Showing papers on "Axial compressor published in 1980"

Review—Axial Compressor Stall Phenomena

Abstract: Stall in compressors can be associated with the initiation of several types of fluid dynamic instabilities. These instabilities and the different phenomena, surge and rotating stall, which result from them, are discussed in this paper. Assessment is made of the various methods of predicting the onset of compressor and/or compression system instability, such as empirical correlations, linearized stability analyses, and numerical unsteady flow calculation procedures. Factors which affect the compressor stall point, in particular inlet flow distortion, are reviewed, and the techniques which are used to predict the loss in stall margin due to these factors are described. The influence of rotor casing treatment (grooves) on increasing compressor flow range is examined. Compressor and compression system behavior subsequent to the onset of stall is surveyed, with particular reference to the problem of engine recovery from a stalled condition. The distinction between surge and rotating stall is emphasized because of the very different consequences on recoverability. The structure of the compressor flow field during rotating stall is examined, and the prediction of compressor performance in rotating stall, including stall/unstall hysteresis, is described.

Velocity measurements inside a rotating cylindrical cavity with a radial outflow of fluid

Abstract: Flow visualization and laser-doppler anemometry have been used to determine the flow structure and measure the velocity distribution inside a rotating cylindrical cavity with an outer to inner radius ratio of 10, and an axial spacing to inner radius ratio of 2·67. A flow structure comprising an inner layer, Ekman layers, an outer layer and an interior potential core has been confirmed for the cases where the inlet air enters the cavity either axially, through a central hole, or radially, through a central gauze tube, and leaves radially through a series of holes in the peripheral shroud. Velocity measurements in the laminar Ekman layers agree well with the ‘modified linear theory’, and long-and short-wavelength disturbances (which have been reported by other experimenters) have been observed on the Ekman layers when the radial Reynolds number exceeds a critical value. The phenomenon of reverse flow in the Ekman layers and the possibility of ingress of external fluid through the holes in the shroud have also been observed.

The Influence of the Blading Surface Roughness on the Aerodynamic Behavior and Characteristic of an Axial Compressor

Abstract: The conversion of energy in an axial compressor is influenced in great measure by the surface quality of the blading. To achieve low flow losses, the roughness values of the blade surface must be below certain limits. However, the blade surface, which is hydraulically smooth on commissioning of the machine, is in many cases attacked by dirt, corrosion and erosion during operation. For investigation of the influence of the surface quality on the efficiency, flow rate, pressure ratio, and the shifting of the characteristic curves, systematic measurements were taken on a three-stage axial compressor with smooth and uniformly rough blading. The roughness was produced by applying loose emery grain of different grades.

Experimental and Analytical Investigation of the Effects of Reynolds Number and Blade Surface Roughness on Multistage Axial Flow Compressors

Abstract: The general effect of Reynolds Number on axial flow compressors operating over a sufficiently wide range is described and illustrated by experimental data for four multistage axial compressors. The wide operating range of military aircraft engines leads in the back stages of high pressure ratio compression systems to three distinctly different regimes of operation, characterized by the boundary layer conditions of the cascade flow: • laminar separation, • turbulent attached flow with hydraulically smooth blade surface, • turbulent attached flow with hydraulically rough blade surface. Two “critical” Reynolds Numbers are defined, the “lower critical Reynolds Number” below which laminar separation occurs with a definite steepening of the efficiency/Reynolds Number relation and an “upper critical Reynolds Number” above which the blade surface behaves hydraulically rough, resulting in an efficiency independant of Reynolds Number. The permissible blade surface roughness for hydraulically smooth boundary layer conditions in modern high pressure ratio compression systems is derived from experimental data achieved with blades produced by grinding, electrochemical machining and forging. A correlation between the effect of technical roughness and sand type roughness is given. The potential loss of efficiency in the back end of compression systems due to excessive blade roughness is derived from experimental results. The repeatedly experienced different sensitivity of front and back stages towards laminar separation in the low Reynolds Number regime is explained by boundary layer calculations as a Mach Number effect on blade pressure distribution, i.e. transonic versus subsonic flow.

