An experimental investigation of the design variables for NACA

Emmet A. Mossman, Lauros M. Randall
January, 1948

submerged duct entrances Information concerning the parameters and design variables affecting an NACA submerged duct design is presented. The principal variables investigated include entrance width-to-depth ratio, ramp-wall divergence, ramp angle, and deflector size. Tests were also made to show the effect of variation of boundary-layer thickness and ramp-floor contour. Pressure recovery at the duct entrance and after slight diffusion, pressure distribution over the lip and ramp, and drag are given as functions of the inlet velocity ratio of the entrance. An evaluation of the NACA submerged entries indicates that satisfactory duct characteristics may be found for a range of the test variables. It appears that an optimum NACA submerged inlet design should employ curved diverging ramp walls, a 5 degree to 7 degree ramp angle, and a width-to-depth ratio of from 3 to 5. The boundary-layer thickness of the surface into which the inlet is placed was found to have a large effect on the pressure recovery. Possible applications of this types of inlet and their particular advantages are discussed.

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