CFD ACTIVITY AT DIEM DEPARTMENT - unibo.it PRESENTATI… · CFD ACTIVITY AT DIEM DEPARTMENT. DIEM...
Transcript of CFD ACTIVITY AT DIEM DEPARTMENT - unibo.it PRESENTATI… · CFD ACTIVITY AT DIEM DEPARTMENT. DIEM...
1/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
CFD ACTIVITY AT DIEM DEPARTMENTCFD ACTIVITY AT DIEM DEPARTMENT
2/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Introducing D.I.E.M.
Review of main projects: Basic Research
Review of main projects: Design support
SI IGNITION MODEL
LES
WALL FILM MODEL
PRESENTATION OUTLINE
A Focus On:
3/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Human Resources
Hardware Facilities
CFD Codes
Research and Application Fields
Contracts
A Way to Work
INTRODUCING D.I.E.M.
4/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
FULL PROFESSOR: Piero Pelloni
ASSOCIATED PROFESSOR: Gian Marco Bianchi
ASSISTANT PROFESSORS: Stefania Falfari,PhD
Giulio Cazzoli, PhD
PERMANENT ENGINEERS: Federico Brusiani, PhD
Claudio Forte
Ph.D. STUDENTS: Sergio Negro (2008->)
ENGINEER FELLOWS: Marco Costa
Rodolfo Piccioli Giacomo Bastia
INTRODUCING DIEM Human Resources
5/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
DELL Blade 20 processor Linux Cluster
Linux Cluster (9 processors)
DELL-Linux Cluster (5 processors)
8 DELL Workstation Two-Processors
INTRODUCING DIEM Hardware Facilities
6/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
INTRODUCING DIEM CFD Codes
ENGINE SIMULATIONS:
PREMIXED – NON-PREMIXED COMBUSTION KIVA3_UNIBO
PFI-GDI SIMULATION FIRE8.4
LES SIMULATION FLUENT 6.2
OpenFOAM 4.1
GENERAL FLUID-DYNAMICS: FLUENT 6.2
HYDRAULIC SIMULATION OF
FLUID-POWER/ INJECTION SYSTEMS: AMESIM
LIQUID JET ATOMIZATION: SURFER
7/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
CFD ANALYSIS OF ICE INTAKE/EXHAUST SYSTEMS
CFD ANALYSIS OF ICE COMBUSTION SYSTEMS
CFD ANALYSIS OF VACUUM PUMP
ANALYSIS OF INJECTION SYSTEMS
ANALYSIS OF FLUID-POWER SYSTEMS
INTRODUCING DIEM Research and application Fields
8/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
FERRARI RACING DE LONGHI
DUCATI RACING DVP VACUUM TECHNOLOGY
PIAGGIO & C S.p.A VARIAN VACUUM TECHNOLOGY
VM-MOTORI BUCHER HYDRAULICS
INTERNAL COMBUSTION ENGINES GENERAL CFD APPLICATIONS
INTRODUCING DIEM Contracts
Former Partner: Magneti Marelli, FIAT-GM Powertrain
9/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
ADVANCED RESEARCH
DESIGN SUPPORT OR TECHNOLOGY TRANSFER TO COMPANYCFD is available: it must be used since it offers a unique tool of investigation
- New CFD methodologies or models development - Knowledge of model behaviour via implementation in our own codes- Test of models and numerics - Investigations of basics physics
INTRODUCING DIEM A way of work: To know and to apply
10/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Liquid Jet Atomization
3-Phase Nozzle Flow Simulation
OOP CFD Code
REVIEW OF MAIN PROJECTSBasic Research
11/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
REVIEW OF MAIN PROJECTS Liquid Jet Atomization
ANALYSIS OF BASIC PROCESSES VIA QUASI-DIRECT SIMULATION
IMPROVEMENT OF ATOMIZATION MODELS
3D INVESTIGATION OF ATOMIZATION BASIC PHYSICS
RELATED MAIN PAPER: Bianchi, G.M., et al. ” 3D Large Scale Simulation of the High Speed Liquid Jet
Atomization”, SAE 2007-01-0244 Accepted for -SAE Journal of Engines
CFD Grid
1 mm0
10
20
30
40
50
60
70
80
90
100
Caso
turbolento
Caso
laminare
Nucleo
Struttureliquide
Turbulent LaminarTurbulent Laminar
Core
