Local dissipation scales in turbulent jets

This paper reports an experimental investigation of the characteristics of local dissipation length-scale field  in turbulent (round and square) jets with various jet-exit Reynolds numbers. Results reveal that the probability density function (PDF) of , denoted by Q(), in the central fully-turbulent region, is insensitive to initial flow conditions and the departure from anisotropy. Excellent agreement is demonstrated with distributions previously measured from pipe flow and Direct Numerical Simulation (DNS) calculated from box turbulence. In the shear layer where the flow is not fully turbulent, Q() exhibits higher probabilities at small  and the PDFs of velocity increments Lu across the integral length scale L are found to have exponential tails, suggesting the increased level of small-scale intermittency at these scales. This feature may come from the large-scale intermittency induced by the engulfment in the shear layer. In addition, the influence of the mean shear rate and Reynolds number on Q() is negligible. Therefore, the current results indicate that the smallest-scale fluctuations in fully turbulence are universal, but depend on the large-scale intermittency not being fully turbulent.