An experimental study on a wake behind a torus using the UVP monitor

 The flow around a torus has a complicated three-dimensional structure. Measuring the spatiotemporal field of velocity by means of conventional methods such as hot-wire anemometers and other one-point measuring instruments is thus difficult. Research is made on the spatiotemporal structure of the wake behind the torus by using a flow-visualizing technique and an ultrasonic velocity profile (UVP) monitor, in which two kinds of tori with different diameter ratios or solidity are set in a uniform flow with zero inclination and oblique postures. For the torus with zero inclination, there are two modes of flow structure according to the diameter ratio; at lower ratio, a disk mode is dominant, and at higher ratio, a ring wake mode appears. For the torus set with an oblique posture, the structure of the wake changes with respect to the oblique angle in a complicated fashion. The power spectra of the fluctuating velocities reveal an aspect of the character of this structural change. The Strouhal numbers estimated from the power spectra suggest that the flow patterns can be classified into four categories with respect to the oblique angle. Received: 15 May 1997/Accepted: 10 September 1998