Interaction of Rim Seal and Annulus Flows in an Axial Flow Turbine

Abstract

A combined computational fluid dynamics (CFD) and experimental study of interaction of main gas path and rim sealing flow is reported. The experiments were conducted on a two stage axial turbine and included pressure measurements for the cavity formed between the stage 2 rotor disc and the upstream diaphragm for two values of the diaphragm-to-rotor axial clearance. The pressure measurements indicate that ingestion of the highly swirling annulus flow leads to increased vortex strength within the cavity. This effect is particularly strong for the larger axial clearance. Results from a number of steady and unsteady CFD models have been compared to the measured results. Good agreement between measurement and calculation for time-averaged pressures was obtained using unsteady CFD models, which predicted previously unknown unsteady flow features. This led to fast response pressure transducer measurements being made on the rig, and these confirmed the CFD prediction.

Inertial waves in turbine rim seal flows

“…The first published experimental observation of these large-scale unsteady flow modes was reported by Cao et al [16] the T-C instability include Boudet et al [17], O'Mahoney [18] and Gao et al [19], and those proposing the K-H instability include Rabs et al [20], Chilla et al [21], Savov et al [22] and Horwood et al [15]. Another possible source of unsteadiness, suggested by Berg et al [23], are the Helmholtz and shallow cavity modes.…”

A Comparison of Single and Double Lip Rim Seal Geometries

“…Some experimental evidence for such large scale cavity unsteadiness has been provided in open literature (e.g. Jakoby et al [26], Cao et al [25], Roy et al [29] and Mirzamoghadam et al [28]). However, the existence of a clear link between unsteadiness (coherent or otherwise) and ingestion remains an open research question.…”

“…Advances in computational power have enabled full annulus Unsteady RANS (URANS) simulations (e.g. Cao et al [25], Jakoby et al [26], Wang et al [27] and Mirzamoghadam et al [28]) which show improved results compared to experimental data. These studies all show large scale flow structures (at frequencies unrelated to blade passing) in the rotor-stator cavity which provide a mechanism for increased levels of ingress.…”

Numerical Simulation of the Flow Interaction Between Turbine Main Annulus and Disc Cavities

“…Interaction between the blade and vane flows may also be important. Recent CFD and experimental studies [3,[11][12][13] have shown that at low sealing flow rates unsteady flow features, unrelated to the blade passing frequency, are important and that complete 360 deg models may be required to fully represent these features. Flow structures similar to those identified for ingestion due to disc pumping have been identified in CFD solutions, and confirmed experimentally by unsteady pressure measurements.…”