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

LinkBack  Thread Tools  Display Modes 
May 13, 2013, 18:55 
Projectile shockwave in 2d using Roe solver? General discussion...

#1 
Member
Andrew Somorjai
Join Date: May 2013
Posts: 77
Rep Power: 6 
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 
Senior Member
Join Date: Dec 2011
Location: Madrid, Spain
Posts: 134
Rep Power: 8 
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  
Member
Andrew Somorjai
Join Date: May 2013
Posts: 77
Rep Power: 6 
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 
Senior Member
Join Date: Dec 2011
Location: Madrid, Spain
Posts: 134
Rep Power: 8 
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  
Member
Andrew Somorjai
Join Date: May 2013
Posts: 77
Rep Power: 6 
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 
Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
general discussion on UDF in Fluent  doki  FLUENT  0  October 13, 2008 07:57 
why the solver reject it? Anyone with experience?  bearcat  CFX  6  April 28, 2008 14:08 
CFX 5.5  Roued  CFX  1  October 2, 2001 16:49 
Roe scheme for general equation of state  zouchu  Main CFD Forum  3  August 10, 2000 16:46 
Eigenvalues & Eigenvectors in General Geometries for 3D TVD Solver  Axel Rohde  Main CFD Forum  3  October 6, 1999 14:48 