if Mach number>4.0 ,fluent will give me some mistake message .why? can you tell me how to setup in fluent?thank you!!

(1). First of all, you need to find out whether the code is designed to handle your kind of problems or not. (2). After you are sure that the code has the capability to solve your problem, you should try to get a sample case, so that you can follow the instruction and get a solution. (3). The first hypersonic scramjet vehicle has just crashed during the first few seconds of the first test run (X43A?), so "trial-and-error" approach is not going to work for cfd codes. (4). Since no aircraft is currently flying at Mach 4, your problem must be related to some kind of hypersonic vehicle or missiles. (5). My suggestion is: find a density-based method, at least 20 years old, and write your own code based on it.

I have run couple of hypersonic problems (2D axysimmetric) and I haven't had any problem and the results have been great

I have done any test in 3D but I would be really surprise if fluent can't handle it. In the last NewsLetter and 3D work for the Mars PathFinder was presented (Italian University).

The only restriction is that to be careful with the procedure in this type of cases:

Procedure to get a converge solution ----------------------- 1. Initial run with cold combustion 2. Once that we have a good convergence in cold combustion, then we activate the dissociating equations 3. If we consider catalytic effects, these ones have to be considered as a third stage. That is, run the point 2 without catalytic effects and once that we have a converged solution - set the catalytic BC

It is important to start with a good mesh, although it will needed a couple of refine mesh to get accuracy results

Solver: Couple Implicit important: don't increase the Clk number more than 1 Start with a low Clk number (0.01 or 0.1) and increase it very little by little - otherwise the process will not converge

In case that this won't help you, please contact your support engineer

Patxi

thanks a lot!ccg