Showing papers on "Axial compressor published in 1990"

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. © 1990 by ASME.

Magnetic resonance imaging and modeling of flow in hollow-fiber bioreactors

Abstract: Nuclear magnetic resonance flow imaging (MRFI) was used to measure fluid flow noninvasively in the extracapillary space (ECS) of a hollow-fiber bioreactor without cells. Agreement between these axial flow measurements in a single hollow-fiber module and predicted axial velocity contour plots at various image planes along the path length was good. Flow in a solid-wall tube (phantom) was first used to calibrate pixel intensities with axial velocities. Flow images at several locations along the permeable hollow fiber length were then obtained in order to observe the well-known leakage or Starling flow in the ECS. These quantitative spatially dependent velocity measurements were then compared to theoretically derived velocities obtained from a solution of Poisson's equation with a constant pressure gradient and no slip at the solid surfaces. A mathematical transformation was used to simplify the numerical methods. Leakage flow through the ECS of a multifiber bioreactor (40 fibers) was also measured by MRFI, illustrating the applicability of this method for optimizing operational procedures and design of membrane bioreactors and filtration devices.

Tip Leakage Flow in Axial Compressors

Abstract: Experimental measurements in a linear cascade with tip clearance are complemented by numerical solutions of the three-dimensional Navier-Stokes equations in an investigation of tip leakage flow. Measurements reveal that the clearance flow, which separates near the entry of the tip gap, remains unattached for the majority of the blade chord when the tip clearance is similar to that typical of a machine. The numerical predictions of leakage flow rate agree very well with measurements and detailed comparisons show that the mechanism of tip leakage is primarily inviscid. It is demonstrated by simple calculation that it is the static pressure field near the end of the blade which controls chordwise distribution of the flow across the tip. Although the presence of a vortex caused by the roll-up of the leakage flow may affect the local pressure field, the overall magnitude of the tip leakage flow remains strongly related to the aerodynamic loading of the blades.Copyright © 1990 by ASME

Counterflow single rotor turbojet and method

Abstract: A small gas turbine engine for generating thrust and shaft horsepower is provided. The engine is comprised in a flow series arrangement of an inlet, a diffuser, a single stage compressor, a fuel slinger combustor, a single stage turbine, and an exhaust nozzle. The compressor circumscribes the turbine and is mounted on the same rotating wheel so that the flow of air in the compressor is in the direction opposite to the direction of hot gas flow in the turbine. Accordingly, both the compressor and turbine are on the same side of the combustor and hence only a single bearing support structure is required.

Aircraft engine starter integrated boundary bleed system

Abstract: An aircraft gas turbine engine is provided with a compressed air supply system generally used for meeting customer or aircraft bleed air requirements. The compressed air supply system comprises an auxiliary compressor, a means for mechanically driving the system from a rotor of the gas turbine rotor, and a cycle varying means, such as a variable speed drive, for operating the auxiliary compressor cycle independently of the aircraft gas turbine engine compressor cycle. The preferred embodiment provides a means for bleeding boundary layer air off the nacelle or another part of the aircraft outer skin and using it as a source of air for the auxiliary compressor. One embodiment includes an air turbine on a common shaft with the auxiliary compressor and a means to direct an unused portion of the airflow form the auxiliary compressor to the air turbine to help power the auxiliary compressor and another embodiment includes a means to direct compressed startling air to the air turbine for on ground and in flight starting of the gas turbine engine through the variable speed drive and a mechanical linkage to the high rotor of the gas turbine engine.

