The Effects of Suction and Blowing on Tonal Noise Generation by Blunt Trailing Edges

Abstract

Direct numerical simulations (DNS) of unsteady low-to-moderate Reynolds number flows past a NACA 0012 airfoil are carried out to assess the effects of suction and blowing on noise generation by blunt trailing edges. The tonal noise that arises from the interaction of wake and boundary layers with blunt trailing edges is computed for flow configurations at different freestream Mach numbers (M∞ = 0.1 to 0.5), angles of incidence (AoA = 0 and 3 deg), and Reynolds numbers based on the airfoil chord (Rec = 5000 and 100000). The influence of compressibility on sound generation is analyzed along with the effects of scattering by blunt trailing edges for different radii of curvature. Numerical results for the low Reynolds number flow studied show that the airfoil emits a single “narrow-band” tone; however, results for the moderate Reynolds number flow analyzed show that the airfoil emits multiple “narrow-band” tones superimposed on a broadband hump, depending on the flow configuration, indicating the existence of an acoustic feedback loop as discussed in literature. For those cases where a broadband hump with multiples tones are observed, trailing edge blowing and suction considerably modify the near-field region responsible for the noise generation. It is shown that the presence of secondary tones is very dependent on compressibility effects as well as angle of incidence and trailing edge bluntness. For some of the flow configurations analyzed blowing can completely eliminate the secondary tones.