The Flowfield Near the Propeller of a Self-Propelled Slender Body with Appendages

Abstract

An experimental investigation of the flow in the immediate vicinity of the propeller for a propeller-driven, slender body with and without appendages was conducted in the Virginia Tech wind tunnel, including measurement stations both immediately upstream and downstream of the propeller. Mean and turbulent flow quantities were examined for the disturbances induced by the appendages (a sail and/or a deck) which were added to the basic axisymmetric body to give it either a submarine-or airship-like arrangement and their interaction with the propeller. Five different model configurations were placed in a uniform free-stream flow corresponding to a Reynolds number of 4.5 x 105 based on body diameter. The streamlined appendages and their smooth, contoured junctures produced measurable disturbances in the flow behind the propeller of the body. The effect of adding the deck was to spread and flatten the velocity profile. Addition of the sail had no large influence on the mean flow quantities, whereas the combination of a sail and deck appeared to negate the stronger effect which the deck alone had on the wake. The other measured mean flow quantities - static pressure and flow angularity, appeared to have been dominated by the swirling motion produced by the propeller. The axial turbulence intensity was observed to increase in the wake of the sail outside the propeller slipstream. A peak in the turbulence profiles occurred at the radial stations in line with the tip of the propeller and along-the body axis centerline. A shift in position and decrease in magnitude of the peaks were observed when the sail was mounted on the body. The deck, on the other hand, produced no measurable increase in turbulence intensity, even though it increased the drag on the model more than did the sail. The performance of the propeller operating both behind the body and in an open "water" condition was analyzed with a computerized theory, and the predictions were compared with experimental results. Fair to good agreement was found.