Development of an Open-Source CFD Library for Fluid ... · generated‘isotropic’ turbulence, J....
44
Introduction Outline Development - synth. turbulence - SGS models - quality index - NSCBC - sliding interface Validation tests - BFS - engine Conclusions Current work - moving mesh - Region model CPU Resources Contact References Development of an Open-Source CFD Library for Fluid Mechanics Simulation A. Montorfano, F. Piscaglia Dipartimento di Energia, POLITECNICO DI MILANO
Transcript of Development of an Open-Source CFD Library for Fluid ... · generated‘isotropic’ turbulence, J....
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Development of an Open-Source CFD Library
for Fluid Mechanics Simulation
A. Montorfano, F. Piscaglia
Dipartimento di Energia, POLITECNICO DI MILANO
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Introduction
Motivation:
- To develop models, algorithms and solvers for compressible turbulent flows
- To provide a consolidated tool for engine and CFD modeling, to be used both fordevelopment and diagnostic purposes
Main requirements:
- Implementation of the state of models into a single CFD platform
- reliable mesh-management techniques to handle moving grids with complex ge-ometry
2/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
OpenFOAM®
OpenFOAM® - Project Status Summary:
- Free software, available to all at no charge: GNU Public License,
- Open-source development model, public contributions, documentation
- Object-oriented approach facilitates model implementation
- Domain decomposition parallelism is integrated at a low level
- Equation mimicking opens new grounds in Computational Continuum Mechanics
- Extensive capabilities already implemented; open design for easy customisation
LibICE® has been developed using OpenFOAM® as base platform.
3/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
OpenFOAM®
OpenFOAM® - Project Status Summary:
- Free software, available to all at no charge: GNU Public License,
- Open-source development model, public contributions, documentation
- Object-oriented approach facilitates model implementation
- Domain decomposition parallelism is integrated at a low level
- Equation mimicking opens new grounds in Computational Continuum Mechanics
- Extensive capabilities already implemented; open design for easy customisation
LibICE® has been developed using OpenFOAM® as base platform.
4/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Outline
- OVERVIEW OF RECENTLY IMPLEMENTED MODELS:
- Synthetic turbulence
- Subgrid Scale Models
- NSCBC coupling with implicit solvers
- Fully-parallel automatic mesh motion with topological changes
- Definition of quality indices:
- Length Scale Resolution parameter (LSR)
- APPLICATION AND VALIDATION AGAINST EXPERIMENTS:
- LES simulation of compressible/incompressible in-cylinder flows
- Validation of NSCBC: acoustics of silencers
- UNDER CURRENT DEVELOPMENT:
- region model to simulate acoustical buffer zones
- simulation of engine-like and real engine geometries with parallel topologi-cally moving meshes
5/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Synthetic Turbulence
The purpose of inlet turbulence can be regarded as to reproduce some salientturbulent characteristics, rather than reproducing a turbulent fields under all as-pects.
