A. B. Turner

Performance of Radial Clearance Rim Seals in Upstream and Downstream Rotor–Stator Wheelspaces

A new experimental facility for the investigation of rim sealing is described and measurements are presented for two representative radial clearance seals with a nominally axisymmetric external flow. One radial seal has an upward rotor lip and is upstream of the rotor while the other has an upward stator lip and is downstream of the rotor. Measurements include surface pressures, tangential velocities in the core region of the disc cavity flow, and traverses of gas concentration in the cavity showing the distribution of mainstream ingestion. Tests were conducted at rotational Reynolds numbers up to 3 × 106 with nominal seal clearance to radius ratios in the range 0.002 to 0.01. For the radial seals a differential pressure criterion is found to overestimate the minimum sealing flow. Tangential velocity measurements in the wheelspace are in excellent agreement with other workers measurements and with theoretical predictions.

Rim sealing of rotor-stator wheelspaces in the absence of external flow

Sealing of the cavity formed between a rotating disc and a stator with an asymmetric external flow is considered. In these circumstances circumferential pressure variations in the external flow and the pumping action of the disc may draw fluid into the cavity. Gas concentration measurements, showing this effect, have been obtained from a model experiment with a simple axial clearance seal. In the experiment, guide vanes, fitted upstream of the rim seal, generate an asymmetric external flow. The measurements are shown to be in reasonable agreement with three-dimensional computational fluid dynamics (CFD) calculations and are also compared with more elementary models. The CFD results give further insight into the effects of ingestion within the cavity.

Computational and Mathematical Modeling of Turbine Rim Seal Ingestion

Understanding and modelling of main annulus gas ingestion through turbine rim seals is considered and advanced in this paper. Unsteady 3-dimensional computational fluid dynamics (CFD) calculations and results from a more elementary model are presented and compared with experimental data previously published by Hills et al (1997). The most complete CFD model presented includes both stator and rotor in the main annulus and the inter-disc cavity. The k-e model of turbulence with standard wall function approximations is assumed in the model which was constructed in a commercial CFD code employing a pressure correction solution algorithm. It is shown that considerable care is needed to ensure convergence of the CFD model to a periodic solution. Compared to previous models, results from the CFD model show encouraging agreement with pressure and gas concentration measurements. The annulus gas ingestion is shown to result from a combination of the stationary and rotating circumferential pressure asymmetries in the annulus. Inertial effects associated with the circumferential velocity component of the flow have an important effect on the degree of ingestion. The elementary model used is an extension of earlier models based on orifice theory applied locally around the rim seal circumference. The new model includes a term accounting for inertial effects. Some good qualitative and fair quantitative agreement with data is shown. Copyright

Measurement and Analysis of Ingestion Through a Turbine Rim Seal

Experimental measurements from a new single stage turbine are presented. The turbine hits 26 vanes and 59 rotating blades with a design point stage expansion ratio of 2.5 and vane exit Mach number of 0.96. A variable sealing flow is supplied to the disk cavity upstream of the rotor and then enters the annulus through a simple axial clearance seal situated on the hub between the stator and rotor. Measurements at the annulus hub wall just downstream of the vanes show the degree of circumferential pressure variation. Further pressure measurements in the disk cavity indicate the strength of the swirling flow in the cavity, and show the effects of mainstream gas ingestion at low sealing flows. Ingestion is further quantified through seeding of the sealing air with nitrous oxide or carbon dioxide and measurement of gas concentrations in the cavity. Interpretation of the measurements is aided by steady and unsteady computational fluid dynamics solutions, and comparison with an elementary model of ingestion.

Rim sealing of rotor-stator wheelspaces in the presence of external flow

Sealing of the cavity formed between a rotating disc and a stator with an asymmetric external flow is considered. In these circumstances circumferential pressure variations in the external flow and the pumping action of the disc may draw fluid into the cavity. Gas concentration measurements, showing this effect, have been obtained from a model experiment with a simple axial clearance seal. In the experiment, guide vanes, fitted upstream of the rim seal, generate an asymmetric external flow. The measurements are shown to be in reasonable agreement with three-dimensional computational fluid dynamics (CFD) calculations and are also compared with more elementary models. The CFD results give further insight into the effects of ingestion within the cavity.

Casing Treatment and Blade-Tip Configuration Effects on Controlled Gas Turbine Blade Tip/Shroud Rubs at Engine Conditions

Experimental results obtained for an Inconel ® compressor blade rubbing bare-steel and treated casings at engine speed are described. Since 2002 a number of experiments were conducted to generate a broad database for tip rubs, the Rotor-Blade Rub database obtained using the unique experimental facility at the The Ohio State University Gas Turbine Laboratory. As of 2007, there are seven completed groups of measurements in the database. Among them a number of blade-tip geometries and casing surface treatments have been investigated. The purpose of this paper is to provide a detailed interpretation of this database. Load cell, strain, temperature, and accelerometer measurements are discussed and then applied to analyze the interactions resulting from progressive and sudden incursions of varying severity, defined by incursion depths ranging from 13 μm to 762 μm (from 0.0005 in. to 0.030 in.). The influence of blade-tip speed on these measurements is described. The results presented describe the dynamics of rotor and casing vibro-impact response at representative operational speeds similar to those experienced in flight. Force components at the blade tip in the axial and circumferential directions are presented for rub incursions ranging in depth from very light (13 μm) to severe (406 μm). Trends of variation are observed during metal-to-metal and metal-to-abradable contacts for two airfoil tip shapes and tip speeds 390 m/s (1280 ft/s) and 180 m/s (590 ft/s). The nonlinear nature of the rub phenomena reported in earlier work is confirmed. In progressing from light rubs to higher incursion, the maximum incurred circumferential load increases significantly while the maximum incurred axial load increases much less. The manner in which casing surface treatment affects the loads is presented. Concurrently, the stress magnification on the rubbing blade at root midchord, at tip leading edge, and at tip trailing edge is discussed. Computational models to analyze the nonlinear dynamic response of a rotating beam with periodic pulse loading at the free-end are currently under development and are noted.

