Three-dimensional separation over swept and tapered finite span cantilevered wings

Experimental investigation is presented to elucidate flow structures and corresponding frequencies on finite span, cantilevered wings as functions of sweep angle and taper ratio. A detailed parameters sweep of planform geometry varied the leading and trailing edge sweep angles of NACA 0015 wings with a semi-aspect ratio of 2. The experiments were performed at Reynolds numbers O ( $10^5$ ) and angles of attack $12^\circ$ – $22^\circ$ . The experiments included flow visualisations, volumetric flow measurements, time-resolved measurements at selected spanwise planes and aerodynamic loads. This is the first time, to the best knowledge of the authors, that multiple configurations were tested under the same exact conditions. The correlation between three-dimensional (3-D) Reynolds stress distributions and 3-D flow separation is presented. Moreover, spectral content reveals modes that vary along the span, as well as for different planforms. For all wings, at the locations of largest reversed flow, power spectral density (PSD) peaks were seen at $0.1\lt St\lt 0.2$ , corresponding to vortex shedding. At spanwise locations near surface spirals the PSD exhibits peaks at lower frequencies of St = O (0.01) due to focus point wandering. The mean flow fields presented here show similarities to previous numerical simulation findings on similar geometries at Reynolds number O ( $10^2$ ). Moreover, the spanwise location of the largest magnitude of turbulent kinetic energy corresponds to the location of the most amplified mode at a Reynolds number of 400 found previously. The present research, complemented by previous low-Reynolds-number work, provides fundamental insights into global flow structures on multiple finite span wings, their corresponding spectral content and the effect on their aerodynamic performance.