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/ dn) from 3 to 10 (where dn = 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 < [Formula: see text] < 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, [Formula: see text], the particle image velocimetry results showed that the ground vortex mean streamwise position varied from 5 dn to 16 dn and the root mean square fluctuation in this position varied from 0.7 dn to 1.5 dn. Further analysis of the ground vortex temporal characteristics did not reveal any dominant non-dimensional frequencies.