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SUBMERSIBLE PUMP DESIGN EVALUATION &

PERFORMANCE PREDICTION USING CFD Kiran Patel

EnCore Consultancy Services, Vadodara, Gujarat, India

Abstract:Submersible Pump design is consists of two parts, one is hydraulic design and

other is mechanical design of various components. Pump performance is mainly depending

on hydraulic design ofimpeller & bowl. Computational Fluid Dynamics (CFD) is very

much useful tool for evaluation of hydraulic design of impeller & bowl. Present paper

objective is to evaluate the submersible pump hydraulic design and predict the performance

characteristics. Cavitation analysis of impeller is also conducted and NPSHr of impeller is

predicted.

Keywords:Bowl, CFD, Cavitation, Impeller, Submersible Pump.

INTRODUCTION

The Computational Fluid Dynamics (CFD) is the present day state-of-art

technique in fluid engineering flowanalysis.It has wide range of applications-like

pumps, fans, compressors, turbines, automobiles, processindustries, aerospace, in fact in

any areas of study, where there is fluid in motion, air, water, steam etc.CFD analysis is

very useful for predicting pump performance at various mass-flow rates. For

submersible pump designers,prediction of operating characteristics curve is most

important. All theoretical methods for prediction ofefficiency merely give a value; but

one is unable to determine the root cause for the poor performance. Dueto the

development of CFD code, one can get the hydraulic efficiency value as well as observe

actual behavior. Onecan find the root cause for poor performance by using CFD

Analysis of equipment.Submersible pumps are widely used for water transportation in

irrigation, house hold application and other industrial applications. Their operating

range spans from full-load down to close to the shut-off head. In order to developa

reliable machine for this highly demanding operation, the behavior of the flow in the

entire pump has tobe predicted by a reliable computational method.For pumps,

important questions are-to what extent can the current 3D Navier-Stokes design tools be

used toidentify the onset of instabilities in the flow, and how accurately can the pumps

characteristic be predicted.Steady state simulation is used for the prediction of the flow

in the single stageand entire machines in the design process. However, due to unsteady

effects, it is difficult to predict thepump characteristic correctly. Unsteady effects in

turbo machinery, include the interaction of the rotor andstator, the surge and stall

limits in compressors, and the instabilities in pumps. The comparison of

theexperimental data and the results of the steady and unsteady flow simulations show

the capability ofmodern CFD codes.

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STEADY STATE NUMERICAL SIMULATION

Present day- recent advances in computing power, advanced computer graphics and

robust solvers make CFD a cost effective engineering design tool. CFD is very cost effective

design tool for Submersible Pump design evaluation which is used by all modern day Pump

manufacturers of the world.

PROCESS OF COMPUTATIONAL FLUID DYNAMICS

GEOMETRIC MODELLING

Submersible pump main components 3D Fluid model is prepared using software as

shown in Figure 1.

Figure 1: Submersible Pump component (Impeller & Bowl)

MESHING

Meshing is most important step for CFD analysis. Accuracy of result is depending on

the mesh. We have used tetra elements for mesh generation of both components of

submersible pump impeller & bowl. Final optimized mesh is shown here in Figure 2 after

grid sensitivity testing. Total 3127547 elements are used for calculation. For accurate

boundary layer prediction & y+ value, prizm layers are created around the blade. Also a

good quality mesh is created having low aspect ratio, less skewness with optimum sizing.

Figure 2: Submersible Pump component Meshing (Impeller & Bowl)

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PROBLEM DEFINITION

The steady state simulation with water as fluid is conducted for submersible pump.

Total pressure in stationary frame as 1 atmwas specified at the inlet whilemass flow rate was

defined at the outlet boundary. Blade, hub and shroud of both impeller & bowl is defined as

wall with no-slip boundary condition. High resolution scheme was selected as advection

scheme and convergence criteria as RMS 10-5

has been considered. Impeller is defined as

rotating domain and bowl as stationary domain. Both are connected by Multiple Frame of

Reference (MFR) models. Multiphase Cavitation analysis is conducted for only impeller with

various NPSHr value and head drop is determined at 120% discharge. Rayleigh Plesset

cavitation model is used for cavitation analysis.

