Discussion Forum

Hi everyone,

I want to solve a 2D Euler equations using Comsol to save programming and debugging time. Here the Euler equation is used to describe gas expansion, thus it includes conservation of mass, momentum and energy, and four independent variable exist (rho, u, v, and p).

I treated this problem following the way in the blog about shock tube: www.comsol.com/model/shock-tube-100, where the 1D Euler equation is modified to a 2D example (t was represented by the y) to save time. In my module as attached, I use a 3D module to represent the 2D problem (using z to stand for t). A weak contribution is also added as in the shock tube blog. The 2D Euler equation were derived and added in my attached module.

The initial condition is read from a 2D Riemann problem (6.1 2D Riemann problem) from: www.oxygen8.org/HTML/numerical_pdes_final_project/MUSCL_for_2D_Euler.html.
And this initial condition is expressed by Matlab function. For example, density is expressed by function initial_rho, as attached.

My question is, I cannot get a solution from this module, the comsol error informing that "Failed to find a solution. Maximum number of Newton iterations reached." I tried to increase the iteration number, but it seems it cannot figure out this problem perfectly.

I want discuss following problems:

1). For CFD problem, is there special solver or configuration or special meshing scheme if we want to use FEM to solve these equations? I noticed that in the shock tube example, the Adaptive Mesh Refinement is used. I tried it, but failed.

2). I don't think this 4 PDEs problem is more difficult than solving Navier STokes equation. If Comsol can handle the CFD problem properly, there should be a proper way for me to carry out this module calculation.

3). I also tried to calculate this problem in 2D using Time dependent, but it is too slow.

Thank you very much for any suggestion about this module.
Hao