| An experimental study of the flow around and behind an axisymmetric body driven by a marine propeller is reported. Three types of experiments were performed in a wind tunnel to isolate and clarify the essential features of this complex, unsteady, three-dimensional, turbulent shear flow. Measurements were made in the boundary layer and wake of the bare body, with a fixed dummy hub for the propeller, to document the basic flow field in the absence of the propeller. Next, measurements were made with the dummy hub rotating to study the resulting swirling flow in the central core of the wake. Finally, the development and decay of the swirling flow in the wake and details of the slipstream were investigated in the main series of experiments with the propeller in operation. A Pitot tube and a five-hole yaw probe were employed for the mean-flow measurements, and a X-wire and a triple-sensor hot-wire were used to obtained the mean and turbulent velocity fields. The experimental techniques and methodology for measuring such a periodic turbulent flow, with large flow angles and high turbulence levels, are described. Phase-averaging techniques were utilized to reconstruct the instantaneous velocity and Reynolds-stress fields downstream of the propeller. The measurements show many of the principal flow features of interest, including the contraction of the propeller slipstream, the evolution of the wakes of the individual propeller blades and blade-tip vortices, and a complex flow near the hub and in the core of the body wake, associated with horseshoe-type vortices generated from hub-blade junctions. It is found that the individual blade wakes and features of the tip and hub flow are evident upto about 2 propeller diameters, beyond which the wake of the body-propeller combination can be regarded as a rotationally-symmetric flow. Finally, comparisons were made between the circumferentially-averaged data and the recent steady-flow calculations of Stern, Toda and Kim (1990), and these indicate that the method of Stern et al. (1988) is successful in predicting the overall aspects of the flow past the propeller-body combination. |
