Showing papers on "Tip clearance published in 1989"

The measurement and formation of tip clearance loss

Abstract: The detailed development of tip clearance loss from the leading to trailing edge of a linear turbine cascade was measured and the contributions made by mixing, internal gap shear flow, and endwall/secondary flow were identified, separated, and quantified for the first time

Structure of Tip Clearance Flow in an Isolated Axial Compressor Rotor

Abstract: Ensemble-averaged and phase-locked flow patterns in various tip clearances of two axial compressor rotors were obtained by aperiodic multisampling technique with a hot wire in the clearance and with a high-response pressure sensor on the casing wall. A leakage flow region distinct from a throughflow region exists at every clearance. In the case of a small tip clearance, the leakage jet flow interacts violently with the throughflow near the leading edge, and a rolling-up leakage vortex decays downstream. As the clearance increases, a stronger leakage vortex comes into existence at a more downstream location, and a reverse flow due to the vortex grows noticeably. A scraping vortex is recognized at the pressure side near the trailing edge only for the small clearance. A horseshoe vortex appears in the upstream half of the through flow region for every tip clearance. The solidity does not affect the flow pattern substantially except for the interaction of the leakage vortex with the adjacent blade and wake.

Endwall Flow/Loss Mechanisms in a Linear Turbine Cascade With Blade Tip Clearance

Abstract: This paper discusses the mechanisms of three-dimensional flows and of the associated losses occurring near the tip endwall region of a linear turbine cascade with tip clearance. The clearance gap sizes and the cascade incidences were chosen as the most important variables affecting the mechanisms

Stall Inception in Axial Compressors

Abstract: Detailed measurements have been made of the transient stalling process in an axial compressor stage. The stage is of high hub-casing ratio and stall is initiated in the rotor. If the rotor tip clearance is small stall inception occurs at the hub, but at clearances typical for a multistage compressor the inception is at the tip. The crucial quantity in both cases is the blockage caused by the endwall boundary layer. Prior to stall disturbances rotate around the inlet flow in sympathy with rotating variations in the endwall blockage; these can persist for some time prior to stall, rising and falling in amplitude before the final increase which occurs as the compressor stalls.Copyright © 1989 by ASME

Effects of tip clearance and fin density on the performance of heat sinks for VLSI packages

Abstract: Motivated by the high heat dissipation requirements of the advanced VLSI packages, experiments were performed with several heat sinks to study their heat transfer characteristics. The thermal resistances and pressure drops of the heat sinks were measured for fin densities of 1.3, 4.6, and 5.6 fins/cm and tip clearances varying from 0 to 2 cm. The mass flow rate varied from 0.01 to 0.1 kg/s. For a fixed mass flow rate and zero tip clearance, the 1.3-fins/cm heat sink dissipated four times more heat than a heat sink without fins, and the 5.6-fins/cm heat sink dissipated seven times more. Accompanying this increased heat transfer, however, is an increase in pressure drop. With an increase in tip clearance, the pressure drop penalty is reduced, but the heat transfer gain is also lower. This information is presented for different fin densities and tip clearances and should be useful to packaging engineers for the optimal design of high-density finned heat sinks. >

Turbine blade clearance controller

Abstract: A control system (30) for measuring the clearance ''x'' between the tip (26) of a blade (24) and wall (28) in a turbine engine (8). A series of probes (32, 32' and 32N) located in the wall (28) each have a reference orifice (52) and a sensing orifice (54). Fluid from a source flows through the reference orifices (52) into the turbine engine. This fluid flow is substantially unrestricted and as a result a fluid pressure P?2? is established in a reference chamber (44). Fluid flow from the sensing orifice (54) is restricted by the relationship of the tip (26) of each blade (24) and as a result fluid pressure P2' is created in chamber (48). A multiplexer (62) sequentially provides transducer (92 and 94) with fluid pressure P2 from the reference chamber (44) and P2' from sensing chamber (48). The transducers (92 and 94) convert the pneumatic signals into electrical signals which are supplied to a computer (116). The computer (116) supplies a control member (118) with an operational signal to allow cooling air to flow to housing (10) to maintain a desired tip clearance ''x'' for the blades of the turbine.

