14-07-2014, 12:26 PM
NUMERICAL INVESTIGATION OF FLOW TRANSITION FOR NACA-4412 AIRFOIL USING COMPUTATIONAL FLUID DYNAMICS
[attachment=65820]
ABSTRACT
: Numerical investigation of aerodynamics phenomena in the post stall region using Computational Fluid
Dynamics is critical task due to the strong vortex dynamics involved. Literatures cited in this filed indicates that the Turbulence
models employed in most of the commercial CFD software’s will assume the boundary layer around the airfoil as fully
turbulent and hence the physical phenomena is wrongly addressed and also this approximation will lead to deviation in results
from experimentally measured data in the post stall region. Research in this area concluded that the flow transition (boundary
layer transition) from laminar to turbulent around the surface of the airfoil needs to be properly implemented in CFD analysis in
order to have a reliable prediction in post stall region. This work aims in predicting the flow transition from laminar to turbulent
for flow over NACA4412 airfoil in the incompressible flow regime.CFD analysis methodology involves the use of Mentors
Shear Stress Transport Turbulence model(k-ω model)with transitional flow option.CFD analysis results are compared with wind
tunnel test data.CFD analysis is also carried out with Spalart allmaras turbulence model which assumes the boundary layer as
fully turbulent.
INTRODUCTION
The rapid evolution of computational fluid dynamics (CFD) has been driven by the need for faster and more
accurate methods for the calculations of flow fields around configurations of technical interest. In the past decade, CFD
was the method of choice in the design of many aerospace, automotive and industrial components and processes in
which fluid or gas flows play a major role. In the fluid dynamics, there are many commercial CFD packages available
for modeling flow in or around objects. The computer simulations show features and details that are difficult,
expensive or impossible to measure or visualize experimentally. When simulating the flow over airfoils, transition from
laminar to turbulent flow plays an important role in determining the flow features and in quantifying the airfoil
performance such as lift and drag. Hence, the proper modeling of transition, including both the onset and extent of
transition will definitely lead to a more accurate drag prediction
MATHEMATICAL MODELS
The flow around the airfoil has been simulated by solving the equations for conservation of mass and
momentum. Finite volume based method has been used to convert the governing equations of flow in to algebraic
equations that can be solved numerically. The pressure-velocity coupling has been achieved by SIMPLE algorithm.
Turbulence of the flow has been modeled by using standard k-omega model with boundary layer transition prediction
capabilities and spalart allamaras turbulence model[01].
This chapter deals with the computational details viz. governing equations that are solved, turbulence models
incorporated in the simulations, geometrical modelling and the details of the geometry, grid generation for the wing
under study, boundary conditions that are enforced are discussed and presented in this chapter.
Assumptions: The flow around the airfoil is treated as steady, incompressible and turbulent.
RESULTS AND DISCUSSIONS
Table 2 shows the lift and drag coefficients obtained by the wind tunnel test (experimental) results, they are taken
from the books “theory of wing sections” by Abott. And this table also contains the lift and drag coefficients obtained
by the two different modeling approaches that is K-ω model and Spalart-Allmaras model, comparing these approaches
with the wind tunnel results.
By comparing the Fluent results with wind tunnel results at different angle of attack from 0-18o
K- ω model is well
predicted at stalled region. The comparing lift and drag plots are shown in fig 4.
Here we observed that shows the lift coefficient plotted against the angle of attack. It is observed that K-ω SST
turbulence model with transition capabilities gives close prediction of lift and drag coefficient both in pre stall and post
stall region
CONCLUSIONS
Three dimensional CFD analysis is carried out for viscous incompressible flow around NACA 4412 subsonic
airfoil using FLUENT commercial CFD software at a free stream Reynolds number of 3 million. The analysis is
carried out with Spalart allmaras turbulence model and K-ω SST turbulence model with transition capabilities
Lift and drag coefficients obtained with CFD analyses are compared with the wind tunnel test data available in open
literatures. It is observed by these comparisons the two models gives near prediction to the experimental results.
