Turbulence Measurements in Three Dimensional Boundary Layer and Wake around a Ship Model

Abstract

This paper presents results of turbulence measurements in the three dimensional boundary layer and wake around a ship model in a low-speed wind tunnel. Measurements were carried out with a single channel hot-wire anemometer, where two or three types of probes were used to measure the different components of the velocity fluctuations.The conclusions obtained in the present study are summarized as follows. 1) It is possible to measure the three dimensional mean flow, turbulence intensities and Reynolds shearing stresses by using a single channel hot-wire anemometer. 2) The three dimensional direction characteristics of a hot-wire can be approximately expressed by the following equation.Ueff = |U| {sin2α+ a cos2 α + b cos2β} 1/2where Ueff is the effective velocity.α is the angle between the hot-wire and mean flow direction.β is the angle between normal vector to the hot-wire/wire-support plane and mean flow direction.a and b are the experimental constants.3) In three dimensional boundary layer and near wake, the distributions of turbulence intensities are significantly affected by the velocity gradient and the bilge vortices.4) Along a stern stream-line, as the boundary layer thickness grows thicker, the dimensionless eddy viscosity ε/Ueδ* is more reduced.