Noise Control Due to the Stator Wake Blade Interaction via Tail Articulation

The biologically inspired method of tail articulation is investigated as a means of reducing tonal noise due to wake deficit blade interaction in underwater vehicles. Experiments are carried out in a water tunnel under typical operating conditions for underwater vehicles. Tail articulation is implemented using a life scale stator model with a hinged flapping tail operating both in free-stream velocities corresponding to Reynolds number in the range 75000 < Re < 300000 and at frequencies up to 30 Hz to investigate the range of Strouhal number 0.0 < St < 0.35. Velocity measurements of the active stator wake are carried out by laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) to investigate the effects of tail articulation on the stator wake. Time-averaged measurements of the stator wake by LDV show that of the tail articulation has a dominant effect on the time mean stator drag. Instantaneous phase-averaged measurements of the stator wake by PIV show a transition in the unsteady stator wake as is increased, from a deflected vortex sheet to a series of rolled up, discrete vortices. Measurements are made of the wake due to both sinusoidal and nonsinusoidal tail motion profiles, which show that significant wake alteration is achieved with tail articulation. A low-order model describing the creation and convection of vorticity by tail articulation is developed which describes wake phenomena observed in LDV and PIV measurements. Finally, a 3-D unsteady propeller simulation using both experimental wake velocity data by PIV and simulated wake velocity data generated with the reduced-order model are used to predict the effect of sinusoidal tail articulation on radiated noise. Results using simulated data indicate that a significant noise alteration is achieved in all cases, and noise reduction of 5-8 dB is achieved in some cases.