Separating and Separated Boundary Layers

摘要

The low-pressure turbine of an aircraft engine operates with a low chord Reynoldsnumber. As such, there are regions of strong streamwise acceleration and diffusion effects. This results in extended regions of transition from laminar to turbulent flow and large zones of flow separation. In response to a need to learn more about the mechanisms that lead to transition and separation in the engine environment, a low-Reynolds-number-flow study initiated during the Summer of 1994 at Wright Labs. In this project, a low-pressure turbine airfoil cascade was installed in a wind tunnel. To simulate the engine environment, high background turbulence was imposed on the flow and a device for imposing passing wakes upon the flow was fabricated. A program for measurement of the characteristics of the boundary layer; laminar-like or turbulent, separated or attached, was initiated. The Summer project resulted in an effective start on the problem but considerably more remained to be done. This report documents the subsequent work on this project. At the University of Minnesota, an easily accessible facility which had the essential elements of the low-pressure turbine flow was designed, built, and qualified. This facility now provides a convenient means for documenting the flow and developing measurement techniques. The Wright Lab experimental program continued with the completion of the construction, the implementation of the turbulence generating device, and the qualification of the tunnel. Both facilities are now producing data to the program. These data are summarized herein. The University of Minnesota facility has generated pressure profiles for various cases of different Reynolds number and turbulence intensity. The Wright Labs facility has given pressure profiles for various Reynolds numbers.