INLET TURBULENCE PROPERTIES
- Stochastic variation (up to filter scale)
- Compatibility with continuity equation (solenoidal velocity field, ∇ · (ρU) = 0)
- Similarity to DNS with respect to some statistics (〈U〉, 〈uiuj 〉)- Ease of turbulence specification
- Ease of implementation and adjustement
F. Piscaglia, A. Montorfano, A. Onorati “Boundary conditions and subgrid scale models for LES simulation
of IC Engines in OpenFOAM”, 7th OpenFOAM® Workshop, Darmstadt, 2012
6/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Synthetic Turbulence
Synthetized turbulence is generated using N random Fourier modes:
u′
i (xj ) = 2
N∑
n=1
un cos (κnj xj + ψn) σn
i
where, for the nth Fourier mode:
- un = velocity amplitude
- κnj
= random wavenumber vector
- ψn = random phase
- σnj = random direction
ALGORITHM
1) random angles φn, αn and θn and random phase φn are created for each mode n
2) the highest and the lowest wave numbers κmax and κmin are defined and thewavenumber space is divided into N modes which size is ∆κ
3) the randomized components of κn are computed
Davidson, Lars. Hybrid LES-RANS: Inlet Boundary Conditions for Flows Including Recirculation, TS5, 2007
7/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Synthetic Turbulence: Random Angles
u′
i(xj ) = 2
∑Nn=1
un cos (κnjxj + ψn) σn
i
Randomized components of κnj must be computed by considering:
- Solenoidality is enforced by generating σnj that are orthogonal to κn
j
- Wavenumber vector κnj is oriented according to angles ϕn and θn
- Velocity vector σnj
lies in a plane orthogonal to κnj
and is oriented according toαn
- Random angles are generated according to the following distributions:
8/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
P(ϕn) = 1/(2π) 0 ≤ ϕn ≤ 2π
P(ψn) = 1/(2π) 0 ≤ ψn ≤ 2π
P(θn) = 1/ sin(θ) 0 ≤ θn ≤ π
P(αn) = 1/(2π) 0 ≤ αn ≤ 2π
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Synthetic Turbulence: Energy Spectrum
Amplitude of the κth turbulent mode u(κ)n
un =√
E(|κnj |)∆κ
is generated according to a modified von-Karman spectrum:
E(κ) = αu2rms
κe
(κ/κe)4
[1 + (κ/κe)2]17/6
exp[
−2(κ/κη)2]
α=1.4256
κ =√κjκj
κη = ε1/4ν−3/4
κe = 9π55
αL
- the highest wave number κmax is based on mesh resolution κmax = 2π2∆
(∆=gridspacing)
- ∆κ is obtained by equally dividing κmax -κ1 into N modes
9/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Synthetic Turbulence: Final Processing
Once the ‘raw’ fluctuations u′
i(x, t) are generated, they need some postprocessing
before they can be added to the average field 〈u(x, t)〉:
1) Temporal correlation must be enforced: Billson’s temporal filtering
(u′
inlet)m = a(u′
inlet)m−1 + b(u′)m
where a = exp (−∆t/T ), b =√
1 − a2 and T is the integral timescale
2) A blending function fbl is applied to limit freestream turbulence and to blendfluctuations close to the wall:
fbl = max[
0.5 tanh n−δb, 0.1
]
Finally, the inlet velocity is calculated:
uinlet (y , z , t) = Uinlet + fbl · u′
inlet(y , z , t)
10/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
0 2 4 6 8 100
0.2
0.4
0.6
0.8
1
y
f bl b
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Synthetic Turbulence: validation
Evaluation of synthetic turbulence generation methods (in collaboration with FreibergUniversity of Technology, Prof. C. Hasse): the aim of the work is to study how farany unphysical spectrum generated by the methods penetrates into a flow field be-fore it relaxes on the spectrum.
10 100 1000
kappa [m-1]
1e-06
1e-05
0.0001
0.001
E [m2/s2]
Exp (Comte-Bellot)
Sim: 323 cells
Sim: 643 cells
Sim: 1283 cells
Results were kindly provided by Dirk Dietzeld (advisor: Prof. C. Hasse), Freiberg University of Technology.
G. Comte-Bellot, S. Corrsin, Simple Eulerian correlation of full- and narrow-band velocity signals in grid-generated ‘isotropic’ turbulence, J. Fluid. Mech (1971), 48:273:337
11/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
SGS models for LES
WALE – Wall-Adapting Local Eddy viscosity model: algebraic SGS model withautomatic scaling of SGS viscosity near solid walls.
