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Incompressible Fluid Flow: Its Special Features

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Compressible and incompressible fluid flows are integral parts of Fluid mechanics. In compressible fluid flow we deal with that part of fluid mechanics in which we deal with a kind of fluid flow where fluid density gets changed significantly with the change of pressure. The effects shown by this flow property is named as the compressibility of the fluid. Alternatively, incompressible flow is the ideal flow and this flow obeys Newton’s Law.


Incompressible flow contains the specific fluid which is density constant and mathematically the fluid divergence of the velocity of the fluid is zero. Incompressible flow Simulation does not signify that the fluid is incompressible. Rather the fact signifies that incompressible fluid contains unvarying density all over the fluid. Incompressible fluids are tough to condense or we can say that their density remains unaffected if its volume is altered up to some extent. In contrast, chocked flow or internal flow and the presence of acoustic waves are the prime factors of compressible flow. These two factors determine if there are compression waves or there are expansions in the fluid and its flow pattern.

In incompressible fluid flow the absolute pressure is absolutely irrelevant. What really matters is if the inclined pressure is found present. In case of compressible flow, fluid properties like density and viscosity are found complementary to each other. Because streamlines are best applied to convective-dominated displacements it is the best and safest practice for setting up an incompressible model first, before executing a compressible fluid flow version.

When a Fluid Flow Modeling is compressible, the fluid density varies with its pressure. Compressible flows are generally high-speed flows with Mach numbers bigger than about 0.3. Samples include aerodynamic uses such as flowing over a wing or aircraft nacelle; it is used in industrial applications such as flow-through high-performance valves.

However, Incompressible fluid flows do not have such a variation of density. The key differentiation between compressible and Incompressible Fluid Pressure is the velocity of the flow. A fluid like air that is moving slower than Mach 0.3 is considered incompressible, although it’s a gas. A gas that runs through the compressor is not truly considered compressible from the aspect of thermodynamic unless its velocity surpasses Mach 0.3. This is significant to note down because analyses indicates it as compressible can be harder to run, and need longer analysis-times than incompressible flows.

All fluids can be categorized as compressible to some extent as if there is some changes in pressure or temperature, it will result in abrupt changes in density. However, there are several situations when the changes in pressure and temperature are measured quite small that the changes in density can be overlooked. In these cases the fluid flow can be categorized as an incompressible fluid flow. Otherwise users should avail general compressible flow equations for deriving result.

May be you like to read more about : The Influence of Computational Fluid Dynamics on the Application of Mixer Design

Mehul Patel

About Author: Mehul Patel specializes in handling CFD projects for Automobile, Aerospace, Oil and Gas and building HVAC sectors. He works as a CFD consultant with Hi-Tech CFD for the past 5 years and has successfully executed numerous CFD projects of high complexities. He is an expert in turbo-machinery, gas dynamics, Combustion, Fluid Dynamics, multiphase flow analysis, computational fluid dynamics etc.