The velocity spectra and turbulence length scale distributions in the near to intermediate regions of a round free turbulent jet

摘要

Stationary and flying single hot-wire measurements were made to investigate the near to intermediate field in a round free turbulent jet,let. Measurements were carried out at Reynolds numbers Re-D based oil the jet exit mean velocity and the nozzle diameter, between 6000 and 100 000. The objective of this Study was to investigate the concept of a mixing transition proposed by Dimotakis ["The mixing transition in turbulent flows," J. Fluid Mech. 409, 69 (2000)]. This was done through the measurement of the velocity spectra and the Calculation of Kolniogorov lambda(K), Taylor microscale lambda(T) the Liepmann-Taylor microscale lambda(L), and the viscous length scale lambda(v), at different positions in the near to intermediate regions of a round tree jet. The present results demonstrate the local nature of mixing transition. It is found that the Kolmogorov, Taylor, and viscous length scales all decrease in magnitude With the local Reynolds number Re-delta based oil the local center line mean velocity and the local time-averaged diameter of the jet and appear to be only weakly dependent oil the radial position. although the ratio Re-T/Re delta(1/2) varies nonlinearly across the jet radius. The ratio of the laminar to viscous length scale exceeds unity beyond the potential core of the jet. Moreover. the skewness of the axial velocity is approximately -0.4 over 30