Showing papers on "Axial compressor published in 1986"

A Theory of Post-Stall Transients in Axial Compression Systems: Part I—Development of Equations

Abstract: An approximate theory is presented for post-stall transients in multistage axial compression systems. The theory leads to a set of three simultaneous nonlinear third-order partial differential equations for pressure rise, and average and disturbed values of flow coefficient, as functions of time and angle around the compressor. By a Galerkin procedure, angular dependence is averaged, and the equations become first order in time. These final equations are capable of describing the growth and possible decay of a rotating-stall cell during a compressor mass-flow transient. It is shown how rotating-stall-like and surgelike motions are coupled through these equations, and also how the instantaneous compressor pumping characteristic changes during the transient stall process.

A Theory of Post-Stall Transients in Axial Compression Systems: Part II—Application

Abstract: Using the theory developed in Part I, calculations have been carried out to show the evolution of the mass flow, pressure rise, and rotating-stall cell amplitude during compression system post-stall transients. In particular, it is shown that the unsteady growth or decay of the stall cell can have a significant effect on the instantaneous compressor pumping characteristic and hence on the overall system behavior. A limited parametric study is carried out to illustrate the impact of different system features on transient behavior. It is shown, for example, that the ultimate mode of system response, surge or stable rotating stall, depends not only on the B parameter, but also on the compressor length-to-radius ratio. Small values of this latter quantity tend to favor the occurrence of surge, as do large values of B. Based on the analytical and numerical results, several specific topics are suggested for future research on post-stall transients.

Predictions of Endwall Losses and Secondary Flows in Axial Flow Turbine Cascades

Abstract: The development of a semi-empirical model for estimating endwall losses is described in this paper. The model has been developed from improved understanding of complex endwall secondary flows, acquired through review of flow visualization and pressure loss data for axial flow turbomachine cascades. The flow visualization data together with detailed measurements of viscous flow development through cascades have permitted more realistic interpretation of the classical secondary flow theories for axial turbomachine cascades. The re-interpreted secondary flow theories together with integral boundary layer concepts are used to formulate a calculation procedure for predicting losses due to the endwall secondary flows. The proposed model is evaluated against data from published literature and improved agreement between the data and predictions is demonstrated.Copyright © 1986 by ASME

Behavior of Tip Leakage Flow Behind an Axial Compressor Rotor

Abstract: Performance testing and detailed flow measurements were made in an axial compressor rotor with various tip clearances. The experiments were conducted on the condition of the same incidence angle at midspan. Thus, the effect of tip clearance distinguished from that of incidence angle was investigated on the overall performance, work-done factor, blockage factor, and increases in displacement, momentum, and blade-force-deficit thicknesses of the casing wall boundary layer, The phase-locked flow patterns obtained by the multisampling technique show clear evidence of a leakage vortex core behind the rotor. Behavior of the leakage vortex was clarified for various tip clearances by examining loci of the vortex center, decay characteristics of the vorticity at the center, and the total amount of vorticity shed from the blade tip. These results were compared with the leakage vortex model presented by Lakshminarayana.

Compressors: Selection and Sizing

Abstract: Overview. Basic relationships. Reciprocating compressors. Rotary compressors. Centrifugal compressors. Axial compressors. Drivers. Accessories. Dynamics. Testing. Negotiation and purchasing. Reliability issues. Appendix. Index.

Gas turbine engine/load compressor power plants

Abstract: Single shaft, air breathing auxiliary power units having a single stage centrifugal load compressor driven by a gas turbine engine. The latter has a single stage centrifugal compressor and a single stage radial inflow turbine mounted in back-to-back relationship on the same shaft as the load compressor. Control systems for these auxiliary power units feature turbine exhaust gas temperature and turbine speed responsive fuel flow control; a bypass valve control which causes air to be dumped overboard when the pneumatic load demand drops to prevent load compressor surge; and an inlet guide vane control.

