A note on the pressure-velocity correlation and coherence normalisation

In aerodynamic and aeroacoustic research, pressure-velocity correlation and coherence have been increasingly utilised to identify and understand the motions of large-scale structures and their collective effects on the surface pressure fluctuations due to the boundary layer. Nevertheless, when a relatively sharp transition from turbulent boundary layer to low turbulence free-stream takes place, it is observed that 'spurious' regions of elevated correlation and coherence level arise as a result of this transition and the use of conventional normalisation. The present study identifies this issue using measurements from a NACA 0012 aerofoil and proposes a modified normalisation by taking the flow turbulence into account. The results have clearly demonstrated that the modified procedure helps successfully preclude these spuriously heightened p - u correlation and coherence regions. [GRAPHICS] .