Question

Hello! I am using Ansys Fluent to discuss air-flow in a 2D channel, so which solver should I use? Do I need to use density based solver or Pressure base solver? Is air-flow compressible flow or incompressible flow? ( For me, I think I should use density based solver, because air-flow is compressible flow, but I am not sure about myself, this is why I ask for help from everyone who can help me). Thank You in advance! I will thumb you up!

Answer 1

Basically the fluids such as air are considered to be incompressible below 0.3 Mach number and since you are simulating the flow at Mach number 1, the flow is purely considered as compressible.

Further, the pressure-based solver is developed for low speed as well as incompressible flows whereas for high-speed flow as well as compressible flow, the density-based solver is mainly used.

Thus, As your Mach number is 1 you should go with the density-based solver.

The divergence occurs when I use a density-based solver with pressure outlet boundaries with the acoustic wave model - nonreflecting condition is enabled and the simulation is run from t = 0.

The settings of the model are:

General:

Density-based solver; Absolute velocity formulation; Transient; 2D Space: Axisymmetric.

Models:

Energy: on; Viscous: laminar.

Materials:

Air, density: ideal-gas; thermal conductivity and viscosity: kinetic-theory.

Boundary conditions:

Intel > Pressure inlet; Gauge total pressure: 105000 Pa; Normal to the boundary.

Outlet > Pressure outlet; Gauge pressure: 100000 Pa; Backflow direction: Normal to the boundary; Acoustic wave model: nonreflecting, Exit pressure specification: pressure at infinity.

Solution methods:

Formulation: implicit; Flux-type: Roe-FDS; Spatial discretization > Gradient: Least squares cell-based, Flow: 2nd Order Upwind; Transient formulation: 2nd Order implicit.