Laser anemometer measurements in a transonic axial flow compressor rotor

Abstract: A laser anomometer system employing an efficient data acquisition technique has been used to make measurements upstream, within, and downstream of the compressor rotor. A fluorescent dye technique allowed measurements within endwall boundary layers. Adjustable laser beam orientation minimized shadowed regions and enabled radial velocity measurements outside of the blade row. The flow phenomena investigated include flow variations from passage to passage, the rotor shock system, three-dimensional flows in the blade wake, and the development of the outer endwall boundary layer. Laser anemometer measurements are compared to a numerical solution of the streamfunction equations and to measurements made with conventional instrumentation.

Mean velocity and decay characteristics of the guidevane and stator blade wake of an axial flow compressor

Abstract: Pure tone noise, blade row vibrations, and aerodynamic losses are phenomena which are influenced by stator and IGV (inlet guide vane) blade wake production, decay, and interaction in an axial-flow compressor. The objective of this investigation is to develop a better understanding of the nature of stator and IGV blade wakes that are influenced by the presence of centrifugal forces due to flow curvature. A single sensor hot wire probe was employed to determine the three mean velocity components of stator and IGV wakes of a single stage compressor. These wake profiles indicated a varying decay rate of the tangential and axial wake velocity components and a wake profile similarity. An analysis, which predicts this trend, has been developed. The radial velocities are found to be appreciable in both IGV and the stator wakes.

Heat pump operated by wind or other power means

Abstract: A heating and/or cooling system comprising a windmill for driving a first refrigerant compressor in parallel with a second refrigerant compressor driven by an electric motor or other power means. The second compressor operates the system when the wind velocity is low. When the wind velocity becomes high enough, the refrigerant pressure created by the wind driven compressor, is used to automatically shut off power to the second compressor. The wind driven compressor then takes over the function of the second compressor.

Performance of single-stage axial-flow transonic compressor with rotor and stator aspect ratios of 1.19 and 1.26 respectively, and with design pressure ratio of 2.05

Abstract: The overall and blade-element performances of a low-aspect-ratio transonic compressor stage are presented over the stable operating flow range for speeds from 50 to 100 percent of design. At design speed the rotor and stage achieved peak efficiencies of 0.876 and 0.840 at pressure ratios of 2.056 and 2.000, respectively. The stage stall margin at design speed was 10 percent.

Modulated clearance control for an axial flow rotary machine

Abstract: OF THE DISCLOSURE A structure and method for providing cooling fluids from a compression section to a turbine section of an axially flow rotary machine is disclosed. Various construction details and steps of the method enable the machine to minimize the effect that un-scheduled variations in the temperature of the cooling fluids have on operating clearances in the turbine section. These unscheduled variations may result from changes in ambient temperature and component deterior-ation. An internal cooling fluid from the discharge region of the rearmost compressor is used to modulate the flow of a second fluid impinged on the exterior of the outer case for controlling the clearance between an array of rotor blades and a coolable stator shroud spaced radially outwardly of the rotor blades. In one embodiment, a valve for modulating the flow of the second fluid has at least one thermostatic bi-metallic spring for transducing a change in temperature into a displacement. The displacement changes the flow area Af between a valve head and a conical seat in the conduit for the second fluid through the valve.

Airfoil shape for arrays of airfoils

Abstract: An Airfoil Shape for Arrays of Transonic Airfoils Abstract A flow directing assembly 14 having an airfoil section or shape 28 of the type adapted for use in an axial flow gas turbine engine is disclosed. The cambered meanline MCL of the airfoil shape is formed of a front circular arc FA and a rear circular arc RA. Athickness distribution TD is applied to the meanline to form the convex suction surface 20 and the concave pressure surface 22. The airfoil section exhibits good aerodynamic performance as compared with an equivalent circular arc airfoil in a transonic flow field.method for making the airfoil shape is disclosed. The method includes the steps of: forming a cambered mean-line of two circular arcs; forming a thickness distri-bution about the conical chord line Bt; and applying thickness distribution to the cambered meanline such that a portion of the suction surface is stretched and a portion of the pressure surface is compressed. .