It is concluded that K-ω SST turbulence model with transition capabilities gives close prediction of lift and drag
coefficient both in pre stall and post stall region
[attachment=65820]
ABSTRACT
: Numerical investigation of aerodynamics phenomena in the post stall region using Computational Fluid
Dynamics is critical task due to the strong vortex dynamics involved. Literatures cited in this filed indicates that the Turbulence
models employed in most of the commercial CFD software’s will assume the boundary layer around the airfoil as fully
turbulent and hence the physical phenomena is wrongly addressed and also this approximation will lead to deviation in results
from experimentally measured data in the post stall region. Research in this area concluded that the flow transition (boundary
layer transition) from laminar to turbulent around the surface of the airfoil needs to be properly implemented in CFD analysis in
order to have a reliable prediction in post stall region. This work aims in predicting the flow transition from laminar to turbulent
for flow over NACA4412 airfoil in the incompressible flow regime.CFD analysis methodology involves the use of Mentors
Shear Stress Transport Turbulence model(k-ω model)with transitional flow option.CFD analysis results are compared with wind
tunnel test data.CFD analysis is also carried out with Spalart allmaras turbulence model which assumes the boundary layer as
fully turbulent.
INTRODUCTION
The rapid evolution of computational fluid dynamics (CFD) has been driven by the need for faster and more
accurate methods for the calculations of flow fields around configurations of technical interest. In the past decade, CFD
was the method of choice in the design of many aerospace, automotive and industrial components and processes in
which fluid or gas flows play a major role. In the fluid dynamics, there are many commercial CFD packages available
for modeling flow in or around objects. The computer simulations show features and details that are difficult,
expensive or impossible to measure or visualize experimentally. When simulating the flow over airfoils, transition from
laminar to turbulent flow plays an important role in determining the flow features and in quantifying the airfoil
performance such as lift and drag. Hence, the proper modeling of transition, including both the onset and extent of
transition will definitely lead to a more accurate drag prediction
MATHEMATICAL MODELS
The flow around the airfoil has been simulated by solving the equations for conservation of mass and
momentum. Finite volume based method has been used to convert the governing equations of flow in to algebraic
equations that can be solved numerically. The pressure-velocity coupling has been achieved by SIMPLE algorithm.
Turbulence of the flow has been modeled by using standard k-omega model with boundary layer transition prediction
capabilities and spalart allamaras turbulence model[01].
This chapter deals with the computational details viz. governing equations that are solved, turbulence models
incorporated in the simulations, geometrical modelling and the details of the geometry, grid generation for the wing
under study, boundary conditions that are enforced are discussed and presented in this chapter.
Assumptions: The flow around the airfoil is treated as steady, incompressible and turbulent.
RESULTS AND DISCUSSIONS
Table 2 shows the lift and drag coefficients obtained by the wind tunnel test (experimental) results, they are taken
from the books “theory of wing sections” by Abott. And this table also contains the lift and drag coefficients obtained
by the two different modeling approaches that is K-ω model and Spalart-Allmaras model, comparing these approaches
with the wind tunnel results.
By comparing the Fluent results with wind tunnel results at different angle of attack from 0-18o
K- ω model is well
predicted at stalled region. The comparing lift and drag plots are shown in fig 4.
Here we observed that shows the lift coefficient plotted against the angle of attack. It is observed that K-ω SST
turbulence model with transition capabilities gives close prediction of lift and drag coefficient both in pre stall and post
stall region
CONCLUSIONS
Three dimensional CFD analysis is carried out for viscous incompressible flow around NACA 4412 subsonic
airfoil using FLUENT commercial CFD software at a free stream Reynolds number of 3 million. The analysis is
carried out with Spalart allmaras turbulence model and K-ω SST turbulence model with transition capabilities
Lift and drag coefficients obtained with CFD analyses are compared with the wind tunnel test data available in open
literatures. It is observed by these comparisons the two models gives near prediction to the experimental results.
It is concluded that K-ω SST turbulence model with transition capabilities gives close prediction of lift and drag
coefficient both in pre stall and post stall region