[PXY]

Hello everyone,
I'm writing a code to define the wall shear stress, but it's always wrong. How to write it correctly?

τzx=-(σz*f+(ρ*g*vx^2)/ξ)

#include"udf.h"
#define F 0.3 /*friction coefficient*/
#define B 1000 /*turbulence parameter*/
#define D 1630 /*density*/
#define g 9.81
DEFINE_PROFILE(taux_profile, t, i)
{
real u, p;
face_t f;
Thread* t0;
cell_t c0;
begin_f_loop(f, t)
{
t0 = THREAD_T0(t);
c0 = F_C0(f, t);
p = C_P(c0, t0);
u = C_U(c0, t0);
F_PROFILE(f, t, i) = p * F + D * g * u * u / B;
}
end_f_loop(f, t)
}
DEFINE_PROFILE(tauy_profile, t, i)
{
real v, p;
face_t f;
Thread* t0;
cell_t c0;
begin_f_loop(f, t)
{
t0 = THREAD_T0(t);
c0 = F_C0(f, t);
p = C_P(c0, t0);
v = C_V(c0, t0);
F_PROFILE(f, t, i) = p * F + D * g * v * v / B;
}
end_f_loop(f, t)
}

[pakk]

Please explain how you concluded that it's wrong.

[AlexanderZ]

check values of P and V/U you are extracting from adjusted to wall cells
you may do it using Messages to console

p = C_P(c0, t0);
u = C_U(c0, t0);
Message0("u = %f, p = %f\n",u,p);

[PXY]

Originally Posted by pakk

Please explain how you concluded that it's wrong.

Similarly, when I don't use UDF, the result is convergent, but when I add UDF, my result shows "floating point exception"

[pakk]

Initialize, don't run, plot the shear stress.

Is it what you expect?

[PXY]

Originally Posted by pakk

Initialize, don't run, plot the shear stress.

Is it what you expect?

Initialize but do not run, why is the shear stress a straight line equal to 0? Is my UDF written wrong?


I checked the units, length (m)， Pressure (Pascal), but when I run it, it shows that the shear stress of wall is especially small.