- It is based on the (incompressible) eddy-viscosity hypothesis :
dev[
τ(s)ij
]
= νsgs S ij with: νsgs = Cw∆2OP
- The operator OP is defined as:
OP =
(
SijSij
)3/2
(
S ijS ij
)
5/2
+(
SijSij
)
5/4
where:
Sij =1
2(g2
ij + g2
ji ) −1
3δij g
2
kk gij =∂uj
∂xi
F. Nicoud and F. Ducros, “Subgrid-Scale Stress Modelling Based on the Square of the Velocity GradientTensor”, Flow, Turbulence and Combustion, 62:183-200, 1999
12/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
WALE model: motivation
10−1
100
101
102
103
10−12
10−9
10−6
10−3
y+ [−]
νsg
s [m
2/s
]
x/H = −0.75
10−1
100
101
102
103
10−12
10−9
10−6
10−3
y+ [−]
νsg
s [m
2/s
]
x/H = −3.00
10−1
100
101
102
103
10−12
10−9
10−6
10−3
y+ [−]
νsg
s [m
2/s
]
x/H = −0.75
−◦− dynamic Smagorinsky, −△− WALE; - - - y3 slope.
- Eddy-viscosity, algebraic model with constant coefficient
- Favourable aspects of the operator OP :
- it accounts for both resolved strain rate and resolved vorticity
- it vanishes at walls as O(y3)
- it remains bounded within the flow
- Very low computational overhead
- appealing for ICE simulations (solid walls, complex flow configurations, . . . )
13/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
WALE model: extension
WALE – Wall-Adapting Local Eddy viscosity model
- A compressible version is also available:
µsgs = ρ(Cw∆)2(
SijSij
)
3/2
(
S ijS ij
)5/2
+(
SijSij
)5/4
and:
τ sgsij
= 2µsgs
(
S ij −1
3Skkδij
)
− 2
3
C ′
I
ρ
(µt
∆
)2
δij
- The constant Cw was determined by tuning the model for several test cases andthen taking an average value
- A dynamic procedure can be implemented to render the model more generalwrt. the type of flow
14/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Quality index: LSR
subgrid scales
LENGTH SCALE RESOLUTION (LSR):
LSR =∆
ℓDI
where:
ℓDI ≈ 60 η
η = ν3/4ε−1/4
ε ≃ Cεk3/2
∆
Features:
- LSR estimates the completeness of a LES, not its global quality
- LSR ≤ 5 indicates quasi-complete LES
- High values of LSR point out those mesh regions that need refinement
15/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Quality index: LSR
Advantages:
- gives information on the local mesh refinement
- directly related to magnitude of smaller resolved scale
- compatible with Adaptive Grid Refinement
Drawbacks:
- Estimation of η not trivial: a correct estimation of ε is implied
- LSR is reliable only if different meshes have similar structure
- it does not account neither for modeling errors nor for numerical dissipation
16/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
NSCBC in local Cartesian coords
- For each cell face at the boundary, a local reference frame (ξ, η, ζ), having itsorigin in the cell face center, has been defined:
x = x(ξ, η, ζ)
y = y(ξ, η, ζ)
z = z(ξ, η, ζ)
- Governing equations in the global reference frame take the form:
∂U
∂t+∂F1
∂x+∂F2
∂y+∂F3
∂z= −∇p+∇ · T
U =U
J
∂F1
∂x=
F1xξ + F2xη + F3xζ
J
∂F2
∂y=
F1yξ + F2yη + F3yζ
J
∂F3
∂z=
F1zξ + F2zη + F3zζ
Jx
y
z
17/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
NSCBC: numerical solution
- Governing equations solved by a multistage time stepping scheme in tn,k :
tn,k ≡ tn + k · δt = tn +k
K∆t k ∈ [1;K ] (1)
where tn,k is a variable local fractional time-step.
- The method consists of the iteration of two main steps:
1) Evaluation of backward spatial derivatives at tn and of the fluxes at timetn + k
K∆t; cons. eq. solved sequentially. The solution is 1st order in time.
2) Fluxes and source terms calculated at the previous step are used to findthe solution at time tn + k+1
K∆t. The time accuracy of this method is 2nd
order at this stage.
- Process iterated until the solution at the new time tn+1 ≡ t +∆t is calculated.
