BOUNDARY-LAYER DEVELOPMENT IN AXIAL COMPRESSORS AND TURBINES .1. COMPOSITE PICTURE

Comprehensive experiments and computational analyses were conducted to understand boundary layer development on airfoil surfaces in multista ge, axial-flow compressors and LP turbines. The tests were nln over a broad range of Reynolds numbers and loaning levels in large, low-speed research facilities which simulate the relevant aerodynamic features of modem engine components. Measurements of boundary layer characteris tics were obtained by using arrays of densely packed, hot-film gauges mounted on airfoil surfaces and by making boundary layer surveys with hot wire probes. Computational predictions were made using both steady pow codes and an unsteady flow code. This is the first time that time -resolved boundary layer measurements and detailed comparisons of meas ured data with predictions of boundary layer codes have been reported for multistage compressor and turbine blading. Part I of this paper su mmarizes all of our experimental findings by using sketches to show ho w boundary layers develop on compressor and turbine blading. Parts 2 a nd 3 present the detailed experimental results for the compressor and turbine, respectively. Part 4 presents computational analyses and disc usses comparisons with experimental data. Readers not interested in ex perimental detail can go directly from Part I to Part 4. For both comp ressor and turbine blading, the experimental results show large extent s of laminar and transitional flow on the suction surface of embedded stages, with the boundary layer generally developing along two distinc t but coupled paths. One path lies approximately under the wake trajec tory,while the other lies between wakes. Along both paths the boundary layer clearly goes from laminar to transitional to turbulent. The wak e path and the non-wake path are coupled by a calmed region, which, be ing generated by turbulent spots produced in the wake path, is effecti ve in suppressing flow separation and delaying transition in the non-w ake path. The location and strength of the various regions within the paths, such as wake-induced transitional and turbulent strips, vary wi th Reynolds number, lending level, and turbulence intensity. On the pr essure surface, transition takes place near the leading edge for the b inding rested. For both surfaces, bypass transition and separated-flow transition were observed. Classical Tollmien-Schlichting transition d id nor play a significant role. Comparisons of embedded and first-stag e results were also made to assess the relevance of applying single-st age and cascade studies to the multistage environment. Although doing well under certain conditions, the codes in general could not adequate ly predict the onset and extent of transition in regions affected by c alming. However, assessments are made to guide designers in using curr ent predictive schemes to compute boundary layer features and obtain r easonable loss predictions.