Experimental investigation of a single spanwise vortex gust impinging on a rectangular wing

Abstract

The aim of this study is to investigate the effects of a single spanwise vortex impingement on flow structures around and loading on a rectangular wing. An experimental approach is adopted to investigate by gathering force data from the wing and visualization of flow structures with DPIV technic. The experiments are conducted in the large scale water channel located in Trisonic Laboratory of Istanbul Technical University's Faculty of Aeronautics and Astronautics. A Reynolds Number of 10.000 is chosen for all experiments which corresponds to 𝑈∞ = 0.1 m/s. A flat plate upstream of the model undergoing clockwise 180 degree turn is used for the generation of a single vortex and the vortex impacts a stationary rectangular flat plate wing with 𝐴𝑅𝑒𝑓𝑓= 4 located downstream of the vortex generator. Forces acting on the model during experiments are acquired by a force/torque sensor. Simultaneously, flow structures around the wing are captured by a DPIV system during vortex impingement. The mounting arrangements of the gust generator and the wing, are such that both are able to do pitch and plunge motions. A total of 7 different angle of attack values for the stationary wing and 3 different offsets only varying in y-axis for the gust generator with respect to model to change the vortex path are combined to generate 21 test cases of this study. The difference in wing loading due to the vortex impingement for various angle of attack values are compared for the same offset value. Likewise, they are compared when only the gust generator offset changes and angle of attack of the model is kept the same. Following this procedure, images gathered by DPIV system are investigated in conjunction with the force data. The general trend of the aerodynamic forces acting on the model due to vortex impingement shows agreement with the literature work on the subject. Drag coefficient is less affected by the vortex impingement especially when the model has a high angle of attack. However, the lift coefficient shows that asthe angle of attack value increases, the effect of the vortex impingement on lift becomes drastic. The wing loading is correlated with the effective angle of attack calculated quarter chord upstream of the leading edge using the quantitative velocity field obtained using the DPIV system. The study actually mimics a transient vortex gust encounter. The strength and width of the gust is also determined using the DPIV images. Although the impinging vortex is the same for all cases investigated, the offset value and the angle of attack affect the vortex trajectory and therefore wing loading.