The 1991 IGTI Scholar Lecture: The Role of Laminar-Turbulent Transition in Gas Turbine Engines

Abstract

A critical study of laminar-turbulent transition phenomena and their role in aerodynamics and heat transfer in modern and future gas turbine engines is presented. In order to develop a coherent view of the subject, a current look at transition phenomena from both a theoretical and experimental standpoint are provided and a comprehensive state-of-the-art account of transitional phenomena in the engine’s throughflow components given. The impact of transitional flow on engine design is discussed and suggestions for future research and developmental work provided.

Prediction of laminar-turbulent transition on an airfoil at high level of free-stream turbulence

“…However, in this case, the turbulence model demonstrates an optimistic behavior, which is undesirable, since it can lead to unsafe and misleading underprediction of the friction drag. The transition Reynolds number in experiment is around 200 for the two low-velocity cases (and presumably around 200 at 18 m/s) which agrees well with the reported in [1,3] interval 150 200. The acceleration parameter, K, is below −2.5 at 5 m/s (separation-induced transition), equal to −2 at 9 m/s, and presumably equal to 0.5 at 18 m/s.…”

“…The most debated is the in §uence of such parameter as surface curvature. Mayle [1] concludes that the curvature e¨ect in turbomachinery components applies only to convex surfaces and that even for convex surfaces, the onset of transition at high free stream turbulence virtually identical to that for a §at plate.…”

“…The e¨ect of the turbulence length scale is also substantial but can be incorporated into the turbulence intensity by introducing a well-known scaling [1]. Surface roughness, heat transfer, compressibility, and wall curvature are the secondary e¨ects, which typically have an order of magnitude weaker in §uence on transition as compared to the primary e¨ects.…”

“…According to famous review by Mayle [1], the most important parameters for the onset of transition on an airfoil are the pressure gradient and incoming §ow turbulence intensity. The e¨ect of the turbulence length scale is also substantial but can be incorporated into the turbulence intensity by introducing a well-known scaling [1].…”

An experimental study on laminar-turbulent transition at high free-stream turbulence in boundary layers with pressure gradients

“…In another study, Salomon et al [7] presented a new method for calculating intermittency in transitional boundary layers with rapidly changing pressure gradients, which is based on experimental studies using the pressure gradient parameter. Mayle in his well-known paper, [8] mentions some experiments performed by Görtler in 1940 and Liepman in 1943, who analysed the effect of curvature on transition. From the experiments carried out by the latter, the transition Reynolds number depends on the turbulence level and on how strong the curvature is and seems to have a non-negligible effect in low pressure turbines and small engines, where a delay can be found.…”