGUT, M., MEŽNAR, P., NOBILE, E.. Numerical simulation of flow in a high

head Francis turbine with prediction of efficiency, rotor stator interaction and vortex structures in the draft tube.

V: Francis-99 Workshop 1: Steady Operation of Francis Turbines 2014 : Trondheim, Norway, 15 - 16 December

2014, (Journal of physics. Conference series, ISSN 1742-6588, Vol. 579). Bristol: Institute of Physics Publishing.

2015, 012006 (20 str.). http://dx.doi.org/10.1088/1742-6596/579/1/012006.

http://dx.doi.org/10.1088/1742-6596/579/1/012006


12

OpenFOAM in turbomachinery

Maja Ondračka

Summary

In my presentation I will guide you through the basic structure of the installed distribution of

OpenFOAM, solvers and utilities. I will show some basic procedures on the icoFoam/cavity case. This

is only one of many tutorial cases. For each solver there is a tutorial case that is usually copied to the

working directory and adapted for the use of a real problem. One can find all this tutorial cases in a

special directory of the installed OpenFOAM distribution OpenFOAMxx/tutorials. Each case contains

three directories with various subdirectories and files.

In the cavity case the mesh is created with a blockMesh utility that comes with the OpenFOAM package.

We will learn about the contents of the case directory and its subdirectories, how to create the simplest

mesh and how to run the solver. The mesh can be visualized with paraview, the third party software that

also comes with the installation.

I am using a commercial software TurbomachineryCFD (TCFD®), which is the software package and

workflow based on the OpenFOAM, developed by CFDSupport from Prague, Czech Republic

https://cfdsupport.com). It includes GUI as a pluging to paraview which simplifies the use of the

software, but originally doesn't come with the OpenFOAM distribution.

The structure of a typical Francis turbine case will be shown and also how to handle external meshes. I

am using Numeca meshing tools AutoGrid5™ and IGG™. Sometimes snappyHexMesh, an OpenFOAM

utility for automatic generating meshes is very frequently used for more complicated geometries, e.g.

spiral cases. The snappyHexMesh utility generates 3-dimensional meshes containing hexahedra (hex)

and split-hexahedra (split-hex) automatically from triangulated surface geometries in Stereolithography

(STL) format.

There will be a few words about the boundary conditions, which need special care, about the interfaces

between stationary and rotational parts. We will go through some basic settings. At the end I will show

some very basic features in paraview. Some results of a CFD analyses of different types turbines will

also be presented.

There is very good documentation that comes with OpenFOAM installation. One can find in a special

directory OpenFOAM-xx/doc. On the internet, http://www.openfoam.com/documentation/, there is even

more. Various forums can also be very helpful.


13

Comparison of results obtained with OpenFOAM and Ansys-CFX

Dragica Jošt


Summary

Comparison of results obtained with OpenFOAM and ANSYS-CFX was done for 6 cases:

High head Francis turbine (Tokke model from Workshop Francis99)

Middle head Francis turbine

Kaplan turbine

Bulb turbine

Cavitation prediction: Attached cavity flow around a hydrofoil

Cavitation prediction: Attached cavity flow around E779A model scale marine propeler Approximately the same level of accuracy of numerical results was achived with both codes. CPU time

was significantly longer in case of simulations with OpenFOAM.

Figure 1: High head Francis turbine, computational domain and mesh with a detail of mesh in stay

and guide vane cascade (left) and comparison of predicted efficiency to the measured values (right).

Figure 2: Predicted attached cavity around a hydrofoil, results of CFX and OpenFOAM, both with Kunz

mass transfer model.

References: JOŠT, D., ŠKERLAVAJ, A. MORGUT, M., MEŽNAR, P., NOBILE, E.. Numerical simulation of flow in a high

head Francis turbine with prediction of efficiency, rotor stator interaction and vortex structures in the draft tube.

V: Francis-99 Workshop 1: Steady Operation of Francis Turbines 2014 : Trondheim, Norway, 15 - 16 December

2014, (Journal of physics. Conference series, ISSN 1742-6588, Vol. 579). Bristol: Institute of Physics Publishing.

