Numerical Analysis of Blade-Vortex Interaction Noise in Maneuvering Flight Using Moving Overlapped Grid Method

Helicopters are used in various fields such as EMS (Emergency Medical Service), fire fighting, disaster relief, news report, and so on because of the capabilities of hovering and VTOL. However, noise, cost, and VFR (Visual Flight Rules) problems prevent helicopters from being widely used as a means of intercity transportation in densely populated area. In Japan, MLIT (the ministry of land, infrastructure and transport) has a plan to enforce IFR (Instrument Flight Rules) to helicopters like fixed wing aircrafts in the near future. If it comes true, all-weather flying will be possible and noise problem will get a great deal of attention because the number of helicopters flight is expected to grow after the permission. One of the major companies of helicopter flight operation in Japan says that it will be difficult to promote their business without having helicopters more than 5dB quieter than the present quiet helicopters in the near future. It requires about 10dB reduction from the new regulation of ICAO, which has been applied since 2002. Blade-vortex interaction (BVI) is one of the main noise sources of helicopter, which is known to occur mainly in two typical conditions: (1) descending flight for landing, and (2) during maneuver. The objectives of present research are to construct an analysis tool as a middle step for maneuvering helicopter analysis, and to develop an advanced CFD code for fully-unsteady movement using moving overlapped grid method. Flight path and blade motion data are prescribed as input data, and the final flow solution includes unsteady pressure on blade surface as well as trace of tip vortex.