Flow Visualization and Measurements in a Short Take-off, Vertical Landing Fountain Flow

摘要

The interaction of multiple jets with the ground is of great importance for the design and operation of short take-off, vertical landing aircraft. The fountain upwash flow, generated by the impingement of two axisym-metric, compressible, turbulent jets onto a ground plane, was studied using laser-based flow visualization and particle image velocimetry. Measurements were made with nozzle pressure ratios of between 1.05 and 4 and nozzle height-to-diameter ratios of between 2.4 and 8.4, whilst nozzle spacing remained fixed at seven diameters. Mean fountain vertical velocity magnitude was observed to decrease with increasing nozzle height. Mean fountain upwash velocity profiles were found to be self-similar for all test conditions. A distinct frequency of fountain oscillation was identified at a nozzle height of 4.4 diameters.