Secondary flows and developing, turbulent boundary layers in a rotating duct

Abstract

The work presented in this paper represents an experimental investigation into secondary flows, turbulent boundary layers and the interaction of the two as they develop in a zero-pressure-gradient rotating flow field. A duct of intermediate aspect ratio was used to examine secondary flows and determine when they begin to govern the boundary layer development. The aspect ratio (A) was defined as duct height/width at the upstream end of the working section. Measurements were taken at three aspect ratios: A=1, 2 and 4.

A qualitative indication of secondary flow strength was established with mean-cross-stream-plane velocity measurements. A first-order analysis of the secondary flow is presented which provides a reasonable estimation of their strength. Mid-span mean-flow, turbulence and spectra profiles were measured on the duct walls parallel to the axis of rotation. Results are generally presented for A=2 and 1. For A=4 and 2 there were minor effects of secondary flows observed on the mid-span mean flow parameters. The turbulent shear measurements showed some secondary flow effect for A=2. All turbulence and mean-flow quantities were strongly affected by secondary flows for A=1. Spectra results presented for A=2 showed most variation at the low-to-mid wavenumber end. Spectra results for A=1 showed a bodily shift of the whole spectrum towards low wavenumber on the pressure side and high wavenumber on the suction side.