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James Date November 26, 1999 12:50

Unsteady Boundary Conditions
Hi, Could anyone tell be if they have had any experience using unsteady boundary conditions in CFX4.2 using the USRBCS FORTRAN routine. I'm interested in modelling an NACA0012 aerofoil with a transient inflow boundary condition. So far i've managed to implement an oscillating inflow condition in the USRBCS FORTRAN routine and obtained transient solutions. However, when you look at the dump file after a no of periods there doesn't seem to be any downstream wake response.The Lift & Drag force's are changing. Could someone shed some light on these initial findings? Am i doing someting fundamentally wrong!!

Regards James Date

Erik Torbergsen November 29, 1999 09:09

Re: Unsteady Boundary Conditions
Hi James.

I have been using USRBCS successfully for varying the inlet flow of a centrifugal pump for detecting hysteresis in rotating stall onset. So principally it should work, as far as I understand your case. If you have problems with the wake, perhaps the outlet boundary condition should be looked at.


Erik Torbergsen

Duane Baker November 30, 1999 00:44

Re: Unsteady Boundary Conditions
Hi James,

what is your outlet BC treatment and where is it? Also, what is your grid ie. do you have walls in the near field like an airfoil in a tunnel or do you use far field conditions?



James Date November 30, 1999 09:08

Re: Unsteady Boundary Conditions
Hi Duane, Thanks for your reply.I'm using a C-Grid + H-Grid round the aerofoil.My outlet bounday is located 10 chord lengths down stream, i've set it as a constant pressure bounday (Is this correct?)The upper and lower boundaries on the grid i've also set as pressure boundaries. The inlet boundary condition is set in the user FORTRAN routine;i.e. Alpha(angle of attack)=Alpha0*sin(wt). U=V0*cos(Alpha), V=V0*sin(Alpha). Regards James Date

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