2015, 012006 (20 str.). http://dx.doi.org/10.1088/1742-6596/579/1/012006.

http://dx.doi.org/10.1088/1742-6596/579/1/012006


14

Advanced experimental and numerical techniques for cavitation erosion

prediction

Matevž Dular


University of Ljubljana

Askerceva 6

1000 Ljubljana

SLOVENIA

Voice: +386 (0)1 4771 314

E-mail: matevz.dular<at>fs.uni-lj.si

Web: www2.arnes.si/~mdula

Summary

Currently we have two larger scientific/engineering projects running at the Laboratory for Water and

Turbine Machines, University of Ljubljana. The first one is funded by the national research agency

(ARRS) and deals with fundamental aspects of cavitation erosion and the development of the tools for

its prediction. The second one is funded by the European Space Agency (ESA) - the new generation of

rocket engines will also feature the possibility of re-ignition while in orbit; hence long term operation

of LH2 and LOX turbo-pumps under cavitation conditions is becoming an issue. The project is aimed

to understanding of cavitation and cavitation erosion in cryogenic liquids.

An overview of the developments during the last 15 years will be given with special emphasis on the

most recent findings in the understanding and predicting of cavitation erosion. This will be given from

three points of consideration

1 Erosion from the cavitation cloud point of view

Recently we have confirmed that cavitation cloud shedding causes different typical hydrodynamic

mechanisms and results in extreme conditions which are connected with material erosion (Fig. 1).

Fig. 1: Mechanisms that lead to occurrence of cavitation erosion.

2 Single bubble cavitation erosion

A collapse of a single cavitation bubble is shown in Fig. 2. Its maximal diameter reaches about 5mm

and the process was recorded at 300 kfps. On frame 7 one can observe a pressure wave traveling at

approximately 1500m/s.

We developed a technique that enables simultaneous high speed visualizations of single bubble

cavitation collapse and the damage sustained during the process.


15

Fig. 2: Collapse of a single bubble.

3 Cavitation erosion from the material point of view

In the study we observed the formation of individual pits by means of high speed cameras and

quantitatively evaluated the series of images by stereoscopy and the shape from shading method. This

enabled the reconstruction of the time evolution of the pit shape. To improve the algorithm we combined

the shape from shading technique with photometric stereo.

Fig. 3: Reconstructed shape of the damaged surface as a function of time.

References

[1] M. Dular, M. Petkovšek, On the mechanisms of cavitation erosion – Coupling high speed videos to damage

patterns, Experimental Thermal and Fluid Science 68 (2015), 359-370.

[2] M. Dular, Hydrodynamic cavitation damage in water at elevated temperatures, Wear 346–347 (2016), 78-86.

[3] W. Jian, M. Petkovšek, L. Houlin, B. Širok, M. Dular, Combined numerical and experimental investigation of

the cavitation erosion process, ASME J. Fluids Eng. 137 (2015), 051302.

[4] M. Petkovsek, M. Dular, Simultaneous observation of cavitation structures and cavitation erosion. Wear 300

(2013), 55-64.

[5] M. Dular, O. Coutier-Delgosha, M. Petkovsek, Observations of cavitation erosion pit formation. Ultrasonics

Sonochemistry 20 (2013), 1113-1120.

[6] A. Osterman, B. Bachert, B. Sirok, M. Dular, Time dependant measurements of cavitation damage. Wear 266

(2009), 945-951.

[7] M. Dular, O. Coutier-Delgosha, Numerical modelling of cavitation erosion. Int. j. numer. methods fluids 61

(2009), 1388-1410.

[8] M. Dular, B. Stoffel, B. Sirok, Development of a cavitation erosion model. Wear 261 (2006), 642-655.

[9] M. Dular, B. Bachert, B. Stoffel, B. Sirok. Relationship between cavitation structures and cavitation damage.

Wear 257 (2004), 1176-1184.


16

Calibration of mass transfer models for the numerical prediction of sheet

cavitation around a hydrofoil

Mitja Morgut

Dipartimento di Ingegneria e Architettura

University of Trieste, P.le Europa 1

34127 Trieste ITALY

Summary

Cavitating flows, which can occur in a variety of practical cases, can be modelled with a wide range of

methods/models [1]. Here, a so-called homogeneous model [2, 3] is applied to the numerical predictions

of sheet cavity flow around a hydrofoil. In the considered model the working fluid is treated as a

homogeneous mixture of two fluids, i.e. water and vapour, behaving as a single one, and the mass

transfer rate due to cavitation is modelled by the mass transfer model. Here, three widespread mass

transfer models are alternatively used. The considered mass transfer models share the common feature

of employing empirical coefficients to tune the condensation and evaporation processes, whose values

affect the accuracy and the stability of the numerical predictions. Thus, in order to ensure stable and

accurate predictions, the empirical coefficients of the considered mass transfer models are properly and

congruently tuned using a calibration strategy driven by the modeFRONTIER [4] optimization platform.

