Takashi Aoyama

In the present study, the interaction between a wind turbine tower and blades and its aerodynamic effect on the wake structure are investigated using the rFlow3D CFD code, which was developed by JAXA. NREL Phase VI experimental wind turbine is selected as the computational test case. The result shows the shed vortex from the tower does not affect the total wind turbine performance significantly. However, cyclic fluctuation of the aerodynamic load and the change of vortex structure behind the tower are captured clearly. The rotational flow and shed vortex from the tower cause the increase of turbulence intensity and irregular velocity distributions. This is considered as one of the key features for capturing the wake vortex breakdown accurately. It is shown that the tower and blade interaction is important for detailed wake investigation even in this upwind wind turbine case.

Insects generate sound by their flapping wings as a consequence of spatial and temporal changes of pressures on the wing surface and vortices generated by the wing motion. To clarify the mechanism of sound generation, hybrid method combining CFD techniques and acoustic analysis is incorporated here and detailed characteristics of flapping sound, e.g. directivity of transmission or spectrum distributions, are clarified.

We are developing helicopter noise prediction system MENTOR. It calculates BVI noise caused by the interaction of rotor blades and tip votices shed by them. In this system, we used Beddose vortex model to prescribe the geometrical allignment of tip vortecies. This model practically well predicted the BVI noise with low cost of calculation, but sometimes overestimated the noise because of not including vortex decay. In this study, we added the vortex decay parameter into Beddose model and evaluated its effect on the BVI noise of helicopter.

Two types of prediction tools for helicopter noise have been developed under the cooperative research between Advanced Technology Institute of Commuter Helicopter Ltd. (ATIC) and National Aerospace Laboratory (NAL) . One of them is a combined method of CAMRAD II, interpolation code for blade motion and wake geometry, aerodynamic code of 3D unsteady Euler solver, and aeroacoustic code based on Ffowcs Williams and Hawkings (FW-H) formulation. The other consists of CAMRAD II, 3D unsteady Euler solver using moving overlapped grid method, and FW-H code. The acoustic waveform of Blade-Vortex Interaction (BVI) noise predicted by the former tool is in good agreement with the experimental data of 1/7-scale model AH-1 Operational Loads Survey (OLS) rotor. This method is applied to investigate the effect of blade-tip shape on the intensity of BVI noise. As a result, it is shown that anhedral and swept-forward tip shapes effectively reduce the BVI noise of OLS rotor in a descent flight condition. The predicted Effective Perceived Noise Level (EPNL) of a helicopter is also compared with the experimental data obtained by ATIC and reasonable correlation is obtained. The latter tool successfully predicts the distinct spikes in the BVI wave-form of ATIC model rotor tested in German-Dutch Wind Tunnel (DNW) . In the comparison of measured and calculated carpet noise contours, reasonable agreement is obtained. The present tools are expected to be useful for the design of low-noise helicopters in the future.