Laminarescent, relaminarizing and retransitional flows

The status of experimental determinations concerning accelerated turbulent boundary layers and subcritical pipe or channel flows undergoing relaminarization and possible retransition is assessed. It is found that despite the large number of experiments conducted, insufficient variation of the range of such parameters as Reynolds number has been instituted, and many sets of data are incomplete, through the neglect of careful measurement of skin friction. Those sets of experimentally obtained data can alone be considered useful whose flows satisfy the two-dimensional momentum integral equation and which incorporate cross-checks on calculation and measurement accuracy. It is recommended that future experiments in this field be undertaken in wind tunnels capable of producing constant pressure boundary layers, with Reynolds numbers in the vicinity of 10,000, uniformly two-dimensional flow, and reliable skin friction measurements.