Noise is generated by many engineering systems and is now recognized as a form of environmental pollution. In our laboratory, we are interested in aeroacoustics, where noise is generated by the fluid flow. For example, periodic shedding of vortices, such as those seen in Video 2a, over a trailing edge of an airfoil can produce strong tonal noise emissions.
Figure 3 illustrates different flow regimes where tonal noise emissions can generate and can also affect flow development over the airfoil itself. Specifically, tonal emissions can be generated by the flow events originating either from the suction or pressure side of an airfoil (or both). Moreover, the resulting acoustic perturbations can influence flow development, establishing a strong feedback loop with separation bubble.
Figure 3. Schematics of flow regimes related to separation bubble development on the suction side: (a) suction side dominated trailing edge tone; (b) pressure side dominated trailing edge tone, with contribution from the suction side feedback loop; (c) pressure side dominated trailing edge tone; (d) suction side separation bubble in the absence of significant tonal emissions. Some elements are not drawn to scale.