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Rahul Ponginan

Run time and Time Step in VWT

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In analysis setup of VWT,

Run time is calculated using, Run time = (30* object length)/ (inflow speed)
and for time increment = (2* object height)/(inflow speed* 30)

Can anyone explain how this is derived?

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You need a certain run time to "wash out" the initial phenomena. The idea behind this formula is, we need 30 sweeps of air over the car to reach a stationary "clean" flow (NOT steady, stationary means a flow which has some kind of periodicity in it).
The formula for the time step is based on the expected shedding frequency determined by object height and flow speed. You want to have 30 result points in one cycle for good accuracy.

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