Detached
liquid
12/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
REVIEW OF MAIN PROJECTS Liquid Jet Atomization
DEVELOPMENT OF ATOMIZATION MODEL FOR LIQUID JET
BASED ON SIMPLE 2D SIMULATIONS
0
2 104
4 104
6 104
8 104
1 105
0 5 10 15 20 25 30 35 40
100 m/s200 m/s400 m/s
pd
f
Droplets Diameter (µm)
DROPLET SIZE PDF
21
22
2
2
2
)()2()2(
1)(
χχχχ
χχχχχχχχ−−−−−−−−
ΓΓΓΓ⋅⋅⋅⋅==== e
np
n
nn
500
300
200
100
400
150
250
Injection velocity
[m/s]
500
300
200
100
400
150
250
Injection velocity
[m/s]
30
1
15
Back density
[kg/m3]
30
1
15
Back density
[kg/m3]
30
10
20
Mean fluctuation level
[% of vinj]
30
10
20
Mean fluctuation level
[% of vinj]
130
200
Orifice diameter
[µm]
130
200
Orifice diameter
[µm]
126 CASES
ILASS 2004HTCE 2004
RELATED MAIN PAPERS: Bianchi, G.M., et al. (ASME PAPER No. ICEF2004-848 and Proceeding ILASS 2004)
13/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
REVIEW OF MAIN PROJECTS 3-Phase Nozzle Flow RANS Simulation
Internal Flow
Simulation
Generations of
Nozzle FilesSpray
Simulation
FROM NOZZLES TO SPRAYS
Internal Flow
Simulation
Generations of
Nozzle FilesSpray
Simulation
FROM NOZZLES TO SPRAYS
COUPLED NOZZLE FLOW – LIQUID JET ATOMIZATION
RELATED MAIN PAPERS: AVL AST UGM 2005
14/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
REVIEW OF MAIN PROJECTS OOP Code
DEVELOPMENT OF A NEW PARALLEL OBJECT ORIENTED
CODE FOR COMPUTATIONAL CONTINUUM MECHANICS
(CCM) IN FORTRAN 95.
NEMO -Numerical Engine for MultiphysicsOperators
Contributors:
- University of Bologna – Main Driver (with fundamental contribution by Dr. Stefano Toninel)
- University of Rome ”Tor Vergata” (Prof. Bella & Dr. Filippone): parallel solvers.
- University of Massachusetts at Amherst (Prof. Schmidt): node smoothing algorithm
based on cell quality
http://www.ce.uniroma2.it/nemo/
15/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
ICE Non-Reactive Flow Simulation
SI Engines Combustion Optimization
HSDI Diesel Engine Modeling
Port-Fuel Optimization in SI Engines
Injection System Development
REVIEW OF MAIN PROJECTSDesign Support
16/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
APPLICATION OF BOUNDARY LAYER SOLUTION IN RANS STEADY FLOW SIMULATION
REVIEW OF MAIN PROJECTS ICE Non-Reactive Flow Simulation
Recirculation
NORecirculation
Valve lift
Discharge coeff.
W.F.
T.B.L
EXP
RELATED MAIN PAPERS: SAE Papers: 2002-01-1118, 2003-01-0003 (Both in Journal of Engines)
Two-layer Wall-functions
17/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
13.480 bar
13.490 bar
13.500 bar
13.510 bar
13.520 bar
13.530 bar
13.540 bar
13.550 bar
13.560 bar
13.570 bar
13.580 bar
13.590 bar
64.00 °
[BTDC]
64.50 °
[BTDC]
65.00 °
[BTDC]
65.50 °
[BTDC]
66.00 °
[BTDC]
66.50 °
[BTDC]
67.00 °
[BTDC]
67.50 °
[BTDC]
68.00 °
[BTDC]
68.50 °
[BTDC]
69.00 °
[BTDC]
Anticipo Ottimale
p583
p583cmd052a
p681
p681cmdStudio2
p681cdm053EStep4
Studio1
Studio2
Studio2cmdp583
Studio2cmdp681
p747cdm053EStep4
p747cdm053EStep4.2
p747cdmp681
13.480 bar
13.490 bar
13.500 bar
13.510 bar
13.520 bar
13.530 bar
13.540 bar
13.550 bar
13.560 bar
13.570 bar
13.580 bar
13.590 bar
64.00 °
[BTDC]
64.50 °
[BTDC]
65.00 °
[BTDC]
65.50 °
[BTDC]
66.00 °
[BTDC]
66.50 °
[BTDC]
67.00 °
[BTDC]
67.50 °
[BTDC]
68.00 °
[BTDC]
68.50 °
[BTDC]
69.00 °
[BTDC]
Anticipo Ottimale
p583
p583cmd052a
p681
p681cmdStudio2
p681cdm053EStep4
Studio1
Studio2
Studio2cmdp583
Studio2cmdp681
p747cdm053EStep4
p747cdm053EStep4.2
p747cdmp681
+0.59% PMI
-2.78%ANT.
