Browsing by Author "Cabrita, P. M."

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    Large-scale instabilities in a STOVL upwash fountain
    (2005-12-31T00:00:00Z) Saddington, A. J.; Cabrita, P. M.; Knowles, Kevin; W., Rodi and M. Mulas
    The fountain flow created by two underexpanded axisymmetric, turbulent jets impinging on a ground plane was studied through the use of laser-based experimental techniques. Velocity and turbulence data were acquired in the jet and fountain flow regions using laser doppler velocimetry and particle image velocimetry. Profiles of mean and rms velocities along the jet centreline are presented for nozzle pressure ratios of two, three and four. The unsteady nature of the fountain flow was examined and the presence of large-scale coherent structures identified. A spectral analysis of the fountain flow data was performed using the Welch method. The results have relevance to ongoing studies of the fountain flow using large eddy simulation techniques.
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    On the Characteristics of a Twin-Jet STOVL Fountain
    (2015-03-03) Saddington, A. J.; Knowles, Kevin; Cabrita, P. M.
    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, nozzle height-to-diameter ratios of between 2.4 and 8.4, nozzle splay angles of between 15 degrees and a nozzle spacing-to-diameter ratio of seven. The effect of varying these parameters on the fountain velocity decay, spreading rate and momentum flux ratio are discussed. 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.