hi,every one,I am using fluent simulations a solid rocket motor interial flow,and use the mass flow inlet bc.but I meet some problems.in my case,the total pessure is 4.4mpa,total temperature is 3500k,the throat is 0.0105629m2,from this we can calculate the mass flow rate is 26.7kg/s.(k=1.25 and molecular weight is 22).but when i set the mass flow rate as this ,the calculation of total pressure is 5.3mpa not the 4.4mpa,why?please help me!

Have you set Solve/Monitors/Residuals to small values? Is the mesh fine enough? Have you tried second order thing?

How can i know the mesh fine enough?the residual I set is small enough,but they cannot reduce when iterate increase.

well, i am a relative newbie with fluent. i know there is mesh adaptation but i never tried it.

with gambit or tgrid you can create mesh with smaller cells. If you want more accuracy your mesh must contain smaller cells and the computation time will be longer.

I read some documentation in it a postgraduated man wrote that, based on his experience, the real and simulated things can differ 6-10% with the finest meshes.

ok,thanks i will try it.

What have you set your supersonic/intial gauge pressure at? And what outlet parameters are you using? Also are you using an operating pressure? Is this the pressure you are getting once you initialize the case and view the total pressure profile at the inlet?

yes,it is my fault. thanks to all!