Transient and time-averaged characteristics of a compressible ground vortex flow

Abstract

Particle image velocimetry data are presented from a scaled jet-lift aircraft ground vortex compressible flow. The scaled ground vortex is generated by a vertical compressible jet in cross-flow impinging on a moving ground plane. Particle image velocimetry is used to generate both transient and time-averaged flow statistics from the ground vortex region over a range of nozzle pressure ratios from 2.3 to 3.7, nozzle height-to-diameter ratios (h/d_n) from 3 to 10 (where d_n = 12.7 mm) and cross-flow velocities (V_∞) from 10 to 20 m/s. These conditions correspond to effective (jet-to-cross flow) velocity ratios of 15 <  $V_e^{-1}$ < 60. For each condition, mean and root mean square ground vortex core position was analysed from sets of 72 instantaneous particle image velocimetry vector maps. Over the range of effective velocity ratios, $V_e^{-1}$ , the particle image velocimetry results showed that the ground vortex mean streamwise position varied from 5d_n to 16d_n and the root mean square fluctuation in this position varied from 0.7d_n to 1.5d_n. Further analysis of the ground vortex temporal characteristics did not reveal any dominant non-dimensional frequencies.