I wonder if anyone could kindly give me some advices with Momentum Exchange method(MEM). I doubt maybe I didn’t understand well with the related paper. Renwei Mei’s paper–Force Evaluation in the Lattice Boltzmann Method Involving Curved Geometry

I made code to calculate Poiseuille flow, the velocity contour looks good. then I tried to calculate the Drag force and lift force on the top wall with MEM, as following fortran codes. But the result is totally wrong… Dragforce is around -1, and Liftforce is around -77., I think reasonally the drag force should be large value and liftforce should be very small…–!

Model: incompressible LBGK model.

Parameters: Re=20, Umax=0.05, nx=200,ny=40…

BCs: Top and bottom is simple bounce back; inlet: parabolic velocity profile; outlet: 0-gradient of velocity and fixed density to 1.

Calculation seququnce: Collision step–>>Boundary Condition treatment–>> Force evaluation–>>Stream step–>>Collision…

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subroutine evaluatingForce

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m(4)=0

n(4)=-1

m(7)=-1

n(7)=-1

m(8)=1

n(8)=-1

fdrag=0.d0

flift=0.d0

do i=1,nx

fdrag = fdrag + m(7)*(f(7,i,ny+1)+f(5,i-1,ny)) + m(8)*(f(8,i,ny+1)+f(6,i+1,ny))

flift = flift + n(7)*(f(7,i,ny+1)+f(5,i-1,ny)) + n(8)*(f(8,i,ny+1)+f(6,i+1,ny)) + n(4)*(f(4,i,ny+1)+f(2,i,ny))

enddo

return

end

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Your comments would be highly appreciated…

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