## Fluids

#### Pressure based coupled solver for supersonic internal flow

• imungan
Subscriber

Hello. I am working on supersonic internal flow. When i run the case in density based solver, i got temp triggered error. However when i switch to pressure based coupled solver, it solves without error.

I have a few questions;

1) if pressure based coupled solver is alternative for density based, can we say that pressure based coupled solver could be used whereever density based solver is used?

2) What may rise temperature triggered error while iterating?

• C N
Ansys Employee

Hello,

1) The pressure-based approach was developed for low-speed incompressible flows, while the density-based approach was mainly used for high-speed compressible flows. However, recently both methods have been extended and reformulated to solve and operate for a wide range of flow conditions beyond their traditional or original intent.
In both methods the velocity field is obtained from the momentum equations. In the density-based approach, the continuity equation is used to obtain the density field while the pressure field is determined from the equation of state.
On the other hand, in the pressure-based approach, the pressure field is extracted by solving a pressure or pressure correction equation which is obtained by manipulating continuity and momentum equations.
The pressure-based solver traditionally has been used for incompressible and mildly compressible flows. The density-based approach, on the other hand, was originally designed for high-speed compressible flows. Both approaches are now applicable to a broad range of flows (from incompressible to highly compressible), but the origins of the density-based formulation may give it an accuracy (i.e. shock resolution) advantage over the pressure-based solver for high-speed compressible flows.

In incompressible flows, pressure is not a function of density and temperature ( or a weak function of for for very low mach flows).

In compressible flows, pressure is a function of both density and temperature and is determined by state equation.

2) Temperature triggered error can arise if there are more number of skewed cells. Check the mesh region around the complex geometry region and also create fine mesh regions in only areas where the physics is important. Then try to do higher order relaxation to the scheme. These steps may reduce the temperature triggered errors in iterations. You can also lower the value of URF for energy.

Thank you!

• imungan
Subscriber

Ok thank you. So will i consider the same recommendations for "turbulent viscosity limited to viscosity ratio of 1 in ... cells"?

• C N
Ansys Employee

hello

yes you can try this settings in this scheme.

thank you

• imungan
Subscriber