CFD Online Discussion Forums - Shock-bubble interaction and potential grid error

Hello,

I was curious if anyone has had experience with shock-bubble interactions. Before I go further with my issue, I want to first say that I have validated my code on Rayleigh-Taylor instability, Kelvin-Helmholtz instability, and various Riemann problems.

On to my issue. When defining my bubble I am using the classical formula

sqrt((X(i,j,k)-XCenter)^2.0 + (Y(i,j,k)-YCenter)^2.0 + (Z(i,j,k)-ZCenter)^2.0) < r

However I notice that when I use a non-square domain (lets say a 3 x 1 x 1 domain), my simulation blows up (NaNs.) After some time I noticed that if I remove the bubble, I do not have blow up. Maybe this is the wrong conclusion, but is it possible the way I'm defining my bubble numerically problematic?

In terms of my problem setup. On the inflow and outflow I have Neumann BCs (i.e. dq/dn = 0) and on the walls I have reflective boundary conditions.

As a little code snippet (not too important) here is how I am defining my IC:

Code:

        

!Bubble

if ((X(i,j,k)-0.50)**2.0 + (Y(i,j,k)-0.50)**2.0 + (Z(i,j,k)-0.50)**2.0 <= 0.1**2.0) then

rho(i,j,k) = 0.1358

u(i,j,k) = 0.0

v(i,j,k) = 0.0

w(i,j,k) = 0.0

p(i,j,k) = 1.0

gamma = 1.67

else

!Pre-shock

rho(i,j,k) = 1.0

u(i,j,k) = 0.0

v(i,j,k) = 0.0

w(i,j,k) = 0.0

p(i,j,k) = 1.0

gamma = 1.4

end if



!Post-shock

if (X(i,j,k) > 0.9) then

rho(i,j,k) = 0.13764

u(i,j,k) = -0.394

v(i,j,k) = 0.0

w(i,j,k) = 0.0

p(i,j,k) = 1.5698

gamma = 1.4

end if