[PierceH]

I write a UDF to generate a different pressure than created from Fluent's static pressure. I want to calculate the lift and drag that this produces. My first thought was to use a define adjust where C_P(c,t)=C_UDS(c,t,i), however, that does not change values on the surface that I need in order to calculated lift and drag. Any thoughts?

Thank You


This has been solved, for anyone reading in future: In order to solve the Force a UDS creates acting on a body -1) create a custom field function: x-face-area * UDS/p_substitute , then 2) perform a surface integral summation, this will give you the drag force.

[AlexanderZ]

C_UDS(c,t,i) is wrong macro
at least it should be C_UDSI(c,t,i)

to define values on surfaces you may use F_UDSI(c,t,i)

[PierceH]

Originally Posted by AlexanderZ

C_UDS(c,t,i) is wrong macro
at least it should be C_UDSI(c,t,i)

to define values on surfaces you may use F_UDSI(c,t,i)

Alexander, apologies for the typo, I did have it in as UDSI. I also tried using F_P(c,t)=F_UDSI(c,t,i), however it does not resolve my issue, where the pressure is not recalculating around the airfoil boundary, the pictures may explain better. For reference, the UDSI(c,t,i)=0 as a test case here.

My second option to calculate the lift and drag force from the UDS would be to obtain the boundary normal vector around the airfoil and use that to calculate the total drag force, i.e. (UDS*normal vector*direction vector) then use the integral report for this but unsure how to go about calculating.

[AlexanderZ]

I believe the problem with your second picture is visualization only, switch of node values in contour options

[PierceH]

Originally Posted by AlexanderZ

I believe the problem with your second picture is visualization only, switch of node values in contour options

Alexander, are you sure that this is simply a visualisation error? to me it's suggesting that face values are accurately obtained but nodal values are not on near the boundaries, thoughts?