ADVANTAGES:
- requires a relatively small amount of memory storage
- it is more stable and accurate than an explicit method
- larger global time steps in the simulation than a traditional explicit method
18/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
NSCBC: validation
0 250 500 750 1000 1250 1500 1750 2000
Frequency [Hz]
0
10
20
30
40
50
Tra
nsm
issio
n loss [dB
]
RC-l1
- Implementation of a true non-reflecting outlet based on the NSCBC theory: vari-ables are computed on the boundaries by solving the conservation equations asin the inner domain
- absence of reflection is enforced by correcting the amplitude of the ingoingcharacteristic (wave reflected by the boundary).
F. Piscaglia, A. Montorfano, A. Onorati “Development of a non-reflecting boundary condition for multi-dimensional non-linear duct acoustic computation”, Journal of Sound and Vibration, in press, doi:10.1016,2013.
19/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Parallel Topologically Changing Meshes (OF-2.1.x)
- Deforming geometries of reciprocating engines requires dynamic meshhandling for:
- Piston motion
- Valve opening/closing
- Scavenging ports (2-stroke engines)
- Dynamic mesh modifiers without topological changes:
- Deforming mesh (stretching)
- Smooth solver (Laplace equation)
- Dynamic mesh modifiers with topological changes:
- Attach/detach boundary
- Layer addition/removal
- Sliding interface
All topological changes have been developed to correctly work with decom-posed meshes (parallel computations) in the OpenFOAM® 2.1.x technology.
20/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Layer addition/removal mesh modifier
layerAdditionRemoval removes cell layers when the mesh is compressed andadds cells when the mesh is expanding
- Only one cell layer is stretched
- Layer is removed if thickness is lowerthan minLayerThickness
- Layer is added if thickness is greaterthan maxLayerThickness
right{
type layerAdditionRemoval;faceZoneName rightExtFaces;minLayerThickness 0.0002;maxLayerThickness 0.0005;active on;
}
21/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Sliding interface mesh modifier (OF-2.1.x)
A slidingInterface allows relative sliding of components.
1. Decoupled interface: the mesh isdivided in different regions
2. Motion solver is applied to the regions
3. Interfaces are coupled: slave points areprojected onto the master patch; themesh is stitched
4. Fluid-dynamic solution is calculated
5. Regions are decoupled to prepare tothe next topological change
scavengingPort{
type slidingInterface;masterPatchName cylPort;slavePatchName ductPort;projection visible;active on;
}
22/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Sliding Interface mesh modifier (OF-2.1.x)
- In the slidingInterface, the topology of different mesh regions is stored forlater decoupling.
- The implementation of the algorithm is strictly dependent on the mesh handlingstrategy of the code:
- OpenFOAM®-ext: mesh definition contains the topology of the decoupledmesh as a set of faces, cells and points labeled as “inactive”
- OpenFOAM®-2.1.x: mesh definition contains the topology of the current cal-culation only. Additional information about the topological changes is storedseparately → official version 2.1.x is not configured to allow for the de-coupling of the mesh through an interface
Novel algorithm for parallel topologically changing meshes in LibICE-2.1.x
(F. Piscaglia, A. Montorfano)
23/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Application: two-stroke engine
24/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Application: two-stroke engine
25/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Validation tests
26/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Backward Facing Step
L1 L2
H
W1W2
W3
x
y
J. Eaton, J. Johnston, and R. Westphal. ”Experimental study of flow reattachment in a single-sided sudden expansion”.
Contractor report 3765, NASA Ames Research Center, NASA, 1986.
- Similarity with IC engines: strong detachment between the intake ports andthe cylinder
- Re = 50000
- Mesh resolution at walls: ∆x+ ≈ 200, ∆y+ ≈ 0.8, ∆z+ ≈ 60
- Cell size is too large to solve wall structures: same situation of realengine cases.
