Why Are Multiple Pressure-Velocity Coupling Algorithms Used in ANSYS Fluent?

[humphreybogart]

In Fluent, there are several 'pressure-velocity coupling' algorithms.

Why are these necessary when, in many fluid mechanics textbooks, it is proposed that for incompressible fluids, an equation for Pressure can be found by taking the divergence of the Navier-Stokes equation, and inverting using the Biot-Savart law?

 

[Mech_Engineer]

ANSYS's documentation package describes in great detail the applications of each solver. It appears most of the reasons you would choose one solver over another relate to the kind of problem you're solving, and the FEA model's parameters.

See here: https://www.sharcnet.ca/Software/Fluent6/html/ug/node1021.htm

SIMPLE vs. SIMPLEC
For relatively uncomplicated problems (laminar flows with no additional models activated) in which convergence is limited by the pressure-velocity coupling, you can often obtain a converged solution more quickly using SIMPLEC. With SIMPLEC, the pressure-correction under-relaxation factor is generally set to 1.0, which aids in convergence speed-up.

PISO
(25.4.3) with neighbor correction is highly recommended for all transient flow calculations, especially when you want to use a large time step. (For problems that use the LES turbulence model, which usually requires small time steps, using PISO may result in increased computational expense, so SIMPLE or SIMPLEC should be considered instead.) PISO can maintain a stable calculation with a larger time step and an under-relaxation factor of 1.0 for both momentum and pressure. For steady-state problems, PISO with neighbor correction does not provide any noticeable advantage over SIMPLE or SIMPLEC with optimal under-relaxation factors.

Fractional Step Method
25.4.3, is available when you choose to use the NITA scheme (i.e., the Non-Iterative Time Advancement option in the Solver panel). With the NITA scheme, the FSM is slightly less computationally expensive compared to the PISO algorithm. Whether you select FSM or PISO depends on the application. For some problems (e.g., simulations that use VOF), FSM could be less stable than PISO.

Coupled
25.4.3. This solver offers some advantages over the pressure-based segregated algorithm. The pressure-based coupled algorithm obtains a more robust and efficient single phase implementation for steady-state flows. It is not available for cases using the Eulerian multiphase, NITA, and periodic mass-flow boundary conditions.