Rotating Waves as a Stall Inception Indication in Axial Compressors

Abstract: Stall inception has been studied in two low speed compressors (a single-stage and a three-stage) and in a high speed three-stage compressor, using temporally and spatially resolved measurements. In all three machines, rotating stall was preceded by a period in which small amplitude waves were observed travelling around the circumference of the machine at a speed slightly less than the fully developed rotating stall cell speed. The waves evolved smoothly into rotating stall without sharp changes in phase or amplitude, implying that, in the machines tested, the prestall waves and the fully developed rotating stall are two stages of the same phenomenon. The growth rate of these disturbances was in accord with that predicted by current analytical models. The prestall waves were observed both with uniform and with distorted inflow, but were most readily discerned with uniform inflow. Engineering uses and limitations of these waves are discussed.Copyright © 1990 by ASME

Effects of Endwall Suction and Blowing on Compressor Stability Enhancement

Abstract: An experimental investigation was carried out to examine the effects on stall margin of flow injection into, and flow removal out of, the endwall region of an axial compressor blade row. A primary objective of the investigation was clarification of the mechanism by which casing treatment (which involves both removal and injection) suppresses stall in turbomachines. To simulate the relative motion between blade and treatment, the injection and removal took place through a slotted hub rotating beneath a cantilevered stator row. Overall performance data and detailed (time-averaged) flowfield measurements were obtained.Flow injection and removal both increased the stalling pressure rise, but neither was as effective as the wall treatment. Removal of high blockage flow is thus not the sole reason for the observed stall margin improvement in casing or hub treatment, as injection can also contribute significantly to stall suppression. The results also indicate that the increase in stall pressure rise with injection is linked to the streamwise momentum of the injected flow, and it is suggested that this should be the focus of further studies.Copyright © 1989 by ASME

Compressor Blade Boundary Layers: Part 2—Measurements With Incident Wakes

Abstract: This paper follows directly from Part 1 by the same authors and describes measurements of the boundary layer on a supercritical-type compressor blade with wakes from a simulated moving upstream blade row convected through the passage. (The blades and the test facilities together with the background are described in Part 1)

Unsteady Transition in an Axial-Flow Turbine: Part 1—Measurements on the Turbine Rotor

Abstract: Previously published measurements in a low-speed, single-stage, axial-flow turbine have been reanalyzed in the light of more recent understanding. This paper investigates the suction surface boundary layer transition process, using surface-distance time plots and boundary layer cross sections to demonstrate the unsteady and two-dimensional nature of the process

Recirculating rotary gas compressor

Abstract: A positive displacement, recirculating Roots-type rotary gas compressor which operates on the basis of flow work compression. The compressor includes a pair of large diameter recirculation conduits (24 and 26) which return compressed discharge gas to the compressor housing (14), where it is mixed with low pressure inlet gas, thereby minimizing adiabatic heating of the gas. The compressor includes a pair of involutely lobed impellers (10 and 12) and an associated port configuration which together result in uninterrupted flow of recirculation gas. The large diameter recirculation conduits equalize gas flow velocities within the compressor and minimize gas flow losses. The compressor is particularly suited to applications requiring sustained operation at higher gas compression ratios than have previously been feasible with rotary pumps, and is particularly applicable to refrigeration or other applications requiring condensation of a vapor.

Overall mass transfer in swirling decaying flow in annular electrochemical cells

Abstract: Mass transfer coefficients between an electrolyte solution and the inner cylinder of an annulus were determined experimentally, using the electrochemical technique, for both laminar and turbulent swirling flows of a liquid induced by means of a tangential inlet in the annular gap. The average mass transfer coefficients were determined as a function of the axial distance from the entrance, for various diameters of the inlet duct and thicknesses of the annular space, for a Reynolds number range of 100 to 5900. Enhancement of mass transfer up to 400% was achieved in comparison to that obtained in fully developed axial flow. Correlations of the experimental data, taking into account the geometrical and hydrodynamic parameters influencing the overall mass transfer, are presented.

