CFD-simulation of the rotor head influence to the rotor-fuselage interaction

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Kowarsch, U.
Kessler, M.
Krämer, E.
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The presented paper investigates a fluid-structure interaction phenomenon of a helicopter in fast forward flight, called tail shake. Due to the interaction of the rotor wake with the tail boom, a high vibration level is introduced under unfavorable conditions. To achieve a more detailed insight into the main rotor wake structure, a Computational Fluid Dynamics (CFD) simulation of a complete helicopter configuration is performed. Due to the high influence of the main rotor head on the wake structure a, detailed model is considered, including the swashplate and the control rods. In order to resolve the influence of the components, the configuration of the rotor head is simulated in several variants. Former investigations showed the necessity to ensure a low numerical dissipation to preserve the rotor wake. For this investigation the compact reconstruction fifth order Weighted Essentially Non-Oscillatory fluid state reconstruction scheme for an improved rotor wake conservation is used. In addition, the flux computation is solved using an upwind HLLC Riemann solver. The analysis of the flow field and forces shows a fundamental change of the unsteady flow behavior. Especially due to interaction effects at the cowling and tail, the character of the incoming flow from the rotor wake has substantial impact. The comparison of the different configurations revealed a strong difference particularly in the low frequency intensity of the wake. Due to the natural frequencies of concern for the dynamic of tail in this low frequency range, the consideration of the rotor hub geometry is essential to investigate rotor-fuselage interaction phenomena with focus on possible dynamic excitation. Therefore, this investigation confirmed the necessity of modeling the rotor hub including the control rods.