The numerical predictions based on the three different well-tuned mass transfer models are very close

to each other and in line with the available experimental data.

References

[1] Koop, A.H., 2008. Numerical Simulation of Unsteady Three-Dimensional Sheet Cavitation. PhD Thesis.

University of Twente.

[2] Asnaghi, A., Feymark, A., Bensow, R.E., 2017. Improvement of cavitation mass transfer modeling based on

local flow properties. Int. J. Multiphase Flow 93 (2017) 142-157, doi:10.1016/j.ijmultiphaseflow.2017.04.005.

[3] Morgut, M., Nobile, E., Biluš, I. 2011. Comparison of mass transfer models for the numerical prediction of

sheet cavitation around a hydrofoil. Int. J. Multiphase Flow 37 (6) 620-626, doi:

10.1016/j.ijmultiphaseflow.2011.03.005

[4] www.esteco.com


17

Cavitation prediction for water turbines

Dragica Jošt


Summary

Cavitation predictions were done for models of Francis and Kaplan turbines and for prototypes of bulb

and Pelton turbines. For all cases homogeneous multiphase model was used. Mass transfer due to

cavitation was modelled by Zwart model with standard and in cases of Kaplan and Francis turbines also

with previously on a hydrofoil calibrated evaporation and condensation constants. For Kaplan and

Francis turbines extent and shape of cavitation were compared to the experimental observation on the

test rig. Also the effect of cavitation on turbine efficiency was investigated.

Steady-state simulations of flow in a middle head Francis turbine were performed at overload operating

regime with high flow rate. SST turbulence model with curvature correction and with the Kato-Launder

limiter of production term in equation for turbulence kinetic energy was used. Simulations were done

for different values of cavitation coefficient, which means from non-cavitating to strongly cavitating

regimes. Numerical results agree well with the experimental ones. Differences due to standard and

calibrated evaporation and condensation constants are small.

a) b)

Figure 1: Cavitation in the Francis turbine at full load. a) vapour at suction side of runner blades, left -

standard, right - calibrated coefficients. b) Cavitation on suction side of runner blades near the trailing

edges and rotating vortex rope, left - test rig, right - CFD.

For a Kaplan turbine numerical simulations were done at one operating point for maximal runner blade

angle and nominal head. Steady state results, obtained with the SST (Shear Stress Transport) turbulence

model, were improved by transient simulations with the SAS (Scale Adaptive Simulation) SST model.

The numerical results were compared with the observation of cavity size on the test rig and with the

measured sigma break curve. Steady state simulations predicted a significant too small efficiency level

and too small extent of cavitation on the runner blades. The reason was too high pressure level in the

runner due to overestimated losses in the draft tube. With transient simulations, the shape and size of

the predicted sheet cavitation agreed well with the cavitation observed on the test rig. In addition, also

the predicted efficiency was more accurate, although the value of σ (cavitation or Thoma number) where

the efficiency dropped for 1% was a bit too large. The difference between the results obtained with

standard and calibrated model parameters of the Zwart mass transfer model was small.

Figure 2: Comparison of shape and size of cavity, a) experiment, b) steady state simulation, calibrated

coefficients, c) time dependent simulation, calibrated coefficients.


18

For a prototype of a bulb turbine numerical flow simulation

was performed with a purpose to obtain pressure distribution

for the stress analysis. To get accurate pressure on runner

blades the cavitation modelling has to be included. The

prototype diameter of the turbine was very large (Dp = 7.5

m.) therefore hydrostatic pressure has to be included in the

simulation. Due to hydrostatic pressure a cavity at upper

blades is much larger than at the bottom ones. During

transient simulation a size of a cavity at each blade increases

when the blade rotates up and decreases when it rotates

down.

Figure 3: Pressure distribution and

attached cavity at suction side of bulb

turbine runner blades

Prediction of cavitation in a two jet Pelton turbines was performed. Three-component flow consisting

of water, air and water vapour was modelled with homogeneous model. Modelling of free surfaces and

mass transfer between water and vapour due to cavitation and condensation processes were included in

the transient simulation.

The presence of water vapour does not necessary cause material erosion. The conditions for cavitation

pitting on Pelton buckets are:

Vapour cavity is sticking to the bucket surface.

Water vapour is condensed in a very short time.

The condensation of water vapour is developed in absence of air.

In Fig. 4 regions with water vapour on inner and back side of a bucket are presented. At inner side the

vapour is condensing very slowly. At the back side the condensation is also slow and the vapour is in

contact with air. So no cavitation damages are expected in this case.

Figure 4: Detail of computational grid (left), water vapour on inner side of the bucket (middle), water

vapour at back side of the bucket (right). Water vapour is coloured with wall distance.

References:

[1] MORGUT, M., JOŠT, D., NOBILE, E., ŠKERLAVAJ, A. Numerical predictions of the turbulent cavitating

flow around a marine propeller and an axial turbine. V: 9th International Symposium on Cavitation (CAV2015) :

6-10 December 2015, Lausanne, Switzerland, (Journal of physics. Conference series, ISSN 1742-6588, Vol.

656). Bristol: Institute of Physics Publishing. 2015, http://dx.doi.org/10.1088/1742-6596/656/1/012066,

http://iopscience.iop.org/article/10.1088/1742-6596/656/1/012066/pdf.

[2] JOŠT, D., MORGUT, M., ŠKERLAVAJ, A., NOBILE, E. Cavitation prediction in a Kaplan turbine using

standard and optimized model parameters. V: LIPEJ, Andrej (ur.), MUHIČ, Simon (ur.). Cavitation and

dynamic problems : proceedings, 6th IAHR Meeting of the Working Group, IAHRWG 2015 Ljubljana,

Slovenia, September 9-11, 2015. Novo mesto: Faculty of Technologies and Systems. 2015.

[3] JOŠT, D., ŠKERLAVAJ, A., MORGUT, M., NOBILE, E. Napoved kavitacije v vodnih turbinah z

računalniško dinamiko tekočin – rezultati projekta ACCUSIM, Akademija strojništva 2016, 18. oktober 2016,

Cankarjev dom Ljubljana.

[4] D. Jošt, A. Škerlavaj, M. Morgut, R. R. Stopar, E. Nobile. Numerical simulation of different forms of cavitation

in Francis turbines. ANSYS Convergence Conference, Ljubljana, 25th of May 2016.

http://dx.doi.org/10.1088/1742-6596/656/1/012066

http://iopscience.iop.org/article/10.1088/1742-6596/656/1/012066/pdf



19

Numerical predictions of the cavitating flow around model scale propellers

working in uniform and non-uniform inflow

Mitja Morgut

Dipartimento di Ingegneria e Architettura

University of Trieste, P.le Europa 1

34127 Trieste ITALY

Summary

The numerical predictions of the turbulent cavitating flow around two model scale propellers,

recognized as international benchmarks, are presented. In particular, the predictions of the PPTC

propeller working in uniform inflow [1] and of the E779A propeller working in uniform as well as non-

uniform inflow [2] are discussed.

The simulations are performed using commercial and open source CFD (Computational Fluid Dynamics)

codes. The cavitating flow is modelled using the homogeneous model along with three different

widespread mass transfer models, previously calibrated considering the sheet cavity flow around a two-

dimensional hydrofoil [3]. The turbulence effect is modelled using the RANS (Reynolds Averaged

Navier Stokes) approach.

The numerical results are compared with the available experimental data. The simulations performed

with the three different calibrated mass transfer models are very similar to each other and in line with

the experimental data, even though the numerical cavitation patterns are generally slightly overestimated

[4, 5].

References

[1] https://www.sva-potsdam.de/pptc-smp11-workshop/

[2] Salvatore, F., Streckwall, H., van Terwisga, T., 2009. Propeller Cavitation Modelling by CFD-Results from

the VIRTUE 2008 Rome Workshop. The First International Symposium on Marine Propulsors, smp'09,

Trondheim, Norway.

