Flow Physics - Mach Number
Within the realm of fluid dynamics, dimensionless numbers are extremely important. Dimensionless numbers are values that have no units of measurement attached (such as meters or kilograms).
These dimensionless numbers are important because they can be used to compare different fluid flows regardless of outside variables. In regard to fluid flow through nozzles, one of the most important dimensionless numbers is known as the Mach number, which is represented in equations by the symbol Ma.
The Mach number of a flow is found by dividing the velocity of the flow by the speed of sound at the given flow conditions. Mach numbers range from very small (Ma < 0.3) to very large (Ma > 3.0). The ranges found between these extremes are very important and reveal many details about the flow.
Any flows with a Mach number less than 0.3 are classified as incompressible flows, and are not relevant to nozzle calculations. Mach numbers in the range of 0.3 to 0.8 are known as subsonic flows, since they travel at a slower speed than sound. Mach numbers falling between 0.8 and 1.2 are known as transonic flows, and are extremely important to nozzle physics. Any flows with a Mach number greater than 1.2 are known as supersonic flows, and exhibit behavior not found in any other Mach range (such as shock waves). A flow with a Mach number of exactly 1.0 is known as a sonic flow and is the most important value in nozzle dynamics.
These dimensionless numbers are important because they can be used to compare different fluid flows regardless of outside variables. In regard to fluid flow through nozzles, one of the most important dimensionless numbers is known as the Mach number, which is represented in equations by the symbol Ma.
The Mach number of a flow is found by dividing the velocity of the flow by the speed of sound at the given flow conditions. Mach numbers range from very small (Ma < 0.3) to very large (Ma > 3.0). The ranges found between these extremes are very important and reveal many details about the flow.
Any flows with a Mach number less than 0.3 are classified as incompressible flows, and are not relevant to nozzle calculations. Mach numbers in the range of 0.3 to 0.8 are known as subsonic flows, since they travel at a slower speed than sound. Mach numbers falling between 0.8 and 1.2 are known as transonic flows, and are extremely important to nozzle physics. Any flows with a Mach number greater than 1.2 are known as supersonic flows, and exhibit behavior not found in any other Mach range (such as shock waves). A flow with a Mach number of exactly 1.0 is known as a sonic flow and is the most important value in nozzle dynamics.
JL