Design of an Improved Turbine Rim-Seal

Abstract

Rim seals are fitted in gas turbines at the periphery of the wheel-space formed between rotor disks and their adjacent casings. These seals, also called platform overlap seals, reduce the ingress of hot gases which can limit the life of highly stressed components in the engine. This paper describes the development of a new, patented rim-seal concept showing improved performance relative to a reference engine design, using unsteady Reynolds-averaged Navier–Stokes (URANS) computations of a turbine stage at engine conditions. The computational fluid dynamics (CFD) study was limited to a small number of purge-flow rates due to computational time and cost, and the computations were validated experimentally at a lower rotational Reynolds number and in conditions under incompressible flow. The new rim seal features a stator-side angel wing and two buffer cavities between outer and inner seals: the angel-wing promotes a counter-rotating vortex to reduce the effect of the ingress on the stator; the two buffer cavities are shown to attenuate the circumferential pressure asymmetries of the fluid ingested from the mainstream annulus. Rotor disk pumping is exploited to reduce the sealing flow rate required to prevent ingress, with the rotor boundary layer also providing protective cooling. Measurements of gas concentration and swirl ratio, determined from static and total pressure, were used to assess the performance of the new seal concept relative to a benchmark generic seal. The radial variation of concentration through the seal was measured in the experiments and these data captured the improvements due to the intermediate buffer cavities predicted by the CFD. This successful design approach is a potent combination of insight provided by computation, and the flexibility and expedience provided by experiment.

Effects of Purge Jet Momentum on Sealing Effectiveness

“…The majority of the rim seal studies in the literature, however, have used simplified geometries and provided important fundamental knowledge of cavity flows, rim seals, and hot gas ingestion. Although some engine-realistic rim seals have been published [7][8][9][10], there is a need for more studies in the open literature that include the complex overlaps, buffer cavities, and flow physics of enginerealistic rim seals.…”

Effect of Rim Seal Geometry on Rotationally-Driven Ingestion

“…Researchers at the University of Bath have investigated the effects of rim seal configurations and turbine conditions on ingestion on both a single and a 1.5 stage turbine rig [19][20][21][22][23]. As shown in previous research, a consistent trend in seal performance was identified with the radial seal outperforming a simple axial seal.…”

Harmonisation of Coolant Flow Pattern with Wake of Stator Vane to Improve Sealing Effectiveness Using a Wave-Shaped Rim Seal

“…Additional studies were conducted to characterise the tendency of the flow around the rim seal according to the flow conditions (such as coolant flow rate, rotational Reynolds number, and rotational speed of the disk) [17] and the shape parameter of the rim seal [8,18]. Recently, a study was reported on the performance of a rim seal with an inner cavity and a rib structure added to the rotor side [19], and with two buffer cavities that attenuate the circumferential pressure asymmetries of the flow introduced from the mainstream gas path [20]. In contrast, a number of three-dimensional modified rim seals have been proposed.…”