The Effects of Inlet Boundary Layer Condition and Periodically Incoming Wakes on Secondary Flow in a Low Pressure Turbine Cascade

Abstract

A particular turbine cascade design is presented with the goal of providing a basis for high quality investigations of endwall flow at high-speed flow conditions and unsteady inflow. The key feature of the design is an integrated two-part flat plate serving as a cascade endwall at part-span, which enables a variation of the inlet endwall boundary layer conditions. The new design is applied to the T106A low pressure turbine cascade for endwall flow investigations in the High-Speed Cascade Wind Tunnel of the Institute of Jet Propulsion at the Bundeswehr University Munich. Measurements are conducted at realistic flow conditions (M2th = 0.59, Re2th = 200 000) in three cases of different endwall boundary layer conditions with and without periodically incoming wakes. The endwall boundary layer is characterized by 1DCTA measurements upstream of the blade passage. Secondary flow is evaluated by Five-hole-probemeasurements in the turbine exit flow. A strong similarity is found between the time-averaged effects of unsteady inflow conditions and the effects of changing inlet endwall boundary layer conditions regarding the attenuation of secondary flow. Furthermore, the experimental investigations show, that all design goals for the improved T106A cascade are met.

Near-Wall Flow in Turbomachinery Cascades—Results of a German Collaborative Project

“…Thus, despite the flow field changes, seen in MP2 (Figures 22 and 23), the effect of the periodically incoming wakes on the time-averaged integral losses in the turbine exit flow is very small. This finding is consistent with the total pressure field measurements [45] as well as DNS of a previous T106A cascade [31,32].…”

“…Compared to a conventional turbine cascade, the present design, which is discussed in detail in [45], delivers several improvements regarding aerodynamics and integration of measurement techniques. The main feature is an integrated flat plate at part-span which serves as a turbine cascade endwall and provides well defined, and adjustable, inlet endwall boundary layer conditions.…”

“…As opposed to the fixed position of the downstream plate, the upstream plate can be displaced in spanwise direction, varying the boundary layer augmentation on the aft plate. The value of ∆z denotes the misalignment of the two flat plates, with ∆z < 0 resulting in decreased inlet endwall boundary layer height, as shown by the velocity profiles in Figure 18b, along with a lower turbulence intensity peak [45].…”

“…The overall uncertainty estimate of a velocity sample is ∆v ≤ 2.5 m/s. Further details on the experimental setup, measurement techniques, the particular turbine cascade design, which was implemented, and a discussion of the full experimental results can be found in [45].…”

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

“…In contrast to the relatively small effects of incoming wakes, Volino et al [7] found the influence of the inlet boundary layer to be much larger. Schubert and Niehuis [8] came to a similar conclusion when evaluating the turbine cascade exit flow; however, they found that the endwall flow development inside the blade passage is significantly affected by both factors, but in different manners. The vast majority of research dealing with secondary flow investigations has been centered around probe-based measurements: mostly up-and downstream of the blade passage.…”