- no use of wall functions: boundary layer directly resolved at the walls
27/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Mfreestream 0.03
Re freestream 50000
Pamb 101325 Pa
Tamb 298 K
mesh size: ≈ 800 · 103 cells
solver: incomp. (tr-SIMPLE)
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Backward Facing Step
L1 L2
H
W1W2
W3
x
y
J. Eaton, J. Johnston, and R. Westphal. ”Experimental study of flow reattachment in a single-sided sudden expansion”.
Contractor report 3765, NASA Ames Research Center, NASA, 1986.
Numerical setup:
- Temporal discretization: second-order backward differencing
- Convection terms ∇ · (UU): pure second-order centered scheme
- SGS model: incompressible WALE vs. dynamic Smagorinsky
- Solver: incompressible transient-SIMPLE
27/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Mfreestream 0.03
Re freestream 50000
Pamb 101325 Pa
Tamb 298 K
mesh size: ≈ 800 · 103 cells
solver: incomp. (tr-SIMPLE)
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Backward Facing Step
0 0.5 10
0.5
1
1.5
y/c
[−
]
U/U0
x/H = −9.75
0 0.2 0.40
0.5
1
1.5
y/c
[−
]
RMS(u’)/U0
0 0.5 10
0.5
1
1.5x/H = −3
0 0.2 0.40
0.5
1
1.5
0 0.5 10
0.5
1
1.5x/H = −0.75
0 0.2 0.40
0.5
1
1.5
0 0.5 1−1
−0.5
0
0.5
1
1.5x/H = 4
0 0.2 0.4−1
−0.5
0
0.5
1
1.5
0 0.5 1−1
−0.5
0
0.5
1
1.5x/H = 6
0 0.2 0.4−1
−0.5
0
0.5
1
1.5
0 0.5 1−1
−0.5
0
0.5
1
1.5x/H = 8
0 0.2 0.4−1
−0.5
0
0.5
1
1.5
0 0.5 1−1
−0.5
0
0.5
1
1.5x/H = 12
0 0.2 0.4−1
−0.5
0
0.5
1
1.5
0 0.5 1−1
−0.5
0
0.5
1
1.5x/H = 16
0 0.2 0.4−1
−0.5
0
0.5
1
1.5
◦ experimental data; — dynamic Smagorinsky; — WALE.
28/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Backward Facing Step
Near-wall velocity
10−1
100
101
102
103
0
5
10
15
20
25
30
35
40
y+ [−]
U+ [
−]
x/H = −9.75
10−1
100
101
102
103
0
5
10
15
20
25
30
35
40
y+ [−]
U+ [
−]
x/H = −3.00
10−1
100
101
102
103
0
5
10
15
20
25
30
35
40
y+ [−]
U+ [
−]
x/H = −0.75
Near-wall SGS viscosity
10−1
100
101
102
103
10−12
10−9
10−6
10−3
y+ [−]
νsg
s [m
2/s
]
x/H = −0.75
10−1
100
101
102
103
10−12
10−9
10−6
10−3
y+ [−]
νsg
s [m
2/s
]
x/H = −3.00
10−1
100
101
102
103
10−12
10−9
10−6
10−3
y+ [−]
νsg
s [m
2/s
]
x/H = −0.75
−◦− dynamic Smagorinsky, −△− WALE; − · − Law-of-the-wall - - - y3 slope.
29/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
cold flow LES of IC-engines
20 mm70 mm
plane 1 plane 2 Ld = 300 mm
Lu = 104 mm
Di = 16 mm
De = 34 mm
D = 120 mm
h = 10 mm
Ds = 27.6 mm
Ls = 4.24 mm
Ld
D
De
Di
Ds
Ls
h
Experiments:
- Simple IC engine geometry: one axis-centered valve, expansion ratio=3.5
- Mean velocity at the inlet: 65 m/s
- LDA measurements @ z=20 mm and z=70 mm(z= distance from the cylinder top)
- axial mean flow velocity
- velocity fluctuations (radial and tangential direction)
L. Thobois, G. Rymer, T. Soulères, and T. Poinsot. “Large-eddy simulation in IC engine geometries”.SAE Technical Paper 2004-01-1854, 2004.
