Experimental Investigation of Intake Ground Vortices During Takeoff

Abstract

A quantitative experimental investigation has been conducted to simulate intake ground vortex formation during aircraft takeoff under headwind conditions. The experiments were performed using a small-scale intake model in conjunction with a rolling ground plane in a low-speed wind tunnel. The Reynolds number was fixed at 1.26 x 10 6 based on the inner diameter and average intake velocity. Stereoscopic particle image velocimetry was used to measure the ground vortex velocity field, and in-duct total pressure measurements have been performed to assess the internal flow. Measurements were taken for an extensive range of configurations, including a static and simulated moving intake under a variety of headwind conditions. A moving intake was simulated in the wind tunnel by synchronizing the ground and tunnel wind velocities and using extensive suction to remove the approaching boundary layer. The results show that at high velocity ratios there are no substantial differences due to the moving ground plane. At low velocity ratios, the simulated moving intake results in a significantly different flowfield in which the ground vortex is weaker, steadier in space, and more symmetric relative to the static ground case. These results indicate the relative importance of the ground vortex vorticity sources and highlight the importance of including the effects of a moving ground when simulating an aircraft takeoff.