Predictions of flows around vehicle in crosswinds are important applications of time-dependent numerical simulations. Predictions of crosswind flows using steady RANS methods are unreliable even if winds are steady. Unsteady winds acting on vehicle are more realistic and their gusty character is often the reason for lateral instability of vehicles. Gusty flows around vehicles are impossible to study with steady RANS methods due to their steady character. Furthermore, experimental investigations of these flows are very difficult because of the requirements for right boundary conditions, vehicle must be moving and wind simulated in the wind tunnel must have unsteady character.
We have experience in simulating vehicles traveling in both steady and unsteady winds. Dependent on the character of the wind we can simulate flow on stationary or moving computational grids.
An example of our DES of flow around a train traveling first in the tunnel and then exiting on a bridge exposed to strong crosswind can be seen in this animation:
This is an example of the result of such a simulation which illustrates the flow around a vehicle. However, even more interesting for an engineer is that such simulation can provide us with time histories of aerodynamic forces or moments as shown in the following animation: