Transient Force Evolution of Swept Flat-Plate Wings Pitching at a Constant Acceleration Amplitude

摘要

This paper presents the experimental evolution of transient hydrodynamic forces acting on swept wings undergoing a constant pitching acceleration/deceleration. The pitching maneuver concerns a wing from a zero-incidence angle to several maximum angles of attack in a free stream with a mean-chord-based Reynolds number of 8900. Two planform shapes include a right trapezoid and a right triangle. Both wings are flat plates with a geometric aspect ratio of four. A swept-forward configuration adapts the axis of pitching pivot about a wing straight-edge upstream; however, a downstream-pivot-a.xis configuration yields the swept-back wing. The experimental force data disclose the domination of the normal force over the axial force on the pitching wings in the transient flow. During the phase of pitching acceleration, the swept-forward wings experience much more hydrodynamic forces than swept-back wings. During the period of relaxation, the transient phenomena are dependent on the planform shape, not the swept angle. As the maximum angle of attack lower than 18 degrees, the triangle wing is susceptible to the typical oscillating flow. However, the trapezoid wing confronts more severe transitory force generation as the maximum angle of attack higher than 21 degrees.