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DTIC ADA245326: The Effect of Turbulence Ingestion on Propeller Broadband Thrust

This report presents the theoretical prediction of the low frequency unsteady broadband thrust for propellers/rotors in a turbulent flow, such as those on any surface ship. Broadband thrust forces are predicted by the use of a new correlation method and are compared with existing theoretical models based on both correlation and spectrum approaches. In contrast to the available theories, the new theory predicts low blade rate humps and broadband forces simultaneously. For a homogeneous and isotropic turbulent inflow and for a given advance coefficient, turbulence length scale and turbulence level, the present theory produces an unsteady broadband thrust level which is proportional in the high frequency region to the third power of ship speed. At low frequencies, predictions of propeller unsteady thrust spectra show peaks near the first and second blade rate frequencies and those peaks skew to the higher frequency side of the blade rate frequencies. The physics of the phenomena are discussed and numerical results are compared with limited experimental data.

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