Experimental Measurements of Ingestion Through Turbine Rim Seals—Part I: Externally Induced Ingress

Abstract

This paper describes a new research facility which experimentally models hot gas ingestion into the wheel-space of an axial turbine stage. Measurements of the CO2 gas concentration in the rim-seal region and inside the cavity are used to assess the performance of two generic (though engine-representative) rim-seal geometries in terms of the variation of concentration effectiveness with sealing flow rate. The variation of pressure in the turbine annulus, which governs this externally-induced (EI) ingestion, was obtained from steady pressure measurements downstream of the vanes and near the rim seal upstream of the rotating blades. Although the ingestion through the rim seal is a consequence of an unsteady, three-dimensional flow field and the cause-effect relationship between the pressure and the sealing effectiveness is complex, the experimental data is shown to be successfully calculated by simple effectiveness equations developed from a previously published orifice model. The data illustrate that, for similar turbine-stage velocity triangles, the effectiveness can be correlated using a nondimensional sealing parameter, Φo. In principle, and within the limits of dimensional similitude, these correlations should apply to a geometrically-similar engine at the same operating conditions. Part II of this paper describes an experimental investigation of rotationally-induced (RI) ingress, where there is no mainstream flow and consequently no circumferential variation of external pressure.

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

“…The effectiveness in the front wheel-space (location D in Fig. 7) and at the purge hole radius in the rim cavity (location C) exhibited behavior that deviated from the previously measured effectiveness curves [11,21,25], like that shown for the outer radius in the rim cavity (location B). The data shown for location B were similar to the previous effectiveness curves for which the orifice model was derived, and it will be shown later that the model fits the data well.…”

“…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].…”

Use of Pressure Measurements to Determine Effectiveness of Turbine Rim Seals

“…Sangan et al [17] used the Bath orifice model to derive the so-called effectiveness equations that express e, the sealing effec tiveness, in terms of ®n, the nondimensional sealing flow rate. For El ingress, 3>o ____________£__________ ®min,£/ " [1 + Tc -2/3(1 -g)2/3]3/2…”

Effect of a rib on rim seal performance

“…Their results revealed that the mass flow rate of the ingression flow depends strongly on the rim seal configuration, and a specific rim seal geometry led to the reduction of hot gas ingestion into the rim seal. Sangan et al [5,6] experimentally studied the sealing performances of two types of rim seal, i.e., single and double radial rim seals, under the stationary and rotating conditions. They found that the rotating cases show better sealing performances than the stationary cases.…”