Effects of Purge Jet Momentum on Sealing Effectiveness

Abstract

Driven by the need for higher cycle efficiencies, overall pressure ratios for gas turbine engines continue to be pushed higher thereby resulting in increasing gas temperatures. Secondary air, bled from the compressor, is used to cool turbine components and seal the cavities between stages from the hot main gas path. This paper compares a range of purge flows and two different purge hole configurations for introducing the purge flow into the rim cavities. In addition, the mate face gap leakage between vanes is investigated. For this particular study, stationary vanes at engine-relevant Mach and Reynolds numbers were used with a static rim seal and rim cavity to remove rotational effects and isolate gas path effects. Sealing effectiveness measurements, deduced from the use of CO2 as a flow tracer, indicate that the effectiveness levels on the stator and rotor side of the cavity depend on the mass and momentum flux ratios of the purge jets relative to the swirl velocity. For a given purge flow rate, fewer purge holes resulted in better sealing than the case with a larger number of holes.

Effects of Purge Flow Configuration on Sealing Effectiveness in a Rotor–Stator Cavity

“…The experiments presented in this paper were performed in the Steady Thermal Aero Research Turbine (START) facility, the design of which was previously described by Barringer et al [16]. The previous papers by Clark et al [17,18] also described the facility commissioning, the half-stage turbine configuration, and instrumentation. In this section, the facility will be briefly reviewed, and the 1.5 stage turbine used for these experiments will be described in more detail.…”

“…2. Similar to the research of Clark et al [17,18], partial span airfoils were used for this study to reduce the mass flow requirements while maintaining an engine-relevant axial Reynolds number, rotational Reynolds number, and Mach number. Other researchers have also proven the use of partial span airfoils for studying rim seals and ingestion [20][21][22].…”

“…The rationale for not using the TOBI flow in this initial test campaign was the desire to perform a systematic study understanding the effects of increasing complexity. The experiments in the test turbine began with no rotation [18], and the next step was to determine the effects of the number of purge holes without the TOBI flow. Results will be presented in the future for TOBI flow.…”

“…The turbine test section was heavily instrumented as shown in Fig. 3 and previously described by Clark et al [17,18]. Several static pressure taps, pressure probes, and thermocouples composed the instrumentation in the turbine.…”

“…In addition to pressure measurements, the static pressure taps were used for concentration effectiveness measurements. According to the method described in detail by Clark et al [17,18], the secondary air supply was seeded with 1% CO 2 to be used as a tracer gas in the turbine. Flow was sampled at specific locations in the front rim seal, rim cavity, and wheel space through the static pressure taps.…”