2D and 3D Numerical Investigation of the Laminar and Turbulent

2D and 3D Numerical Investigation of the Laminar and Turbulent Flow Over Different Airfoils Using

OpenFOAM

H. Rahimi, W. Medjroubi, and J. Peinke

Carl von Ossietzky University Oldenburg & ForWind GmbH Workgroup TWiSt - Turbulence, Wind Energy & Stochastics

First Symposium on OpenFOAM in Wind Energy 20. – 21. March 2013 – Oldenburg, Germany

Overview §  Motivations

§  Objectives

§  Numerical methods and turbulence models

§  Mesh and simulation settings

§  Results

§  Conclusions

Hamid Rahimi SOWE-2013 / page 2

Motivations §  Need for numerical investigations to optimize wind turbine output

through wind turbine blade optimization

§  Airfoil sections optimization

§  Understand the complex flow over different airfoil sections

§  Investigate the suitability of the different turbulence models for

airfoil sections

§  Need for validation for OpenFOAM simulations


Objectives

§  Simulate the turbulent flow over different wind turbine airfoil

sections

§  Use different turbulence and transition models

§  Compare and validate the simulation results with experimental

and other numerical results

§  Simulating the flow over airfoil sections using OpenFOAM 2.1.0


Numerical Methods

•  Reynolds Averaged Navier-Stokes Simulations (RANS)

•  RANS Simulations with transition modeling

•  Unsteady RANS Simulations (URANS)

•  Delayed Detached Eddy Simulation (DDES) with a Spalart-Allmaras

background model


Turbulence models

Spalart-Allmaras model

•  A one equation turbulence model

•  Developed for aerodynamical applications

•  Solves a modeled transport equation for a modified eddy viscosity.

•  Fast, numerically stable and reasonably accurate for both boundary

layers and shear layers


Turbulence models

K-ω SST model

•  Two-equation eddy viscosity model

•  Solves a transport equations for k and ω

•  Switches to k-ϵ behavior in the free stream region

•  Avoids k- ω sensitivity to the inlet free-stream turbulence condition

•  Produces too large turbulence levels in some regions


Turbulence models

Transition model KKL- ω

•  Based on the k- ω SST model

•  Three transport equations are for the turbulent kinetic energy (kT ), the

laminar kinetic energy (kL) and the scale-determining variable (ω)

•  Addresses laminar, transitional and fully turbulent flows with the

use of Reynolds averaging


Simulations

•  For performing the simulation we used the FLOW * cluster •  The FLOW cluster consist of 2232 CPU cores

•  For k-ω SST, Spalart-Allmaras and OpenFoam with transition modeling 32 CPU cores were used per simulation

•  For DDES turbulence model 128 CPU cores were used per simulation

•  The typical simulation time for a RANS simulation is 3 days •  The typical simulation time for a DES simulation is 60 days

* The Facility for Large-Scale cOmputations in Wind energy research (FLOW)


Mesh

§  Schematic representation of the numerical domain


Airfoils


FX 79-W-151A NACA 63-430

FX 79-W-151A

•  Commonly used in wind turbines

•  Maximum thickness of 15.2% at 33.9% chord

•  The maximum camber of 3.8% at 37.1% chord

•  Re=700,000

•  Inflow velocity 10.5m/s

•  Turbulence intensity of 1%

Reference for experimental result: J. Schneemann. Auftriebmessungen in turbulenter Umgebung Master thesis, Institut of Physics, University of Oldenburg, 2009.


FX 79-W-151A simulation conditions


Element K-ω SST Transition model Spalart-Allmaras

Total number of cell 134,400 1,500,000 191,000

The height of the closest cell to the wall

Reynolds number

Freestream velocity

Solver K-ω SST UnSteady-PisoFoam

KKL- ω Steady-SimpleFoam

Spalart-Allmaras Steady-SimpleFoam

sm5.10

5107∗

sm5.10 s

m5.10

5107∗ 5107∗

m3103.8 −∗ m5107.2 −∗ m5108.8 −∗200≈+y 1≈+y 1≈+y

FX 79-W-151A simulation conditions



Total number of cell 134,400 1,500,000 191,000


Reynolds number

Freestream velocity




sm5.10

5107∗

sm5.10 s

m5.10

5107∗ 5107∗

m3103.8 −∗ m5107.2 −∗ m5108.8 −∗200≈+y 1≈+y 1≈+y

FX 79-W-151A


Pre-Stall Stall+Post-Stall

FX 79-W-151A



FX 79-W-151A



NACA 63-430

•  Maximum thickness of 30%

•  Re=1.5 million

•  Inflow velocity 24 m/s

•  Turbulence intensity 1%

Reference for experimental result: F. Bertagnolio, N. Sørensen, J. Johansen, and P. Fuglsang. Profile Catalogue for Airfoil Sections Based on 3D Computations, Risø-R-1581. Technical report, Risø National Laboratory, Roskilde, Denmark, 2006.


NACA 63-430 Simulation conditions



Total number of cell 128,400 590,000 934,000


Reynolds number

Freestream velocity




sm24

6105.1 ∗

sm24 s

m24

6105.1 ∗ 6105.1 ∗

m3103.8 −∗ m6104.1 −∗ m4109 −∗400≈+y 1≈+y 30≈+y

NACA 63-430 Simulation conditions



Total number of cell 128,400 590,000 934,000


Reynolds number

Freestream velocity




sm24

6105.1 ∗

sm24 s

m24

6105.1 ∗ 6105.1 ∗

m3103.8 −∗ m6104.1 −∗ m4109 −∗400≈+y 1≈+y 30≈+y

NACA 63-430



NACA 63-430



NACA 63-430



NACA 63-430 §  Cp for the kkl- ω transition model and Reθ transition model at

AOA=6°


Conclusions §  Good agreement using Spalart-Allmaras model for the pre-stall

and stall region but not for Post-stall region §  Using the OpenFoam transition model and k- ω SST , very good

agreement is found compared to the experimental and other numerical results

§  This transition model delivers much better results than other

transition models used in the literature (like the Reθ model)

§  Computational results obtained from DDES for the post-stall region are not correctly predicted

§  the sensitivity of the turbulence models to the normalized wall

distance y + is studied Hamid Rahimi SOWE-2013 / page 25

§  Thank you for your attention


Contact: [email protected]

Mesh

§  Schematic representation of the numerical domain


FX 79-W-151A


Transition model KKL- ω §  24 constants - Difficult to implement


NACA 63-430 §  Cp for the kkl- ω transition model and Reθ transition model at

AOA=18°


Documents

2D and 3D Numerical Investigation of the Laminar and Turbulent