Previous observations of turbulent motion at large wave-numbers have revealed the existence of an uneven distribution of turbulent energy. The spotty distribution of the turbulent motion at high wave-numbers is here studied experimentally for the turbulent boundary layer. The high wave-number intermittency is observed at all locations through and along the boundary layer from near transition to near separation.The flatness factors for the longitudinal turbulent component at different wave-numbers are measured to give a quantitative value for the intermittency at particular wave-numbers. Upstream of the separation region the flatness factors are found to depend on wave-number and longitudinal distance, but not on the distance from the wall. It appears that the intermittency develops in the transition region and does not diminish very rapidly with distance downstream. Near separation the flatness factors change radically in distribution near the wall, and are there no longer independent of distance from the wall.

Physical evidence on stall inception from visual studies, mean-velocity-profile correlations, shear measurements, and fluctuations in separating boundary layers in the neighborhood of stall are discussed. Direct visual studies suggest that stall inception in the laminar boundary layer follows the classical model, but does not necessarily do so in the turbulent shear layer. It is useful to describe stall as a certain type of transition region, which can be long or short. Adoption of these ideas is shown to lead to better correlation of stall data and more complete understanding of available physical evidence. However, physical data on the relation between the various types of evidence in the turbulent case and their respective connections with the events in the transition region leading to stall are not presently complete. This suggests experiments of a certain type which should lead to further clarification of the process of stall inception in the turbulent boundary layer.

An experimental and analytical study of the separation of a turbulent boundary layer is reported. The turbulent boundary-layer separation model proposed by Sandborn & Kline (1961) is demonstrated to predict the experimental results. Two distinct turbulent separation regions, an intermittent and a steady separation, with correspondingly different velocity distributions are confirmed. The true zero wall shear stress turbulent separation point is determined by electronic means. The associated mean velocity profile is shown to belong to the same family of profiles as found for laminar separation. The velocity distribution at the point of reattachment of a turbulent boundary layer behind a step is also shown to belong to the laminar separation family.Prediction of the location of steady turbulent boundary-layer separation is made using the technique employed by Stratford (1959) for intermittent separation.

A general Nusselt number correlation is presented for transverse cylinders in subsonic and supersonic air flows where dissociation is negligible. New and existing data in the following experimental range have been correlated: Mach M = 0.001 to 6.0, Reynolds NRe = 0.02 to 300,000, Knudsen NKn = 4 × 10−6 to 37. In subsonic flow, heat transfer from a cylinder yawed at an angle to the air velocity is predicted by the transverse cylinder Nusselt number correlation when the normal velocity component is used as the characteristic velocity. Finally, recovery temperature data from cylinders are divided into three regimes by a Knudsen number criterion.