START CONFIGURATION
IME
P
SPARK ADVANCE
REVIEW OF MAIN PROJECTS SI Engines Combustion System Optimization
OPTIMIZATION OF RACING ENGINE COMBUSTION EFFICIENCY: CFD IN DESIGN STEPS FERRARI F1 (1996-2005) AND DUCATI MotoGp (2003->)
18/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
DEVELOPMENT OF NON-EQUILIBRIUM TURBULENCE CORRECTION
ADVANCED COUPLING BETWEEN INJECTOR FLOWAND ATOMIZATION MODEL
DEVELOPMENT OF SUITABLE ATOMIZATION MODELS
APPLICATION TO HSDI DIESEL ENGINE DEVELOPMENT
LOW COMBUSTION TEMPERATURE CONCEPTDEVELOPMENT BASED ON HIGHLY COOLED EGR RATE
REVIEW OF MAIN PROJECTS HSDI Diesel Engine Modeling
RELATED MAIN PAPERS: SAE Papers: 2000-01-1179, 2001-01-1068, 2002-01-1115
IN COOPERATION WITH VM-Motori (1996->) AND FIAT-GM (2003-2004)
19/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
REVIEW OF MAIN PROJECTS Port-Fuel Optimization in SI Engines
MIXTURE FORMATION ANALYSIS
WALL-FILM ANALYSIS
EFFECT OF LUBRICANT CONTAMINATION WITH FUEL
DEVELOPMENT OF SUITABLE METHODOLOGIES FOR SPRAY COMPUTATIONS
PFI TWO-PHASE SIMULATION
20/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
REVIEW OF MAIN PROJECTS Port-Fuel Optimization in SI Engines
0
0,025
0,05
0,075
0,1
0
0,5
1
1,5
2
360 420 480 540 600 660
Advanced injection
Retarded injection
Standard injection
Perc
en
tag
e o
f to
tal
ma
ss
in
jecte
d [
%]
Pe
rce
nta
ge
of to
tal m
ass
inje
cte
d (s
tan
dard
cas
e) [%
]
Angle [°]
CFD PROVIDED A ZERO COST SOLUTION TO REDUCE LUBRICANT CONTAMINATION WITH FUEL
RELATED MAIN PAPERS: SAE Papers 2006-32-0022 (In Journal of Engines) and 2007-24-0041
21/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
REVIEW OF MAIN PROJECTS Port-Fuel Optimization in SI Engines
Racing Application
RELATED MAIN PAPERS: BEST PAPER AWARD AVL – UGM 2005
22/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
DEVELOPMENT OF ELECTRO-MAGNETIC MODEL
DEVELOPMENT OF ADVANCED DRIVING CIRCUIT
1D-3D SIMULATION OF INJECTOR AND SYSTEM DYNAMICS FOR DESIGN
SIMULATION OF TWO-PHASE FLOW
COUPLING BETWEEN INTERNAL NOZZLE FLOWAND ATOMIZATION MODEL
REVIEW OF MAIN PROJECTS Injection System Development
RELATED MAIN PAPER: SAE Papers: 2000-01-2042, 2003-01-0006, 2004-01-0019, 2005-01-1236
(all in SAE Journals), ASME PAPER No. ICEF2004-847
A PROJECT IN COOPERATION WITH MAGNETI MARELLI (2001-2005)
23/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
FEATURES
BACKGROUND
BASIC TEST CASE
ENGINE APPLICATION
SI IGNITION MODEL
24/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
FLAME KERNEL FORMATION IS A CRITICAL ISSUE IN ICE SINCE:
ITS FEATURES AFFECT THE COMBUSTION DURATION
CYCLE-TO-CYCLE VARIABILITY AFFECTS RIGHT EARLY BURNING RATE
THE 5%MFB TAKES 35-40% OF TOTAL COMBUSTION DURATION
PHYSICS OF SPARK DISCHARGE
FLOW CONVECTIVE EFFECTS (ARC ELONGATION)
TURBULENCE
PHYSICAL CHARACTERISTICS OF THE MIXTURE (p, T, φφφφ or pdf of φφφφ)
PHYSICAL PROCESS TO BE CONSIDERED
SI IGNITION MODEL Background
RELATED MAIN PAPERS: SAE Papers 2007-01-0148 (In Journal of Engines)
25/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Ignition time and lenght scales are too small to be resolved during
kernel formation
Electrical circuit too complex to be modelled in detail
Coupling with main combustion model
Grid dependency
Many 1D models decoupled from CFD solver have
been presented and referenced.