30/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
cold flow LES of IC-engines
20 mm70 mm
plane 1 plane 2 Ld = 300 mm
Lu = 104 mm
Di = 16 mm
De = 34 mm
D = 120 mm
h = 10 mm
Ds = 27.6 mm
Ls = 4.24 mm
Ld
D
De
Di
Ds
Ls
h
Simulations:
- Two grids used: 1.4 M cells, 14 M cells
- Boundary conditions
- inlet: turbulence synthetic inlet
- outlet: unsteady convective
- walls: no-slip condition
- SGS model: WALE
- Solver: incompressible transient-SIMPLE
- Temporal discretization: 2nd order, backward differencing
- Convection terms: 2nd order, TVD-limited
30/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
n. cells n+ ∆x
+ax
∆x+tg
1.4 M 200 10 500
14 M 100 5 500
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
cold flow LES of IC-engines
0 0.2 0.4 0.6 0.8 1−1
−0.5
0
0.5
1x = 20 mm
r/Rmax
[−]
<U
>/U
0 [
−]
(a)
0 0.2 0.4 0.6 0.8 10
0.1
0.2
0.3
0.4
0.5x = 20 mm
r/Rmax
[−]
RM
S(u
’)/U
0 [
−]
(b)
0 0.2 0.4 0.6 0.8 10
0.1
0.2
0.3
0.4
0.5x = 20 mm
r/Rmax
[−]
RM
S(t
’)/U
0 [
−]
(c)
0 0.2 0.4 0.6 0.8 1−1
−0.5
0
0.5
1x = 70 mm
r/Rmax
[−]
<U
>/U
0 [
−]
(d)
0 0.2 0.4 0.6 0.8 10
0.1
0.2
0.3
0.4
0.5x = 70 mm
r/Rmax
[−]
RM
S(u
’)/U
0 [
−]
(e)
0 0.2 0.4 0.6 0.8 10
0.1
0.2
0.3
0.4
0.5x = 70 mm
r/Rmax
[−]
RM
S(t
’)/U
0 [
−]
(f)
— coarse mesh; - - fine mesh; ◦ experiments.
a, d) mean axial velocity b, e) mean axial velocity fluctuations c, f) mean tangential velocity fluctuations.
31/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Quality index: LSR
32/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
cold flow LES of IC-engines
33/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Conclusions
Advanced models and algorithms for LES of IC engines (OF-2.1.x)
- Moving mesh: parallel topologically changing meshes (OF-2.1.x)
- Inlet BC: synthetic turbulence inflow
- Outlet BC: NSCBC-based non-reflecting outflow
- SGS models: dynSmag, WALE (incomp/compr/compr dynamic)
- Completeness estimator: LSR parameter
- Discretization: 1st/2nd order blending schemes with 2nd order central dif-ference schemes to limit the numerical dissipation
Models have been tested on simple test-cases:
- Backward-facing step (pure 2nd order centered schemes)
- Simplified engine-like geometry (blended 1st-2nd order schemes with TVDlimiter)
34/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Current Work
35/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
LES with Moving Mesh
LES of engine-like configuration with moving mesh, in collaboration with ETH-Zürich:M. Schmitt (phD stud), Dr. C. Frouzakis, Prof. K. Boulouchos, Prof. A. Tomboulides
- Comparison with DNS data (ETH)
- Cell stretching/deformation
- Change in filter length scale
- Remapping of fields
- Fully hexahedral mesh (≈ 13 M cells)
36/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Region model
Couple fluid-dynamic mesh with a boundary region where the NSCBC equationsare solved.
