# Dynamic pressure and blade surface

Dear Jonson,
I need your help. I am trying to apply the aerodynamic loads to a 3D blade model. Where should the pressure distribution along the blade (Dynamic pressure obtained by AeroDyn) be applied to the blade structure, high pressure surface or suction surface?
Please help me, thank you.**

Best regards**
Wang Baoxuan**

Dear @Baoxuan.Wang,

I’m not sure I understand your question. AeroDyn is a lifting line model, where aerodynamic loads are calculated as applied forces and moments distributed per unit length along the lifting line representation of the blade. AeroDyn does not compute a pressure distribution across the airfoil surface.

Best regards,

Dear Janson,
Thank you for your reply. If the output parameter–“B1N1DynP (unit is Pa)” listed in the “OutListParameters.excel” can be employed to approximately simulate the pressure distribution on a certain blade element?
Best regards,

Dear @Baoxuan.Wang,

The dynamic pressure output you are referring to is computed as `q = 1/2*AirDens*V_rel^2`, such that force per unit length along the blade is computed as `f = c*q*BlChord`, where `c` is the force coefficient (e.g., `c = c_l` for lift or `c = c_d` for drag). This dynamic pressure is not calculated as a pressure distributed across the suction and pressure surfaces of the airfoil.

Best regards,

Dear Janson,
Thank you very much for your kindness. So how can I obtain and apply the pressure distribution to a 3D blade model? Do you have any suggestions?
Best regards,

Dear @Baoxuan.Wang,

Considering that blade structural dynamics are often modeled with 1D beam elements, I’d first ask whether you really need the pressure distribution or if the lifting loads output from AeroDyn are OK for your needs.

If you are modeling the blade with 3D FEA, it may be OK to assume some pressure distribution to apply the lifting line loads output from AeroDyn. If the lift and drag coefficients where derived from a pressure distribution, you could use that pressure distribution based on the lift and drag calculated by AeroDyn. It may also be reasonable to assume a uniform pressure distribution if you are mostly interested in the blade root loads (not local loads), which are dominated by aerodynamic loads applied far away from the root.

Calculating the pressure distribution directly would require that you simulate with blade-resolved CFD instead of using the lifting line representation of AeroDyn.

Best regards,

Dear Jason,
That’s very helpful. I have learnt alot.
Best Regrads.

Dear Jason,
Sorry to bother you again. I want to know whether the coordinate systems of B1N1Fx and B1N1Fy (in Aerodyn) change with respect to span and time, just as Spn1FLxb1, Spn1FLyb1, Spn1FLzb1 (in local CS in Elastodyn)? I cannot find out it. Please guide me, thank you.
.

Dear @Baoxuan.Wang,

If you are asking whether the AeroDyn coordinate system follows the deflection of the blade over time, then the answer is “yes”.

Best regards,