Compressible Flow LES Using OpenFOAM - Dutch OpenFOAM… · Compressible Flow LES Using OpenFOAM I. B. Popov supervisor: S. J. Hulshoff promoter: H. Bijl PhD student, TU Delft, Delft,

Compressible Flow LES Using OpenFOAM

I. B. Popovsupervisor: S. J. Hulshoff

promoter: H. Bijl

PhD student, TU Delft, Delft, The Netherlandsresearcher, NEQLab Research B.V., The Hague, The Netherlands

March 10, 2011

I. B. Popov supervisor: S. J. Hulshoff promoter: H. Bijl ( PhD student, TU Delft, Delft, The Netherlands researcher, NEQLab Research B.V., The Hague, The Netherlands )Compressible Flow LES March 10, 2011 1 / 27

Introduction: Nanosecond plasma actuation forseparation control

Actuation designTwo electrodes, dielectriclayerPulse: U = 12 kV,τ = 12ns

Typical frequency∼ 100Hz . . . 1 kHz

-10

-5

0

5

10

-50 0 50 100 150 200 250V

olta

ge

, kV

Time, ns

Single: Ein = 11.6 mJDouble: Ein = 10.0 mJ

Triple: Ein = 9.5 mJ

Incident energy: 15 mJ


Experimental resultsGiuseppe Correale, TUDelft, 2010

Integral effectsCL ↑, CD ↓Stall delay of severaldegreesRe up to 3× 106 (60 cmchord, V = 80m/s)

Observed mechanismsAir jet up to 0.2 m/sShock waveHeated gas

α [deg]35


Schlieren imaging results


Proposed mechanism

1 Discharge ∼ 10ns

2 Fast heating of gas ∼ 1µs3 Formation of the shock wave4 Shock-flow interaction5 Creation of some coherent flow structures6 Separation elimination


Nanosecond actuator modelInstantaneous (1µs� Tflow)Constant-volume∆T ∼ 100K for 0.5× 0.5mm

Flow-wise distribution: filaments length ∼ 3 . . . 5mm,most energy released in ∼ 0.5mm at the electrodeSpan-wise distribution — two models:

1 Uniform2 Filaments with thickness ∼ 0.5mm and pitch of several

mm


Hybrid simulation

LES model

Nanosecond actuator

Separation zoneBoundary layer

DES or RANS model

1 3D LES simulation of near-actuator region2 RANS simulation of the rest of the flow3 Interaction between them


Periodic channel case

Flow

Wall

Wall y

xz

2

46

PropertiesDomain size 6× 4× 2Channel flow case, Reτ = 180Constant pressure gradient ∇p = 1x, z — periodic, top and bottom — no slipDNS data by Jimenez used as a reference


LES of incompressible channel flow

Verification pointsTemporal convergenceMesh refiningNumerical dissipationSGS modelsComputational costs

DifficultiesAveraging in OpenFoam’sdynamic Smagorinskymodel⇒ implementedtruly dynamic model

13

13.5

14

14.5

15

15.5

16

16.5

0 20 40 60 80 100 120

Ubulk

t

Reference value (15.68)Smag 64

dynSmag 32dynSmag 64

dynSmag 128

0.1

100

RM

S e

rror

n

1/nUmean


locDynSmagorinsky turbulent model

dynSmagorinsky

Averaging over whole domain⇒ used with vanDriestdumping

locDynSmagorinsky

Local computation of turbulent viscosityClipping of negative values


Temporal convergence

13

13.5

14

14.5

15

15.5

16

16.5

0 20 40 60 80 100 120

Ubulk

t

Reference value (15.68)Smag 64

dynSmag 32dynSmag 64

dynSmag 128


Comparison of turbulent modelsIntroduction

linear spatial schemebackward time scheme

Smagorinsky

dynSmagorinsky

locDynSmagorinsky

laminar (= no SGS model)


Comparison of turbulent modelsMean velocity profiles

0

2

4

6

8

10

12

14

16

18

20

0 0.2 0.4 0.6 0.8 1

Um

ea

n

y

DNSno model 64

3

Smag 643

dynSmag 643

locDynSmag 643


Comparison of turbulent modelsu variations profiles

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8 1

<u

’2>

y

DNSno model 64

3

Smag 643

dynSmag 643

locDynSmag 643


Comparison of turbulent modelsv variations profiles

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.2 0.4 0.6 0.8 1

<v’2

>

y

DNSno model 64

3

Smag 643

dynSmag 643

locDynSmag 643


Comparison of turbulent modelsw variations profiles

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1

<w

’2>

y

DNSno model 64

3

Smag 643

dynSmag 643

locDynSmag 643


Comparison of turbulent modelsReynolds stress profiles

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 0.2 0.4 0.6 0.8 1

<u

’v’>

y

DNSno model 64

3

Smag 643

dynSmag 643

locDynSmag 643


Comparison of turbulent modelsConclusions

Laminar equations have surprisingly the bestperformanceStatic Smagorinsky with default coefficient has worstperformanceDynamic variants of Smagorinsky are somewhereinbetween.


Performance on stretched meshesMean velocity profiles

0

2

4

6

8

10

12

14

16

18

20

0 0.2 0.4 0.6 0.8 1

Um

ea

n

y

DNSuniform 64

3

grading 25 643


Performance on stretched meshesu variations profiles

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8 1

<u

’2>

y

DNSuniform 64

3

grading 25 643


Performance on stretched meshesv variations profiles

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.2 0.4 0.6 0.8 1

<v’2

>

y

DNSuniform 64

3

grading 25 643


Performance on stretched meshesw variations profiles

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1

<w

’2>

y

DNSuniform 64

3

grading 25 643


Performance on stretched meshesReynolds stress profiles

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 0.2 0.4 0.6 0.8 1

<u

’v’>

y

DNSuniform 64

3

grading 25 643


Comparison of turbulent modelsConclusions

Stretching does not improve performanceFilter delta for SGS model? (used cubeRootVol)


LES of compressible channel flow

RequirementsTransient solverConservative variablesTurbulence modelling

Self-made solverρ, ρU, ρETemporal scheme: implicit iterated or Runge-Kutta 4/3


Periodic hill case


Periodic hill case


Appendix: Discharge simulation

Poisson equation for electric field ε∆ϕ = qSeveral species: neutrals, positive and negative ions,electronsSeparate convection velocitiesKinetics (coupled solution is desired)Boltzman equation


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Compressible Flow LES Using OpenFOAM - Dutch OpenFOAM… · Compressible Flow LES Using OpenFOAM I. B. Popov supervisor: S. J. Hulshoff promoter: H. Bijl PhD student, TU Delft, Delft,