1 st Automotive Workshop, Oxford, UK Paul Batten, Jian Wang & - - PowerPoint PPT Presentation

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1 st Automotive Workshop, Oxford, UK Paul Batten, Jian Wang & - - PowerPoint PPT Presentation

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1 st Automotive Workshop, Oxford, UK Paul Batten, Jian Wang & Oshin Peroomian Dec. 11/12, 2019 1 Overview Challenges Software Case 1 Case 2A Summary 2 Challenges Attached BLs Massive Small/shallow

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SLIDE 1

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1st Automotive Workshop, Oxford, UK

Paul Batten, Jian Wang & Oshin Peroomian

  • Dec. 11/12, 2019
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SLIDE 2

Overview

  • Challenges
  • Software
  • Case 1
  • Case 2A
  • Summary

2

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SLIDE 3

Challenges

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Attached BLs Small/shallow separation Massive separation

N.B. In anticipation of the various separation types and extents, hybrid RANS/LES simulations that used IDDES imposed a box over the forward sections of the simulated vehicles in which IDDES was maintained in RANS mode (this is referred to as an “LES deactivation box”)

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SLIDE 4

Software

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  • CFD Solver Used: CFD++ by Metacomp Technologies, Inc.
  • Steady-state and transient finite-volume solutions
  • Linear eddy-viscosity RANS models
  • Non-linear eddy viscosity (EARSM) RANS models
  • Hybrid RANS/LES (DDES and IDDES)
  • Meshing Software: MIME by Metacomp Technologies, Inc.
  • Multipurpose Intelligent Meshing Environment
  • General size automation and curvature-based refinement
  • Hex-dominant meshes
  • Solve-to-wall meshes created for each MIME mesh
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SLIDE 5

Case 1 - Models

  • RANS:
  • SA
  • SARC+QCR
  • Realizable k-epsilon (RKE)
  • Cubic k-epsilon (CKE/cubic k-e EARSM)
  • SST
  • Hellsten (quartic k-w EARSM)
  • Hybrid RANS/LES
  • IDDES + LES deactivation box

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SLIDE 6

Case 1 - Meshes

  • Workshop RANS Mesh:
  • 4 M cells
  • Half-model mesh (plus symmetry plane)
  • y+ > 1 over much of the body
  • Large spacings near underside wedge/ramp
  • MIME RANS Meshes:
  • Three half-model meshes generated: coarse (5M), medium (10M), fine (15M)
  • Only fine-mesh results presented in subsequent slides
  • y+ < 1 everywhere, for all three meshes

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MIME fine RANS half-mesh

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SLIDE 7

Case 1 - Meshes

  • Workshop Hybrid RANS/LES Mesh:
  • 30.6 M
  • Full-model mesh
  • Growth rate 1.15, 30 cell layers in BL
  • Cell size at rear refined region = 1.7 mm, base (1.2 mm), underbody (2.4

mm), ground (4.8 mm), rear window (1.2 mm), top and front (2.4 mm)

  • First layer height = 3.7e-5m

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SLIDE 8

Case 1 - Meshes

  • MIME Hybrid RANS/LES Mesh:
  • 99 M
  • Full-model mesh
  • Growth rate 1.17, 45 cell layers in BL
  • Cell size at rear refined region = 1.7 mm, base (1.2 mm), underbody (2.4

mm), ground (4.8 mm), rear window (1.2 mm), top and front (2.4 mm)

  • First layer height = 7.5e-6 m

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SLIDE 9

Case 1 - RANS Convergence on Fine MIME Mesh

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Realizable k-epsilon Cubic k-epsilon

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SLIDE 10

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SA SARC+QCR

Case 1 - Convergence on Fine MIME RANS Mesh

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SLIDE 11

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SST Hellsten

Case 1 - Convergence on Fine MIME RANS Mesh

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SLIDE 12

Case 1 - IDDES Force History for Fine MIME Hybrid RANS/LES Mesh

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IDDES

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SLIDE 13

Case 1 - Selected Mesh- Convergence Plots: Cd

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0.14 0.16 0.18 0.2 0.22 0.24 2 4 6 8 10 12 14 16

