Experimental Study of Ingestion in the Rotor–Stator Disk Cavity of a Subscale Axial Turbine Stage

Abstract

This paper describes experiments in a subscale axial turbine stage equipped with an axially overlapping radial-clearance seal at the disk cavity rim and a labyrinth seal radially inboard which divides the disk cavity into a rim cavity and an inner cavity. An orifice model of the rim seal is presented; values of ingestion and egress discharge coefficients based on the model and experimental data are reported for a range of cavity purge flow rate. In the experiments, time-averaged pressure distribution was measured in the main gas annulus and in the disk cavity; also measured was the time-averaged ingestion into the cavity. The pressure and ingestion data were combined to obtain the discharge coefficients. Locations on the vane platform 1 mm upstream of its lip over two vane pitches circumferentially defined the main gas annulus pressure; in the rim cavity, locations at the stator surface in the radially inner part of the “seal region” over one vane pitch defined the cavity pressure. For the sealing effectiveness, two locations in the rim cavity at the stator surface, one in the “mixing region” and the other radially further inward at the beginning of the stator boundary layer were considered. Two corresponding sets of ingestion and egress discharge coefficients are reported. The ingestion discharge coefficient was found to decrease in magnitude as the purge flow rate increased; the egress discharge coefficient increased with purge flow rate. The discharge coefficients embody fluid-mechanical effects in the ingestion and egress flows. Additionally, the minimum purge flow rate required to prevent ingestion was estimated for each experiment set and is reported. It is suggested that the experiments were in the combined ingestion (CI) region with externally induced (EI) ingestion being the dominant contributor.

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

“…The double seals shown by Sangan et al [11] also had a "buffer cavity," which was similar to the rim seal in this paper and had higher values of C c of 0.86 and 1.54. A review of ingress by Scobie et al [29] used the data of Johnson et al [27] and Balasubramanian et al [30] to derive a value of C c of 0.66 and 0.14, respectively, for the same radial overlap rim seal. Although the seal studied in this paper was a hybrid between a single radial overlap and a double radial overlap seal, the ratio of discharge coefficients for location B compared most closely to the single radial overlap seal (C c ¼ 1:32) or the data in the buffer cavity in the double seal (C c ¼ 0:86) [11,21].…”

Experimental Investigation of the Effect of Purge Flow and Main Flow Interaction in a Low-Speed Turbine Cascade Passage

“…Owen [11,12] indicated that there were three kinds of hot gas ingestions according to their origins, the externally induced (EI) ingress, the rotationally induced (RI) ingress, and the combined ingress (CI). This method of classification was widely used by the following researchers [13][14][15].…”

Numerical modeling of hot gas ingestion into the rotor-stator disk cavities of a subscale 1.5-stage axial gas turbine

“…Balasubramanian et al [11] measured time-averaged static pressure distribution and ingestion of main gas into the disk cavity of a subscale single-stage axial turbine equipped with an axially overlapping radial-clearance seal at the disk cavity rim and a labyrinth seal radially inboard. Their objective was to estimate the empirical discharge coefficients, based on an orifice model, over a range of purge flow rates.…”