HEAT TRANSFER IN HIGH-PRESSURE COMPRESSOR GAS TURBINE INTERNAL AIR SYSTEMS: A ROTATING DISC-CONE CAVITY WITH AXIAL THROUGHFLOW

This article reports on heat transfer measurements made on a rotating test rig representing the internal disc-cone cavity of a gas turbine high-pressure (H.P.) compressor stack. Tests were carried out for a range of flow rates and rotational speeds at engine representative nondimensional conditions. The rig also had a central drive shaft, which could rotate in the same direction as the discs, contrarotate relative to the discs, or remain static. Measurements of heat transfer were obtained from a conduction solution method using measured surface temperatures as boundary conditions. Results from the outer surface of the cone are in reasonable agreement with theoretical predictions for the heat transfer from a free cone in turbulent flow. The heat transfer measurements from the inner surface of the cone reveal two regimes of heat transfer: one governed by rotation, the other by action of the throughflow. In the rotationally dominated regime, the heat transfer from the inner surface of the cone is higher for a co-rotating shaft than for either a static or contra-rotating shaft. In the throughflow-dominated regime the heat transfer shows little consistent dependence on the direction of shaft rotation. Tests carried out at different values of surface-to-fluid temperature difference add support to the hypothesis that in the rotationally dominated regime the heat transfer occurs through a process of free convection, where the buoyancy force is induced by rotation. The heat transfer from the disc is significantly lower than that from the inner surface of the cone and more or less insensitive to the sense of shaft rotation. The disc average Nusselt numbers show similar behavior to those from the inner surface of the cone and suggest that the disc heat transfer too is governed either by rotationally induced buoyancy or by the axial throughflow.This article reports on heat transfer measurements made on a rotating test rig representing the internal disc-cone cavity of a gas turbine high-pressure (H.P.) compressor stack. Tests were carried out for a range of flow rates and rotational speeds at engine representative nondimensional conditions. The rig also had a central drive shaft, which could rotate in the same direction as the discs, contrarotate relative to the discs, or remain static. Measurements of heat transfer were obtained from a conduction solution method using measured surface temperatures as boundary conditions. Results from the outer surface of the cone are in reasonable agreement with theoretical predictions for the heat transfer from a free cone in turbulent flow. The heat transfer measurements from the inner surface of the cone reveal two regimes of heat transfer: one governed by rotation, the other by action of the throughflow. In the rotationally dominated regime, the heat transfer from the inner surface of the cone is higher for ...

Discharge Coefficients for Flow Through Holes Normal to a Rotating Shaft

A possible design for a more compact gas turbine engine uses contra-rotating high pressure (HP) and intermediate pressure (IP) turbine discs. Cooling air for the IP turbine stages is taken from the compressor and transferred to the turbine stage via holes in the drive shaft. The aim of this work was to investigate the discharge coefficient characteristics of the holes in this rotating shaft, and, in particular, to ascertain whether the sense of rotation of the shaft with respect to the discs affected these significantly. This paper reports mostly on experimental measurements of the discharge coefficients. Some CFD modelling of this flow was carried out and this has helped to explain the experimental work. The experimental results show the effects on the discharge coefficient of rotational speed, flow rate, and co- and contra-rotations of the shaft relative to the discs. The measured values of the discharge coefficient are compared with established experimental data for non-rotating holes in the presence of a cross-flow. For stationary shaft and discs, co-rotation of the shaft and discs and differential rotation with the disc speed less than the shaft (in the same rotational direction), the discharge coefficients are in reasonable agreement with these data. For differential rotation (including contra-rotation) with the disc speed greater than the shaft, there is a significant decrease in discharge coefficient.

Aerodynamics of Turbine Rim-Seal Ingestion

This paper describes the theoretical modelling of the flow in a rotor-stator wheelspace with ingestion through the rim-seal. The predictions are compared with experimental measurements of pressure taken for an axial clearance rim-seal downstream of a set of nozzle guide vanes. The mainstream pressure asymmetry caused by the guide vanes was measured in the absence of coolant flow. Using this data, three-dimensional CFD calculations were carried out, providing both predictions of the cavity pressures and insight into the flow mechanisms involved. The CFD predictions gave good agreement with experiment at low coolant flow rates. However, at high coolant flow rates, disagreement with the experimental results is evident, suggesting that the interaction between the coolant flow and the mainstream flow through the nozzle guide vanes could no longer be ignored.Copyright

Measurement and Analysis of Flow in a Pre-Swirled Cooling Air Delivery System

Measurements and analysis for a pre-swirl cooling air delivery system are reported here. The experimental rig used is representative of aero-engine conditions, having 18 pre-swirl nozzles, 72 receiver holes, capable of speeds up to 11 000 rpm, and giving differences between total temperature upstream of the pre-swirl nozzles and relative total temperature measured in the receiver holes of up to 26K. Pressure and temperature measurements are reported. An elementary model is developed for calculation of the cooling air delivery temperature. This accounts for the pre-swirl nozzle velocity coefficient, moments on the stationary and rotating surfaces in the pre-swirl chamber, and flows through the inner and outer seals to the chamber. The model is shown to correlate the measurements well for a range of disc speeds and pre-swirl velocity to disc speed ratios.Copyright