Influence of the Upstream Wakes on the Boundary Layer of a High-Lift Low-Pressure Turbine at Positive Incidence

Abstract

The wake-induced transition, natural transition, and instability induced by the Klebanoff streaks complicate the transition process. In this paper, the boundary layer on the suction surface of a high-lift low-pressure turbine (LPT) was investigated at the design and +10° incidence with upstream wakes under numerical simulations and experiments. The interactions between the wakes and boundary on the leading edge of the blade at two incidences are mainly discussed. A positive incidence gives rise to an adverse pressure gradient (APG) over the forward suction surface. The adverse pressure gradient enhances the shear sheltering effect and, as a result, reduces penetration. However, strong Klebanoff streaks are amplified by the APG at +10° incidence and experience a weak viscous decay due to the moderately favorable pressure gradient (FPG). Between the wake passing events, weak Klebanoff streaks are also amplified by the APG at +10° incidence but barely amplified at 0° incidence. Klebanoff streaks appear almost in the whole wake passing cycle, resulting in an earlier transition onset and a longer transition process at +10° incidence.