Showing papers on "Tip clearance published in 1992"

Tip clearance control apparatus for a turbo-machine blade

Abstract: An apparatus is provided for controlling rotating blade tip clearance in a turbo-machine utilizing conical tipped blades. The apparatus comprises an approximately conical blade ring mounted for axially sliding displacement in the turbo-machine cylinder. The conical blade ring encircles the tips of the rotating blades and forms a blade tip clearance therebetween. The tip clearance is controlled during operation of the turbo-machine by axially displacing the conical blade ring. Piston cylinders, actuated by pressurized fluid extracted from the turbo-machine, are used to displace the blade ring. Springs, adapted to bias the blade ring into a position of increased tip clearance, oppose the piston cylinder so that failure of the piston cylinder will not result in a loss of tip clearance. A blade tip clearance sensor transmits information on the tip clearance to a controller that automatically adjusts the blade ring axial position to continuously maintain the optimum tip clearance by regulating the pressure of the fluid supplied to the piston cylinders.

Three-Dimensional Flow and Mixing in an Axial Flow Compressor With Different Rotor Tip Clearances

Abstract: The effect of difference in rotor tip clearance on the mean flow fields and unsteadiness and mixing across a stator blade row were investigated using hot-wire anemometry, pressure probes, flow visualization, and the ethylene tracer-gas technique on a single- stage axial flow compressor. The structure of the three-dimensional flow fields was discussed based on results of experiments using the 12-orientation single slanted hot- wire technique and spectrum analysis of velocity fluctuation

The Development of Axial Turbine Leakage Loss for Two Profiled Tip Geometries Using Linear Cascade Data

Abstract: To assess the possibility of tip clearance loss reduction and to explore the nature and origin of tip clearance loss, blade tip geometries which reduce the roughly 40% of total loss occurring within the gap were studied. The shapes investigated aimed at reducing or avoiding the gap separation bubble thought to contribute significantly to both internal gap loss and to the endwall mixing loss. It was found that radiusing and contouring the blade at gap inlet eliminated the separation bubble and reduced the internal gap loss but created a higher mixing loss to give almost unchanged overall loss coefficients when compared with the simple sharp edged flat tipped blade. The separation bubble does not therefore appear to influence the mixing loss. Using a method of assessing linear cascade experimental data as though it were a rotor with work transfer, one radiused geometry, contoured to shed radial flow into the gap and reduce the leakage mass flow, was found to have a significantly higher efficiency. This demonstrates the effectiveness of the data analysis method and that cascade loss coefficient alone or gap discharge coefficient cannot be used to accurately evaluate tip clearance performance. Contouring may ultimately lead to better rotor blade performances.Copyright © 1990 by ASME

Compressor bore cooling manifold

Abstract: To control disc temperature, provide blade tip clearance control, and purge the rotor bore of a high pressure compressor in a gas turbine engine, an axially elongated manifold is disposed coaxially in the rotor bore to distribute cooling air bleed from the compressor inlet airstream to selected cavities between successive rotor discs in amounts tailored to the particular cooling needs of the neighboring discs.

Three-dimensional Navier-Stokes heat transfer predictions for turbine blade rows

Abstract: Results are shown for a three-dimensional Navier-Stokes analysis of both the flow and the surface heat transfer for turbine applications. Heat transfer comparisons are made with the experimental shock-tunnel data of Dunn and Kim, and with the data of Blair for the rotor of the large scale rotating turbine. The analysis was done using the steady-state, three-dimensional, thin-layer Navier-Stokes code developed by Chima, which uses a multistage Runge-Kutta scheme with implicit residual smoothing. An algebraic mixing length turbulence model is used to calculate turbulent eddy viscosity. The variation in heat transfer due to variations in grid parameters is examined. The effects of rotation, tip clearance, and inlet boundary layer thickness variation on the predicted blade and endwall heat transfer are examined.