Moving blade tip clearance measurement apparatus and method with moveable lens

Abstract: A laser-optical apparatus for measuring blade tip clearance, e.g. of a compressor or gas turbine, uses a laser beam, fiber optics, a light probe and electrical circuits (14, 25) for processing data from the probe, and includes a light probe (16) having a lens (17) for making parallel a light beam from the optical fiber cable (15) for illumination, a half-mirror (18) for separating illuminating light and reflected light, a movable lens (19) for adjusting focus of the light beam on the object (12), an object lens (21), and a lens (22) for collected reflected light from half-mirror (18) and directing it to an entrance to the optical fiber cable (24) which transmits received light to the light reception circuit (25). The method for measuring blade tip clearance includes focusing a parallel light beam from a laser source (14, 15) through a half-mirror (18), adjustable lens (19) and object lens (21) onto an object (12), adjusting the focus by oscillating movement of the adjustable lens, detecting the reflected light received, and determining the tip clearance from the position of the adjustable lens at the time the reflected light is at a maximum value.

A Comparison Between the Design Point and Near Stall Performance of an Axial Compressor

Abstract: Detailed measurements have been made within an axial compressor operating both at design point and near stall. Rotor tip clearance was found to control the performance of the machine by influencing the flow within the rotor blade passages. This was not found to be the case in the stator blade row, where hub clearance was introduced beneath the blade tips. Although the passage flow was observed to be altered dramatically, no significant changes were apparent in the overall pressure rise or stall point.Small tip clearances in the rotor blade row resulted in the formation of corner separations at the hub, where the blade loading was highest. More representative clearances resulted in blockage at the tip due to the increased tip clearance flow. The effects which have been observed emphasize both the three dimensional nature of the flow within compressor blade passages, and the importance of the flow in the endwall regions in determining the overall compressor performance.Copyright © 1989 by ASME

An Investigation of End-Wall Vortex Cavitation in a High Reynolds Number Axial-Flow Pump

Abstract: : Relative motion of a turbomachinery blade row and the casing requires finite clearance between the rotor tips and the end-wall to avoid rubbing. Presence of this gap, relative motion of the blade tip and the end-wall, and pressure difference across the blade give rise to tip clearance flow which causes many adverse effects, including end-wall vortex cavitation. The vortex is formed by interaction of the clearance flow with the through flow on the suction side of the blade. This report formulates a correlation of the appropriate variables which predict the inception of end-wall vortex cavitation using the following approach: 1) identification of necessary parameters and relationships; 2) experimental measurements of the parameters in the High Reynolds Number Pump facility, a 42-inch diameter pump specifically designed for this purpose; 3) formulation of the correlation model from relationships among the measured variables; and 4) verification of the model with existing databases. The resulting model provides guidance to turbomachinery designers. The model of end- wall vortex cavitation successfully correlates the subject data existing databases. An optimum tip clearance has been theoretically identified. The correlation model contains the boundary layer, lift coefficient, tip clearance, vortex core size, and tip geometry as input variables. Submodels have been developed for the core radius and tip lift coefficient as a function of tip clearance. Laser velocimeter measurements show that additional circulation is shed into the tip vortex from the suction side trailing edge. Water tunnels.

Rotor blade tip clearance setting in gas turbine engines

Abstract: A turbine rotor stage has at least one blade 24 tipped with abrasive material which extends to a diameter greater than the diameter of the remaining blades 22 and which is capable of cutting a running groove in an internal ceramic liner 34 on the turbine casing 32. A method of setting a clearance gap G comprises overspeeding the rotor assembly by a predetermined RPM and at a temperature such that the tips of the cutting blades 24 cut into the liner and thereby set a clearance gap for the remaining blades. The remaining blades 22 may be ground to a uniform height when the rotor assembly is assembled without the slightly longer cutting blades. The abrasive tips may comprise crystals of boron nitride carried in a non-oxidisable matrix.

Secondary flow due to the tip clearance at the exit of centrifugal impellers.

Abstract: The velocity distribution is measured at the exit of two different types of unshrouded centrifugal impellers under four different tip clearance conditions each, one with twenty radial blades and inducers and the other with sixteen backward-leaning blades. The secondary flow induced by the tip leakage is similar in both impellers, and the underturning near the blade tip due to the stationary shroud is reduced significantly with the increase of tip clearance. The local change of angular momentum due to the tip clearance is related to the flow rate ratio of leakage-flow and through-flow, and an almost proportional relationship between them is found. Despite a similar secondary flow in both impellers, the input power is hardly changed in the radial blades impeller and is decreased in the backward-leaning blades impeller by the increase of tip clearance.

