[Daryun]

1. What is the difference between density-based compressible flow and pressure-based compressible?

2.What should be done when divergence occurs in a desired solution to solve pressure-based for speed input and pressure output? Should a density-based solvent be used? The input mach number is 0.14. Here's the subsonic compressible flow. The speed input is 27.5 m / s and the temperature is 408.15K. The pressure output is 120350Pa gauge pressure. Can I do what I mentioned in point 3 for the solution to converge? When I do, the solution converges. When I don't, the contunity equation diverges.

3.Divergence was observed when ideal gas was used. Is it correct to apply the "Solution Strategies for Compressible Flows" section in the user guide?
* "(Pressure-based solver only) Initialize the flow to be near stagnation (that is velocity small but not zero, pressure to inlet total pressure, temperature to inlet total temperature) 1. Set the pressure under-relaxation to 0.4, and the momentum under-relaxation to 0.3. After the solution stabilizes and the energy equation has been turned on, the pressure increases to 0.7. "

When he says "after the solution stabilizes", does he mean the convergence of the solution?

thanks

[ngoctm]

Hi Daryun,

1. Please refer to the Fluent help document.

Historically speaking, 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.

2. In your case, M = 0.14 < 0.3, so the flow is considered incompressible. Using Pressure-based solver is suitable.

3.

When he says "after the solution stabilizes", does he mean the convergence of the solution?

- Yes, that means you should get the result converged with the inactive energy equation in the first run. After that, active the E-quation in the second run.

Hope this help,

[Daryun]

Is the air in the turbocharger a compressible flow or an incompressible flow? I've been modeled as a subsonic compressible flow for months. In addition to a 63mm diameter circular pipe, I added an octagonal pipe. Then the outlet continues with a 63mm circular pipe. Should I take the air density as constant or as the ideal gas? There should be pressure at the outlet and this is a gauge pressure of 120350Pa.