Laser velocimeter measurements in highly turbulent recirculating flows

Both a two-dimensional, rearward facing step and a cylindrical, sudden expansion geometry are considered in the present study of subsonic separated flows using a laser Doppler velocimeter (LDV). Study objectives extended to determination of whether a velocity bias error occurs in turbulent flow LDV measurements, and if so, whether it can be eliminated; a comparison of results with numerical predictions based on the kappa-epsilon turbulence model; and the mapping of mean velocity, turbulence intensity, Reynolds stress, etc., including the entire recirculation zone. Velocity bias is noted and overcome by means of suitable data acquisition procedures. Although the kappa-epsilon turbulence model yields a good qualitative view of the flow field, it does not result in an adequate quantitative description.