Lexington, MA One day, while riding down the freeway, you open your sunroof and begin to hear a loud, rumbling cyclic noise. You look around to see if something is wrong with your car. You find nothing, but notice that when you close the sunroof the noise stops. Little did you know that the sound was created by a low frequency pressure wave that resonates at the same frequency as your head!
"A booming effect is created when a vehicle is traveling between 20-50 mph and a recirculation close to the sun roof excites a layer of air at 20-25 Hz between the passenger and the outside of the car," says Mike Kayat, Senior Application Engineer of EXA corp. "And as it happens, the human head resonates at the same frequency."
Vehicle and sunroof manufacturers have been working to solve this problem using CFD software. One CFD package achieving success in the field of vehicle sound simulation is PowerFlow by EXA Corp.
PowerFlow is particularly effective at simulating noise because it uses a new approach to fluid-mechanic simulation. Traditionally, CFD solvers have used the Navier-Stokes equations to solve real-time flow using high-order numerics and cumbersome numerical mesh creation. PowerFlow, on the other hand, solves a discrete Lattice-Boltzman equation that closely matches the kinetic theory of particle dynamics on a simple rectangular grid.
"PowerFlow sets up a statistical distribution of the flow, such that fluid particles move from one cell to the other," says Jackie Halliday, director of technical business Development at EXA.