[3] Morgut, M., Nobile, E., Biluš, I., 2011. Comparison of mass transfer models for the numerical prediction of

sheet cavitation around a hydrofoil. Int. J. Multiphase Flow 37 (6) 620-626, doi:

10.1016/j.ijmultiphaseflow.2011.03.005

[4] Morgut, M. and Nobile, E., 2012. Numerical Predictions of Cavitating Flow around Model Scale Propellers

by CFD and Advanced Model Calibration. International Journal of Rotating Machinery, special issue: Marine

Propulsors and Current Turbines: State of the Art and Current Challenges. Doi:10.1155/2012/618180.

[5] Morgut, M., Jošt, D., Nobile, E., Škerlavaj, A., 2015. Numerical investigations of cavitating propeller in non-

uniform inflow. Fourth International Symposium on Marine Propulsors, smp’15, Austin, Texas.


20

Sheet and cloud cavitation prediction in double suction centrifugal pump

Aljaž Škerlavaj


Summary

Cavitation at the leading edges of the impeller blades in a pump is quite a usual phenomenon, due to the

limitations in the available suction head (or, in simple words, due to too low "submergence" of the

pump). Usually the sheet-type cavitation (also called blade cavitation) is of small size and occurs on the

suction side of the blade, so the pump performance is only negligibly affected. At specific conditions,

the so-called cloud cavitation can appear (Fig. 1), when large clouds of vapour are torn-off of the sheet

cavity, and are carried along with the stream.

Figure 1: Cloud cavitation, observed on the double-suction pump at HPP Fuhren [1].

In this presentation, a short introduction to cloud cavitation (conditions, patterns, mechanisms [2, 3])

will be given, followed by the video of observation of cloud cavitation in a double-suction centrifugal

pump at our test rig (Fig. 2).

Figure 2: Geometry of the double-suction pump. Left: numerical model (in green: inlet pipe with suction

chambers; in blue: impeller; in red: volute with outlet pipe). Right: experimental setup with visible observation

window.

Two types of numerical approaches for the prediction of cloud cavitation in a centrifugal pump will be

discussed: a single-blade simulation and a (symmetrical) half-geometry simulation. For both

approaches, simulations were performed with the default and with the modified [4, 5] parameters of the

mass transfer model. Simulations, performed with the modified parameters, were found to be less stable

than the ones with the default parameters.

The single-blade simulation with the modified parameters of the mass transfer model produced cloud

cavities of dubious origin (Fig. 3). The results obtained on a single-blade mesh are of limited use due to

the negligence of the suction chamber effect on the inlet velocity distribution.


21

Figure 3: Prediction of cavity (isosurface of 10% water vapour) with single-blade passage simulation

It is possible to conclude that simulations performed on the geometry of a half-pump, using the default

and the optimized parameters, can predict the pinch-off of vapour clouds (Fig. 4).

Figure 4: Half-geometry simulation with default constants (isosurface of 10% water vapour).

References

[1] Škerlavaj A, Titzschkau M, Pavlin R, Vehar F, Mežnar P and Lipej A 2012 Cavitation improvement of double

suction centrifugal pump HPP Fuhren IOP Conference Series: Earth and Environmental Science 15(2) p

022009

[2] Franc JP 2014 Fluid Dynamics of Cavitation (2) Proc. of Cavitation Instabilities and Rotordynamic Effects in

Turbopumps and Hydroturbines July 7-11 (Udine: CISM)

[3] Ganesh H 2015 Bubbly Shock Propagation as a Cause of Sheet to Cloud Transition of Partial Cavitation and

Stationary Cavitation Bubbles Forming on a Delta Wing Vortex (Michigan: The University of Michigan) p.

172

[4] Morgut M, Nobile E, Biluš I 2010 Comparison of mass transfer models for the numerical prediction of sheet

cavitation around a hydrofoil Int. Journal of Multiphase Flow 37(6) pp 620-626

[5] Morgut M, Nobile E 2012 Numerical Predictions of Cavitating Flow Around Model Scale Propellers by CFD

and Advanced Model Calibration International Journal of Rotating Machinery 2012. Article ID 618180.


22

Simulation of cavitating vortex rope in the draft tube of a Francis turbine

Dragica Jošt


Summary

Transient simulations of flow in a Francis turbine were performed with a goal to predict pressure

pulsation frequencies and amplitudes caused by rotating vortex rope at part load operating regime.

