Wave Velocity and Communication Time
Wave Velocity
The wave velocity (sometimes referred to as characteristic speed) for gas transients is the velocity at which the pressure waves will propagate through the gas, as is calculated by the Method of Characteristics. For gas flow the wave velocity is equivalent to the sonic velocity of the gas (a) plus the velocity of the gas (V). The sonic velocity and velocity will vary with pressure and density.
Communication Time
An important consideration in fluid transient studies is how long it takes a wave to propagate through the system.
The time it takes for a wave to travel from one end of a system to the other is the distance (L) divided by the wave velocity. Note that the wave velocity is not constant since the sonic velocity and velocity will vary with pressure and density. However, a minimum communication time can be estimated using the maximum sonic velocity (i.e. sonic velocity at the maximum temperature) and maximum velocity (i.e. sonic velocity), as is discussed in Pipe Sectioning - Introduction to Method of Characteristics.
When a transient event occurs at one end of a pipe, the wave travels at the wave velocity to the other end of the pipe. However, this is not sufficient time to analyze the problem. While the disturbance has propagated through the entire system, the point of transient initiation has not yet seen the result of the reflected wave. For the wave to both travel to the end of the pipe and back requires double the above time. This time is known as the Pipe Period or Communication Time.
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