A high tip speed turboprop is being considered as a future energy conservative airplane. When the turboprop airplane is at cruise, the combination of the airplane forward speed and the propeller rotational speed results in supersonic helical velocities over the other portions of the propeller blades. These supersonic blade sections could generate noise that is a cabin environment problem. Three 0.622 m (24.5 in.) diam propellers were acoustically tested in the NASA Lewis 8-by 6-ft. wind tunnel. This wind tunnel does not have acoustic damping material on its walls and is therefore not an ideal location for taking noise data. However, it was felt that information obtained about the noise differences among the three propellers would be useable. The propellers were tested at tunnel through flow Mach numbers of 0.6, 0.7, 0.75, 0.8, and 0.85 with different rotational speed and blade setting angles. The three propellers incorporated different plan forms and different amounts of sweep and yielded different noise levels. The acoustically designed propeller had 45° of tip sweep and was significantly quieter than the straight bladed propeller. The intermediate 30° tip sweep propeller exhibited noise that was between the other two blades. Noise trends with varying helical tip Mach number and blade loading were also observed.
A combined experimental and analytical program has been conducted N at the NASA Lewis Research Center, to investigate the effects of boundary layer changes on the flow over high angle boattail nozzles. The tests were cô j run on an isolated axisymmetric sting mounted model. Various boattail geometries were investigated at high subsonic speeds over a range of boundary layer thicknesses. In general, boundary layer effects were small at speeds up to Mach 0.8. However, at higher speeds significant regions of separated flow were present on the boattail. When separation was present large reductions in boattail drag resulted with increasing boundary layer thickness. The analysis predicts both of these trends.
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