Numerical Solution

The strategy for computing the lift force using the UDF is as follows:

1. Turn on a 'user defined scaler' φ which Fluent will solve for
2. On the cylinder surface, set the below equation by implementing the UDF as a boundary condition for φ 
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   \begin

   Unknown macro: {eqnarray}

   \phi = -psin(\theta)
   \end

     

Once the user defined function is implemented, we can use liftFunc to integrate the specified user defined scalar over the entire specified surface. Note that the liftFunc UDF calculates a side force that is NOT normalized. So you'll have to divide the reported value by 0.5*rho*v^2*D*1 to get the normalized side force. This is because when you integrate liftFunc, you get the integral of -p*sin(theta) on the chosen surfaces.

User-defined function implementation to obtain the lift coefficient around the cylinder is as follows.

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