遠心羽根車の流動に関する研究 : 第1報,半開放形羽根車の翼間流れ計測

Abstract: Flow measurements were made in an unshrouded centrifugal impeller running at 1000 rpm. The impeller has 10 blades which are two-dimensional and radial at the outlet. for a flow rate in the shockless inlet to the blade, the relative velocities and the reduced static pressures were measured on nice cross-sectional planes within the rotating impeller passage, using a five-hole pressure probe fixed on the impeller-hub-wall. The rotary stagnation pressures were calculated from the measured values of the relative velocities and the reduced static pressures. In the mid-passage of the impeller, the wake due to the effects of the turbulent mixing, the Coriolis force, the curvature of the passage, the tip clearance flow and the friction on the casing wall, is shown about mid-position between the suction and pressure surface near the casing. The wake region increases on the suction surface at the outlet of the impeller, because of the turbulent mixing due to the uniformity of the pressure.

Effects of Tip Clearance of Nozzle Vanes on Performance of Radial Turbine Rotor

Abstract: In radial turbines with variable nozzles, the flow downstream of the nozzles could be distorted by the leakage flow through the tip-clearance of the upstream nozzle vanes. To investigate the effects of flow distortion on the performance of turbine rotors, two rotors with different number of blades were tested for three types of distorted velocity distributions at the rotor inlet. In the case of the 20 blade rotor with moderate blade loading, the flow distortion at the rotor inlet had negligible effect on the rotor characteristics, and the measured data on the turbine performances agreed well with a prediction. Predictions were made with a conventional one-dimensional flow model applied to the rotor flow while a two-layer flow model was applied to the flow in the nozzle with clearance. In the case of the 10 blade rotor with heavy blade loading, however, the rotor performance was found to be sensitive to the inlet flow distortion and was considerably lower than the prediction.Copyright © 1989 by ASME

Effect of blade tip configuration on tip clearance loss of a centrifugal impeller

Abstract: According to the theory presented by the authors, the tip clearance loss of an unshrouded centrifugal impeller mainly consists of two kinds of loss; one is the drag due to the leakage flow through the blade tip clearance and the other is the pressure loss to support the fluid in the thin annular clearance space between the shroud and the blade tip against the pressure gradient in the meridional plane without blades. The former is proportional to the leakage flow or the contraction coefficient of leakage flow. The authors have conducted performance tests using an impeller with sixteen backward-leaning blades in three configurations of the blade tip: round edge, sharp square edge and edge with an end-plate. The experimental tip clearance effects can be predicted by the theory assuming reasonable contraction coefficients. They are 0.91, 0.73 and 0.53 for the respective tip configurations. The impeller efficiency is improved by about 1.5 point by reducing the contraction coefficient from 0.91 to 0.53 providing that the tip clearance ratio at the exit of impeller is 0.1. More improvement is expected for an impeller with highly loaded blades where the leakage loss shares the major part of the tip clearance loss.Copyright © 1989 by ASME

The Vortex-Filament Nature of Reverse Flow on the Verge of Rotating Stall

Abstract: On the verge of rotating stall, very orderly reverse flow forms from the outlet of the rotor/impeller along the casing/shroud toward the inlet in axial/centrifugal compressors (Koch, 1970; Haupt, et al., 1987). The experiment on a centrifugal compressor reveals furthermore that the reverse flow is composed of stable spiral vortex filaments. Their vorticity can be transferred to the inlet tip vortex, known as prerotation. The behavior of these vortex filaments is examined based on the fundamental research work on rotating bodies available in the literature. This result shows that the vortex filaments are composed of Taylor’s vortex pairs, but with unequal vortex strengths within the pair. They form the transition range from a laminar to a turbulent three-dimensional boundary layer with a very steep tangential velocity profile. This profile is associated with the appearance of a toroidal ring vortex in the rotor/impeller, acting as a recirculatig secondary flow. It can be further shown from the analysis of the extensive literature that the orderly path of the reverse flow is enabled by the cessation of the leakage flow of the rotor tip clearance. The reason for this is that the growing tangential flow field extends beyond the rotor tip up to the close proximity of the endwall, so that the tip clearance is blocked.