- The use of a buffer region instead of a boundary allows for smaller numericalreflections
- Strong coupling between buffer region and internal domain is achieved by Open-FOAM regionModel feature
- Better numerical stability is expected
37/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Computing Resources
- IBM-BlueGene/Q (CINECA)
- Architecture: 10 BGQ Frame with 2 MidPlanes each
- Processor Type: IBM PowerA2, 1.6 GHz
- Computing Nodes: 10.240, 16 CPU each(163.840 computing cores)
- RAM: 16 GB/node; 1 GB/core
- Peak Performance: 2.1 PFlop/s
- PLX cluster (CINECA)
- 276 nodes, 3312 cores (Xeon E5645 2.40GHz 12MB Cache 1333 MHz 80W)
- RAM: 48 GByte/node DDR3 1333MHz
- 528 GPU nVIDIA Tesla M2050
- 2 Remote Visualization Nodes: 2 nVidia Quadro Plex 2200 128GB RAM
- SGI cluster (ICE-PoliMi)
- 12 nodes, 192 cores (Xeon E5645 2.40GHz 12MB Cache 1333 MHz 80W)
- RAM: 64 GByte/node DDR3 1333MHz
38/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Thank you for your attention!
39/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
Federico Piscaglia, Ph.D.
Assistant Professor of Internal Combustion Engines
Address: Dip. di Energia, Politecnico di Milano
via Lambruschini 4, 20156 Milano (ITALY)
E-Mail: [email protected]
Phone: +39 02 2399 8620
Web page: http://www.engines.polimi.it/
Andrea Montorfano, Ph.D.
Post-doc Researcher
Address: Dip. di Energia, Politecnico di Milano
via Lambruschini 4, 20156 Milano (ITALY)
E-Mail: [email protected]
Phone: +39 02 2399 3909
Web page: http://www.engines.polimi.it/
40/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
References I
1. F. Piscaglia, A. Montorfano, A. Onorati, and J. P. Keskinen. Boundary conditions and subgrid scale models for les simulation ofinternal combustion engines. In International Multidimensional Engine Modeling User’s Group Meeting 2012, Detroit, 2012.
2. F. Piscaglia, A. Montorfano, and A. Onorati. Improving the simulation of the acoustic performance of complex silencers for ice by
a multi-dimensional non-linear approach. Journal of Sound and Vibration, X(X):xxx–xxx, 2013. doi:10.1016/j.jsv.2012.09.030.
3. A. Montorfano, F. Piscaglia, and G. Ferrari. Inlet boundary conditions for incompressible les: A comparative study. Mathematical
and Computer Modelling, 2011.
4. F. Piscaglia, A. Montorfano, G. Ferrari, and G. Montenegro. High resolution central schemes for multi-dimensional non-linear
acoustic simulation of silencers in internal combustion engines. Mathematical and Computer Modelling, 54(7-8):1720–1724,2011.
5. A. Onorati, G. D’Errico, T. Lucchini, G. Montenegro, and F. Piscaglia. Development of a multi-dimensional tool for the simulation
of the combustion and in-cylinder flows using the openfoam technology. In 11th Stuttgart International Symposium on
Automotive and Engine Technology, Stuttgart, 2011.
6. F. Piscaglia, A. Montorfano, and A. Onorati. Development of nscbc for compressible navier-stokes equations in openfoam. In
Sixth OpenFOAM Workshop, Penn State, June 12th-16th, 2011.
7. F. Piscaglia, A. Montorfano, and A. Onorati. Multi-dimensional computation of compressible reacting flows through porous media
to apply to internal combustion engine simulation. Mathematical and Computer Modelling, 52(7-8):1133 – 1142, 2010.
8. F. Piscaglia, A. Montorfano, A. Onorati, and G. Ferrari. Modeling of pressure wave reflection from open-ends in i.c.e. duct
systems. SAE Technical Paper 2010-01-1051, 2010.
9. G. Montenegro, F. Piscaglia, A. Montorfano, and A. Onorati. Multi-dimensional parallel simulation of diesel exhaust
after-treatment systems. In International Multidimensional Engine Modeling User’s Group Meeting 2010, Detroit, 2010.
10. F. Piscaglia, A. Montorfano, G. Montenegro, A. Onorati, H. Jasak, and H. Rusche. Lib-ice: a c++ object oriented library for ice
simulation - acoustics and aftertreatment. In Fifth OpenFOAM Workshop, goteborg, June 21-24, 2010., 2011.
