Coherent noise removal from dynamic wall pressure and vibration signals

Fluid-structure interaction experiments often include measurements of the fluid excitation force (or pressure) and the resulting structural vibration. In addition to the desired information, measured dynamic pressure data can contain unwanted signals such as acoustic pressures and vibration induced pressures. Measured structural vibration data can include unwanted electrical noise and vibration energy from adjacent structures. In this paper, a noise removal technique is presented in which an unlimited number of unwanted correlated signals can be removed from a set of measured data. In its simplest form, this technique is related to the coherent output power (COP). However, unlike COP noise removal, multiple signals can be removed from measured data while retaining the magnitude and phase of the original data. These advantages often yield useful information concerning the flow field and structure under investigation. This technique is demonstrated using dynamic wall pressure and vibration measurements from a thin-walled aluminum cylinder filled with water flowing at 20 ft/sec. This technique is compared to several historical noise removal methods. The historical methods include an algorithm based on the physics of the measured pressures and an adaptive signal processing approach based on an unwanted noise reference.