Aeroelastic simulation of the tail shake phenomenon

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Schäferlein, U.
Kessler, M.
Krämer, E.
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Rotor-fuselage interactions continue to pose a challenge during the design phase of a new helicopter. Quite often, the prototype phase is faced with problems in fast-forward flight caused by strong interactions at the tail, the so-called tail shake phenomenon. The wake of the main rotor, the rotor hub and the airframe impinges on the tail boom causing an excitation of low-frequency eigenmodes of the entire helicopter airframe. The resulting vibrations reduce flight comfort and flight stability in some critical cases. Previous approaches to solve the problem were restricted to wind tunnel tests due to the lack of predictability in terms of numerical methods. A high-fidelity simulation presented in this study by means of a time-resolved coupling between the flow and structural behavior of the helicopter shows significant progress in the prediction potential of the investigated phenomenon. Utilizing higher order methods for the CFD simulation, tightly coupled with a modal-based CSD simulation of the airframe, very good agreement with flight test data of the relevant low-frequency eigenmodes could be achieved.