Compressor Blade Boundary Layers: Part 1—Test Facility and Measurements With No Incident Wakes

Abstract: This paper and its companion, Part 2 by the same authors, describes an experiment to study the effect of the moving wakes on the boundary layer of a compressor blade. This paper describes the background and facility devised to introduce wakes together with results obtained on the blades in tests without the wakes present

Cooling system for a gas turbine

Abstract: A cooling system is disclosed including a drive shaft interconnecting a turbine rotor wheel with a compressor rotor wheel, a heat exchanger, and an auxiliary air compressor formed as part of the drive shaft which draws air from a portion of the compressor, through the heat exchanger and directs it onto portion of a gas turbine. The auxiliary air compressor may be a mixed-flow air compressor having a plurality of axial flow stages located upstream of a rotor portion with an impeller wheel to direct the cooling air onto portions of the gas turbine rotor and the stationary vanes. The heat exchanger may also be located externally of the gas turbine engine to improve the cooling of the cooling air before it is directed onto the gas turbine. It is envisioned that the system will be utilized with a gas turbine engine having a generally annular combustion chamber and that the auxiliary air compressor will be formed as part of the driving shaft interconnecting the gas turbine rotor wheel with the compressor rotor and be located within the space between the drive shaft and the interior of the combustion chamber. Thus, the rotation of the gas turbine rotor which drives the compressor rotor will also drive the rotating portion of the auxiliary, cooling air compressor.

Axial Flow Compressor Design Optimization: Part I—Pitchline Analysis and Multivariable Objective Function Influence

Abstract: The design of an axial flow compressor stage has been formulated as a nonlinear mathematical programming problem with the objective of minimizing the aerodynamic losses and the weight of the stage, while maximizing the compressor stall margin. Aerodynamic as well as mechanical constraints are considered in the problem formulation. A method of evaluating the objective function and constraints of the problem with a pitchline analysis is presented. The optimization problem is solved by using the penalty function method in which the Davidon-Fletcher-Powell variable metric minimization technique is employed. Designs involving the optimization of efficiency, weight of the stage, and stall margin are presented and the results discussed with particular reference to a multivariable objective function.

Flow in curved ducts. Part 2. Rotating ducts

Abstract: When a coiled tube is rotated about the coil axis, the effects of rotation interact with centrifugal and viscous effects to complicate the flow characteristics beyond those seen in stationary curved ducts. The phenomena encountered are examined for steady, fully developed Newtonian flow in circular tubes of small curvature. The governing equations are solved using orthogonal collocation, and the results presented cover both the nature of the flow and the bifurcation structure. When rotation is in the same direction as the axial flow imposed by a pressure gradient, the flow structure remains similar to that seen in stationary ducts, i.e. with two- or four-vortex secondary flows in addition to the axial flow. There are, however, quantitative changes, which are due to the Coriolis forces resulting from rotation. The bifurcation structure also shows only quantitative changes from that for stationary ducts at all values of Taylor number examined. More complex behaviour is possible when rotation opposes the flow due to the pressure gradient. In particular, the direction of the secondary flow may be reversed at higher rotational strengths, and the mechanism of the flow reversal is explored. The flow reversal occurs smoothly at low Taylor numbers, but at higher rotational strengths a cusp appears in the primary solution branch in the vicinity of the flow reversal.

Unsteady Transition in an Axial-Flow Turbine: Part 2—Cascade Measurements and Modeling

Abstract: This paper investigates the significance of the wake jet and the unsteady frequency parameter. Supporting experiments carried out in a linear cascade with varying inlet turbulence are described, together with a simple unsteady transition model explaining the features seen in the turbine

Bifurcation Analysis of Surge and Rotating Stall in Axial Flow Compressors

Abstract: In this paper, the surge and rotating stall post instability behaviors of axial flow compressors are investigated from a bifurcation-theoretic perspective. A sequence of local and global bifurcations of the nonlinear system dynamics is uncovered. This includes a previously unknown global bifurcation of a pair of large amplitude periodic solutions. Resulting from this bifurcation are a stable oscillation ("surge") and an unstable oscillation ("antisurge"). The latter oscillation is found to have a deciding significance regarding the particular post-instability behavior experienced by the compressor. These results are used to reconstruct Greitzer's (1976) findings regarding the manner in which post-instability behavior depends on system parameters. Moreover, the results provide significant new insight deemed valuable in the prediction, analysis and control of stall instabilities in gas turbine jet engines.

