Time-Resolved Measurements of the Unsteady Boundary Layer in an Annular Low-Pressure Turbine Configuration With Perturbed Inlet

Abstract

In this study the unsteady behavior of the boundary layers developing on a LPT stator profile and their effect on secondary flow patterns in a 1.5-stage turbine configuration are investigated under the influence of periodic inflow perturbations. For this the experimental setup has been enhanced by hot-film sensor arrays placed on the stator profiles to provide time-resolved data from within the passage. The inflow is perturbed by periodically passing bars and a modified T106-profile has been considered for the blading. The profile, labeled as T106RUB, was developed for matching the transition and separation characteristics of the original T106 profile at low flow speeds, thus facilitating measurements to be taken in a large-scale test rig with its improved accessibility. The transition phenomena occurring in the profile boundary layers are investigated under both unperturbed and periodically perturbed inflow by means of spectral analysis, the characterization of the wall-stress system and an evaluation of the statistic quantities. In particular, the periodic changes of the suction side boundary layer flow region towards the trailing edge are studied in detail. Furthermore, time-resolved hot-film measurements at different blade height positions facilitate a detailed comparison of the quasi two-dimensional mid-span profile flow and the near end wall profile flow which is subject to influence of secondary flow structures. These information are employed to assess to which extent the additional turbulence originating from the wakes affects the blade boundary layers and thus the secondary flow structures.

Characterization of the Endwall Flow in a Low-Pressure Turbine Cascade Perturbed by Periodically Incoming Wakes, Part 1: Flow Field Investigations with Phase-Locked Particle Image Velocimetry

“…More recently, some published works have diverged from this classic approach by incorporating more modern experimental methods. For example, Sinkwitz et al [9] and Lopez et al [10] utilized hot-film sensor arrays on the near-endwall suction surface, and Chemnitz and Niehuis [11] analyzed the potential of particle image velocimetry (PIV) in comparison to five-hole-probe (FHP) and constant temperature anemometry (CTA) measurements in turbine cascade exit flow.…”