They would be considered all Eulerian except AKTIM AND DPKI.
SI IGNITION MODEL Background
WHY ARE CFD IGNITION MODELS NOT COMPLETELY RELIABLE ?
26/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Electrical sub-model for Spark plug
Lump model based on the main available specifications
Lagrangian kernel submodel
Reignition submodel (Simple first step)
Mass and energy conservation solved in a variable control volume defined by mean flame surface
Coupling with main solver enforced with particular emphasis on flame surface
SI IGNITION MODEL Features
27/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LUMP/EASY MODELLING (NO WEAK POINT)
PLASMA FORMATION NEGLECTED (time and length scales too short)
gapbd
bdbd
dC
VE
⋅=
2
2
unb
unb
bi T
T
T
kT
+
−= 11
1
2/1
0
,
1
1
−
⋅−
=
πi
unbgap
bdik
T
Tdp
E
k
kr
),( tEfE spglow =&
Energy released during breakdown and glow phases:
Initial kernel conditions after plasma formation (Song and Sunwoo, 2000) :
(Duclos and Colin, 2001)
SI IGNITION MODEL Features: Spark Model
28/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
AFTER THE PLASMA PHASE:
One flame kernel is deposited and initialized
Flame Kernel is discretized by a set of triangular elements which expand radially
Each of these elements varies its area surface because of expansion and wrinkling by turbulence
It contributes to reaction rate in its own reference fluid cells I-th
I-th cell
SI IGNITION MODEL Features: Kernel Model
29/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
−−Ξ⋅=
dt
dp
pdt
dT
TA
Vs
dt
dr k
kk
kklam
k
unbk 11,
ρ
ρ
Mass Conservation for a lagrangian system
)(, Ξ⋅⋅⋅= kklamunb
kAs
dt
dmρ
Rearranged -> An expression for the mean kernel expansion rate
Turbulence wrinkling
SI IGNITION MODEL Features: Kernel Model
Energy Conservation for open system
30/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
MASS SOURCE TERMS IN I-TH CELL FROM FUEL CONSUMPTION RATE
thiklamunbthik s −− Σ⋅⋅= ,, ρω&
ENERGY SOURCE TERMS IN I-TH CELL FROM:
1. Fuel oxidation2. Spark discharge during breakdown and glow phase
(Equivalent to ECFM)
SI IGNITION MODEL Features: Kernel Model
31/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
FLAME SURFACE DENSITY IN I-TH CELL CONTINUOSLY UPDATED
thi
thithi
V
S
−
−−
Ξ⋅=Σ ∑
=−− =
M
i
thjkthi AS1
,j-th kernel element
surface
SI IGNITION MODEL Features: Kernel Model
IGNITION MODEL IS SWITCHED OFF ONCE THE KERNEL RADIUS IS 2.00 mm -> Reasonable flow lenght resolved in RANS (grid size 0.5 -> 1 mm)
MASS SOURCE TERMS IN I-TH CELL FROM FUEL CONSUMPTION RATE
thiklamunbthik s −− Σ⋅⋅= ,, ρω& (Equivalent to ECFM)
32/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Main Combustion model ECFM – Flamelet
Mono-component Fuel CnHm according to actual gasoline fuel used
Laminar flame speed
( )EGRLL Xp
p
T
Tss 21
00
0 −⋅
⋅
⋅=
βα
Metchalghi & Keck
Meintjes and MorganPost-flame chemistry
Flame front chemistry 1-step chemistry
SI IGNITION MODEL Features: Combustion Model
33/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Herweg and Maly (SAE paper 922243).
Side chamber to promote a swirl motion in the incoming charge.
