Generation and Development of Klebanoff Streaks in Low-Pressure Turbine Cascade Under Upstream Wakes

Modern ‘high-lift’ blade designs incorporated into the low pressure turbine (LPT) of aero-engines typically exhibit a separation bubble on the suction surface of the airfoil. The separation size and the turbulence loss are governed by the transition process in the separated shear layer. However, the wake-induced transition, the natural transition and the instability induced by the Klenbanoff streaks complicate the transition process.

The boundary layer on the suction surface of a high-lift LPT was investigated at Re=50,000 with upstream wakes. The numerical simulation was performed with the CFX software using large eddy simulations (LES), and the experiment was performed on a linear cascade. In this study, the wake is divided into the wake center and wake tail, the unsteady formation process of the streaks and wall shear stress caused by the wake are analyzed. A new mechanism of generation and development of Klebanoff Streaks was presented to better understand the effect of the wake on the boundary layer.

Moreover, it was found that after entering the blade passage, the wake center does not contact the blade but causes the wall shear stress of the front part on the suction surface to increase. However, it is not possible to form strong Klebanoff streaks at the leading edge of the blade by shear sheltering effect. Only the wake tail can form Klebanoff streaks when it contacts the blade.