# CFD question

1. Feb 6, 2004

### that_guy

I'm an EE trying to learn the basics of fluid dynamics and CFD, due to my interest in car racing. Currently I'm looking at the flow through exhaust systems to get a feel for what allows the most airflow and therefore the most horsepower.

I set up the problem by forcing a boundary condition at the inlet of a certain speed. My question is how to interpret the results to determine what configuration flows the most. Do I want to look for the lowest peak pressure, or the smallest pressure differential from inlet to outlet, or something else? I orginally though it would be the lowest peak pressure, but looking at the results I'm not 100% sure of that now.

Some details: I know exhaust is really pulses, but to keep things simple I'm assuming steady-state flow. I've calculated the average exhaust speed based on an assumed horsepower number and the cross sectional area of the exhaust. It gives me a Mach number of 0.06, so I'm assuming incompressible flow. I've estimated Re at 30,000 so I'm treating the flow as turbulent.

Thanks,
Tom S.