Turbulent wake behind slender bodies, including self-propelled configurations

Abstract

The turbulent wakes behind a streamlined drag body, a jet-propelled body, and a propeller-driven body are studied experimentally in a subsonic wind tunnel at a principal nominal free-stream velocity of 206 ft/sec. The wakes produced by the latter two bodies are momentum-less. Mean flow data taken at five axial stations (X/D = 2, 5, 10, 20, and 40) downstream of the sterns of these bodies include velocity and static pressure distributions. The streamwise variation of the maximum values of axial turbulence intensity and radial shear stress are also presented.

The mean flow data for the wake behind the drag body compare favorably with previous experiments and establish a rigid reference for the wakes behind slender, self-propelled configurations. The downstream rate of decay of |(U_E-U_c)_max U_E| is essentially the same for the drag and propeller-driven bodies, whereas the decay for the jet-propelled body is substantially faster. A self-similar character is exhibited in the wake of the drag body, but the wake of the propeller- driven body appears to be self-similar in the usual sense only in the inner region. As for the basic turbulence behavior, the magnitude of the axial turbulence intensity is greater for the jet-propelled model than the other models, and the absolute value of the radial shear stress is greater (beyond X/D = 2) for the propeller driven model. The rate of decay of (√u'²)_max is faster for the propeller-driven model than the jet-propelled model; however, the rate of decrease of radial shear stress is faster for the jet-propelled model.

A comparison of the axial variation of |(U_E-U_c)_max U_E| with numerical predictions using a turbulent kinetic energy method shows very good agreement for the drag and jet-propelled bodies. The shear stress trends are predicted well in all cases.