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Projectile shockwave in 2d using Roe solver? General discussion... 

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May 13, 2013, 18:55 
Projectile shockwave in 2d using Roe solver? General discussion...

#1 
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Andrew Somorjai
Join Date: May 2013
Posts: 77
Rep Power: 4 
I'm trying to solve a simple model graphically in 2 dimensions where a bullet traveling faster than sound moves to the right along the xaxis and generates shock waves around itself. So far I understand that a Roe solver is used to calculate the fluxes on the edges of adjacent cells and I'm working with the code on this site called twod_euler_fluxes_v2.f90. I'm actually good with C/C++ so I decided to convert the Fortran code to something more easily readable (in my own taste). The question I have ultimately asks how do I...
1.Setup the initial grid. With the bullet having different attributes (e.g. density) compared to the "medium" (Air is the medium in this case). 2. How would I update the grid. Do I basically check every cell in one timestep and update the bullet a certain position (maybe one cell per time step). I'm thinking that using a simple array called GRID[100][100] would be looped over within a nested double for loop? Forgive me for being a noob. 

May 14, 2013, 03:21 

#2 
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Join Date: Dec 2011
Location: Madrid, Spain
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Hi. Here's what I think:
1) The bullet is not a fluid, therefore you do not solve any equations inside it. The mesh encompasses the fluid domain and surrounds the bullet, which define the inner boundaries of the fluid domain, and where you must define wall boundary conditions. 2) There's no need to update the mesh. If you set a reference frame on the bullet, the problem becomes steadystate. Cheers, Michujo. 

May 15, 2013, 02:34 

#3  
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Andrew Somorjai
Join Date: May 2013
Posts: 77
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Quote:
Code:
real :: uL(4), uR(4) ! Input: conservative variables rho*[1, u, v, E] real :: nx, ny ! Input: face normal vector, [nx, ny] (LefttoRight) real :: Roe(4) ! Output: Roe flux function (upwind) Quote:


May 16, 2013, 07:00 

#5 
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Join Date: Dec 2011
Location: Madrid, Spain
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Hi, I am not sure to understand your problem.
Being the fluid flow stationary with respect to the bullet, the mesh does not need to be recomputed at every time step. Only the fluid flow will be calculated until convergence. At the walls of the bullet the fluid velocity is zero (noslip boundary condition) in the reference frame you used (travelling with the bullet). The upwind scheme works no matter the direction in which the bullet is travelling (or the fluid with respect to the bullet in your problem). The scheme will always take the right upstream value locally. Cheers, Michujo. 

May 18, 2013, 18:37 

#6  
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Andrew Somorjai
Join Date: May 2013
Posts: 77
Rep Power: 4 
You've been very helpful thanks.
Quote:
What I mean by updating is that the flux is determined for every single fluid cell and solved using a matrix based on the previous state of each cell because the bullet is moving through the system... Quote:


Tags 
projectile, roe solver, shockwave, twodimensions 
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