Capacitance-type blade-tip clearance measurement system using a dual amplifier with ramp/DC inputs and integration

Abstract: The analysis and prototype results for a dual-amplifier circuit for measuring blade-tip clearance in turbine engines are presented. The capacitance between the blade tip and mounted capacitance electrode within a guard ring of a probe forms one of the feedback elements of an operational amplifier (op amp). The differential equation governing the circuit taking into consideration the nonideal features of the op amp was formulated and solved for two types of inputs (ramp and DC) that are of interest for the application. Under certain time-dependent constraints, it is shown that (1) with a ramp input the circuit has an output voltage proportional to the static tip clearance capacitance, and (2) with a DC input, the output is proportional to the derivative of the clearance capacitance. and subsequent integration recovers the dynamic capacitance. The technique accommodates long cable lengths and environmentally induced changes in cable and probe parameters. System implementation for both static and dynamic measurements having the same high sensitivity is also presented. >

The Use of 3D Viscous Flow Calculations in the Design and Analysis of Industrial Centrifugal Compressors

Abstract: The 3D viscous codes of Denton and Dawes have been used to predict the flow field and performance of a back-swept industrial centrifugal impeller without an inducer (the Eckardt impeller “B”). The calculated flow field and performance agree very well with measurements at several operating points from surge to choke. Both codes predict that the suction surface flow near the impeller inlet is on the verge of separation at the design point. Calculations with tip clearance using the Dawes code predict a thin region of backflow in the clearance jet near the casing wall. The secondary flows arising from the meridional curvature in the impeller redistribute the losses generated on the blades and give rise to a spanwise stratification of the circumferentially mass-averaged losses. The resulting spanwise entropy gradient can be included in a throughflow calculation to improve the prediction of the meridional velocity distribution at impeller exit.

Apparatus to hold compressor or turbine blade during manufacture

Abstract: A turbine or compressor blade holding fixture and machining method contemplates the subassembly of all the blades upon the rotor of the compressor or turbine. Fixture rings along with radial biasing members in the form of annular o-rings are intersecured to opposite sides of the blades so as to radially position the latter in their normal "running position" while so mounted on the rotor of the wheel. In such condition all of the blades may be simultaneously machined such that the outer tips thereof lie on a true uniform, desired outer diameter to provide subsequently uniform tip clearance to the surrounding shroud when mounted in a gas turbine engine for operation.

Compressor of turbine blade manufacture

Abstract: A turbine or compressor blade holding fixture and machining method contemplates the subassembly of all the blades 20 upon the rotor 12 of the compressor or turbine. Fixture rings 30, 32 along with radial biasing members in the form of annular o-rings 40, 42, 44 are intersecured to opposite sides of the blades 20 so as to radially position the latter in their normal "running position" while so mounted on the rotor 12 of the wheel. In such condition all of the blades 20 may be simultaneously machined such that the outer tips 24 thereof lie on a true uniform, desired outer diameter to provide subsequently uniform tip clearance to the surrounding shroud when mounted in a gas turbine engine for operation.

The Measurement and Prediction of the Tip Clearance Flow in Linear Turbine Cascades

Abstract: This paper describes a simple two-dimensional model for the calculation of the leakage flow over the blade tips of axial turbines. The results obtained from calculations are compared with data obtained from experimental studies of two linear turbine cascades. One of these cascades has been investigated by the authors and previously unpublished experimental data is provided for comparison with the model. In each of the test cases examined, excellent agreement is obtained between the experimental and predicted data. Although ignored in the past, the importance of pressure gradients along the blade chord is highlighted as a major factor influencing the tip leakage flow.Copyright © 1992 by ASME

Aircraft gas turbine engine backbone deflection control

Abstract: A gas turbine engine backbone deflection control apparatus to counter the effects of backbone bending due to gust, thrust. and maneuver loads by introducing a controlled backbone counter-bending moment by applying controlled tensioning forces only between axially spaced apart frames connected by the backbone. One embodiment of the invention, for a high bypass ratio turbofan engine, provides a hydraulically powered actuator to produce tensioning forces in cables connected between a fan frame and a turbine frame and the actuator is controlled by the engines digital electronic control system using input signals generated by inlet moment load sensors and/or blade tip clearance sensors.

