Experimental Analysis and Prediction of Wake-Induced Transition in Turbomachinery

Abstract

The paper presents an experimental and numerical analysis of the interaction between wakes and boundary layers on aerodynamic blade profiles. The experiment revealed that incoming wakes interact with boundary layers and cause the significant increase of velocity fluctuations in the boundary layer and in consequence shift the transition zone towards the leading edge. The full time evolution of periodic wake induced transition was reproduced from measurements. The numerical simulation of the flow around the blade profile has been performed with the use of the adaptive grid viscous flow unNEWT PUIM solver with a prescribed unsteady intermittency method (PUIM) developed at Cambridge University, UK. The results obtained give evidence that the turbulence transported within the wake is mainly responsible for the transition process. The applied CFD solver was able to reproduce some essential flow features related to the bypass and wake-induced transitions and the simulations reveal good agreement with the experimental results in terms of localisation and extent of wake-induced transition.

Modeling of Wake-Induced Transition in Linear Low-Pressure Turbine Cascades

“…The second test case considered is blade TC4, studied experimentally by Elsner et al 21 The experiments show that, in contrast to the preceding case, transition occurs well ahead of the trailing edge, at S/S max ≈ 0.5, and is effectively completed at S/S max ≈ 0.8. Here, the wake has a weaker effect, with unsteady features confined within the range S/S max ≈ 0.5 − 0.8.…”

“…The first blade, designated T106, has been studied experimentaly by Opoka and Hodson,28 whereas the second blade, TC4, has been studied by Elsner et al 21 The blades are shown in Fig. 1, both having profiles used in lowpressure (LP) stages.…”

“…This is also why a full, interactive bar-blade computation is not appropriate. The dissipation rate within the inlet wake was then estimated from the mixing-length relationship ε in = c 3 4 μ k 3 2 l mix (21) where l mix = αδ is the mixing length for a wake, α is equal to 0.18 (Wilcox 29 ), and δ is the half-width of the wake. Outside the wake, the freestream-turbulence level is fixed at the experimentally given value of 4%, whereas the inlet dissipation rate has been estimated by a trial-and-error matching of the decay of the freestream turbulence within the passage to the experimentally observed variation.…”

“…The present paper now reports the application of the extended model to two new configurations for which experimental data have only recently emerged and in which the freestream-turbulence level is much higher, namely, 4%, closer to realistic operating conditions. One set of data pertains, again, to the linear cascade considered earlier; the other is for an entirely different blade geometry with a much more rounded leading edge, investigated by Elsner et al 21 The experimental observations suggest significant differences in the detailed mechanisms of bypass transition and their effects. Hence, taken together, the two configurations represent a searching test of the present transition-modified model.…”

Comparison of Two Unsteady Intermittency Models for Bypass Transition Prediction on a Turbine Blade Profile

“…Zarzycki and Elsner [1] presented an experimental analysis of the wake parameter influence on the position and the extent of the induced transition zone, for wakes generated by 4 and 6 mm bars. The case for 4 mm bars was also numerically analysed with the prescribed method by Elsner et al [18] and with the transport method by Lodefier et al [19]. For the investigations presented in this paper, the unsteady data obtained with 6 mm bars are used.…”