# incompressible flow

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## Incompressible flow

Fluid motion with negligible changes in density. No fluid is truly incompressible, since even liquids can have their density increased through application of sufficient pressure. But density changes in a flow will be negligible if the Mach number, Ma, of the flow is small. This condition for incompressible flow is given by the equation below, where V is the fluid velocity and a is the speed of sound of the fluid. It is nearly impossible to attain Ma = 0.3 in liquid flow because of the very high pressures required. Thus liquid flow is incompressible. See Mach number

Gases may easily move at compressible speeds. Doubling the pressure of air—from, say, 1 to 2 atm—may accelerate it to supersonic velocity. In principle, practically any large Mach number may be achieved in gas flow. As Mach number increases above 0.3, the four compressible speed ranges occur: subsonic, transonic, supersonic, and hypersonic flow. Each of these has special characteristics and methods of analysis.

Air at 68°F (20°C) has a speed of sound of 760 mi/h (340 m/s). Thus inequality indicates that air flow will be incompressible at velocities up to 228 mi/h (102 m/s). This includes a wide variety of practical air flows: ventilation ducts, fans, automobiles, baseball pitches, light aircraft, and wind forces. The result is a wide variety of useful incompressible flow relations applicable to both liquids and gases. See Compressible flow, Fluid flow

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

## incompressible flow

[¦in·kəm′pres·ə·bal ′flō]
(fluid mechanics)
Fluid motion without any change in density.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In all the studies above, the entropy productions in the flow of viscous incompressible fluid flow through porous medium have not been investigated.
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Muhammad G.: Boundary Element Methods for Incompressible Fluid Flow Problems.
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Steady state incompressible fluid flow was assumed.
Fatemi, "An Efficient, Interface Preserving Level Set Re-Distancing Algorithm and Its Application to Interfacial Incompressible Fluid Flow," SIAM J.
Whether you are an early-career or experienced engineer, you can make use of the organized solutions to problems involving such subjects as: water and steam hammer phenomena; gravity flow of liquid in pipes; siphon seals and water legs; regulating steam pressure drop; industrial risk insurers' fuel gas burner piping valve train; controlling differential air pressure of a room with respect to its surroundings; water chiller decoupled primary-secondary loops; pressure drop calculations of incompressible fluid flow in piping and ducts; water chillers in turndown; hydraulic loops; radiation heat transfer, and thermal insulation.
* incompressible fluid flow (Navier-Stokes equations)
The numerical technique used to couple the velocity and pressure fields is similar to the one proposed by Raithby and Schneider (15) for incompressible fluid flow in ducts.
Many authors investigated the two-dimensional incompressible fluid flow through porous channels theoretically.

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