Numerical Study on Unsteady Flow Field Structure over Wing within Propeller Slipstream at Low-Reynolds-Number

Abstract

This study aims to clarify the unsteady flow field structure over a fixed wing positioned within propeller slipstream and its effects on lift fluctuation of the fixed wing at a low Reynolds number (Re = 30,000). Numerical analyses were conducted with the configuration of a two-bladed propeller (APC Propellers 6x4E) and a fixed wing (Ishii airfoil) at three advance ratios (J = 0.8, 0.6, and 0.4) at the angle of attack 5°. Consequently, it was shown that a spanwise vortex structure involving very low pressure was induced over the fixed wing, even under the highest thrust condition (J = 0.4). In addition, three primary causes for the lift oscillation of the fixed wing were observed: 1) periodic vortex passage over the trailing edge, 2) periodic impingement of blade wake, which was shed from the propeller blade to the leading edge of the fixed wing, and 3) the high pressure behind the propeller owing to the high thrust, which periodically increased the lower surface pressure of the fixed wing. The C_L fluctuation by 1) and its synchronization with the blade passing frequency are considered distinctive characteristics of the low-Reynolds-number flows (Re ∼ O(10⁴)).