The flow about a slender propellor-driven body in a temperature stratified fluid

Abstract

An experimental study of the turbulent wake produced by a stern-propellor-driven body moving in a temperature-stratified fluid is presented. The velocity and thermal boundary layers on the body upstream of the propellor are also examined. Mean flow velocities, static pressure, flow angularity and mean temperature distributions are reported at five downstream stations, Z/0 = 0.33, 1 .0, 2.0, 3.0, and 4.0. Turbulence data, including temperature fluctuations are reported at Z/D = 0.33 and Z/D = 4.0. The measurements were taken using thermocouples and pitot tubes of various size, a yawhead probe, a cross-wire hot-wire, and a straight-wire hot-wire as appropriate. For measuring the temperature fluctuations, the straight hot-wire probe was operated in the low-overheat mode to maximize temperature sensitivity. The testing was conducted in the Virginia Tech 6’ X 6’ subsonic wind tunnel at free-stream Re_D = 2.04 X 10⁵. The temperature variation provides a means of tracing the wake development in the near-body region. The principal effect of the propellor is to induce a more or less rigid rotation immediately downstream of the body. The fluid is apparently mixed much less than was anticipated. Temperature fluctuation is mild across the wake except in the vicinity of the propellor tips where it becomes relatively large. The high temperature fluctuation often occurred in regions of low mean temperature gradients which indicates that current modeling techniques should be re-examined.