on drag reduction for automotive vehicles
Brizotti, Patrick Rambaud and Florian Visentin
the SST K-Omega models to simulate the flows around the car.
The K-Omega model is a two-equation model that is an alternative to the
K-Epsilon model. The transport equations solved are for the turbulent
kinetic energy k and a
ω, which is defined as the dissipation
rate per unit turbulent kinetic energy (
The advantage of the K-Omega model over the K-Epsilon model is its
performance for boundary layers under adverse pressure gradients.
However, The biggest disadvantage of the K-Omega model, in its original
that boundary layer computations are very sensitive to the values of ω in the free stream.
In an attempt to address this shortcoming, Menter introduced
modifications to the K-Omega models and his model is called the SST
(Shear-Stress Transport) K-Omega model. The SST model has seen fairly
wide application in aerodynamics problems, where viscous flows are
typically well resolved and
turbulence models are generally applied throughout the boundary layer.
Three types of wall treatment are provided with
StarCCM+, although all three might not always be available because they
depend on the turbulence model used:
- The high-y+
wall treatment implies the wall-function-type approach in which it is
assumed that the near-wall cell lies within the logarithmic region of
the boundary layer (y+~30).
- The low-y+
wall treatment is suitable only for low-Reynolds number turbulence
models in which it is assumed that the viscous sublayer is properly
resolved (y+=1 or lesser).
- The all-y+ wall treatment is a hybrid treatment
attempts to emulate the high-y+ wall treatment for coarse meshes and
wall treatment for fine meshes.
We used the third wall
treatment (ally+) for our simulation.
For the non-stationnary simulation,
we used the 2nd order implicit unsteady model and we
set the time step as 1.0E-4 s.