Modification in airfoil's tonal noise using periodic suction-blowing excitation.

This paper examines the modifications in the flow and sound fields due to the application of a periodic suction-blowing excitation strip on the top and bottom surfaces of a NACA0012 airfoil. The flow and sound fields have been directly computed (D N S approach) by solving unsteady, two-dimensional compressible Navier–Stokes equations using physical dispersion relation preserving schemes. The flow approaches the airfoil at a Reynolds number of 5000 and 5 o angle of attack. In the no-excitation case, the sound is mainly created by the lift and drag dipole equivalent sources associated with vortex shedding. However, the application of suction-blowing excitation results in two additional sound sources: monopole-equivalent sound sources due to fluid movement in and out of the airfoil surface and the drag dipole-equivalent sound sources due to periodic change in the airfoil's effective cross-sectional area. The combined effects of these sound sources result in significant mitigation of sound on the suction side of the airfoil. The excitation amplitude and forcing frequency effects on sound field modifications have been studied in depth. Beats of sound have been observed when the forcing frequency is close to the excitation frequency. • Direct Numerical Simulation approach is used for Navier–Stokes equations. • Suction-blowing excitation induces monopole and drag dipole sound sources. • Excitation provided near the leading edge increases the lift-to-drag ratio. • Bias in sound directivity is observed for excitation near the trailing edge. • Sound beat is observed for frequencies close to vortex shedding frequency. [ABSTRACT FROM AUTHOR]