The effect of spatial wandering on experimental laser velocimeter measurements of the end-wall vortices in an axial-flow pump

Abstract: In a high Reynolds number axial-flow pump, laser velocimeter (LV) measurements were made to study the size and structure of the end-wall vortex. The time mean measurements show that the core size of the end-wall vortex increased with decreasing tip clearance, which is contrary to existing theory. Observations of cavitation in the vortex showed that the flow was unsteady. The vortices emanating from the smaller clearances were observed to wander or meander spatially and to develop kinks more than the vortices emanating from the larger tip clearances. This observed unsteadiness has a significant effect on the time mean size and velocity distribution of the vortex as measured with the LV employing the field point measurement technique. In order to obtain an estimate of the true size and velocity distribution, computational experiments were conducted which modelled a periodically wandering vortex and the LV measurement process. The computational and experimental results show good agreement, including a broadened and reduced tangential velocity distribution. In this paper, the end-wall vortex LV measurements are presented, and the method of analyzing the vortex wandering is described.

Tip Clearance Effect on Heat Transfer and Leakage Flows on the Shroud-Wall Surface in an Axial Flow Turbine

Abstract: An axial flow turbine for a turbocharger is used as a test turbine, and the local heat transfer coefficient on the surface of the shroud is measured under uniform heat flux conditions. The nature of the tip clearance flow on the shroud surface and a flow pattern in the downstream region of the rotor blades are studied, and measurements are obtained by using a hot-wire anemometer in combination with a periodic multisampling and an ensemble averaging technique. Data are obtained under on- and off-design conditions. The effects of inlet flow angle, rotational speed and tip clearance on the local heat transfer coefficient are elucidated. The mean heat transfer coefficient is correlated with the tip clearance, and the mean velocity is calculated by the velocity triangle method for approximation. A leakage flow region exists in the downstream direction beyond the middle of the wall surface opposite the rotor blade, and a leakage vortex is recognized at the suction side near the trailing edge. 16 refs.

Experimental Study on the Three Dimensional Flow Within a Compressor Cascade With Tip Clearance: Part I — Velocity and Pressure Fields

Abstract: Experimental results from a study of the 3-D flow in a linear compressor cascade with stationary endwall at design conditions are presented for tip clearance levels of 1.0, 2.0 and 3.3 percent of chord, compared with the no clearance case. In addition to five-hole probe measurements, extensive surface flow visualizations are conducted. It is observed that for the smaller clearance cases a weak horseshoe vortex forms in the front of the blade leading edge. At all the tip gap cases, a multiple tip vortex structure with three discrete vortices around the midchord is found. The tip leakage vortex core is well defined after the midchord but does not cover a significantly great area in traverse planes. The presence of the tip leakage vortex results in the passage vortex moving close to the endwall and to the suction side.Copyright © 1992 by ASME

The Effect of Compressor Rotor Tip Crops on Turboshaft Engine Performance

Abstract: The results from an experimental study into the effect of compressor rotor tip clearance changes on the steady-state performance and stability margins of a free-power turbine turboshaft engine are presented and discussed. This work was directed at the development of methods to diagnose engine condition from gas path measurements. It was found that the normal production suite of engine instrumentation was able to measure the deterioration in engine performance due to the implanted compressor degradation and the resultant deviations in the measured parameters from their respective nominal baselines do provide useful indicators of engine condition.Copyright © 1992 by ASME

A Computational Study of Tip Leakage Flow and Losses in a Linear Turbine Cascade

Abstract: : A computational study of 3-D flow in the VPI and SU tip leakage turbine cascade is used to show the level of modelling attainable now. Results for the overall flow development are compared with measurements of flow and losses at the exit of the tip leakage gap and downstream of the blade row. Mechanisms for the additional loss due to tip leakage are discussed. Consideration is given to areas where the modelling of fine scale flow structure may be improved. These include the flow in the tip clearance gap, flow in the tip leakage vortex, and flow separation at the trailing edge.

Electromechanical Measurement of Turbomachinery Blade Tip-to-Casing Running Clearance

Abstract: It is difficult to make a reliable measurement of running clearance in the hostile environment over the blading of modern gas turbines. When the engine manufacturers require the measurement to be made during tests lasting many hours, or even days, measurement system ruggedness and reliability are of primary importance.This paper describes how a second generation tip clearance measurement system of much reduced size and weight was developed. The reduction of size and weight facilitates the use of this measurement system for blade tip-to-casing measurements on all engine development tests from rig to flight worthy engines. During the course of commissioning, the measurement system was tested first in the laboratory, then on progressively more demanding test vehicles. The final test was on the high pressure turbine of a modern military full scale development single spool core. During the course of this test, the mean engine Turbine Entry Temperature through the blading over which clearance was measured, exceeded 1800 K and is typical of the applications for this second generation system.Copyright © 1992 by ASME

