Making Use of Labyrinth Interaction Flow

Abstract

It is the aim of this publication to attract the designers attention to the end wall flow interactions of shrouded high pressure turbines. One of the key issue for designing better turbines is the understanding of the flow interactions set up by the presence of labyrinth seals. Those interaction flows are carefully examined in this publication using the control volume analysis and the radial equilibrium of forces acting on streamlines. The consequences on secondary flow development and mixing losses are discussed and quantified. Out of this insight, design recommendations are derived, which attempt to make use of the nature of the labyrinth interaction flow. The open labyrinth cavities are classified in a systematic way. The aim of this approach is to work out the characteristic differences between hub and tip cavities and those having a leakage jet or sucking main flow fluid into the labyrinth. The influence on the main flow is discussed in terms of the incidence flow angle of downstream blade rows and the associated loss production mechanisms. The design strategies presented in this paper follow two paths: (a) Optimization of the mixing losses of the leakage jets at hub and tip is estimated to result in an efficiency increase of up to 0.2%. (b) The non-axisymmetric shaping of the labyrinth interaction flow path aims at the secondary flow control in downstream blade rows. This approach might contribute in the same magnitude of order as reduction in the mixing losses.

Analysis of the shroud leakage flow and mainflow interactions in high-pressure turbines using an unsteady computational fluid dynamics approach

“…The geometry configuration of CYLI_A shows a quite different blockage and flow path near the hub due to the sharp edge cut between the cavity itself and the main passage. Here the flow picture in the cavity resemble very closely what reported by Pfau et al [7] for a similar geometry, as shown comparing the right sketch included in Fig. 9.…”

“…They underlined the importance of considering unsteady measurement and simulations to obtain a more realistic representation of these effects. Pfau et al [7] concentrated their attention on the steady and unsteady flow interactions within large endwall cavities. They classified open cavities in a systematic way and proposed design modifications in order to make use of the labyrinth interaction flows to improve the overall performance of low aspect ratio shrouded turbines.…”

Comparative investigation of unsteady flow interactions in endwall regions of shrouded and unshrouded turbines

“…This causes flow separation at the stator blades and a highly unsteady flow field at the second stator exit. It should be noted that, about the subject of shroud cavity interactions in shrouded turbines, it was addressed the first time by Denton and Johnson [19]; however, it is only in recent years that this subject has become the focus of much researches [20].…”

Investigation on the unsteady pressure fluctuation characteristic in the blade tip seal of steam turbine based on spectrum

“…Wei et al [8] researched the influence of blade tip seal structure on the status of leakage vortex motion in the inlet cavity and outlet cavity of seal by the perspective way. Pfau et al [9] carried out the experimental Corresponding author; E-mail:clh320@126.com analysis on the interaction between the leakage flow and main flow in the passage of two-stage turbine, and attempted to look for the approaches reducing leakage losses and mixing losses. Gao et al [10] studied the influence of tip leakage flow on main flow, and suggested that the ring vortex in the honeycomb seal can significantly reduce the circumferential speed of leakage flow in the seal cavity, so the mixing losses is reduced.…”