The simulations were carried out over a wide range of operating points, from the best

efficiency point (100%) down to 80% of the nominal mass-flow rate and up to 120% on

higher side. Due to higher flow separation at part load especially below 70% severe

convergenceproblems are raised andpredict result are not much reliable.

RESULT & DISCUSSION

Steady state simulation result with water as fluid for submersible pump is shown at

BEP (100%) as well as part load (80% & 120%). In case of Pump rotor is pressure generating

device and stator is flow directing device. For submersible pump, rotor is impeller which is

increasing pressure while stator is bowl which directs the flow to the next stage of impeller.

Figure 3 shows the pressure plot on impeller & bowl at various discharges at mid span. At

80% discharge pressure is increasing compared to 100% and at 120% discharge pressure is

decreasing compared to 100% which can be observed from the Figure 3.

Figure 3: Pressure contour on Impeller & Bowl

Figure 4 shows the total pressure plot from inlet of impeller to exit of bowl. The

charts shows on X-axis scale as 0 to 1 to 2 which means that 0 to 1 is impeller where total

pressure is increasing and 1 to 2 is bowl where total pressure is reducing. This reduction in

total pressure is hydraulic lossdue to flow separation and friction. At part load 80% losses in

bowl is increasing due to high flow recirculation.

Figure 4: Total Pressure plot from inlet of Impeller tooutlet of Bowl

100 Q 120 Q 80 Q

80Q 100Q% 120Q%

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Figure 5 shows the velocity plot from inlet of impeller to outlet of bowl at mid span.

You can find low velocity zone at pressure side of impeller blade. But flow incidence is good

due to which flow recirculation is not observed. Similarly low velocity zone is found in bowl

flow passage which is increases as discharge is getting reduces. Flow recirculation at various

discharge is shown in Figure 6.

Figure 5: Velocity plot from inlet of Impeller to outlet of Bowl

Figure 6: Velocity Vector plot from inlet of Impeller to outlet of Bowl

The main cause of hydraulic losses in submersible pump is flow incidence, flow path

and blade design. Above results gives insight to understand the same and we can evaluate the

design of impeller and bowl. Good design should have been optimized for the above

parameters and CFD analysis will be very much useful for the same. Figure 7 shows the flow

streamline from inlet of impeller to outlet of bowl. Secondary flow is developing inside the

bowl flow passage can be observed from the velocity streamlines.

Figure 7: Velocity streamline plot from inlet of Impeller to outlet of Bowl

Cavitation is one of the main problems of pumping industry as it is creating lots of

damage. Whenever pressure at the inlet of pump is below the vapour pressure of fluid,

cavitation is going to be occurring. Figure 8 shows the cavitation analysis result at different

NPSHr value. As the NPSHr is reducing cavitation zone is increasing and head is getting

dropped. Using the CFD you can determine the NPSH cruve for submersible pump.

100 Q 120 Q 80 Q

100 Q 120 Q 80 Q

100 Q 120 Q 80 Q

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Figure 8: Cavitation zoneonblade of Impeller

Table 1 is show the detail submersible pump performance prediction at 80%, 100%

and 120%.

Table 1: Submersible pump performance prediction

%

Discharge

Discharge

(LPS)

Head

(M)

Power

(Watts)

Hydraulic Efficiency

(%)

80% 44.8 23.26 12213.25075 83.7

100% 56 21.52 13135.808 90

120% 67.2 18.362 13329.8293 90.81

CONCLUSION

1. Submersible pump performance is predicted using CFD. This is very useful as before

actual manufacturing of pump you can evaluate the pump design and check it the

performance. This will reduce the new pump development time as well as cost.

2. Hydraulic losses of the submersible pump are determined in operational range and

hydraulic design of various pump components is evaluated. Pump design will be

optimized and high efficient pump can be design using CFD.

3. Cavitation problem of Pump is detected using CFD and you can optimize the design for

low cavitation. Also low NPSHr Pump design can be developed using CFD for specific

application.

REFERENCES

[01] A.J.Stepanoff, “Centrifugal and Axial Flow Pump – 2 Edition,”

[02] Val. S. Labanff, “ Centrifugal Pumps Design & Application – 2 Edition”

[03] Stephen Lazarkiewicz, “ Impeller Pumps “

NPSHr=4m NPSHr=6m NPSHr=7m