Simulations were done with the SAS SST turbulence model with curvature correction on basic and

refined computational meshes. Without cavitation modelling too small values of frequency and

amplitudes were obtained. With mesh refinement the calculated amplitudes were a bit closer to the

measured values, while the accuracy of predicted frequency did not improve at all. Agreement between

measured and numerical values was significantly improved when cavitation was included in simulations.

In addition, the predicted value of the dominant frequency was slightly more accurate when, in the Zwart

et al. cavitation model, the default condensation and evaporation model constants were replaced with

previously calibrated ones.

Figure 1: Vortex rope a) on the test rig; b) without cavitation modelling, iso-surface of evaporation pressure,

c) default cavitation constants, iso-surface of Vapour Volume Fraction = 0.1; d) calibrated cavitation constants,

iso-surface of Vapour Volume Fraction = 0.1.

Figure 2: Comparison of numerical and experimental results

Exp. - experimental values, 1 - no cavitation modelling, basic mesh, 2 - no cavitation modelling, fine mesh, 3 -

cavitation modelling, standard parameters, basic mesh, 4 - cavitation modelling, calibrated parameters, basic mesh

References:

[1] LIPEJ, A., JOŠT, D., MEŽNAR, P., DJELIĆ, V. Numerical prediction of pressure pulsation amplitude for

different operating regimens of Francis turbine draft tubes. V: Proceedings of 24th IAHR Symposium on

Hydraulic Machinery and Systems, October 27-31, 2008, Foz do Iguassu, Brazil, (International journal of fluid

machinery and systems, vol. 2, no. 4, 2009). Seoul: Korean Fluid Machinery Association. 2009, vol. 2, no. 4,

str. 375-382. https://www.jstage.jst.go.jp/article/ijfms/2/4/2_4_375/_pdf.

[2] JOŠT, D., LIPEJ, A. Numerical prediction of non-cavitating and cavitating vortex rope in a Francise turbine

draft tube. Strojniški vestnik, ISSN 0039-2480, jun. 2011, vol. 57, no. 6, str. 445-456, ilustr., doi: 10.5545/sv-

jme.2010.068.

[3] JOŠT, Dragica, ŠKERLAVAJ, Aljaž, MORGUT, Mitja, STOPAR, Renato Roberto, NOBILE, Enrico.

Numerical simulation of different forms of cavitation in Francis turbines. ANSYS Convergence Conference,

Ljubljana, 25th of May 2016.

[4] JOŠT, Dragica, ŠKERLAVAJ, Aljaž, MORGUT, Mitja, NOBILE, Enrico. Numerical Prediction of Cavitating

Vortex Rope in a Draft Tube of a Francis Turbine with Standard and Calibrated Cavitation Model. IAHR WG

2017, Porto February 2017, http://iopscience.iop.org/article/10.1088/1742-6596/813/1/012045/pdf.

https://www.jstage.jst.go.jp/article/ijfms/2/4/2_4_375/_pdf





23

No-free lunch theorem from an engineering perspective

Carlo Poloni

Università di Trieste & ESTECO Spa

[email protected]

Summary

optimum f

A -837.97

B1 -723.21

B2 -719.53

C1 -608.46

C2 -604.77

C3 -601.09

While design optimization technology is becoming more and more popular still there is the need to look

at the fundamentals of the technology in order to be prepared to exploit at best the opportunities that are

available. It should be clear that the no-free-lunch theorem on optimization as enunciated in (1) is

applicable in any engineering design situation.

While the negative consequence is that a unique superior algorithm does not exist the positive and

creative aspect is that the optimization activity has to be seen as an exploratory task aimed at finding the

best compromise between performance metrics and resources to be used concentrating the effort in

improving performance of the product and knowledge of the problem.

During the talk some theoretical examples and some practical applications involving also design under

uncertainty tasks will be shown in order to illustrate the journey of a multidisciplinary decision maker

(2) (3).

References

1. D.H. Wolpert and W.G.Macready “No free Lunch Theorems for Optimization”, IEEE

TRANSACTIONS ON EVOLUTIONARY COMPUTATION, VOL. 1, NO. 1, APRIL 1997

2. R.Russo, A.Clarich,C.Poloni, E.Nobile “Mission and Shape Optimization using modeFRONTIER:

Application to Boomerang throw” ERCOFTAC Bulletin 102

3. P G.Cassio,A.Clarich, R.Russo, “Reliability based Robust Design Optimization Using Polynomial

Chaos Expansion for aeronautics applications” EUROGEN2017


24

Optimization of a double-sided centrifugal pump

Aljaž Škerlavaj


Summary

Centrifugal pumps are widely used in industrial applications. Compared to single-entry centrifugal

pumps, double-sided pumps allow transportation of greater flow rates due to smaller proneness to

cavitation, and offer counter-balancing of axial hydraulic forces due to double-entry design [1].

