incompressible flow


Also found in: Wikipedia.

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

incompressible flow

[¦in·kəm′pres·ə·bal ′flō]
(fluid mechanics)
Fluid motion without any change in density.
References in periodicals archive ?
In Section 2, we describe the Stokes and Jacobian problems arising from finite element discretization of incompressible flow problems.
The model was based on pure viscous non-Newtonian and incompressible flow with stress tensor [tau], pressure p, and velocity vector v.
SILVESTER, Optimal low order finite element methods for incompressible flow, Comput.
For steady and incompressible flow the balance of mass and the balance of linear momentum become
Equation 1, describes mathematically, the conservation of mass for incompressible flow.
Thus, the problem of finding energy density distribution in space is reduced to the problem of finding the stretching statistics of a material surface (the wavefront) in incompressible flow field.
The characteristics of an incompressible flow [11] are obtained by using the following equations:
To distinguish between compressible and incompressible flow in gases, the Mach number (the ratio of the speed of the flow to the speed of sound) must be greater than about 0.
The governing equations (mass, momentum and energy conservation) for a steady laminar and incompressible flow are:
The equation of motion for incompressible flow may be generalized to atmospheric flows by the use of the so-called anelastic approximation.
A Green's Function Solution for the Case of Laminar Incompressible flow Between Non-Concentric Circular Cylinders," J.