The effect of different parameters on the kernel development has been investigated.
Spark main characteristics: CDI (6mJ) and TCI (60 mJ) Systems
Mixture properties (λλλλ): 1.00 to 1.30
Turbulence: 0.44 to 1.09 m/s
Flow velocity at spark plug: 7.50 to 31.10 m/s
SI IGNITION MODEL Basic Test Case
34/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
0
2
4
6
8
10
0 200 400 600 800 1000 1200 1400 1600
COARSE
MEDIUM
FINE
Fla
me
su
rfa
ce [
cm
2]
Time [µs]
GRID SIZE SENSITIVITY
0
1
2
3
4
5
6
0 200 400 600 800 1000
10002500500010000
Fla
me s
urf
ace [
cm
2]
Time [µs]
TRIANGULAR ELEMENT SENSITIVITY
To ECFM
COARSE: 2.0 mmMEDIUM: 1.0 mmFINE: 0.5 mm
100025005000
10000
To ECFM
SI IGNITION MODEL Basic Test Case
35/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
0
1 104
2 104
3 104
4 104
5 104
6 104
7 104
0 50 100 150 200 250
1.0
1.3
1.5
Kern
el te
mpe
ratu
re [K
]
Time [µs]
0
0.5
1
1.5
2
0 50 100 150 200 250
1.0
1.3
1.5
La
gra
ng
ian
ke
rnel ra
diu
s [
mm
]
Time [µs]
EFFECT OF MIXTURE AIR INDEX @ 1250 rev/min
SI IGNITION MODEL Basic Test Case
36/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
0
0.5
1
1.5
2
0 0.2 0.4 0.6 0.8 1 1.2
1.0 Exp1.0 Sim1.3 Exp1.3 Sim1.5 Exp1.5 Sim
Tim
e a
fte
r spark
onse
t [m
s]
Flame kernel volume [cm3]
0
0.5
1
1.5
2
2.5
3
3.5
4
0 100 200 300 400 500 600
1.0
1.3
1.5
Fla
me s
urf
ace [
cm
2]
Time [µs]
Predictions only
Models slightly under predicts expansion rate (No tuning done)
SI IGNITION MODEL Basic Test Case
EFFECT OF MIXTURE AIR INDEX @ 1250 rev/min
37/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Effect of flow convection - turbulence – λλλλ=1300 rpm 700 rpm 1250 rpm
100 µµµµs
250 µµµµs
500 µµµµs
625 µµµµs
SI IGNITION MODEL
38/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
λλλλ=1 λλλλ=1 .3 λλλλ=1.5
TCI[60 mJ]
CDI [6 mJ]
EFFECT OF AIR INDEX VARIATION CAPTURED
FLAME HOLDER EFFECT MODELLED
SI IGNITION MODEL Basic Test Case
39/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
SI IGNITION MODEL Engine Case
APPLIED TO SI ENGINE TO RECOVERC CYCLIC VARIABILITY
EXPERIMENTAL DATA (DUCATI CORSE SRL) ON REAL ENGINE CONFIGURATIONS
SHOW THE CLOSE RELATIONSHIP BETWEEN THE MEAN LAMBDA CYCLE BY CYCLE
VARIATION) OF THE ENGINE
THE IGNITION MODEL HAS BEEN MODIFIED IN ORDER TO ANALYSE IN DETAIL THE
INFLUENCE OF MIXTURE UNIFORMITY ON CYCLIC VARIATION
40/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
SI IGNITION MODEL Engine Case
Racing Application
41/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
SI IGNITION MODEL Engine Case
Racing Application
42/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
HOW? ICE STEADY FLOW
HOW? BASIC TEST-CASE AND MERIT INDEX
WHEN? ENGINE CASES
LES
OPEN QUESTIONS: HOW AND WHEN ?
43/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LES OPEN QUESTIONS: HOW AND WHEN?
TWO OPEN ISSUES:
HOW (DOES LES HAVE TO BE APPLIED) ?
WHEN (CAN LES BE REASONABLY APPLIED) ?
Focus: simulation of complex case
We do not present only results but the way we got them
Be aware of LES quality at least to know that it is V-LES
RELATED MAIN PAPERS: SAE Papers 2007-01-4145, Best Paper Award Fluent Italia UGM 2006
POLICY
44/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LES OPEN QUESTIONS: HOW AND WHEN?