Investigation of Tip Clearance Phenomena in an Axial Compressor Cascade Using Euler and Navier-Stokes Procedures

Abstract: Three-dimensional Euler and Full Navier-Stokes computational procedures have been utilized to simulate the flow field in an axial compressor cascade with tip clearance. An embedded H-grid topology was utilized to resolve the flow physics in the tip gap region. The numerical procedure employed is a finite difference Runge-Kutta scheme. Available measurements of blade static pressure distributions along the blade span, dynamic pressure and flow angle in the cascade outlet region, and spanwise distributions of blade normal force coefficient and circumferentially averaged flow angle are used for comparison. Several parameters which were varied in the experimental investigations were also varied in the computational studies. Specifically, measurements were taken and computations were performed on the configuration with and without: tip clearance, the presence of an endwall, inlet endwall total pressure profiles and simulated relative casing rotation. Additionally, both Euler and Navier-Stokes computations were performed to investigate the relative performance of these approaches in reconciling the physical phenomena considered. Results indicate that the Navier-Stokes procedure, which utilizes a low Reynolds number k-e model, captures a variety of important physical phenomena associated with tip clearance flows with good accuracy. These include tip vortex strength and trajectory, blade loading near the tip, the interaction of the tip clearance flow with passage secondary flow and the effects of relative endwall motion. The Euler computation provides good but somewhat diminished accuracy in resolution of some of these clearance phenomena. It is concluded that the level of modelling embodied in the present approach is sufficient to extract much of the tip region flow field information useful to designers of turbomachinery.Copyright © 1992 by ASME

Tip clearance control apparatus

Abstract: In a gas turbine engine, conduit [90] delivers pressurized cooling air to a selected group of hollow [87,70,71] struts at a temperature sufficient to induce thermal contraction of the selected group of hollow struts, thereby opposing a downward shift in the rotor axis during high power engine operation, and maintaining a circumferentially uniform tip clearance. Air baffles disposed in the cooled struts ensure radially uniform thermal contraction and efficient heat transfer.

Shock Formation in Overexpanded Tip Leakage Flow

Abstract: Shock formation due to overexpansion of supersonic flow at the inlet to the tip clearance gap of a turbomachine has been studied. The flow was modelled on a water table using a sharp-edged rectangular channel. The flow exhibited an oblique hydraulic jump starting on the channel sidewall near the channel entrance. This flow was analyzed using hydraulic theory. The results suggest a model for the formation of the jump. The hydraulic analogy between free surface water flows and compressible gas flows is used to predict the location and strength of oblique shocks in analogous tip leakage flows. Features of the flow development are found to be similar to those of compressible flow in sharp-edged orifices. Possible implications of the results for high-temperature gas turbine design are considered.Copyright © 1992 by ASME

Stator-averaged, rotor blade-to-blade near-wall flow in a multistage axial compressor with tip clearance variation

Abstract: This paper describes the effect of tip clearance changes on the pressure at the case wall of a second-stage rotor. Wall shear distributions under the rotor tip are also presented. The results show low-pressure areas extending along the rotor suction side but lying away from the blade. Pressure contours indicate the tangential loading at the tip is lower than predicted by two-dimensional calculations; however, the predicted loading is observed between the lowest pressure's path in the passage and the blade pressure side

Clearance control assembly of turbine shroud

Abstract: PURPOSE: To provide a structure which holds adequate clearance according to temperature change and is excellent in maintainability, in relation to a turbine shroud structure for defining a turbine blade tip clearance of a gas turbine engine. CONSTITUTION: The clearances between an array of high pressure turbine blades and its surrounding high pressure turbine shroud as well as the clearances between an array of low pressure turbine blades and its associated low pressure turbine shroud are carefully controlled by a support structure which provides for evenly controlled circumferential cooling of the shroud support structure. Radial loads on the shroud support structure are reduced by counterbalancing loads imposed on the support structure by the shroud with predetermined pressure loads controlled and set through a series of cooling air cavities A, B, C. The high and low pressure turbine shroud segments 83, 85 are formed as integral segments 30. Forward and aft shroud hanger members 58, 60 interconnect the shroud with its support 44.