Three-Dimensional Flows and Loss Reduction in Axial Compressors

Abstract: Measurements have been performed in a low speed high reaction single stage axial compressor. Data obtained within and downstream of the rotor, when correlated with the results of other investigations, provide a link between the existence of suction surface-hub corner separations, their associated loss mechanisms and blade loading. Within the stator, it has been shown that introducing a small clearance between the stator blade and the stationary hub increases the efficiency of the stator compared to the case with no clearance. Oil flow visualisation indicated that the leakage reduced the extensive suction surface-hub corner separation that would otherwise exist. A tracer gas experiment showed that the large radial shifts of the surface streamlines indicated by the oil flow technique were only present close to the blade. The investigation demonstrates the possible advantages of including hub clearance in axial flow compressor stator blade rows.Copyright © 1986 by ASME

Thrust bearing loading arrangement for gas turbine engines

Abstract: A plurality of openings are provided in a stationary wall of a gas turbine engine aft of the compressor discharge to admit compressor discharge air into a sealed cavity formed between the stationary wall and the rotor of the gas turbine engine. A valve, biased to an open position, is associated with each of the openings so that under low speed conditions some of the compressor discharge air is admitted to the cavity to provide supplementary axial force on the rotor in one direction to prevent crossover under such conditions. Under higher speed conditions the increase in compressor discharge pressure overcomes the force biasing the valve to its open position, thereby causing the valve to close and terminate flow of compressor discharge air to the cavity, terminating the aforementioned supplementary axial force on the rotor. Each of the valves includes a housing surrounding the corresponding opening in the stationary wall and a valve piston within the housing is biased to an open position by open or more belleville springs positioned within the housing.

Laser Doppler Velocimeter Measurement in the Tip Region of a Compressor Rotor

Abstract: The axial and tangential velocity components near the tip region of a compressor rotor were measured by a laser Doppler velocimeter. The measurements were taken at 25 radial locations in the outer twenty percent of the blade span and at 10 axial locations upstream, inside and at the exit of the rotor. The results are interpreted to derive the behavior of the leakage flow, annulus wall boundary layer growth, inviscid effects and the rotor wake decay characteristics in the tip region. The inviscid and annulus wall boundary layer effects dominate up to quarter chord, beyond which the leakage phenomena has a major influence in altering the flow characteristics in the outer ten percent of the blade span. The annulus wall boundary layer undergoes drastic change through the passage. The velocity field measured near the leading edge reveals the effects of rapid acceleration near the suction surface and the stagnation point on the pressure surface.

Cooling air flow controlling apparatus for gas turbine

Abstract: Stator blades and rotor blades are cooled by discharge air discharged from an air compressor coupled directly with gas turbine. A signal of the compressor discharge pressure and a signal of turbine exhaust gas temperature are obtained, and cooling air flow is controlled based on these signals.

Modeling the 3-D Flow Effects on Deviation Angle for Axial Compressor Middle Stages

Abstract: A model of the spanwise variation of the three-dimensional flow effects on deviation is proposed for middle-stage rotors and stators. This variation is taken as the difference above or below that predicted by blade element theory at any spanwise location. It was found that the stator variation is strongly affected by the end-wall boundary-layer thickness as well as camber, solidity, and blade channel aspect ratio. Rotor variation was found to depend on end-wall boundary layer thickness and tip clearance normalized by blade span. If these parameters are known or can be calculated, the models provide a reasonable approximation to the spanwise variation of deviation for middle compressor stages operating at low to high subsonic inlet Mach numbers.

Dual entry radial turbine gas generator

Abstract: A compact, highly efficient single spool gas turbine gas generator uses a double-entry centrifugal first stage compressor, a single-entry centrifugal second stage compressor, and a radial inflow turbine to achieve an overall pressure ratio of greater than 15:1. The first stage pressure ratio is more than twice the second stage pressure ratio, and the first stage entrance Mach numbers are greater than about 1.4. The specific speed of each the compressors ranges from 0.65 to 0.85, and of the turbine from 0.50 to 0.75.

Axial flow blade wheel of a gas or steam driven turbine

Abstract: An axial blade wheel of a gas or steam-driven turbine comprising blades having substantially laminar boundary layer flow up to a point of maximum velocity on the upper surface of the blade, the upper surface of the blade being provided in a region downstream of the point of maximum velocity where the fluid flow velocity decreases with a spoiler edge of saw tooth profile which extends substantially over the entire blade length.

Turbine engine with induced pre-swirl at the compressor inlet.

