Effects of freestream disturbances on boundary-layer transition.

The eN Method for Transition Prediction. Historical Review of Work at TU Delft

“…[16] We concluded that beginning and end of transition for Tu >.1% could be predicted by N-factors N l and N 2 respectively according to: N l = 2.13− 6.18 10 log Tu (28) N 2 = 5− 6.18 10 log Tu (29) For values of Tu < 0.1% there is much scatter in the experiments because in this region sound disturbances may become the factor controlling transition rather than turbulence. It was shown by Wells 45 , Spangler and Wells 46 and others that transition Reynolds numbers larger than the Schubauer and Skramstadt values could be obtained by further reducing the turbulence level and the acoustic disturbances (apparently the acoustic disturbances rather than turbulence had caused transition in the Schubauer and Skramstadt experiments for Tu < 0.1%).…”

Influence of Sound upon Separated Flow over Wings

“…8 Pfenninger and Reed, 9 on the other hand, were concerned with determining the maximum sound levels which could be allowed and still maintain laminar flow on wings with suction boundary-layer control. Their studies Received July 10, 1974; revision received September 6, 1974 were initiated in the early 1950's when it was noticed that sound propagating through the suction ducts would initiate boundary-layer transition.…”

An Analytical Study of the Effects of Surface Roughness on Boundary-Layer Transition

“…By measuring the amplitude of the wave as it was swept downstream, they were able to ascertain the rate of growth or decay of the wave for a series More recently, the measurements by Wells (1967) and Spangler and Wells (1968) have shown that transition is strongll dependent upon both the amplitude and the spectrum of the disturbance environment. In these experiments, the transition Reynolds number was delayed to values which were nearly twice as high as the ones observed by Schubauer and Skramstad, even though the magnitude of the free-stream disturbanves was about the same for Conversely, when most of the energy in the external disturbance was in the stable portion of the boundary-layer spectrum, the location of transition was nearly independent of the free-stream disturbances.…”