Hydraulic turbine system with siphon action

Abstract: The hydraulic turbine system includes: an electric generator; rotary turbine blades; a hydraulic pump for operation by rotation of the turbine blades; a hydraulic motor for driving the generator; a hydraulic reservoir; and connections between the pump, the motor and the reservoir for causing the motor to operate in response to rotation of the turbine blades by water flow In the present improvement, the turbine blades and the hydraulic pump are unified in an axial flow unit which has an annular outer casing through which water flows to drive the turbine blades which in turn drive the pump The motor, the generator and the reservoir may be located remotely from the axial flow unit The axial flow unit is preferably generally U-shaped so that it can be placed inverted over a dam with the legs extending down into the water on opposite sides of the dam A priming unit is provided for starting flow of water through the axial flow unit, and the priming unit may preferably include a vacuum pump connected to the casing for pumping air from the casing to draw water up into the legs thereof until water starts flowing by siphon action

Control means for a gas turbine engine

Abstract: Clearance control means is provided for a gas turbine engine In one embodiment relating to compressor blade clearance, means is provided for developing a first signal representative of the actual compressor casing temperature, a second signal representative of compressor inlet gas temperature, and a third signal representative of compressor speed Schedule means is provided for receiving the gas temperature and compressor speed signals and developing a schedule output signal The schedule output signal is representative of a reference casing temperature at which a predetermined compressor blade stabilized clearance is provided Means is provided for comparing the actual compressor casing temperature signal and the reference casing temperature signal and developing a clearance control signal representative of the difference therebetween The clearance control signal is coupled to a control valve which controls a flow of air to the compressor casing to control the clearance between the compressor blades and the compressor casing Means is provided for modification of the clearance control signal to accommodate transient characteristics Other embodiments are disclosed

Turbulence Characteristics in the Near Wake of a Compressor Rotor Blade

Abstract: This paper is concerned with the turbulence properties in the near wake of a rotating compressor blade. The variation of the axial, tangential and radial intensities as well as stresses across the wake and its decay characteristics were measured with a triaxial hot wire probe rotating with the rotor downstream of an axial flow compressor. The turbulence intensities decay very rapidly in the near wake region. The radial component of intensity is found to be higher than the tangential and axial components. This is a consequence of the effect of rotation on the turbulence structure. A qualitative analysis is carried out to predict the effect of rotation on the turbulence structure. These are in general agreement with the measured data.

Algorithm for calculating turbine cooling flow and the resulting decrease in turbine efficiency

Abstract: An algorithm is presented for calculating both the quantity of compressor bleed flow required to cool the turbine and the decrease in turbine efficiency caused by the injection of cooling air into the gas stream. The algorithm, which is intended for an axial flow, air routine in a properly written thermodynamic cycle code. Ten different cooling configurations are available for each row of cooled airfoils in the turbine. Results from the algorithm are substantiated by comparison with flows predicted by major engine manufacturers for given bulk metal temperatures and given cooling configurations. A list of definitions for the terms in the subroutine is presented.

Experimental Study of Low Aspect Ratio Compressor Blading

Abstract: The paper presents a study of low aspect blading for the inlet stages of a high pressure ratio, high-speed core compressor The basic overall design variables were stage pressure ratio and blade aspect ratio; these four stages represent two levels of total pressure ratio, two levels of rotor blade aspect ratio, and two levels of stator vane aspect ratios Comparisons of the overall performance, radial distributions of performance parameters, diffusion factors at the near-stall conditions, blade element data, and the axial distribution of rotor tip static pressures yielded the following results: (1) higher peak pressure ratio, high stage and rotor efficiencies, and greater stall margin were obtained with the lower aspect ratio blading, (2) the lower aspect ratio blading showed improved performance over the entire blade span, and (3) the lower aspect ratio rotors operated at higher diffusion factors and higher incidence angles over the entire blade span

Axial flexible radially stiff retaining ring for sealing in a gas turbine engine

Abstract: An annular ring 22 for an axial flow gas turbine engine disposed inwardly of an array of stator vanes 14 and between an annular flow path 18 for hot working medium gases and an annular flow path 20 for cooling air is disclosed. The ring abuttingly engages the array of stator vanes in the radial direction to provide radial support and abuttingly engages the array of stator vanes and an outer air seal block the intermixing of gases from the working medium flow path and gases from the cooling air flow path. The annular ring includes a first annular section 28 and a second annular section 30. The first annular section has an axial width to radial height ratio greater than one and the second annular section has an axial width to radial height ratio less than one to adapt the ring for axial flexibility and radial stiffness and to enable the ring to accommodate growth and axial growth between the outer air seal and the array of stator vanes while remaining within the elastic limit.

Vane configuration for fluid wake re-energization

Abstract: An airfoil for use in an axial flow compressor, a high-bypass turbofan or as a turning vane in an airflow duct having a crenelated trailing edge. The crenelated trailing edge produces pairs of counterrotating vortices which promote rapid mixing between the low momentum fluid, in the wake of the airfoil, and the adjacent fluid streams. The mixing of the adjacent streams with the low momentum wake acts to re-energize the wake.

