An algebraic intermittency model for bypass, separation-induced and wake-induced transition

An algebraic model using the intermittency concept is proposed for laminar to turbulent transition in attached and separated boundary layers. The model modifies the production terms of the k-omega RANS turbulence model by Wilcox. For attached flows, the model describes bypass transition by taking into account two main effects, which are damping of high-frequency disturbances by a laminar shear layer and breakdown of a near-wall laminar layer perturbed by streaks. For separated flow, the model describes breakdown of a laminar free shear layer. The proposed model is a modified and extended version of an earlier model by the authors for bypass transition only (Kubacki and Dick, Int. J. Heat and Fluid Flow, 58, 68-83, 2016). The primary tuning of the model has been done with flat plate T3C flows of ERCOFTAC with steady approaching flow, relevant for bypass transition and separation-induced transition. Secondary tuning has been done with two cascades with steady approaching flow at high turbulence level, one with N3-60 (Re = 6 x 10(5)) steam turbine stator vanes and one with V103 (Re = 1.385 x 10(5)) compressor blades. Model validation has been done for steady approaching flows of the same cascades, but including a case with low level of free-stream turbulence, and for a cascade with T106A (Re = 1.6 x 10(5)) gas turbine rotor blades for high and low levels of free-stream turbulence. Further validation has been done for flow perturbed by travelling wakes through a cascade of N3-60 vanes at high and low levels of background turbulence level. The transition model produces good results for all cases, both for bypass transition in attached boundary layer state and for transition in separated boundary layer state. (C) 2016 Elsevier Inc. All rights reserved.