Can anyone see why my residuals are so high?

  • Last Post 30 April 2020
Mattobox posted this 30 April 2020

I've finalised my design of an air intake for my dissertation, and all of the geometry should be right. I've also done calculations to verify all boundary conditions, so these should be *at the very least* in the right ball-park figure, if not absolutely correct. I'm using ANSYS Fluent.

However, well, my residuals are... extremely high. Like 10^5 high... And I don't know why.

My mesh isn't the finest thing in the world (for this initial test run), but its not anywhere near bad enough to cause these residuals I wouldn't think.

My boundary conditions should be correct based on what I've calculated. My boundaries are pressure far field, pressure out and walls.

Pressure Far-Field was calculated from altitude data to be 11600Pa, Mach 2 and 218K. From my calculations, the static pressure rise should be approximately 4.93 through the intake. Therefore my outlet pressure is set from this at 57600Pa. I've also calculated temperature at pressure outlet, and I believe this calculation is atleast in the right ball-park at 386K. This is basically all I've input, so I don't see how it can be so wrong.

Reference Value and Initialisation are both set to Farfield, initialisation is standard initialisation.

I've also tried enabling both K-Omega and K-Epsilon turbulence models, which do not reduce residuals.

I'll attach an imgur file going over my mesh and setup, if anyone could give any help you'll be an absolute life saver:

Thanks a lot for any responses

rahkumar posted this 30 April 2020


Try using an explicit formulation with AUSM as flux type. To start off with, you can run the simulation with first order upwind to get convergence and then go to second order. Also make sure the CFL number is small.  Let me know if this works. 



Regards, Rahul