In the modern world of rapidly-improving technologies it is important to design excellent products in

short time. The optimization techniques bring many benefits over the traditional "trial-and-error" design

process: shorter design phase, exploration of design space in a more systematic way, development with

less hard-to-spot human-based errors, etc. In turbomachines, usually multiple objectives have to be

optimized. One of the first multi-objective optimization studies was performed by Lipej and Poloni [2].

The optimization study of a double-sided centrifugal pump with specific speed nq=62 (per impeller side),

presented in Fig. 1, was performed within modeFRONTIER® optimization platform [3]. During the

optimization only the impeller geometry was allowed to be modified, while the rest of the geometry was

fixed. The objective of the study was twofold:

1. To compare different Response Surface Methods (RSMs), also called metamodels or surrogates,

for their ability to predict pump efficiency [4-6]

2. To propose and validate an economical decoupled simulation method for the optimization of a

pump [6, 7].

Figure 1: Geometry of the double-sided centrifugal pump.

In the first phase, during the study of RSMs, a simplified pump geometry comprised of (symmetrical)

half of volute and of one impeller channel (Fig. 2). Since the impeller channel and volute were simulated

simultaneously, we call this model coupled model. An example of successful modification is presented

in Fig. 3.

Figure 2: Geometry and mesh for the coupled model.

Volute

mesh

Single-channel impeller

mesh


25

Figure 3: Blade geometry before (left) and after (right) the optimization. Relative efficiency increased

for 0.9 pp. Green surface: inlet surface. Yellow: outlet surface.

In the second phase of the study, based on flow simulations of the volute, flow losses in the volute were

estimated with a simple function ΔHvolute=(f(α2,hub)+ f(α2,midspan)+ f(α2,shroud))/3, where α2 is angle between

circumferential and absolute velocity at the impeller outlet. Afterwards, geometry optimization was

performed only on one impeller channel (Fig. 3). We call this model decoupled model. Two optimization

objectives were used, namely pump efficiency and reluctance to cavitation. For the latter, a simple

procedure for its estimation was proposed. Results for forty most promising candidates for high pump

efficiency were validated with full-geometry CFD numerical simulations. The following conclusions

were drawn:

The presented method with estimation of flow losses in the volute represents a good approach

for quick optimization;

Angle α2 at hub and at shroud needs small adjustments;

Low value of angle α2, when compared to the average α2 value, acted beneficially on reducing

the volute flow losses.

Figure 3: Geometry and mesh for the decoupled model. Blue arrows represent inlet and outlet boundary

conditions.

References:

[1] Gülich JF 2008 Centrifugal Pumps (Berlin: Springer-Verlag) p 926

[2] Lipej A and Poloni C 2000 Design of Kaplan runner using multiobjective genetic algorithm optimization J.

Hydraul. Res. 38(4) pp 73–9

[3] ESTECO 1999-2016 modeFRONTIER User Manual (ESTECO: Trieste)p 504

[4] Škerlavaj A, Jošt D, Morgut M and Nobile E 2016 Optimization of a single-stage double-suction centrifugal

pump using different Response Surface methods modeFRONTIER User‘s Meeting 2016, Trieste, Italy, 17-18

May 2016. (Presentation)

[5] Škerlavaj A, Morgut M, Jošt D and Nobile E 2017 Optimization of a single-stage double-suction centrifugal

pump Journal of Physics: Conference Series 796(1), 012007. doi:10.1088/1742-6596/796/1/012007

[6] Škerlavaj A, Morgut M, Jošt D and Nobile E 2017 Optimization of a double-sided centrifugal pump

ERCOFTAC Design Optimization Course, University of Trieste, Italy, 5-7 June 2017. (Presentation)

[7] Škerlavaj A, Morgut M, Jošt D and Nobile E 2017 Decoupled CFD-based optimization of efficiency and

cavitation performance of a double-suction pump Journal of Physics: Conference Series 813(1), 012048.

doi:10.1088/1742-6596/813/1/012048


26

Multi-objective optimization of the Francis turbine runner cone



Summary

A multi-objective optimization with a genetic algorithm MOGA-II was used to optimize the shape of a

simplified runner-cone extension (RCE) for a Francis turbine of higher specific speed nq. The objective

of the optimization was the minimization of the draft tube pressure losses for two operating regimes. To

evaluate the progress, a baseline case without the extension was calculated first. Six geometric design

variables, defining the shape of RCE, were being modified during the optimization. Finite-volume based

commercial software ANSYS CFX was employed to calculate the flow field on a structured mesh.