HOW ? These is the minimum check list before performing LES
LOW KIN. ENERGY DISSIPATION SCHEME REQUIRED (2nd, 3rd)
CFL NUMBERS REQUIRED BELOW ONE
CHECK ON CELL SHAPE INFLUENCE
CHECK ON TIME WINDOW LENGTH
PROPER BOUNDARY CONDITIONS
45/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LES OPEN QUESTIONS: HOW AND WHEN?
HOW ? These is the minimum check list before performing LES
MERIT INDEX TO KNOW THE REAL FRACTION OF ENERGY RESOLVED
(NOBODY SHOWS …)
FILTER SIZE ADAPTED TO LOCAL FLOW CONDITIONS
WALL-FUNCTIONS ?
GRID REFINEMENT OR COARSENING EFFECT ON EN. SPECTRA
(Mov. Boundary)
46/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Bounded flow;
Easy 3D geometry;
Flow detachment/reattachment.
Numerical setup in Fluent 6.2
Segregated flow solver together with a fully implicit second-order scheme;
Diffusive fluxes are discretized by using central differencing scheme;
Convective fluxes are discretized by using bounded central differencing scheme;
LES model: WALE and Localized Dynamic 1-EQ. Model (integration at wall)
TEST CASE: Flow over a backward facing step
(Eaton, Johnston, Westphal, Ames Research Center NASA, 1986)
1 2 3
Mean axial velocity profile
4 5 6Flow direction
LES HOW? BASIC TEST-CASE AND MERIT INDEX
Most suitable commercial code for LES
47/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
A LES simulation is accurate when (one needs to know the energy
fraction really resolved (see Pope):
2.0),(),(
),(),( ≤
+=
txktxK
txktxM
sgs
sgs
vrr ),( tx
r∆
LES HOW? BASIC TEST-CASE AND MERIT INDEX
A refinement procedure has to be used1>+
y15≥Rν
Seven refinement steps
(from 0.39 MCells to 2.0 MCells)
An auto-adaptive LES simulation is complete
48/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
0
2
4
6
8
10
12
14
-0,4 0 0,4 0,8 1,2
Y [
cm
]
U/Uo
Experimental
LDKEM
0
2
4
6
8
10
12
14
-0,4 0 0,4 0,8 1,2
Y [
cm
]
U/Uo
0
2
4
6
8
10
12
14
-0,4 0 0,4 0,8 1,2
Y [
cm
]
U/Uo
0
2
4
6
8
10
12
14
-0,4 0 0,4 0,8 1,2
Y [
cm
]
U/Uo
Secti
on
1
Secti
on
2
Secti
on
3
Secti
on
5
(2 M. of cells)
LES HOW? BASIC TEST-CASE AND MERIT INDEX
49/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
M parameter has been used as final merit index.
LES HOW? BASIC TEST-CASE AND MERIT INDEX
0
2
4
6
8
10
12
14
0 0,2 0,4 0,6 0,8 1
Y [
cm
]
M
0
2
4
6
8
10
12
14
0 0,2 0,4 0,6 0,8 1
Y [
cm
]
M
0
2
4
6
8
10
12
14
0 0,2 0,4 0,6 0,8 1
Y [
cm
]
M
Secti
on
2
Secti
on
3
Secti
on
5
0.39 Mcells
2.0 Mcells
50/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
10Valve lift [mm]
132L2 [mm]
300L1 [mm]
34D3 [mm]
16D2 [mm]
120D1 [mm]
ICE STEADY (NON-REACTIVE) FLOWThobois, Rymer, Souleres, Poinsot, SAE Paper, 2004
LDA velocity profiles are available on two planes at 20mm and 70mm from cylinder head.
20m
m
70m
m
LES HOW? BASIC ICE TEST-CASE
Numerical Settings: same as previous using Fluent 6.2
Ckecking: WALE with and w/o wall function
LDKEM -> Merit index for evaluating LES
51/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LES HOW? BASIC ICE TEST-CASE
Questions:
1. How far is LES from providing results in ICE case
(complex geometry, complex wall-bounded effects, ecc) ?
2. Is LES ready for being applied with accuracy or
V-LES is likely performed ?
3. What LES can bring more with respect to RANS ?
52/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Mesh Generation
It provides a good solution level for the turbulent scales in the flow core.