11. F. Piscaglia and G. Ferrari. A novel 1d approach for the simulation of unsteady reacting flows in diesel exhaust after-treatment
systems. Energy, 34(12):2051–2062, 2009.
12. F. Piscaglia and G. Ferrari. “Development of an offline simulation tool to test the on-board diagnostic software for diesel
after-treatment systems”. SAE paper n. 2007-01-0133, 2007.
41/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
Introduction
Outline
Development
- synth. turbulence
- SGS models
- quality index
- NSCBC
- sliding interface
Validation tests
- BFS
- engine
Conclusions
Current work
- moving mesh
- Region model
CPU Resources
Contact
References
References II
13. F. Piscaglia Montenegro G, A. Onorati. Impact of ultra low thermal inertia manifolds on emission performance. Atti del 62°
Congresso Nazionale ATI, Salerno, 2007.
14. G. Montenegro, F. Piscaglia, A. Onorati, G. Catalano, and P. Cioffi. A 1-d unsteady thermo-fluid dynamic approach for thesimulation of the hydrodynamics of diesel particulate filters. In SAE Int. Journal Of Fuels & Lubricants. SAE Technical Paper
2006-01-0262, V115-4(1), 2007.
15. F. Piscaglia and G. Ferrari. Modeling of the unsteady reacting flows in the diesel exhaust aftertreatment systems. In: ECOS2007 Conference: Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy . Padova, Italy, 2007.
16. G. Montenegro, G. D’Errico, A. Onorati, and F. Piscaglia. Integrated 1d-multid fluid dynamic models for the simulation of i.c.e.
intake and exhaust systems. SAE paper n. 2007-01-0495, 2007.
17. G. Montenegro, A. Onorati, and F. Piscaglia. A 1d unsteady thermo-fluid dynamic approach for the simulation of diesel
particulate filters. THIESEL 2006 Int. Conference. Valencia (Spain), p. 139-162, 2006. ISBN: 84-9705-982-4.
18. F. Piscaglia, C. J. Rutland, and D. E. Foster. Development of a CFD model to study the hydrodynamic characteristics and the
soot deposition mechanism on the porous wall of a diesel particulate filter. SAE paper n. 2005-01-0963, SAE 2005 Int.
Congress & Exp. (Detroit, Michigan), April 11-14, 2005.
19. F Piscaglia and A. Onorati. A computational investigation of the hydrodynamics and the soot deposition mechanism on the
channel walls of a diesel particulate filter. 60° Congresso Nazionale ATI. Roma, Italy., 2005.
20. G. Montenegro, A. Onorati, and F. Piscaglia. Integrated 1d-multid fluid dynamic models for the simulation of internal combustion
engines. HTCES 2006, 12° Convegno Internazionale “Automobili e motori Hi-Tech”, Modena, 2006.
21. D. Cacciatore, M. Ceccarani, Onorati A., and F. Piscaglia. 1d fluid dynamic modeling of multi-pipe junctions in the exhaust
system of a v12 lamborghini s.i. engine. In In: HTCES 2004 - 10° Convegno Int. “Automobili e Motori Hi-Tech”, Modena, 2004.
22. G. Ferrari, A. Onorati, F. Piscaglia, and L. Spaggiari. 1d fluid dynamic modeling of secondary air injection in the exhaustaftertreatment system of s.i. engines. In In: HTCES 2003 - 9° Convegno Internazionale “Automobili e Motori Hi-Tech”. Modena,
29-30 maggio, 2003.
23. G. Ferrari, A. Onorati, and F. Piscaglia. Fluid dynamic simulation of a six-cylinder s.i. engine with secondary air injection in the
exhaust after-treatment system. ICE 2003- SAE International Conference on Internal Combustion Engines. Capri, Italy, 2003.
42/42A. Montorfano, F. Piscaglia - "Development of an Open-Source CFD Library for Fluid Mechanics Simulation"
