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.

Developments in turbomachinery internal air systems

“…The relatively very recent study by Cao et al [8] bears some resemblance to that of Bayley and Conway. Cao et al considered a narrow gap turbine rotor/stator cavity with weak net radial outflow.…”

Flow mechanisms in axial turbine rim sealing

“…Since 1994 a considerable number of experimental and CFD studies have been published and understanding has developed further. A particularly interesting development occurred in the early 2000's, with, for example, Cao et al [11] showing experimental evidence that large scale unsteady flow features dominated ingestion on a particular two stage axial turbine cavity. These rotating, unsteady flow structures were unrelated to blade passing.…”

“…For "short seals", such as those in figure 3, the surface areas in the seal may be sufficiently small for the surface drag on the rotor and stator to be negligible in the seal flow. Counter to this argument is the observation in, for example, references [11,24] that rotating cavity, seal and annulus flows may be subject to 3D rotating flow modes that significantly affect ingestion. For more extended seals involving overlapping rotor and stator parts the rotation and surface drag may also affect the flow in the seals as, for example, suggested by Graber et al and supported by computations for a chute rim seal in reference [25].…”

Effect of Bolts on Flow and Heat Transfer in a Rotor-Stator Disc Cavity

“…To understand the influence of mass flow rate, the baseline configuration analysis was repeated for a higher throughflow Reynolds number of C w =10 5 . Figure 17 shows the contours of instantaneous non-dimensional swirl, surface streamlines at x/s = 0.25 from disc surface and disc surface temperature.…”

“…For example, Cao et al [5] and Jakoby et al [6] have observed large scale flow structures in disc cavities with ingestion. These rotate at a lower speed than the disc.…”