Question on moving mesh, mesh velocity is really small!

ripperjack · December 14, 2012, 12:15

Hi guys,

I am coding a finite volume code to calculate the unsteady pressure for a moving airfoil. I used Roe scheme, and I am really confused with the moving mesh method.

I calculate the mesh moving velocity and it is really small (

), and the flow velocity V is larger than 200m/s. And it seems that the mesh moving velocity has no influence on the solution.

As I understand, for Roe scheme, the cell surface flux for moving mesh is nearly the same as for stationary mesh, the only different is that the velocity V in eigenvalue for moving mesh is replaced by

. (

) . However, since

is very small, it seems that it has limited influence on the solution.

Can you guys who had the experience in moving mesh help me? Thanks!

orxan.shibli · April 27, 2014, 13:03

Not only eigenvalues but flux vector changes, too. Considering 3D flux in normal direction:

$F_0 = \rho (u_n - u_b) \\$

$F_1 = \rho (u_n - u_b) u + p n_x \\$

$F_2 = \rho (u_n - u_b) v + p n_y \\$

$F_3 = \rho (u_n - u_b) w + p n_z \\$

$F_4 = (u_n - u_b) E + p u_n \\$

levivad · April 28, 2014, 14:37

from a physics stand point, it makes sense that if the boundary moves slowly relative to the flow velocity it will be insignificant ( unless there's some special case). This is true until the geometry changes enough to impact the flow.
It might be considered quasi-static.

December 14, 2012, 12:15	Question on moving mesh, mesh velocity is really small!	#1
ripperjack Member Jack Join Date: Dec 2011 Posts: 94 Rep Power: 13	Hi guys, I am coding a finite volume code to calculate the unsteady pressure for a moving airfoil. I used Roe scheme, and I am really confused with the moving mesh method. I calculate the mesh moving velocity and it is really small (), and the flow velocity V is larger than 200m/s. And it seems that the mesh moving velocity has no influence on the solution. As I understand, for Roe scheme, the cell surface flux for moving mesh is nearly the same as for stationary mesh, the only different is that the velocity V in eigenvalue for moving mesh is replaced by . () . However, since is very small, it seems that it has limited influence on the solution. Can you guys who had the experience in moving mesh help me? Thanks!

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April 27, 2014, 13:03		#2
orxan.shibli Member Join Date: Aug 2011 Posts: 30 Rep Power: 13	Not only eigenvalues but flux vector changes, too. Considering 3D flux in normal direction: $F_0 = \rho (u_n - u_b) \\$ $F_1 = \rho (u_n - u_b) u + p n_x \\$ $F_2 = \rho (u_n - u_b) v + p n_y \\$ $F_3 = \rho (u_n - u_b) w + p n_z \\$ $F_4 = (u_n - u_b) E + p u_n \\$

April 28, 2014, 14:37		#3
levivad New Member Join Date: May 2013 Posts: 12 Rep Power: 11	from a physics stand point, it makes sense that if the boundary moves slowly relative to the flow velocity it will be insignificant ( unless there's some special case). This is true until the geometry changes enough to impact the flow. It might be considered quasi-static.