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Numerical Solution
A UDF is needed to calculate the lift force over the entire cylinder by integrating the pressure over cylinder segments set to "wall" or "velocity inlet". We cannot use the in-built lift calculator for this case because it does not consider segments set to "velocity inlet." Important point to keep in mind: The UDF only affects the post-processing of the lift coefficient. It does NOT change the base 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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{include: FLUENT Google Analytics} {include: User Defined Functions - Panel} h1. Numerical Solution The user defined function from the Pre-Analysis section defines the lift function in C and defines the pressure and centroid of each face, then calculates the quantity called liftFunc, defined as {latex}\begin{eqnarray} \phi = -psin(\theta) \end{eqnarray}{latex} 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 |
3. Run at least one iteration to integrate φ over the cylinder 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
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get
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the
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normalized
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side
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force.
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This
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is
...
because
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when
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you
...
integrate
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liftFunc,
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you
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get
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the
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integral
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of
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-p*sin(theta)
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on
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the
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chosen
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surfaces.
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User-defined
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function
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implementation
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to
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obtain
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the
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lift
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coefficient
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around
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the
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cylinder
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is
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as
...
follows.
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