Obtaining Pressure Coefficient on the airfoil

[CFD Engineer]

Hello Nek experts,

I am simulating flow over an airfoil (2D & 3D) in Nek5000 and have the results with me for both the cases. I have 2 separate walls (one upper and one lower wall of airfoil) and need to compute average pressure coefficient on both the walls separately (lower and upper).

So far what I came up with is to include the following subroutine in my usr file to get the average pressure. But dont know what should I do to get the pressure coefficient value from it. Any sort of help will be highly appreciated.

Thanks

      subroutine planar_avg_pressure(pa,p,hndl)

      include 'SIZE'
      include 'TOTAL'

      real pa(*)
      real p (*)
      common /scrcg/ wrk(lx2*ly2*lz2*lelv)

      n = nx2*ny2*nz2*nelv

      call copy(wrk,bm2,n)                   ! Set the averaging weights
      call fgslib_gs_op(hndl,wrk,1,1,0) ! Sum weights
      call invcol1(wrk,n)

      do i=1,n
         pa(i) = bm2(i,1,1,1)*p(i)*wrk(i)
      enddo

      call fgslib_gs_op(hndl,pa,1,1,0) ! Sum weighted values

      return
      end 

[Fischer, Paul]

I recommend to look at subroutine torque_calc in navier5.f

There are examples of this being called in nekexamples

(grep torq */*.usr).

You can define the upper surface of your airfoil as object 1

and the lower half as object 2

torque calc will report the integrals over the individual objects (each, just a collection of faces) as well as the sum over all

objects.

You will get forces in x and y direction as well as moments (torque) about a prescribed point, x0.

hth,

Paul

  subroutine torque_calc(scale,x0,ifdout,iftout)

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Subject: [nek5000] Obtaining Pressure Coefficient on the airfoil

 

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[CFD Engineer]

Thank you so much for your reply. I've a bit of confusion, from your explanation it seems that I will get an integral value of cp (pressure coefficient) along each surface of my airfoil. But infact what I am looking for is to obtain cp vs airfoil surface plot. So, I need a sub-routine to plot cp along the wall of my airfoil. Could you please clarify further if I am able to do that somehow?

Thanks.