Abstract: A jet flap construction for the compressor of an aircraft gas turbine engine provided with a bleed for bleeding air interstage of the compressor and communicating with the hollowed-out struts in the airflow path to the compressor. The hollow struts are each provided with one or more rows of discrete openings extending from the shroud to the hub on the strut to form an aligned series of jets for discharging the pressurized bleed air and forming a jet flap, thereby providing pre-swirl at the compressor inlet.

Unsteady flows in a single-stage transonic axial-flow fan stator row

Abstract: Measurements of the unsteady velocity field within the stator row of a transonic axial-flow fan were acquired using a laser anemometer. Measurements were obtained on axisymmetric surfaces located at 10 and 50 percent span from the shroud, with the fan operating at maximum efficiency at design speed. The ensemble-average and variance of the measured velocities are used to identify rotor-wake-generated (deterministic) unsteadiness and turbulence, respectively. Correlations of both deterministic and turbulent velocity fluctuations provide information on the characteristics of unsteady interactions within the stator row. These correlations are derived from the Navier-Stokes equation in a manner similar to deriving the Reynolds stress terms, whereby various averaging operators are used to average the aperiodic, deterministic, and turbulent velocity fluctuations which are known to be present in multistage turbomachines. The correlations of deterministic and turbulent velocity fluctuations throughout the axial fan stator row are presented. In particular, amplification and attenuation of both types of unsteadiness are shown to occur within the stator blade passage.

Rotor wake characteristics of a transonic axial-flow fan

Abstract: State of the art turbomachinery flow analysis codes are not capable of predicting the viscous flow features within turbomachinery blade wakes. Until efficient 3D viscous flow analysis codes become a reality there is therefore a need for models which can describe the generation and transport of blade wakes and the mixing process within the wake. To address the need for experimental data to support the development of such models, high response pressure measurements and laser anemometer velocity measurements were obtained in the wake of a transonic axial flow fan rotor.

Effects of finite geometry on the wave number of Taylor-vortex flow.

Abstract: Richard Heinrichs, Guenter Ahlers, and David S. Cannell Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106 (Received 16 January 1986) We report measurements of the axial variation of the wave number q of Taylor-vortex flow in a system with aspect ratio 17 <. L <. 25 containing ten vortex pairs between rigid nonrotating ends. Near the critical Reynolds number Rc, qis very nonuniform when its average value ^differs significantly from its critical value qc. For sufficiently small \\q — qc\\, the finite geometry eliminates the Eckhaus instability. Our results agree quantitatively with solutions of the Ginzburg-Landau equation.

Stator Endwall Leading-Edge Sweep and Hub Shroud Influence on Compressor Performance

Abstract: Etude experimentale de l'utilisation de la courbure du bord d'attaque du stator pour ameliorer les performances d'un compresseur a ecoulement axial. Examen de l'aerodynamique de trois conditions de moyeu de stator (diametre interieur)

Manifold arrangement for isolating a non-operating compressor

Abstract: In a system with parallel connected compressors, a suction and discharge manifold arrangement for isolating an inactive compressor from the rest of the operating system. A check valve in the discharge line of the compressor prevents fluid flow back into the discharge port from a common system discharge line when the compressor is de-energized. A normally closed, pressure actuated valve in the suction line of each compressor prevents fluid from flowing through the compressor suction port when the compressor is inactive. The valve is connected to the compressor's discharge line, and opens in response to the discharge pressure developed when the compressor begins to operate. Pressure and oil level equalizing lines interconnect the compressor oil sumps, conveying oil between compressors and equalizing pressure in the oil sumps.

Apparatus for mounting, and for maintaining running clearance in, a double entry radial compressor

Abstract: A gas generator having a double entry low pressure centrifugal compressor, a single entry high pressure centrifugal compressor and a radial inflow turbine positioned coaxially and coupled for interdependent rotation by a single shaft assembly for the double entry compressor mounted to the generator frame using a plurality of rigid hollow cross-over ducts which also carry diffused compressed air to the high pressure compressor, where the single shaft assembly uses two shaft portions connected by an expansible coupling having a helical spline torque transmitting device to allow the double entry compressor rotor to "follow" compressor housing axial position changer and to maintain a close running clearance despite thermal expansion in the structure between the low pressure (LP) and high pressure (HP) compressor portions of the gas generator.

