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Next: Shock-Choke Phenomenon Up: General Velocities Issues Previous: General Velocities Issues   Index

#### Piston Velocity

When a piston is moving, it creates a shock that moves at a speed greater than that of the piston itself. The unknown data are the piston velocity, the temperature, and, other conditions ahead of the shock. Therefore, no Mach number is given but pieces of information on both sides of the shock. In this case, the calculations for Us can be obtained from equation (5.24) that relate the shock velocities and Shock Mach number as

Equation (5.64) is a quadratic equation for Msx. There are three solutions of which the first one is Msx=0 and this is immediately disregarded. The other two solutions are

The negative sign provides a negative value which is disregarded, and the only solution left is

or in a dimensionless form

Where the strange'' Mach number is Msx′ = Ux′ /Cx. The limit of the equation when cx⇒ ∞ leads to

As one additional strange'' it can be seen that the shock is close to the piston when the gas ahead of the piston is very hot. This phenomenon occurs in many industrial applications, such as the internal combustion engines and die casting. Some use equation (5.68) to explain the next Shock-Choke phenomenon.

Next: Shock-Choke Phenomenon Up: General Velocities Issues Previous: General Velocities Issues   Index
Created by:Genick Bar-Meir, Ph.D.
On: 2007-11-21