Conditional Sampling Measurements of Steady and Pulsating Round Jets

Conditional sampling measurements were made to reveal the turbulence structures of a steady round jet and a pulsating round jet with low pulsation frequency and relatively large velocity amplitude using a hot-wire anemometer and a laser Doppler velocimeter. Turbulent motions were classified into four distinct categories : ejection, sweep, outward interaction and inward interaction. The fraction of time the velocity signals were in the respective categories and the contributions of each motion to the Reynolds shear stress and turbulence kinetic energy were determined. Ejection and sweep were found to be responsible for turbulence production. The correlation coefficient between the axial and the radial velocity fluctuations showed that large-scale ordered motions existed in the jet. There was little difference between the turbulent structures of the steady and pulsating jets.