2 Million of cells.
5030 ÷≈+y
WALE
4.3 Million of cells.
1≈+y
LDKEM
It provides a quasi-complete LES simulation on all the flow domain execept in turbulent boundary layer.
LES HOW? BASIC ICE TEST-CASE
53/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
-0,6
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
1,2
-1 -0,5 0 0,5 1
LES_LDKEM
LES_WALE
LDA
U(t
)/U
o
r/R
-0,6
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
1,2
-1 -0,5 0 0,5 1
LES_LDKEM
LES_WALE
LDA
U(t
)/U
o
r/R
20mm
70mm
�
�
On the 20mm plane, both LES models allow to obtain a reasonable good agreement between numerical and experimental profiles.
On the 70mm plane, both LES models fit the overallexperimental trend except for the flow under the valve.
LES HOW? BASIC ICE TEST-CASE
54/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
0
0,1
0,2
0,3
0,4
0,5
-1 -0,5 0 0,5 1
LES_LDKEM
LES_WALE
LDA
u'/U
o
r/R
0
0,1
0,2
0,3
0,4
0,5
-1 -0,5 0 0,5 1
LES_LDKEM
LES_WALE
LDA
u'/U
o
r/R
20mm
70mm
�
�
On the 20mm plane, both WALE and LDKEM sgs models match with good agreement the experimental trend. The dynamic model provides better predictions in the evaluation of peak positions and magnitudes.
On 70mm plane, both LES models fit the overallexperimental trend on all the section.
LES HOW? BASIC ICE TEST-CASE
55/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LDKEM Model: M Parameter
0
0,1
0,2
0,3
0,4
-1 -0,5 0 0,5 1
M on the plane at 20mm
M
r/R
0
0,1
0,2
0,3
0,4
-1 -0,5 0 0,5 1
M on the plane at 70mm
M
r/R
LES HOW? BASIC ICE TEST-CASE
20mm
70mm
56/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LES WHEN? ENGINE CASES
Answer (steady flow condition, fixed grid):
1. LES (V-LES) is close to provide answer every time investigationof large-scale unsteadiness is required (lack of experiment)
2. LES might provide effective information of flow separation by adverse pressure gradient accepting a compromise in turbulentboundary layer solution (RANS does it better ?)
3. Still issues in wall-bounded flow solution -> friction prediction
57/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LES OPEN QUESTIONS: HOW AND WHEN?
WHEN ?
LARGE SCALE UNSTEADINESS (I.E., MIXING, DROPLET CONVECTION)
LARGE SCALE UNSTEADINESS INDUCED BY FLOW SEPARATION
BENCHMARK FOR IMPROVING RANS SIMULATIONS
ACOUSTICS
CYCLE-TO-CYCLE VARIABILITY EFFECT IN ICE FLOWS (IFP, …)
LIQUID JET ATOMIZATION
COMBUSTION ? -> Through RANS model (Flame thickness too thin)
58/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
IMPROVING RANS MODELING (ICE TEST-CASE)
LES WHEN? ENGINE CASES
LES
RANS 1
NORANS 2
YES
59/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
IMPROVING RANS MODELING
MEAN FLOW PEDICTIONS IN RANS LES OFFERS MORE FOR (LARGE) SCALEFLOW UNSTEADINESS
LES WHEN? ENGINE CASES
Non-dimensional meax axial velocity Non-dimensional rms axial velocity fluctuation
Non-dimensional Radial Distance Non-dimensional Radial Distance
60/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LES WHEN? ENGINE CASES
Racing Application
61/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LES WHEN? ENGINE CASES
Racing Application
62/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
LES WHEN? ENGINE CASES
Racing Application
63/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
TIPS TO MAKE IT WORK
BASIC EQUATION
BENCHMARK
WALL FILM MODEL
PHYSICAL ISSUES
Related Main Papers: ICES2005-1063, SAE 2007-24-0087
64/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
INTERACTION
WALL
SPRAY
GAS
Two-dimensional flux over three-dimensional surfaces
�Impinging Spray
�Heat transfer with wall and gas
�Fuel evaporation
�Gravity and other body forces
�Shear forces at the interface with gas and wall
WALL FILM PHYSICAL ISSUES
65/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
HYPOTHESIS
Boundary-layer approximation
Laminar Flow
Incompressible Flow
Newtonian FluidThe equations of mass, momentum and energyare written and integrated following a finite volume
approach and ALE time advancement:
( )∑ =⋅+∆
∆ Nside
i w
diiif
w A
SlnV
At ρδ
δˆ
1 r
( )wp
H
wp
wNside
i wp
g
iiifi
