 # Solutions Method in CFD ( Part1 )

1- SIMPLE

In this method, a semi-implicit method for the relationship between momentum equations, continuity and static pressure has a moderate convergence in most simulations, and many of the old soft-user use this method in simulations. The initial guess for pressure is that it converges. Of course, one of the main weaknesses of this method is the need to distribute the proper initial pressure in the initial repetitions.

2- SIMPLEC

This method is very similar to the SIMPLE method, the only difference is being the assumption of load correction velocity values. In the SIMPLE method, neighbors’ correction values are assumed to be zero, but in this method, the values of neighboring corrections are considered equal to the amount of velocity correction on the central cell. None of the two assumptions used in SIMPLE and SIMPLEC are correct in the pre-convergence repeats, but both converges to correct correction values, and both assumptions are correct and have no effect on the accuracy of the results. Because in the SMPLEC method, the amount of corrected override in the SIMPLE method is approximated with the correction of the central cell, it is expected that its convergence is more than the SIMPLE method. In practice, however, this prediction is valid only on smooth networks in the presence of simple and non-turbulent flows (slow), and in most of the complex industrial simulations, SIMPLEC does not have a significant advantage over the SIMPLE method.

3- PISO

The name of this method, derived from the initial letters, is the implicit pressure method, with the separation of operators, and is in fact the result of the SIMPLE family. The main problem with the SIMPLE and SIMPLEC methods is the lack of satisfaction of the momentum failure after solving the pressure equation, while PISO can partially solve this problem by applying two corrections, one on the adjacent and the other on the element’s Lodging. The main idea of this method, the repetitions needed to simultaneously satisfy the equations of momentum and pressure, are corrected within the calculation loop. It is said to be internal repetitions, momentum correction, or correction of an vicinity that can satisfy the momentum and pressure equations to a less extent. In two cases, the first application of the first case is based on time-dependent simulations, especially under conditions Which requires time steps in which PISO is able to ensure high convergence by correction to the neighbor. In this situation, the volume for each repetition is somewhat higher, but in contrast, incredibly, convergence increases the ultimate goal from the general time Performing calculations is reduced.

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