Study of the effects of centrifugal instabilities on flow in a 40 to 1 aspect ratio rectangular curved channel, for Dean numbers from 35 to fully turbulent conditions

Abstract

The development and structure of Dean vortices in a high aspect ratio curved channel were measured and studied for Dean numbers from 35 to fully turbulent conditions. Mean vorticity components were determined from measurements of the three components of mean velocity, which were measured using a miniature five-hole pressure probe. Streamwise, radial and spanwise vorticity components measured 120 deg from the start of curvature, show evidence of Dean vortices in the time-averaged flow field. Peak streamwise and peak spanwise vorticity, as well as streamwise circulation, generally increase as the Dean number increases from 60 to 240. Peak radial vorticity increases as Dean numbers vary from 60 to about 160. Spectra obtained from hot-wire probes show evidence of different frequency events, including twisting and undulation. Twisting is apparent for Dean numbers of 135 to 160 while undulation is observed at lower Dean numbers. Flow visualization results illustrate a variety of time dependent events in the channel.