Three-dimensional laser velocimeter investigation of turbulent, incompressible flow in an axisymmetric sudden expansion

Abstract

An experimental study of the flow in an axisymmetric sudden expansion was carried out using a three-color, three-component laser Doppler velocimeter with computer controlled data acquisition and reduction. The area ratio of the expansion was 121:1 and the Reynolds number, which was based on inlet average velocity and inlet diameter, was 22,000. The axial, radial, and circumferential components of the mean velocity were computed from the measurement of three independent velocity components as were the turbulence intensities and kinetic energy. The results showed the flow to be axisymmetric, with negligible circumferential mean velocity. The nature of the separated flow region was consistent with that of previous studies. The large area ratio had little effect on the location of the reattachment, which occurred approximately six step heights downstream of the expansion. All three normalized turbulence intensities were shown to be of the same order of magnitude, thus showing nearly isotropic turbulence. The centerline velocity decay for this large area ratio was much more rapid than the decay for smaller area ratios and was similar to that of a free jet exhausting to atmospheric pressure.