Experimental Study on the Three Dimensional Flow Within a Compressor Cascade With Tip Clearance: Part II — The Tip Leakage Vortex

Abstract: An analysis of the experimental data of a linear compressor cascade with tip clearance is presented with special attention to the development of the tip leakage vortex. A method for determining the tip vortex core size, centre position and vorticity or circulation from the measured data is proposed, based on the assumption of a circular tip vortex core. It is observed that the axial velocity profile passing through the tip vortex centre is wake-like. The vorticity of the tip vortex increases rapidly near the leading edge and reaches its highest values at a short distance downstream, from which it gradually decreases. In the whole evolution, its size is growing and its centre is moving away from both the suction surface and the endwall, approximately in a linear way.Copyright © 1992 by ASME

Prediction of Secondary Losses in Axial Compressors

Abstract: A large number of both published and own experimental data on secondary losses in straight compressor cascades and compressor blade rows has been reviewed. Published correlations for prediction of secondary losses have been compared to chosen experiments. Two cases of the blade and end-wall design have been investigated-blade with and without tip clearance. On the basis of experimental results, new improved correlations for secondary loss coefficient have been derived. These have been implemented in the program for characteristics computation of axial compressors and an improved agreement between predictions and experiments has been obtained.Copyright © 1992 by ASME

Experimental investigation of tip clearance noise in axial flow machines

Abstract: An experimental investigation is described to identify the aeroacoustic generation mechanism of the tip clearance noise of axial turbomachines. The tip clearance flow is a secondary flow through the radial gap between the blade tip and the casing wall which is driven by the pressure difference between suction side and pressure side of each blade. Tip clearance noise can be a significant source of noise when the tip clearance exceeds a certain limit. It is well known that a small tip clearance is beneficial for both the aerodynamic performance and the noise characteristics of axial flow machines. In this paper experimental results of an ongoing study into the nature of the tip clearance noise are presented. Also, some experimental obversations regarding a hysteresis-type behavior of the aerodynamic fan performance and rotating stall inception are reported.

Pressure Fluctuation on Casing Wall of Isolated Axial Compressor Rotors at Low Flow Rate

Abstract: The pressure fluctuations on the casing wall of two axial flow compressor rotors with various tip clearances have been analyzed by the use of two kinds of correlation functions. Behavior of the pressure fluctuation varies depending on tip clearance and blade solidity. In the case of small tip clearance, the nature of disturbances becomes random as the flow rate is reduced to a stall condition. For moderate tip clearance, coherent-structured disturbances appear intermittently at low flow rate. They appear more frequently as the solidity is increased and the flow rate becomes lower. For large tip clearance, the coherent structured disturbances exist even at considerably higher flow rates. Corresponding to these features there are peculiar patterns in the correlation designated as “phase-locked correlation function”.Copyright © 1992 by ASME

Navier-Stokes analysis of an oxidizer turbine blade with tip clearance

Abstract: The Gas Generator Oxidizer Turbine (GGOT) Blade is being analyzed by various investigators under the NASA MSFC sponsored Turbine Stage Technology Team design effort. The present work concentrates on the tip clearance region flow and associated losses; however, flow details for the passage region are also obtained in the simulations. The present calculations simulate the rotor blade row in a rotating reference frame with the appropriate coriolis and centrifugal acceleration terms included in the momentum equation. The upstream computational boundary is located about one axial chord from the blade leading edge. The boundary conditions at this location were determined by using a Euler analysis without the vanes to obtain approximately the same flow profiles at the rotor as were obtained with the Euler stage analysis including the vanes. Inflow boundary layer profiles are then constructed assuming the skin friction coefficient at both the hub and the casing. The downstream computational boundary is located about one axial chord from the blade trailing edge, and the circumferentially averaged static pressure at this location was also obtained from the Euler analysis. Results were obtained for the 3-D baseline GGOT geometry at the full scale design Reynolds number. Details of the clearance region flow behavior and blade pressure distributions were computed. The spanwise variation in blade loading distributions are shown, and circumferentially averaged spanwise distributions of total pressure, total temperature, Mach number, and flow angle are shown at several axial stations. The spanwise variation of relative total pressure loss shows a region of high loss in the region near the casing. Particle traces in the near tip region show vortical behavior of the fluid which passes through the clearance region and exits at the downstream edge of the gap.