Fan device installed onto heat exchanger

Abstract: PURPOSE: To reduce the noise due to the disturbance of air stream by setting the blade top edge of a cooling fan in inclination for the axis direction and setting a fan shroud oppositely to the blade top edge through a nearly uniform tip clearance CONSTITUTION: As for the radiator 2 of an engine 1, the blade top edge of a cooling fan 8 is not parallel to a shaft 7 and on one supposed conical surface and has a tilt angle (α) for the direction of the shaft 7 Further, also a fan shroud 4 is set oppositely to the blade top edge through a nearly uniform tip clearance (t) on the outer peripheral part 9 of the fan 8 Therefore, the angle θ' which is formed between the outer peripheral part 9 of the fan 8 and the connection part 5 of the fan shroud 4 through the contraction of the outer peripheries of the radiator 2 and the fan 8 reduces by the tilt angle (α) Since the angle formed by the above-described both is small, because of the inclination of the fan shroud 4 in two states, the generation of noise due to the disturbance of air stream can be reduced COPYRIGHT: (C)1991,JPO&Japio

Internal gear rotor for pump or motor

Abstract: PURPOSE:To set a tip clearance between two rotors to zero and thereby improve the discharge capacity of a pump by using metal or ceramics for an inner rotor and elastically deformable resin for an outer rotor, respectively. CONSTITUTION:Two rotors 1, 2, whose tooth number difference is one each, are combined together and thereby an internal gear rotor 4, producing a pumping chamber 3 between tooth surfaces of these rotors, is constituted. The inner rotor 1 may be any mechanical works of metal as iron or the like, but a part of ferrous sintered metal is better in view of manufacturability. As for material for the outer rotor 2, acrylonitrile-butadiene-styrene (ABS) resin may be used, but an engineering plastic resistible to a temperature of more than 100 deg.C is preferable to that. With this, harmonizability in engagement is very good and, what is more, sliding resistance can be made smaller.

Influence of the Radial Component of Total Pressure Gradient on Tip Clearance Secondary Flow in Axial Compressors

Abstract: The interaction of tip leakage and the rotor passage secondary flow is examined. An analytical expression is developed which relates radial components of the total pressure gradient near the wall to the passage geometry, tip speed, skew, throughflow and wall skin friction coefficient. This expression provides a correlation with the differences observed in the passage secondary velocity patterns associated with tip clearance gaps in experimental compressors. The analysis is qualitatively supported by comparison with secondary flow velocity measurements from a small sample of published test data.Copyright © 1989 by ASME

Three-dimensional multigrid Navier-Stokes computations for turbomachinery applications

Abstract: The fully three-dimensional, time-dependent compressible Navier-Stokes equations in cylindrical coordinates are presently used, in conjunction with the multistage Runge-Kutta numerical integration scheme for solution of the governing flow equations, to simulate complex flowfields within turbomechanical components whose pertinent effects encompass those of viscosity, compressibility, blade rotation, and tip clearance. Computed results are presented for selected cascades, emphasizing the code's capabilities in the accurate prediction of such features as airfoil loadings, exit flow angles, shocks, and secondary flows. Computations for several test cases have been performed on a Cray-YMP, using nearly 90,000 grid points.

Effect of Blade Tip Configuration on Tip Clearance Loss of a Centrifugal Impeller

Abstract: According to the theory presented by the authors, the tip clearance loss of an unshrouded centrifugal impeller mainly consists of two kinds of loss; one is the drag due to the leakage flow through the blade tip clearance and the other is the pressure loss to support the fluid in the thin annular clearance space between the shroud and the blade tip against the pressure gradient in the meridional plane without blades. The former is proportional to the leakage flow or the contraction coefficient of leakage flow. The authors have conducted performance tests using an impeller with sixteen backward-leaning blades in three configurations of the blade tip: round edge, sharp square edge and edge with an end-plate. The experimental tip clearance effects can be predicted by the theory assuming reasonable contraction coefficients. They are 0.91, 0.73 and 0.53 for the respective tip configurations. The impeller efficiency is improved by about 1.5 point by reducing the contraction coefficient from 0.91 to 0.53 providing that the tip clearance ratio at the exit of impeller is 0.1. More improvement is expected for an impeller with highly loaded blades where the leakage loss shares the major part of the tip clearance loss.Copyright © 1989 by ASME

Review and evaluation of a turbomachinery throughflow finite element code.

