A study of the flow physics on a swept wing and the application of steady blowing to separation control

Abstract

An experimental study was conducted to understand the effect of steady blowing from segmented jets along the leading edge of a 30° swept wing with an aspect ratio of approximately 4, with a twist of approximately −2.5° between the root and the tip at a chord-based Reynolds number of 260, 000. The objective of the steady blowing is to control the separation that starts at the leading edge of the wing to increase the lift produced by the wing at higher angles of attack and delay the unstable pitch break experienced by the full SWiFT wing so that a higher stable maximum lift can be generated. Hot wire anemometry was used to calibrate the jets on the model. Pressure transducers were used to set the momentum coefficient of each jet. Loads were collected for a range of angles of attack. At select angles of attack, videos of tufts were recorded. At an angle of attack of 19°, stereo particle image velocimetry was performed. Without steady blowing, the wing experiences partial separation in the middle of the span at an angle of attack of approximately 17°, which extends to the tip of the wing at 19°. At 19° a horn-shaped vortex extending from the mid-span to the tip of the wing which merged with the wing tip vortex was observed. The lift curve slope agreed well with two predictions based on theory and on the vortex lattice method. Steady blowing reduces the extent of separation on the wing and delays separation of the flow over the entire wing to higher angles of attack. The steady blowing also moved the focus point (at which the horn vortex is originated from) observed in the near-surface streamlines and disrupted the formation of the horn vortex. Blowing from a single jet located outboard of mid-span reattaches the flow on the wing between the tip and the blowing location. Blowing from additional jets between the tip and this jet does not have a significant effect on the behavior of the flow, which indicates that a single jet acts as a fluidic fence which obstructs the spanwise flow that contributes to the separation at the tip. This effect is limited to jets closer to the tip because blowing from single jets closer to the root of the wing does not have the same effect. For both the case with three outer jets and with the single jet actuated, the horn vortex was present inboard of the blowing location, but was disrupted by the presence of the jet and did not travel all the way to the wingtip. Unlike the case with all of the jets actuated; however, the location of the focus did not move and the horn vortex began to form at the same location as observed on the baseline case.