Numerical investigation around notchback SAE model Franois - - PowerPoint PPT Presentation

Numerical investigation around notchback SAE model

François DELASSAUX 11/12/2019

Numerical setup

2

• Boundary conditions
• Inlet: uniform 𝑊

" = 40 𝑛/𝑡 (notchback) and 16m/s (fastback/estate) and experimental turbulent intensity ~0,2%

• Outlet: pressure outlet condition with gauge pressure = 0 Pa
• No slip wall condition on the body
• Software: ANSYS Fluent
• Grids: HexaPoly provided for the conference
• Numerical schemes – Finite Volume Method
• Advections terms: Bounded Central Differencing

(BCD) scheme

• k, ω and pressure: 2nd order Upwind scheme
• Temporal derivative: Bounded 2nd order implicit

scheme

• Segregated SIMPLEC algorithm
• Computational time - Δ𝑢 = 5.10./ s
• Total physical time = 2 s
• Convergence = 1 s
• Averaging = 1 s
• From 20 to 4 inner iterations

SST DDES RKE RANS

• Numerical schemes – Finite Volume Method
• 2nd order upwind
• Coupled algorithm
• Steady computation using pseudo-transient method

to increase flow convergence

• 1000 iterations

Notchback SAE – Aerodynamics coefficients and Cp centerline

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• Cd

ΔCd

• Cl

ΔCl Exp. 0.2071

• 0.0548
• RKE

0.1925

• 7.0%
• 0.0698

27.4% SST DDES 0.2121 2.4%

• 0.0778

42.0%

• Good agreement on drag prediction
• Bad prediction on lift coefficient
• Not meaningful due to very small

lift values

• 2.5
• 2
• 1.5
• 1
• 0.5

0.5

• 450 -410 -370 -330 -290 -250 -210 -170 -130 -90
• 50
• 10

30 70 110 150 190 230 270 310 350 390 430

Cp [-] X [mm] Cp centerline

Exp. RANS DDES

• Good agreement on Cp coefficient along

the centerline for both turbulence models

Notchback SAE – Cp rear slant surface

4

Exp. RKE SST DDES

• Good pressure recovery over the rear slant with RANS => no

separation

• More energetic C-pillar vortices with DDES compared to RANS
• Not enough Cp probes in experiments to capture the footprint of C-

pillar vortices

Notchback SAE – iso Vx<0 / streamlines

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RKE SST DDES RKE SST DDES

No separation Small separation L/H=1,53 L/H=1,08

Notchback SAE – Y=0 mm backlight – Vx

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Exp. RKE SST DDES

• XX

Separation

0.01 0.02 0.03 0.04 0.05 0.06

• 0.1

0.1 0.3 0.5 0.7 0.9 1.1

Z from surface Vx and fd

Vx and fd evolution at X=-300 mm

Vx fd

Δ123 = max Δ𝑦, Δ𝑧, Δ𝑨 = 2,6 𝑛𝑛 𝜀 ≈ 20 − 30 𝑛𝑛 𝟏, 𝟏𝟗 < 𝒔 = 𝜠𝒏𝒃𝒚 𝜺 < 𝟏, 𝟐𝟒

r should be at least >0,2 [Menter] => 5 mm

Numerical investigation around DrivAer models

François DELASSAUX 11/12/2019

Fastback – Aerodynamics coefficients

8

0.170 0.180 0.190 0.200 0.210 0.220 0.230 0.240 Coarse Medium Fine

Cd

• 0.040
• 0.030
• 0.020
• 0.010

0.000 0.010 0.020 0.030 0.040 Coarse Medium Fine

Cl

Cd Cl Cl Front Cl Rear RKE 0.200 0.018

• 0.065

0.083 DDES SST 0.234

• 0.001
• 0.083

0.082 RKE 0.198 0.023

• 0.067

0.090 DDES SST 0.234

• 0.025
• 0.090

0.066 RKE 0.197 0.031

• 0.065

0.095 DDES SST 0.234

• 0.032
• 0.101

0.069 Coarse Medium Fine

Full body

Cd Cl Cl Front Cl Rear RKE 0.145 0.031

• 0.062

0.093 DDES SST 0.160

• 0.004
• 0.095

0.091 RKE 0.146 0.036

• 0.062

0.099 DDES SST 0.156

• 0.022
• 0.100

0.078 RKE 0.145 0.042

• 0.062

0.104 DDES SST 0.161

• 0.032
• 0.111

0.079 Coarse Medium Fine

0. 0. 0. 0.

Without wheels

Fastback – CFL

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Coarse Fine Y0 Coarse Fine Y300

Time step = 5.10-4s is enough regarding CFL and using implicit temporal scheme

Fastback – Iso surface Vx=0

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Fastback – Cp side

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Fastback – Cp underbody

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Fastback – Y0 – Vx and Vz

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Fine RKE DDES Coarse Fine Coarse

Fastback – Cp top

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Fastback – Streamlines Y0

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Fastback – Streamlines Y3125

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Estate – Aerodynamics coefficients on full body

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Cd Cl

0.000 0.050 0.100 0.150 0.200 0.250 0.300 Coarse Medium Fine

• 0.200
• 0.180
• 0.160
• 0.140
• 0.120
• 0.100
• 0.080
• 0.060
• 0.040
• 0.020

0.000 Coarse Medium Fine

Full body Without wheels

Cd Cl Cl Front Cl Rear RKE 0.230

• 0.112
• 0.072
• 0.040

DDES SST 0.276

• 0.138
• 0.107
• 0.031

RKE 0.226

• 0.104
• 0.070
• 0.034

DDES SST 0.280

• 0.171
• 0.094
• 0.076

RKE 0.226

• 0.104
• 0.071
• 0.033

DDES SST 0.285

• 0.171
• 0.097
• 0.075

Fine Coarse Medium Cd Cl Cl Front Cl Rear RKE 0.170

• 0.097
• 0.066
• 0.031

DDES SST 0.198

• 0.139
• 0.119
• 0.020

RKE 0.171

• 0.090
• 0.064
• 0.026

DDES SST 0.199

• 0.170
• 0.098
• 0.072

RKE 0.171

• 0.090
• 0.065
• 0.025

DDES SST 0.205

• 0.173
• 0.100
• 0.072

Fine Coarse Medium

Estate – Iso surface Vx=0

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Estate – Cp side

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Estate – Cp underbody

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Estate – Y0 – Vx and Vz

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Fine RKE DDES Coarse Coarse Fine

Estate – Cp top

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Estate – Cp rear

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Peugeot 308 SW

Estate – Streamlines Y0

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Coarse Medium Fine RKE Coarse Medium Fine DDES

308 Estate – Streamlines Y0

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DDES

• RANS: 2 massive separations
• DDES: very close to exp.

=> accurate flow topology

Y0 RKE Exp.

Estate – Streamlines Y3125

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Coarse Medium Fine RKE Coarse Medium Fine DDES

Conclusions

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• Notchback SAE
• Good prediction drag coefficient
• Discrepancies on lift coefficient prediction
• Improve DDES flow on the rear slant surface
• DrivAer models
• Higher drag and lift values with DDES compared to RANS
• Both RANS and DDES are insensitive to the tested grid refinements for drag prediction
• Estate shape: good agreement for DDES model compared to PSA work on Peugeot 308 SW