Flow Measurements in a Short Takeoff, Vertical Landing Fountain: Parallel Jets

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 axisymmetric, compressible, turbulent jets onto a ground plane, was studied using laser-based particle image velocimetry and laser Doppler 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, while 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 but only at a nozzle height of 4.4 diameters.