The interaction of multiple jets with the ground is ofgreat importance for the design and operation of shorttake-off, vertical landing aircraft. The fountain upwashflow, generated by the impingement of two axisymmetric,compressible, turbulent jets onto a ground planewas studied using laser-based particle image velocimetryand laser Doppler velocimetry. Measurementswere made with nozzle pressure ratios of between 1.05and 4, nozzle height-to-diameter ratios of between 2.4and 8.4, nozzle splay angles of between 15 degreesand a nozzle spacing-to-diameter ratio of seven. Theeffect of varying these parameters on the fountain velocitydecay, spreading rate and momentum flux ratioare discussed. Mean fountain upwash velocity profileswere found to be self-similar for all test conditions. Adistinct frequency of fountain oscillation was identifiedbut only at a nozzle height of 4.4 diameters.
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