Extraction of turbulent wall-pressure time-series using an optimal filtering scheme

Accurate measurements of pressure beneath turbulent wall-bounded flows are generally difficult to achieve due to signal contamination resulting from facility-induced noise, sensor vibration, etc. This is particularly true at low Reynolds numbers where the noise signature overwhelms the low-level turbulent fluctuations. In the current work a noise-cancellation technique based on an optimal filtering approach is developed. This technique is particularly useful for conditions of low signal-to-noise ratio and therefore it is well suited for low to moderate Reynolds number measurements. Unlike the conventional, subtraction-based, noise-cancellation methods, the utility of the optimal-filter scheme is not limited to the extraction of the turbulent statistics but it can be used to obtain the noise-canceled time-series. Furthermore, the energy of the low-frequency turbulent motion lost due to the application of the noise-cancellation scheme is an order of magnitude smaller in the case of the optimal filter as compared to the subtraction scheme. Employment of the technique developed here is not confined to two-dimensional flows and therefore it is also useful for measurements in applications involving non-equilibrium flows.