Unsteady design-point flow phenomena in transonic compressors

Abstract: High-frequency response probes which had previously been used exclusively in the MIT Blowndown Facility were successfully employed in two conventional steady state axial flow compressor facilities to investigate the unsteady flowfields of highly loaded transonic compressors at design point operation. Laser anemometry measurements taken simultaneously with the high response data were also analyzed. The time averaged high response data of static and total pressure agreed quite well with the conventional steady state instrumentation except for flow angle which showed a large spread in values at all radii regardless of the type of instrumentation used. In addition, the time resolved measurements confirmed earlier test results obtained in the MIT Blowdown Facility for the same compressor. The results of these tests have further revealed that the flowfields of highly loaded transonic compressors are heavily influenced by unsteady flow phenomena. The high response measurements exhibited large variations in the blade to blade flow and in the blade passage flow. The observed unsteadiness in the blade wakes is explained in terms of the rotor blades' shed vorticity in periodic vortex streets. The wakes were modeled as two-dimensional vortex streets with finite size cores. The model fit the data quite well as it was able to reproduce the average wake shape and bi-modal probability density distributions seen in the laser anemometry data. The presence of vortex streets in the blade wakes also explains the large blade to blade fluctuations seen by the high response probes which is simply due to the intermittent sampling of the vortex street as it is swept past a stationary probe.

Stall transients of axial compression systems with inlet distortion

Abstract: A previously derived system of differential equations, based on fluid mechanics, is extended to provide a theory to predict how rotating stall or surge will develop in an axial compression system under combined influences of inlet distortion and throttle ramping. Results are relevant to the problem of stagnation stall of gas turbines. It is found that stall margin is improved by large aerodynamic lag in the compressor. Both stall and recovery transients are considered. A distinction between axisymmetric and in-rotating-stall compressor performance characteristics leads to a concept of rotating-stall stability that explains the appearance of classic stall at low stage loading and the hysteresis associated with rotating stall. The influences of various system parameters are systematically explored, and the large B parameter, tall compressor characteristic diagram, and rapid throttle closure are all found to favor surge, while large distortion and small shut-off head relative to peak pressure rise both favor rotating stall. When surge occurs, rotating stall is usually also present.

Reverse flow in multistage axial compressors

Abstract: This paper reports an experimental study of multistage axial compressor operation under reverse-flow conditions. The experiments were performed on a high hub-tip ratio, three-stage, low aspect ratio compressor. Unstalled and stalled performance characteristics are presented for two builds with different blade-stagger angles. A new finding is the demonstration of a flow-mode transition from large-scale asymmetry (rotating stall) to blade-to-blad e periodic ("annulus stall") at a low reverse-flow coefficient, with a consequent discontinuous drop in the pressure-rise characteristic. The annulus-stall flow regime was examined using high-response measurements of all three velocity components and pressure. These blade-passage-resolved measurements provide the first detailed kinematic picture of the flowfield structure that exists in multistage axial compressors during reverse-flow operation. The experimental results reveal that the flowfield is strongly three-dimensional and show close similarities between the structure of the reverse flow and the rotating-stall cell flowfields.

Redistribution of an inlet temperature distortion in an axial flow turbine stage

Abstract: The results of an experimental program aimed at determining the extent of the redistribution of an inlet temperature distortion in an axial flow turbine stage are presented. The program was conducted in a large-scale, low-speed, single-stage turbine where air, seeded with CO2, was introduced at one circumferential location upstream of the inlet guide vane. The migration of the seeded air through the turbine was determined by sensing CO2 concentration inside the stage. A temperature distortion was introduced by heating the seeded air. The CO2 concentration contours measured downstream of the vane showed h'ttle change with heating, indicating that the vane flowfield was relatively unaffected by the introduction of the temperature distortion. However, the CO2 contours observed on the rotor airfoil surfaces for the case with inlet heating indicated segregation of hot and cold gas with the higher temperature gas migrating to the pressure side and the lower temperature gas migrating to the suction side. Significant increases in rotor secondary flow were also observed. Two separate physical mechanisms are postulated to explain the observed experimental trends. Calculations performed by using a three-dimensional Euler solver show qualitative agreement with the experimental data.