Pseudoincompressible

Pseudoincompressible refers to a property of certain fluids or fluid models in computational fluid dynamics (CFD) that exhibit very low compressibility but are not truly incompressible. In a truly incompressible fluid, the density remains constant under all pressure variations. However, in many practical scenarios, especially with liquids or gases at low Mach numbers, the density changes are so small that they can be neglected for computational purposes. This simplification significantly reduces the complexity of the governing equations, making simulations computationally more efficient.

The core idea behind pseudoincompressibility is to allow for small pressure fluctuations that can propagate information through the fluid, analogous to how sound waves travel, but without significant density changes. This is often achieved by modifying the continuity equation or by employing specific numerical schemes. For example, the pressure-correction method, common in CFD, implicitly treats the fluid as pseudoincompressible. By solving a pressure Poisson equation that enforces mass conservation, the algorithm iteratively adjusts the pressure field until the velocity field is consistent with a nearly constant density. This approach is widely used for simulating flows of water, oil, and other liquids, as well as low-speed gas flows. While it introduces a slight approximation, the benefits in terms of computational speed often outweigh the minor loss of accuracy for many engineering applications.