R. Smyth


Some recent attempts at predicting turbulent two- dimensional recirculating flows have concentrated on modelling the turbulent energy equations used in the finite difference analysis methods of solutions of the elliptic partial differential equations governing these flows. These attempts have to some extent been restricted by the lack of experimental studies of the high turbulence intensities found in separated flows. The improvement of the pulsed hot-wire anemometer and the laser Doppler anemometer have made possible such studies and this paper describes an investigation using the laser Doppler anemometer in a separated flow situation. Results are given of an experimental study of the plane turbulent separated flow of water over a double backward facing step of duct height ratio 3:1. Time mean streamwise, transverse and cross-stream components of velocity are reported, together with the turbulent velocity fluctuations. The measurements were made using a laser Doppler anemometer operating in the differential Doppler mode with forward scattering. The problem of high turbulence intensity and instantaneous flow reversals was overcome by frequency shifting of the incident laser light beams using a pair of Bragg cells. Substantial changes in flow patterns were detected together with turbulence intensities based on local streamwise velocity of up to 100% were recorded in the recirculating zones. Transverse turbulence intensities were in general about half that of the streamwise components, with cross-stream intensities an order of magnitude lower again.

Meeting Name

4th Biennial Symposium on Turbulence in Liquids (1975: Sep., Rolla, MO)


Chemical and Biochemical Engineering

Document Type

Article - Conference proceedings

Presentation Type

Contributed Paper


Separated Turbulent Flows

Document Version

Final Version

File Type





© 1975 University of Missouri--Rolla, All rights reserved.