Assessment of Turbulence Modeling for Compressible Flow Around - - PowerPoint PPT Presentation

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Assessment of Turbulence Modeling for Compressible Flow Around - - PowerPoint PPT Presentation

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Assessment of Turbulence Modeling for Compressible Flow Around Stationary and Oscillating Cylinders by Alejandra Uranga A p p l i e d V e h i c l e Technologies August 21, 2006 Supervisors: Drs Nedjib Djilali and Afzal Suleman Dept. of

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SLIDE 1

Assessment of Turbulence Modeling for Compressible Flow Around Stationary and Oscillating Cylinders

by Alejandra Uranga

Supervisors: Drs Nedjib Djilali and Afzal Suleman

  • Dept. of Mechanical Engineering - University of Victoria

August 21, 2006

A p p l i e d V e h i c l e Technologies

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SLIDE 2

Outline

  • Introduction
  • Simulation Methodology
  • Stationary Cylinder
  • Oscillating Cylinder
  • Conclusions
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SLIDE 3

Introduction

Periodic pattern of counter-rotating vortices caused by unsteady separation from a bluff body

Kármán Vortex Street

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 4

Introduction

Periodic pattern of counter-rotating vortices caused by unsteady separation from a bluff body

Kármán Vortex Street

Introduction Methodology Stationary Oscillating Conclusions

NASA satellite image 1999

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SLIDE 5

Introduction

  • Interaction between 3 shear layers
  • Boundary layer
  • Free shear layer
  • Wake

Flow Around a Circular Cylinder

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 6

Introduction

  • Interaction between 3 shear layers
  • Boundary layer
  • Free shear layer
  • Wake

Flow Around a Circular Cylinder

Introduction Methodology Stationary Oscillating Conclusions

  • Transition to turbulence in
  • Wake

ReD 200 → 400

  • Free Shear layer ReD 400 → 150x103
  • Boundary layer ReD 150x103 → 8x106
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SLIDE 7

Introduction

  • Simulation of turbulent flow around circular

cylinders

  • Stationary

ReD = 3900

  • Oscillating

ReD = 3600

  • Compare accuracy of turbulence models

using same numerical procedure with respect to experiments and other simulations

Scope

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 8

Methodology

Numerical Simulation

  • f Turbulent Flows
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SLIDE 9

Methodology

Example: Incompressible Momentum Equation Applying an average or filter operator (overbar) to the momentum equation yields

 The terms , , are solved for  The cross terms are unknown closure problem

Introduction Methodology Stationary Oscillating Conclusions

The Need for Turbulence Models

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SLIDE 10

Methodology

Introduction Methodology Stationary Oscillating Conclusions

Simulation of Turbulence

DNS Direct Numerical Simulation Solve all Scales very thin grid required

ui

URANS Unsteady Reynolds Averaged Navier-Stokes (One-point closure) mean fluctuating Solve mean quantities Model Reynolds stresses

u

i

LES Large Eddy Simulation large scale Subgrid-Scale Solve large scale eddies Model subgrid-scale stress

u

i

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SLIDE 11

Methodology

  • URANS
  • One equation Spalart-Allmaras
  • K-tau Speziale et al.
  • Large Eddy Simulation (LES)
  • Smagorinsky-Lilly
  • Very Large Eddy Simulation (VLES)
  • Adaptive k-tau Magagnato & Gabi

(uses a URANS type subgrid-scale model)

Introduction Methodology Stationary Oscillating Conclusions

Turbulence Models Considered

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SLIDE 12

Methodology

  • SPARC

Structured PArallel Research Code

  • Finite Volume, Cell Centered, Block-

Structured, Multigrid

  • Simulations are

3D Unsteady Compressible Viscous

Introduction Methodology Stationary Oscillating Conclusions

Computational Code

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SLIDE 13

Stationary Cylinder

Stationary Circular Cylinder in a Uniform Flow

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SLIDE 14

Stationary Cylinder

  • Cylinder diameter

D = 1m

  • Flow velocity

U0 = 68.63m/s

  • Mach number

Mach 0.2

  • Reynolds number

ReD = 3900 Problem Setup

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 15

Stationary Cylinder

2D figures: x-y plane at span center

Computational Domain

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 16

Stationary Cylinder

URANS : Average Fields

Introduction Methodology Stationary Oscillating Conclusions

SA Sp u/U0 ωzD/U0

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SLIDE 17

Stationary Cylinder

URANS : Average Streamlines

Introduction Methodology Stationary Oscillating Conclusions

SA Sp

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SLIDE 18

Stationary Cylinder

URANS : Average Profiles

Introduction Methodology Stationary Oscillating Conclusions

u/U0 at x/D = 1.54 cp around cylinder cf around cylinder

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SLIDE 19

Stationary Cylinder

LES-VLES : Streamlines

Introduction Methodology Stationary Oscillating Conclusions

LES VLES

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SLIDE 20

Stationary Cylinder

LES-VLES : Average Fields

Introduction Methodology Stationary Oscillating Conclusions

LES VLES u/U0 ωzD/U0

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SLIDE 21

Stationary Cylinder

LES-VLES : Average Profiles

Introduction Methodology Stationary Oscillating Conclusions

u/U0 at x/D=1.54 cp around cylinder cf around cylinder

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SLIDE 22

Stationary Cylinder

3-Dimensionality Streamwise velocity iso-surfaces

Introduction Methodology Stationary Oscillating Conclusions

URANS Sp LES

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SLIDE 23

Stationary Cylinder

Comparison

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 24

Oscillating Cylinder

Circular Cylinder in Cross-Flow Oscillations

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SLIDE 25

Oscillating Cylinder

  • Vertical sinusoidal motion
  • 2D URANS k-tau Speziale
  • Reynolds number 3600
  • Lock-in: vortex shedding frequency

matches cylinder motion frequency Motion and Cases

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 26

Oscillating Cylinder

URANS Sp Fields

Introduction Methodology Stationary Oscillating Conclusions

ωzD/U0 u/U0 Case IV fc / f0 = 0.800

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SLIDE 27

Oscillating Cylinder

Lock-in

Introduction Methodology Stationary Oscillating Conclusions 46% 40% 2% 1% 63% 32% motion frequency fc/f0 shedding frequency fS/f0

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SLIDE 28

Conclusions

Summary and Further Work

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SLIDE 29

Conclusions

  • comparison of results from different turbulence

models with same numerical procedure

  • Spalart-Allmaras model
  • error in separation point

flow remains attached too long

small recirculation zone

low back pressure

large drag

  • Accurate Strouhal number

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 30

Conclusions

  • K-tau Speziale model
  • Good mean global quantities

Strouhal number, drag, back pressure, separation point

velocity profiles along the wake

  • LES and VLES
  • reveal secondary eddies
  • LES resolves dynamics in boundary layer
  • Oscillating Cylinder
  • No other numerical results in same regime
  • Lock-in over large range of motion frequencies
  • Further investigation required

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 31

Conclusions

  • Better averages on LES and VLES
  • LES with Dynamic and Dynamic Mixed subgrid-

scale models

  • LES of oscillating cylinder

Further Work

Introduction Methodology Stationary Oscillating Conclusions

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SLIDE 32

Questions