Characteristics of external intermittency in the outer region ofturbulent boundary layers are presented based on single-pointhotwire measurements. The distinction between the turbulentand non-turbulent state of the flow is marked by applying athreshold on instantaneous kinetic-energy, and this criteria isfound to be adequate for this study. Mean intermittency profilesare in consistent agreement with previous observations. Further,conditionally averaged profiles of the streamwise velocityand its standard deviation show good agreement with scalingproposed by Chauhan et al. [3]. Probability density functionsof the lengths of turbulenton-turbulent zones show a range ofintermediate scales over which power-law scaling is observed.The observed power-law scaling provides further evidence for afractal geometry of the turbulenton-turbulent interface (TNTI)over a wide range of Reynolds number and scale separation[8]. Finally, longer lengths (streamwise extent greater than δ=4,where δ is the layer thickness) exhibit exponential probabilitydistribution, indicating that a long turbulenton-turbulent stateoccurs in the flow independent of the length of the alternate statepreceding it.
展开▼
