An investigation of the boundary layer behaviour on the blading of a single-stage axial-flow compressor.

Observations of the boundary layer behaviour on the blading of a single-stage axial-flow compressor are described : detailed measurements were carried out with hot wire, surface visualisation, and surface pitot tube techniques, and the presence of extensive regions of laminar flow was established. The behaviour of the laminar and turbulent boundary layers, and of separated laminar flow regions are reported. A new correlation is developed to describe the boundary layer transition behaviour, and the effects of pressure gradient, Reynolds number, and free stream turbulence on transition are discussed. A new turbulent skin friction law for conditions of large positive pressure gradient is developed, and the problem of the minimum Reynolds number for turbulent flow under a pressure gradient is re-examined. Various existing methods of calculating the turbulent boundary layer are examined and their success in predicting the boundary layer development on a stationary blade of the research compressor is evaluated. The application of the experimental results to the design and performance analysis of axial-flow turbo-machine blading is discussed. A family of surface velocity distributions giving unseparated flow over the suction surface of an axial-flow compressor blade is derived, and their computed performance is analysed. In conclusion, problems needing further investigation are outlined.