Orthogonal Vortex-Propeller Interaction

Abstract

In some situations, concentrated vorticity which forms a vortical flow is involved in the inflow of a propeller. The impingement of the vortex on the propeller has several detrimental effects, e.g., foreign object damage during ground operation, impact on the propeller performance, unsteady loading on the blade, and tonal noise generation. The research presented in this report is conducted for the concern of the effects of the interaction between inflow vortex and propeller, in terms of vortex response to the propeller and vortex impact on the aerodynamic performance of the propeller. The impact of impinging vortex on the propeller is studied by experimental and numerical methods. The variation of the propeller performance caused by the impingement of vortex is dependent on the relatively rotational direction of the vortex and the propeller. For the counter-rotating case, the thrust and torque coefficients are increased by the vortex impingement; and vice versa for the co-rotating case. The variations of the thrust and torque coefficients are proportional to the vortex strength. And it becomes more significant as the radial impingement position moves inwards and the advance ratio increases. However, the impingement of vortex does not evidently affects the efficiency of the propeller. The response of vortex to the propeller is investigated by PIV measurement. The variation of vortex behaviors is dependent on the phase angle of the propeller blade. At the phase angles when the wake of the blade is away from the impinging vortex, the vortex core circulation is independent from the impact of propeller. Due to the contraction of the stream tube caused by the propeller suction, the vortex core radius observed in the measurement plane downstream the propeller is smaller than that in the flow field upstream, and the magnitude of vortex vorticity and the maximum tangential velocity becomes larger. At the phase angle when the vortex core coincides with the propeller blade wake vortices, characteristics of the impinging vortex are dependent on the sign of the vorticity of the impinging vortex and the blade wake. For the case that the impinging vortex and the blade wake have the opposite sign of vorticity, the impinging vortex and the blade wake break each other into fractions with smaller core radius and circulation; for the case with the same sign of vorticity, they merge together, forming a new pattern with higher magnitude of vorticity.