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Title: Modeling shrouded stator cavity flows in axial-flow compressors

Abstract

Experiments and computational analyses were completed to understand the nature of shrouded stator cavity flows. From this understanding, a one-dimensional model of the flow through shrouded stator cavities was developed. This model estimates the leakage mass flow, temperature rise, and angular momentum increase through the cavity, given geometry parameters and the flow conditions at the interface between the cavity and primary flow path. This cavity model consists of two components, one that estimates the flow characteristics through the labyrinth seals and the other that predicts the transfer of momentum due to windage. A description of the one-dimensional model is given. The incorporation and use of the one-dimensional model in a multistage compressor primary flow analysis tool is described. The combination of this model and the primary flow solver was used to reliably simulate the significant impact on performance of the increase of hub seal leakage in a twelve-stage axial-flow compressor. Observed higher temperatures of the hub region fluid, different stage matching, and lower overall efficiencies and core flow than expected could be correctly linked to increased hub seal clearance with this new technique. The importance of including these leakage flows in compressor simulations is shown.

Authors:
; ;
Publication Date:
Research Org.:
Rolls-Royce Allison, Indianapolis, IN (US)
OSTI Identifier:
20086913
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Turbomachinery; Journal Volume: 122; Journal Issue: 1; Conference: 44th International Gas Turbine and Aeroengine Congress and Exhibition, Indianapolis, IN (US), 06/07/1999--06/10/1999; Other Information: PBD: Jan 2000
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; 42 ENGINEERING; 33 ADVANCED PROPULSION SYSTEMS; GAS COMPRESSORS; GAS FLOW; STATORS; MATHEMATICAL MODELS

