Analytical Study of the Noise Generated by a Coanda Wall Jet Circulation Control Device
Final rept. 1 Jan-30 Sep 2000
BOSTON UNIV MA COLL OF ENGINEERING
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An analysis is made of the production of sound by a hydrofoil with a Coanda wall jet circulation control CC- device. Three principal sources of the radiation are identified very low frequency curvature noise generated by the interaction of boundary layer turbulence with the rounded trailing edge of the hydrofoil higher frequency sound produced at the Coanda jet slot. The latter includes passive slot noise caused by the scattering of turbulence near field pressures generated by the exterior boundary layer at the slot lip. The acoustic spectrum is greatly extended to much higher frequencies if the Coanda jet is turbulent the sound produced by the interaction of this turbulence with the lip tends to dominate the spectrum at frequencies f Hz greater than about Ujh where is the slot width and Uj the Coanda jet speed. Sample numerical results are presented for a typical underwater application that indicate that at this and higher frequencies the slot noise can be 20 dB or more greater than conventional trailing edge noise.
- Fluid Mechanics