Shapes of RCE on Pareto front were long and thin. At the best-efficiency point (BEP) the draft tube

pressure losses were larger than without the RCE. At the maximal discharge point (MAX) the draft tube

pressure losses were smaller than without the RCE; turbine efficiency increases for 0,15% at full size

computation grid.

Figure 1: Case 0, total pressure contours at meridional section, QBEP at left, Qmax at right

Figure 2: Design ID_54, total pressure contours at meridional section, QBEP at left, Qmax at right

References

[1] Falvey, H. T.: Draft Tube Surges, A Review of Present Knowledge and an Annotated Bibliography, 1971.

[2] Jošt, D.: U. H. HPP refurbishment, effect of RCE shape change, interno poročilo, Turboinštitut, Ljubljana,

2016

[3] Kovalev, N. N.: Gidroturbiny, Konstruktsii i voprosy proektirovaniya, Gosudartvennoe Nauchno-

Tekhnicheskoe Izdatel'stvo Mashinostroitel'noi Literatury, Moskva, pp. 135-149, 1961

[4] Stopar, R. R.: Deliverable D.4.2: Shape Optimization – Report No.2, Accurate Simulations in Hydro-

Machinery and Marine Propellers, Trst, 2017

[5] Španinger, Ž.: Raziskava tlaka pod rotorjem, nq=53 in nq=30, interno poročilo, Turboinštitut, Ljubljana, 2012-

2014

[6] Thicke, R. H.: Practical solutions for draft tube instability, Int. Water Power and Dam Construction, pp 31-37,

1981

Independent Model Testing at Kolektor Turboinštitut

Model tests are performed in accordance with IEC 60193 standard.

Kolektor Turboinštitut has performed over 230 model acceptance tests and over 1000

development tests for various producers and users of hydraulic turbines.

The following options can be observed and measured:

Energetic performances (efficiency)

Cavitation characteristics

Dynamic performances

Test rigs: 1 Francis 2 Kaplan 3 Pelton 4 Bulb

Main parameters of turbine test rigs

Francis Kaplan Bulb Pelton

Head Hmax 60 m 32 m 32 m 110 m

Flow rate Qmax 0,7 m3s-1 0,9 m3s-1 1,0 m3s-1 0,25 m3s-1

Torque Tmax 1500 Nm 700 Nm 700 Nm 1000 Nm

Power Pmax 150 kW 150 kW 90 kW 150 kW

Rot. speed nmax 1500 rpm 1500 rpm 1500 rpm 2000 rpm

1 2

3 4

Site Testing

MEASUREMENT OF ENERGY AND DYNAMIC CHARACTERISTICS

according to IEC 60041 and IEC 62006

Turboinštitut has performed 72 on-site measurements on 50 power plants since 1996

flow measurement methods can be chosen depending on power plant configuration and

customer requirements

FLOW MEASUREMENT BY CURRENT METERS

measurement and calibration in accordance with standards IEC 60041, ISO 3455, ISO

3354 and ISO 7194

we have performed 56 current-meter flow measurements on 37 power plants since 1996

current-meters are manufactured in Turboinštitut according to our own design and

technology

signals from current-meters are connected to Turboinštitut’s proprietary hardware

connected to the PC and processed with software application developed in Turboinštitut.

velocity profiles are immediately visually checked before the on-site integration of the

flow is performed

The repeatability of our flow measurement is in the range of ±0.2 % and uncertainty always

less than the IEC recommended values.

KOLEKTOR Kolektor Turboinštitut d.o.o. Rovšnikova 7, SI-1000 Ljubljana, Slovenia T: +386 (0)1 582 01 00, F: +386 (0)1 582 01 12 [email protected], www.kolektorturboinstitut.com


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