Numerical Investigation of Aeroacoustic and Aeroelastic Phenomena on a Helicopter Using Higher-Order Methods

Beschreibung

In this thesis, the blade vortex interaction and rotor-fuselage interaction, in particular tail shake, on a helicopter are investigated using numerical simulations. Both phenomena pose major challenges in the helicopter design in terms of acoustics, flight stability, and comfort, and are not yet fully understood. In order to enable reasonable high-fidelity simulations to capture the physics of these phenomena, a rotorcraft simulation framework is extended by higher-order methods to use the computational resources more efficiently. In addition, an optimization for a more efficient utilization of supercomputers is carried out. To represent the aeroelasticity of the fuselage, a fluid-structure coupling is implemented, which allows the mapping of the interaction between aerodynamics and structural dynamics on the helicopter fuselage. The rotorcraft simulation environment is applied a flight state with tail shake vibrations. The extensions prove their advantage by a detailed representation of the physics with a computational efficient simulation. The results are successfully validated against flight test data and show an excellent agreement in the tail shake relevant low-frequency vibrations and loads on the tail boom. A cause study, made possible by the detailed flow field, shows a fluid-structure resonance on the ducted tail rotor, which causes the excitation of the low-frequency mode shapes for the investigated helicopter type. In addition, an investigation of the blade vortex interaction phenomenon is performed by an efficient high-fidelity simulation of a certification-relevant descent flight. Taking into account the complete helicopter geometry in combination with the detailed flow field, acoustic phenomena such as shading, reflection and diffraction can be identified on the helicopter. The comparison of the acoustic noise signature with flight test data shows a very good agreement. An added value can be demonstrated by considering the overall geometry compared to the usual consideration of the isolated main rotor only.

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Ulrich Schäferlein

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Helicopter Computational fluid dynamics Aerodynamics, aeroacoustics, aeroelastics

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