Periodic Blade Loads on Propellers in Tangential and Longitudinal Wakes

Abstract

Periodic single-blade loads were measured on model propellers in inclined flow and in a single-cycle circumferentially non-uniform longitudinal velocity field. The experimental results were correlated with predictions by the following methods: 1. A quasi-steady procedure developed by McCarthy at David W. Taylor Naval Ship Research and' Development Center (DTNSRDC) 2. An unsteady lifting surface theory developed by Tsakonas and his colleagues at Davidson Laboratory, 3 An unsteady lifting Surface theory developed by Kerwin and Lee. at MIT, 4. A refinement by Kerwin to the method of Kerwin and Lee to consider the inclination of the propeller slipstream. In inclined flow, all four of the calculation methods evaluated consistently underprediCted1 the experimental values of the periodic single-blade loads. The method of Kerwin, which considers the inclination of the slipstream relative to the propeller axis, produced the best correlation· with experimental values. These correlations show that the inclination of the propeller slipstream relative to the propeller axis significantly influence the periodic single-blade loads. The importance of this inclination· increases with increasing ,time-average loading.