The effect of boundary layer type on trailing edge noise from sharp-edged flat plates at low-to-moderate Reynolds number

This paper presents an experimental study of the trailing edge noise produced by sharp-edged flat plates with mixed laminar, transitional and turbulent boundary layers at low-to-moderate Reynolds number. Mean and unsteady velocity data in the wake and upstream of the trailing edge have been measured using hot-wire anemometry at Reynolds numbers of Re c = 0.7 × 10 5 – 2.7 × 10 5 , based on chord. These data are related to far-field noise measurements to determine the flow mechanisms responsible for the trailing edge noise in each flow regime. Attached turbulent boundary layers are observed to yield the weakest noise generation mechanism while mixed transitional and laminar boundary layers at the trailing edge yield the strongest mechanism producing both high levels of broadband noise and tonal noise components. Vortex shedding in the wake is only observed when tonal noise is produced and experimental results indicate that in this case, the tonal noise is governed by vortex shedding processes at the trailing edge.