Application of recess vaned casing treatment to axial flow fans

Abstract: The effect of applying a vaned recessed casing treatment to a single stage axial flow fan has been investigated. The influence of the axial position of the recess relative to the rotor leading edge and other geometrical modifications of the vane passage have been examined. Significant improvements in stall margin were observed without (in some builds) loss in peak efficiency.Slow and fast frequency response yawmeter probes have been used in the study to examine both the steady flow conditions and the unsteady flow caused by rotating stall.Copyright © 1989 by ASME

Measured and Predicted Effects of Inlet Distortion on Axial Compressors

Abstract: Encouraging developments have recently been made both in the understanding and the modelling of compressor flowfields. This paper describes an experimental investigation undertaken to assess the validity of the assumptions made in the simple non-linear model for a bladerow operating in an unsteady or non-uniform flowfield. The results show that the basic fluid dynamics of the problem have been correctly modelled and that meaningful predictions may be made. The measurements also indicate that inlet guide vanes may be more sensitive to incidence variations than had been previously thought. The effects of inter-bladerow gaps are also discussed.Copyright © 1990 by ASME

Universal motor oilless air compressor

Abstract: An improved oilless air compressor which is driven by a high speed universal motor. A sprocket and belt driven pulley are arranged to reduce the compressor speed. A motor driven fan and baffles are provided to direct cooling air in predetermined sequences over the motor and compressor components to increase the operating life of the compressor components, to optimize the compressor efficiency and to reduce the temperature of the compressed air output. The compressor is provided with improved intake and exhaust valves.

Heat pump booster compressor arrangement

Abstract: A refrigeration and heat pump system of the refrigerant gas compression type having selectively operable first and second heat exchangers, respectively, in heat exchange relationship with a heat sink or source and a heating or cooling load, and with a an internal combustion engine driving a plurality of refrigerant gas compressors with more than one of the compressors selectively engagable when the system is operated in the heat pumping mode and the heat source is at low ambient temperature. The system includes at least one speed increaser connected between the plurality or compressors, so that the compressors operate at difference speeds although driven by the same engine.

Inlet Distortion Generated Periodic Aerodynamic Rotor Response

Abstract: Fundamental inlet distortion-generated rotor blade row unsteady aerodynamics, including the effects of both the detailed aerodynamic forcing function for the first time and steady loading are experimentally investigated in an extensively instrumented axial-flow research compressor

Inlet Skew and the Growth of Secondary Losses and Vorticity in a Turbine Cascade

Abstract: This paper presents results of an experimental investigation into the effects of inlet skew on the flow field of a large-scale axial flow turbine cascade. The results are presented in terms of the development of the streamwise vorticity since, in classical terms, the streamwise vorticity generates the transverse velocity components that cause the generation of the secondary losses

Stability of Flow Through Multistage Axial Compressors

Abstract: Copyright © 1989 by ASME. This paper describes measurements of the performance of a research stage operating in isolation and as part of a multistage compressor. It is shown that the stall point and the stalled performance of the stage are properties of the system in which it operates rather than a property of the stage itself. The consequences of this for the estimation of the stall point for compressors and compression systems are discussed. The support that the measurements give to assumptions made by mathematical models which use the concept of an 'underlying axisymmetric' characteristic are highlighted.

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.

Regenerative sorption compressor assembly

Abstract: A regenerative sorption compressor assembly for use in a sorption compressor/refrigerator system. The regenerative sorption compressor assembly of the present invention comprises a series of sorption compressor elements connected to a flowing loop of heat transport fluid. The compressor elements are heated and cooled by the heat transport fluid. At some point in the loop the fluid path is broken and the fluid is diverted to a heat source. At another point in the loop the fluid path is broken and the fluid is diverted to a heat sink. The points at which the heating and cooling flows are diverted are switched from compressor element to element in the direction of fluid flow at such a rate that the thermal capacity rate of the fluid in the heat transport loop relative to the moving switch point is equal and opposite to the thermal capacity rate of the compressor assembly relative to the switch point. The unique thermal recovery concept of the present invention provides a significant improvement in operating efficiency for a cryogenic refrigerator.