Static Tap Pressure Measurement Bias Error Introduced by Aerodynamic Noise

Abstract

This work presents experimental and analytical studies to confirm the existence of bias errors introduced in static pressure tap measurement, caused by external aerodynamic noise. Static pressure taps are used widely in the industry to determine fluid velocity and obtain quantities such as flight speed and mass flow rate. The discovered bias error caused by aerodynamic noise greater than ~135dB can introduce a bias error in the mean static pressure measurement that affects the pressure coefficient (Cp) determination on the order of 0.5~1.0%, depending on the internal geometry of the static taps. The presence of the error has been confirmed using a wind tunnel experiment, and studied using computational fluid dynamics (CFD) simulations. Analytical studies show that bias errors occur when external aerodynamic noise causes the static tap to breathe in and out higher total pressure flow away from the wall surface. The magnitude of the bias error depends on the sound pressure level of the aerodynamic noise, as well as the internal geometry of the static tap. Bias errors are larger for static taps that consist of a relatively short neck (length-to-depth ratio below 10) leading to a larger diameter cavity, as it causes the tap to act similarly to a Helmholtz resonator and induces a larger amount of higher total pressure flow to be breathed in and out of the tap.