Citation Formats

Wellborn, S.R., Tolchinsky, I., and Okiishi, T.H.. Modeling shrouded stator cavity flows in axial-flow compressors. United States: N. p., 2000. Web. doi:10.1115/1.555427.
Wellborn, S.R., Tolchinsky, I., & Okiishi, T.H.. Modeling shrouded stator cavity flows in axial-flow compressors. United States. doi:10.1115/1.555427.
Wellborn, S.R., Tolchinsky, I., and Okiishi, T.H.. 2000. "Modeling shrouded stator cavity flows in axial-flow compressors". United States. doi:10.1115/1.555427.
@article{osti_20086913,
title = {Modeling shrouded stator cavity flows in axial-flow compressors},
author = {Wellborn, S.R. and Tolchinsky, I. and Okiishi, T.H.},
abstractNote = {Experiments and computational analyses were completed to understand the nature of shrouded stator cavity flows. From this understanding, a one-dimensional model of the flow through shrouded stator cavities was developed. This model estimates the leakage mass flow, temperature rise, and angular momentum increase through the cavity, given geometry parameters and the flow conditions at the interface between the cavity and primary flow path. This cavity model consists of two components, one that estimates the flow characteristics through the labyrinth seals and the other that predicts the transfer of momentum due to windage. A description of the one-dimensional model is given. The incorporation and use of the one-dimensional model in a multistage compressor primary flow analysis tool is described. The combination of this model and the primary flow solver was used to reliably simulate the significant impact on performance of the increase of hub seal leakage in a twelve-stage axial-flow compressor. Observed higher temperatures of the hub region fluid, different stage matching, and lower overall efficiencies and core flow than expected could be correctly linked to increased hub seal clearance with this new technique. The importance of including these leakage flows in compressor simulations is shown.},
doi = {10.1115/1.555427},
journal = {Journal of Turbomachinery},
number = 1,
volume = 122,
place = {United States},
year = 2000,
month = 1
}
  • Experiments were performed on a low-speed multistage axial-flow compressor to assess the effects of shrouded stator cavity flows on aerodynamic performance. Five configurations, which involved systematic changes in seal-tooth leakage rates and/or elimination of the shrouded stator cavities, were tested. Rig data indicate increasing seal-tooth leakage substantially degraded compressor performance. For every 1 percent increase in seal-tooth clearance-to-span ratio, the decrease in pressure rise was 3 percent and the reduction in efficiency was 1 point. These observed performance penalties are comparable to those commonly reported for rotor and cantilevered stator tip clearance variations. The performance degradation observed with increased leakagemore » was brought about in two distinct ways. First, increasing seal-tooth leakage directly spoiled the near-hub performance of the stator row in which leakage occurred. Second, the altered stator exit flow conditions, caused by increased leakage, impaired the performance of the next downstream stage by decreasing the work input of the rotor and increasing total pressure loss of the stator. These trends caused the performance of downstream stages to deteriorate progressively. Numerical simulations of the test rig stator flow field were also conducted to help resolve important fluid mechanic details associated with the interaction between the primary and cavity flows. Simulation results show that fluid originating in the upstream cavity collected on the stator suction surface when the cavity tangential momentum was low and on the pressure side when it was high. The convection of cavity fluid to the suction surface was a mechanism that reduced stator performance when leakage increased.« less
  • Unlike the free disk in which heat transfer is primarily affected by rotational speed, heat transfer in rotor-stator systems is influenced by the operating conditions as well as system geometry. In a rotor-stator system with no radial shroud, commonly referred to as an open rotor-stator, Kreith et al. (1959, 1963) and Metzger (1970) demonstrated that the presence of the stator influences heat transfer from the disk at axial gap spacings less than 10 percent of the disk diameter. These studies also examined the effects that forced coolant flow introduced at the hub of the system has on the average heatmore » transfer rate. As an extension of these studies, more recent evaluations by Metzger et al. (1979, 1991) and Popiel and Boguslawski (1986) have examined the effects of varying the location and rate of forced coolant flow. 10 refs., 4 figs.« less
  • Detailed measurements of the flow field in the tip region of an axial flow compressor rotor were carried out using a rotating five-hole probe. The axial, tangential, and radial components of relative velocity, as well as the static and stagnation pressures, were obtained at two axial locations, one at the rotor trailing edge, the other downstream of the rotor. The measurements were taken up to about 26 percent of the blade span from the tip region, which involves the interaction of the tip leakage flow, the annulus wall boundary layer and the blade wake. The experimental data show that themore » leakage jet does not roll up into a vortex. The leakage jet exiting from the tip gap is of high velocity and mixes quickly with the mainstream, producing intense shearing and flow separation. There are substantial differences in the structure of tip clearance observed in cascades and rotors.« less
  • Detailed measurements have been performed in a subsonic, axial-flow turbine stage to investigate the structure of the secondary flow field and the loss generation. The data include the static pressure distribution on the rotor blade passage surfaces and radial-circumferential measurements of the rotor exit flow field using three-dimensional hot-wire and pneumatic probes. The flow field at the rotor outlet is derived from unsteady hot-wire measurements with high temporal and spatial resolution. The paper presents the formation of the tip clearance vortex and the passage vortices, which are strongly influenced by the spanwise nonuniform stator outlet flow. Taking the experimental valuesmore » for the unsteady flow velocities and turbulence properties, the effect of the periodic stator wakes on the rotor flow is discussed.« less
  • Using a two-dimensional compressible flow representation of axial compressor dynamics, a control-theoretic input-output model is derived, which is of general utility in rotating stall/surge active control studies. The derivation presented here begins with a review of the fluid dynamic model, which is a two-dimensional stage stacking technique that accounts for blade row pressure rise, loss, and deviation as well as blade row and interblade row compressible flow. This model is extended to include the effects of the upstream and downstream geometry and boundary conditions, and then manipulated into a transfer function form that dynamically relates actuator motion to sensor measurements.more » Key relationships in this input-output form are then approximated using rational polynomials. Further manipulation yields an approximate model in standard form for studying active control of rotating stall and surge. As an example of high current relevance, the transfer function from an array of jet actuators to an array of static pressure sensors is derived. Numerical examples are also presented, including a demonstration of the importance of proper choice of sensor and actuator locations, as well as a comparison between sensor types. Under a variety of conditions, it was found that sensor locations near the front of the compressor or in the downstream gap are consistently the best choices, based on a quadratic optimization criterion and a specific three-stage compressor model. The modeling and evaluation procedures presented here are a first step toward a rigorous approach to the design of active control systems for high-speed axial compressors.« less