Core compressor exit stage study. Volume 4: Data and performance report for the best stage configuration

Abstract: The core compressor exit stage study program develops rear stage blading designs that have lower losses in their endwall boundary layer regions. The test data and performance results for the best stage configuration consisting of Rotor-B running with Stator-B are described. The technical approach in this efficiency improvement program utilizes a low speed research compressor. Tests were conducted in two ways: (1) to use four identical stages of blading to obtain test data in a true multistage environment and (2) to use a single stage of blading to compare with the multistage test results. The effects of increased rotor tip clearances and circumferential groove casing treatment are evaluated.

Pneumatic supply system having variable geometry compressor

Abstract: In a compressed air supply system utilizing a shaft-driven compressor (10,16), the flow capacity of the compressor is changed by varying the compressor outlet stator geometry (16) by an actuator (18) which controls the outlet stator geometry to provide an optimum match between the compressor flow capacity and the requirements of the load. The result is a compressed air supply system which satisfies wide variations in demanded flow by the load, while supplying air at maximum pressure with minimum input shaft horsepower.

Multi-speed fan assembly

Abstract: Apparatus for rotating a fluid impeller of a centrifugal or axial flow fan, at multiple speeds. A fan is provided with a first and a second electric motor for drivingly rotating a fluid impeller at relatively fast and slow speeds, respectively. The rotor of the first motor directly drives the fluid impeller; the second motor is connected to the impeller shaft of the fan through a belt drive, with pulleys sized to reduce the impeller's rotational speed relative to that of the second motor. Only one of the motors is provided with a start winding. Control means selectively energize the first and second motors, and are operative to energize the one motor long enough to bring the other motor up to operating speed.

Capacity control systems for screw compressor based water chillers

Abstract: A control system for a rotary helical screw compressor of the variable speed type includes a variable speed motor driving the compressor for varying the compressor capacity and a slide valve member which is adjusted optimally for varying the volume of gas trapped in the working chamber prior to discharge as a function of the pressure ratio across the compressor. There is also provided a control system for a rotary helical screw compressor of the fixed speed type which include a first slide valve member for varying the compressor capacity through modulating the volume of gas trapped in the working chamber prior to compression and a second slide valve member for adjusting optimally the volume of gas trapped in the working chamber prior to discharge as a function of the pressure ratio across the compressor.

Compression section for an axial flow rotary machine

Abstract: A compression section of a gas turbine engine having an annular flow path is disclosed. Various construction details which increase the efficiency of an array of rotor blades in the compression section are developed. The annular flow path is contoured to cause the streamlines of the flow path to follow a pattern of varying radial curvature. In one embodiment, a conical surface extending between the base of each airfoil on the inner wall causes a flow path contraction and a cylindrical surface on the outer wall facing the tip of each airfoil enables close clearances.

An Axial Flow Research Compressor Facility Designed for Flow Measurement in Rotor Passages

Abstract: An axial flow research compressor facility, which is designed for relative flow measurement, is described in this paper. The facility has a rotating probe traverse mechanism which is capable of traversing hot wire, pitot and other probes at 0.09 deg intervals across the rotor blade passage. The data transmission system includes rotating transducers, pressure transfer device, ten-channel mercury slip ring unit, scanivalve, etc. The instrumentation includes on-line data processing capability. A brief description of probes used as well as some typical data on the rotor blade static pressure, rotor endwall flow and rotor wake characteristics are given in the paper.

Axial-Flow Compressor Turning Angle and Loss by Inviscid-Viscous Interaction Blade-to-Blade Computation

Abstract: A method for computation of the flow field around an arbitrary airfoil cascade on an axially symmetric blade-to-blade surface was developed which takes into account the development and separation of the blade surface boundary layers and mixing in the wake. The method predicts the overall fluid turning and total pressure loss in the context of an inviscid-viscous interaction scheme. The inviscid flow solution is obtained from a compressible flow matrix method. The viscous flow is obtained from a differential boundary layer method which calculates laminar, transitional and turbulent boundary layers. Provisions for the calculation of laminar and turbulent separation regions were added to the viscous scheme. The combined inviscid-viscous interaction scheme described yields results which are quantitatively consistent with experimental data. This suggests that the physical basis for the interactive system is correct and justifies continued exploration and use of the method.