Cd Million Cells

CKE SARC+QCR SA RKE SST

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SLIDE 14

Case 1 - Selected Mesh- Convergence Plots: Cl

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  • 0.115
  • 0.105
  • 0.095
  • 0.085
  • 0.075
  • 0.065
  • 0.055

2 4 6 8 10 12 14 16

CL Million Cells

CKE SARC+QCR SA RKE SST

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SLIDE 15

Case 1 - Cp Centerline Distribution

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Realizable k-epsilon N.B. Red dots = Experiment Cubic k-epsilon

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SLIDE 16

Case 1 - Cp Centerline Distribution

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SA N.B. Red dots = Experiment SARC+QCR

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SLIDE 17

Case 1 - Cp Centerline Distribution

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SST N.B. Red dots = Experiment Hellsten

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SLIDE 18

Case 1 - Cp Centerline Distribution

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DDES N.B. Red dots = Experiment IDDES + box

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SLIDE 19

Case 1 - Wake Profiles

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Exp. Realizable k-epsilon

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SLIDE 20

Case 1 - Wake Profiles

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Exp. Realizable k-epsilon

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SLIDE 21

Case 1 - Wake Profiles

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Exp. Cubic k-epsilon

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SLIDE 22

Case 1 - Wake Profiles

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Exp. Cubic k-epsilon

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SLIDE 23

Case 1 - Wake Profiles

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Exp. SA

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SLIDE 24

Case 1 - Wake Profiles

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Exp. SA

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SLIDE 25

Case 1 - Wake Profiles

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Exp. SARC+QCR

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SLIDE 26

Case 1 - Wake Profiles

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Exp. SARC+QCR

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SLIDE 27

Case 1 - Wake Profiles

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Exp. SST

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SLIDE 28

Case 1 - Wake Profiles

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Exp. SST

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SLIDE 29

Case 1 - Wake Profiles

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Exp. Hellsten

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SLIDE 30

Case 1 - Wake Profiles

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Exp. Hellsten

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SLIDE 31

Case 1 - Wake Profiles

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Exp. DDES

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SLIDE 32

Case 1 - Wake Profiles

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Exp. DDES

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SLIDE 33

Case 1 - Wake Profiles

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Exp. IDDES+box

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SLIDE 34

Case 1 - Wake Profiles

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Exp. IDDES+box

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SLIDE 35

Case 1 - IDDES: Normalized Q-Criterion

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IDDES+box

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SLIDE 36

Case 1 - Fine MIME Mesh Results

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Test Cases

Cd Cl Cm Realizable k-epsilon 0.1917

  • 0.08385
  • 0.1195

Cubic k-epsilon 0.1844

  • 0.07547
  • 0.1121

SA 0.2297

  • 0.1022
  • 0.1097

SARC+QCR 0.2339

  • 0.08895
  • 0.1189

Hellsten 0.1962

  • 0.07850
  • 0.1280

SST (Deep convergence not achieved) 0.2223 (d=0.006)

  • 0.08457 (d=0.014)
  • 0.1406 (d=0.013)

IDDES coarse (28 M cells) 0.1991

  • 0.07384
  • 0.1231

IDDES fine (99 M cells) 0.2002

  • 0.07624
  • 0.1218
  • D. Wood, SAE 2014-01-0590, 2014

0.210 0.055 ß ?

  • D. Wood, PhD Thesis, 2015

0.210

  • 0.035 (-0.0250 ~ -

0.0465) ß ?

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SLIDE 37

Case 2A - Models

  • RANS:
  • SA
  • Realizable k-epsilon (RKE)
  • SST
  • Hellsten (quartic k-w EARSM)
  • Hybrid RANS/LES
  • IDDES (unmodified - for demonstration purposes only)
  • IDDES + LES deactivation box

