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

The flow around a torus has a complicated three-dimensional structure. Meas uring 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 wak e 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 m odes of flow structure according to the diameter ratio; at lower ratio, a d isk mode is dominant, and at higher ratio, a ring wake mode appears. For th e 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 o f the fluctuating velocities reveal an aspect of the character of this stru ctural change. The Strouhal numbers estimated from the power spectra sugges t that the flow patterns can be classified into four categories with respec t to the oblique angle.