Abstract: : The finite element code Q3DFLO 81 was evaluated to determine its suitability for use in a program to investigate axial compressor tip clearance effects. The code was first applied to Dring's fully comprehensive benchmark data set in order to validate the numerical modelling free of experimental uncertainties. It was then applied to the Naval Postgraduate School axial research compressor with which tip clearance effects were to be investigated experimentally. The evaluation identified both limitations in the code and limitations in the data which could be obtained in the experiment. It was recommended that provision be made to accommodate peripherally non-uniform flow effects (blockage) in the throughflow code calculation, and that provision be made to obtain adequate peripheral flow surveys in the experiment. Throughflow analysis, Blockage, Rotor tip clearance studies, Axial flow compressor, Hydraulic equipment. (jes)

Theoretical study on the unsteady aerodynamic characteristics of an oscillating cascade with tip clearance. (In the case of loaded cascade)

Abstract: In this paper, an analytical method developed previously for oscillating cascades was refined to deal with cascades with steady aerodynamic loading. The unsteady aerodynamic force acting on the linear oscillating cascades with tip clearance was calculated numerically be means of a vortex lattice method. Tip vortices were assumed to consist of linear vortex segments, and their paths were determined on the basis of experimental results measured using a 50hole Pilot tube. The calculated damping forces showed good agreement with the corresponding experimental data. The effect of tip clearances on the flutter boundary was also investigated, and it was revealed that the cascade flutter was suppressed owing to the presence of tip clearances. When the blade oscillation was destabilised, it was found that the unsteady aerodynamic force became the existing force at the blade-tip side sooner than at the hub side.

Multi-Stage Compressor Airfoil Aerodynamics: Part I-Airfoil Potential Flow Analysis

Abstract: Potential-flow analysis of the airfoils in an axial flow compressor is an important element of the aerodynamic design. This type of analysis is used both as a tool in the optimization of new airfoil contours and also to predict the design and off-design performance of existing airfoil contours. The analysis is virtually exact in steady, twodimensional applications. The present paper assesses the ability of potential flow theory to predict the pressure distributions on rotor and stator airfoils in the unsteady, three-dimensional environment of a two-stage axial compressor. The paper demonstrates that while excellent agreement between the measured and computed results could be obtained in the core flow region, the unsteadiness and three-dimensionality produced by corner stall and rotor tip leakage can cause significant differences to occur. Nomenclature B = airfoil true chord Bx = airfoil axial chord CP = pressure coefficient (P-PToA) /Qum Cx = axial component of velocity cl = rotor tip clearance N = rotational speed P = pressure Q = incident dynamic pressure Qum = dynamic pressure based on midspan wheel speed: 1/2 pUlm r = radial distance Um = wheel speed at midspan x = axial distance a. = absolute yaw angle from axial (3 = relative yaw angle, from axial 6 circumferential coordiante 9 = flow yaw angle, from axial = flow pitch angle, from axial $ = flow coefficient, Cx/Um p = fluid density T = cascade pitch

Thermal response type automatic control mount for proximity sensor

Abstract: PURPOSE: To conserve a clearance between a blade tip and a sensor by providing a thermally expansive member at a turbine blade tip clearance. CONSTITUTION: A clearance sensor 48 is provided at a position oppositing to a moving turbine 30 of a flow guide for a turbine. A coil spring 22 is engaged with one side of a flange 18 of the sensor 48 and a thermally expansive member 20 is engaged at the other side. Under a room temperature, a clearance between an edge of the blade is g and the sensor but when a turbine is started then heated, the clearance g is decreased by expansion of the blade. Further, when a sensor mount structural body 12 is expanded, the space intends to increase, but the clearance g is conserved to a small fixed valve by expansion of the thermally expansive member 20 and moving of a sensor face 48a toward the blade.

Maintaining blade tip clearance in a gas turbine

Abstract: A method for periodically restoring the blade tip to annular seal clearance in a gas turbine engine (10) includes incrementing (42a, 42b) the flow of external cooling air responsive only to an accumulated engine use parameter (58).

Secondary Flow due to the Tip Clearance at the Exit of Centrifugal Impellers

Abstract: The velocity distribution was measured at the exit of two different types of unshrouded centrifugal impellers under four different tip clearance conditions each; one with twenty radial blades and inducers and the other with sixteen backward-leaning blades. And the effect of tip clearance on input power was also measured. By increasing the tip clearance, the input power was hardly changed in the radial blade impeller and was reduced in the backward-leaning blade impeller. The velocity distribution normalized by the passage width between hub and shroud wall was hardly changed at the exit of the radial blade impeller by varying the tip clearance, on the other hand, the relative flow angle was reduced significantly and monotonously by an increase of tip clearance in the backward-leaning blade impeller. The change in input power due to the tip clearance was clearly related to the change of flow pattern at the exit of impeller due to the secondary flow, which is most likely caused by the component, normal to the blade, of the shear force to support the fluid in the clearance space against the pressure gradient in the meridional plane without blades.Copyright © 1989 by ASME