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SLIDE 38

Case 2A RANS Forces – Coarse Grid

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0.1 0.2 0.3 0.4 0.5

Cd

200 400 600 800 1000 1200 1400

Iteration Instantaneous Cd - Coarse Grid

SA RKE SST Hellsten

0.0 0.1 0.2

Cl

200 400 600 800 1000 1200 1400

Iteration Instantaneous Cl - Coarse Grid

SA RKE SST Hellsten

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SLIDE 39

Case 2A RANS Forces – Medium Grid

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0.1 0.2 0.3 0.4 0.5

Cd

200 400 600 800 1000 1200 1400

Iteration Instantaneous Cd - Medium Grid

SA RKE SST Hellsten

0.0 0.1 0.2

Cl

200 400 600 800 1000 1200 1400

Iteration Instantaneous Cl - Medium Grid

SA RKE SST Hellsten

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SLIDE 40

Case 2A RANS Forces – Fine Grid

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0.1 0.2 0.3 0.4 0.5

Cd

500 1000 1500 2000 2500

Iteration Instantaneous Cd - Fine Grid

SA RKE SST Hellsten

0.0 0.1 0.2

Cl

500 1000 1500 2000 2500

Iteration Instantaneous Cl - Fine Grid

SA RKE SST Hellsten

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SLIDE 41

Case 2A IDDES Forces – Fine Grid

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SLIDE 42

Case 2A Mean Forces – Coarse Grid

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0.20 0.25

Cd

200 400 600 800 1000 1200 1400

Iteration Cumulative Mean Cd - Coarse Grid

SA RKE SST Hellsten

−0.1 0.0 0.1 0.2

Cl

200 400 600 800 1000 1200 1400

Iteration Cumulative Mean Cl - Coarse Grid

SA RKE SST Hellsten

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SLIDE 43

RANS Mean Forces – Medium Grid

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0.20 0.25

Cd

200 400 600 800 1000 1200 1400

Iteration Cumulative Mean Cd - Medium Grid

SA RKE SST Hellsten

−0.1 0.0 0.1 0.2

Cl

200 400 600 800 1000 1200 1400

Iteration Cumulative Mean Cl - Medium Grid

SA RKE SST Hellsten

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SLIDE 44

RANS Mean Forces – Fine Grid

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0.20 0.25

Cd

500 1000 1500 2000 2500

Iteration Cumulative Mean Cd - Fine Grid

SA RKE SST Hellsten

−0.1 0.0 0.1 0.2

Cl

500 1000 1500 2000 2500

Iteration Cumulative Mean Cl - Fine Grid

SA RKE SST Hellsten

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SLIDE 45

Hellsten Model Forces – All Grids

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0.235 0.240 0.245 0.250

Cd

1000 2000 3000 4000 5000

Iterations Hellsten Model - Cd

Coarse Medium Fine

0.02 0.04 0.06 0.08

Cl

1000 2000 3000 4000 5000

Iterations Hellsten Model - Cl

Coarse Medium Fine

N.B. Cl still not well converged on fine mesh!

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SLIDE 46

Case 2A - Mesh Convergence

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SLIDE 47

IDDES Mean Forces – Fine Grid

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SLIDE 48

Wake Profiles – Fine Mesh

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SA RKE SST Hellsten IDDES (no box) IDDES + box

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SLIDE 49

Centerline Cp – Upper Surface

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SLIDE 50

Centerline Cp – Lower Surface

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SLIDE 51

Separation Isosurfaces

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Realizable k-epsilon SA SST Hellsten IDDES (no box) IDDES + box

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SLIDE 52

Spanwise Vorticity

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Realizable k-epsilon SA SST Hellsten IDDES (no box) IDDES + box

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SLIDE 53

IDDES - No Box : NQcrit

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Normalized Q-Criterion

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SLIDE 54

IDDES + Box : NQcrit

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Normalized Q-Criterion

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SLIDE 55

Case 2A - Fine Workshop Mesh Results

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Test Cases

Cd Cl Realizable k-epsilon 0.2097 0.01375 * SA 0.2231 0.01870 * SST 0.2363 0.004877 ** Hellsten 0.2418 0.003583 * IDDES (default, no box) 0.2668

  • 0.003056 *

IDDES + box 0.2512 0.003518 Exp. 0.243

* Results not well converged

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SLIDE 56

Summary

Case 1:

Convergence (other than SST) + mesh convergence demonstrated Hellsten RANS model looks promising IDDES required an LES-deactivation box to avoid partial collapse of the boundary layer prior to the main (rear) separation

Case 2:

Deep convergence challenging with RANS Mesh convergence not convincingly demonstrated using the three workshop-supplied grids Hellsten RANS model again looks promising IDDES again required use of an LES-deactivation box

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SLIDE 57

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Thank you J