Flow Parameter Measurement

Mach Number

Mach number is a measure of how fast the tunnel airflow is moving relative to the speed of sound; at Mach 1, the airflow is moving at the speed of sound. Most modern civil transport aircraft cruise at between Mach 0.8 and Mach 0.9.

Mach number is calculated from the Test Section and Settling Chamber static pressures. These pressures are fully corrected for the effects of the test section porous walls and the model blockage before they are used in the Mach number calculation.

The fully corrected Mach number has an accuracy of ∆M = ±0.001 at Mach 0.8.

Reynolds Number

Reynolds number is a very important parameter used to describe how the airflow behaves very close to the model surface; changes in surface flow behaviour can have a very significant effect on how the entire flow field around the model behaves such as whether a wing stalls or where a shock is positioned.

Reynolds number is calculated from fully corrected values of the Test Section Mach number and the Settling Chamber static pressure and temperature.

Technical Information

The Test Section and Settling Chamber static pressures are measured with an accuracy of ±0.5mB (0.00725psi) by RUSKA pressure gauges.

The Settling Chamber static temperature is measured with an accuracy of ∆T = ±0.22K (±0.4˚R) with a pair of temperature transducers.