w Ac
S
Ac
J
Ac
JlnVT
At
T
ρρρδ ++=⋅+
∆
∆∑ ˆ
1 r
( )( ) ( ) ( )tan
1 1 1 1ˆ ˆ
NedgeNside Nsidef
f f i i i i i ii
i i iw w w w
VV V n l pn l g M A
t A A A A
δδ δ δ τ
ρ ρ ρ
∆+ ⋅ = − + + +
∆∑ ∑ ∑
rr r rr r
WALL FILM BASIC EQUATIONS
66/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
A relative system of coordinates is created on each face
WALL FILM TIPS TO MAKE IT WORK
x’
y’
z’
pgp
p
The different film heights between neighbour cells must be taken into account by appling
the film pressure over the common contact area, while the gas pressure is applied over
the remaining boundary area
67/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
The approximation of constant
film height over the control
volume does not permit to
reconstruct the characteristics
of the interface: high numerical
diffusion and overextimation of
evaporation,
WALL FILM TIPS TO MAKE IT WORK
In order to reproduce the effect of
surface tension a fitting minimum
threshold value is used to impose a
minimum film height into a control
volume the area for surface
evaporation is accordingly
evaluated
Real gas-film interface of boundary edge
Computed gas-film interface of boundary
edge
Real gas-film interface of boundary edge
Computed gas-film interface of boundary
edge
Real interface
Computed
with
threshold
Min Height
Yes No
Real interface
Computed
with
threshold
Min Height
Real interface
Computed
with
threshold
Min Height
Yes No
68/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
174 barInjection pressure
19 C.A.Duration of injection
-19 ATDCStart of injection
12.3 mg/cycleInjected mass
2.94 barInlet air pressure
673 KWall temperature
DieselFuel
14Compression ratio
750 rpmEngine speed
8 Number of cylinders
225 mmStroke
150 mmBore
Two-Stroke DI Diesel Engine
Injection and Combustion simulation
Simulation between IVC and EVO
Small angle between spray direction and bowl wall
Prevalent impinging regime is Stick
WALL FILM VALIDATION: DIESEL
Test Case:
Stanton, D., and Rutland, C. J., 1998. “Multi-dimensional modeling of heat and mass transfer of fuel films resulting from impinging sprays”. SAE Paper 980132
69/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Sensor 1
Sensors position
Sensor 3
WALL FILM VALIDATION: DIESEL
70/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
0.42m3/minAir flow rate
21.5mm3Injected quantity per shot
40HzInjection frequency
45 °Angle injector/tube
6.7msInjection Duration
30°Spray Cone Angle
16m/sDroplet Velocity
90µmSauter Mean Diameter
Reproduces injection and liquid-film
conditions similar to those occuring in PFI gasoline engines
Prevalent impinging regime is Stick
Characterized by low Weber number
Pulsed injection with 8 injection events
WALL FILM VALIDATION: PFI
Test case:
Le Coz, J. F., Catalano, C., and Baritaud, T., 1994. “Application of laser induced fluorescence for measuring the thickness of liquid films on transparent wall”. In 7th International Symposium on Application of Laser Techniques to Fluid Mechanics.
71/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
Sensor 2Sensor 1
WALL FILM VALIDATION: PFI
72/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
WALL FILM VALIDATION: PFIF
ilm
He
igh
t
Sensor 1
Comparison with Fluent and Fire 8.4
FIREFLUENT
KIVA_UNIBO
EXPERIMENTS
73/73DIEM OVERVIEW
University of BolognaUniversity of Bologna
School School of of Engineering Engineering -- D.I.E.M.D.I.E.M.
WALL FILM MODEL INTERFACE
INTERFACE
Wall Film
Model
GeneralCFD CODE
The integration of the equation of the model is fully explicitand it is implemented in Fortran 77
In order to make the model totally indipendent from the CFD code it has been created an interface for the comunication of the variables of interest
INPUT DATA• Geometry information of wall cells- compatibilty with 4 edge-faces tested- mixed 3edge- 4edge faces to be tested
• Velocity and mass of the impinging droplets• Thermodynamic information of the surrounding gas• Temperature of the wall• Shear stress of gas on the wall
OUTPUT DATA• Wall film height evolution• Source terms because of film evaporation