Showing papers on "Axial compressor published in 1975"

The Effect of Reynolds Number and Laminar Separation on Axial Cascade Performance

Abstract: Testing over a range of Reynolds numbers was done for three NACA 65 Profiles in cascade. The testing was carried out in the VKI C-1 Low Speed Cascade Wind Tunnel; blade chord Reynolds number was varied from 250,000 to 40,000. A semiempirical theory is developed which will predict the behavior of the shear layer across a laminar separation bubble. The method is proposed for two-dimensional incompressible flow and is applicable down to short bubble bursting. The method can be used to predict the length of the laminar bubble, the bursting Reynolds number, and the development of the shear layer through the separated region. As such it is a practical method for calculating the profile losses of axial compressor and turbine cascades in the presence of laminar separation bubbles. It can also be used to predict the abrupt leading edge stall associated with thin airfoil sections. The predictions made by the method are compared with the available experimental data. The agreement could be considered good. The method was also used to predict regions of laminar separation in converging flows through axial compressor cascades (exterior to the corner vortices) with good results. For Reynolds numbers below bursting the semiempirical theory no longer applies. For this situation the performance of an axial compressor cascade can be computed using an empirical correlation proposed by the author. Comparison of performance prediction with experiment shows satisfactory agreement. Finally, a tentative correlation, based on the NACA Diffusion Factor, is presented that allows a rapid estimation of the bursting Reynolds number of an axial compressor cascade.

A study of casing treatment stall margin improvement phenomena. [for axial compressor rotor blade tips]

Abstract: The results of a program of experimental and analytical research in casing treatments over axial compressor rotor blade tips are presented. Circumferential groove, axial-skewed slot, and blade angle slot treatments were tested at low speeds. With the circumferential groove treatment the stalling flow was reduced 5.8 percent at negligible efficiency sacrifice. The axial-skewed slot treatment improved the stalling flow by 15.3 percent; 1.8 points in peak efficiency were sacrificed. The blade angle slot treatment improved the stalling flow by 15.0 percent; 1.4 points in peak efficiency were sacrificed. These values are consistent with previous experience at transonic speeds. The favorable stalling flow situations correlated well with observations of higher-than-normal surface pressures on the rotor blade pressure surfaces in the tip region, and with increased maximum diffusions on the suction surfaces. Annulus wall pressure gradients, especially in the 50 to 75 percent chord region, are also increased and blade surface pressure loadings are shifted toward the trailing edge for treated configurations. Rotor blade wakes may be somewhat thinner in the presence of good treatments, particularly under operating conditions close to the baseline stall. Annulus wall boundary layer profiles are only slightly influenced by casing treatment.Copyright © 1975 by ASME

Stall detector for gas turbine engine

Abstract: Stall is detected by monitoring the minimum fuel flow schedule of a gas turbine engine fuel control and another parameter which includes (1) the fuel control acceleration schedule, (2) turbine temperature (inlet or exit) or (3) engine pressure (compressor discharge or burner) and computes these signals so that when both the control fuel metering valve is at its minimum stop position (minimum fuel flow) and one of the following conditions exists, (1) turbine temperature exceeds a predetermined level, (2) the rate of change of pressure exceeds a predetermined negative rate, or (3) the fuel control is on or in proximity to the acceleration schedule, an output will be manifested.

Low noise blades for axial flow compressors

Abstract: A rotor blade configuration is disclosed which greatly reduces noise generated by the low pressure compressor, or fan, of a turbofan engine. The leading edge of the blade is swept forwardly from its hub up to a point of sweep reversal and then swept rearwardly to the tip of the blade. The slope of the curved leading edge line relative to the direction of airflow is gradually decreased from the hub to the tip to maintain the velocity component, of air relative to the blade leading edge, subsonic, while the relative velocity of the air to the blade is above a critical value and supersonic. This substantially eliminates noise producing, standing shock waves along the blade leading edges. Also described are methods for determining the configuration of such blades to obtain these ends with a minimum increase in blade weight and a minimum blade bending and blade attachment stresses.

Gas turbine engine having an improved transition duct support

Abstract: An axial flow gas turbine engine is provided with a plurality of combustion chambers distributed circumferentially about the engine axis and a plurality of transition ducts which carry propulsive gases between the burners and an annular turbine inlet at a bulkhead between the combustion and turbine sections of the engine. Support for the transition ducts at the turbine inlet is provided by an outer support ring fixedly secured to the engine bulkhead and an inner support ring which is held by a plurality of struts from the outer support ring. Flexible sealing means extend between the inner support ring and the bulkhead adjacent the turbine inlet to permit the inner ring to expand or contract radially with the transition ducts and at the same time to prevent compressed air from flowing directly into the turbine section. The outer ring and the flexible sealing means are apertured to permit a limited flow of relatively cool compressor air to enter the turbine along with the propulsive gases and thereby cool the support structure and the inlet guide vanes of the turbine.

Windmill having thermal and electric power output

Abstract: A windmill having thermal and electric power output and including windmill blades rotatably mounted and connected to a speed increaser mechanism of gears and shafts and a centrifugal compressor connected to the windmill thru the speed increaser to be driven by virtue of the wind applied to the blades of the windmill itself A directional control is connected to the windmill head to have the windmill blades face into the wind, as desired The compressor is connected to an insulated heat storage tank which contains storage material, such as brick, and the compressor discharge velocity and pressure difference are converted to heat, and the compressor fluid is returned to the compressor thru a screen which protects the compressor, and there is a flow control which automatically compensates for changes in density of the circulated air or compressor fluid Also, a gas turbine generator can be connected with the compressor to be driven thereby, and electric elements could be connected with the generator for producing electricity Two other embodiments show an impeller type of air brake and a valve and a heat-sensitive control, for generating heat or power

Fluid current turbine with flexible collectors

Abstract: A fluid-current energy-conversion plant, especially useful for electricity generation, utilizing an axial flow turbine as the energy conversion element, has self-inflated flexible collector elements for capturing a portion of the fluid current, increasing its velocity, guiding at least some of each portion into the turbine's mouth, then returning the captured flow into the stream.

A study of casing treatment stall margin improvement phenomena

Abstract: The results of a program of experimental and analytical research in casing treatments over axial compressor rotor blade tips are presented. Circumferential groove, axial-skewed slot, and blade angle slot treatments were tested. These yielded, for reduction in stalling flow and loss in peak efficiency, 5.8% and 0 points, 15.3% and 2.0 points, and 15.0% and 1.2 points, respectively. These values are consistent with other experience. The favorable stalling flow situations correlated well with observations of higher-then-normal surface pressures on the rotor blade pressure surfaces in the tip region, and with increased maximum diffusions on the suction surfaces. Annular wall pressure gradients, especially in the 50-75% chord region, are also increased and blade surface pressure loadings are shifted toward the trailing edge for treated configurations. Rotor blade wakes may be somewhat thinner in the presence of good treatments, particularly under operating conditions close to the baseline stall.

Turbulence and Unsteadiness Measurements Downstream of a Moving Blade Row

Abstract: Turbulence and unsteadiness levels downstream of an axial-flow compressor rotor have been measured using an ensemble-averaging technique. Free-stream turbulence levels are lowest near the compressor design-point, and increase with decreasing flow coefficient as the compressor nears the stalled condition. The unsteady stator incidence angles have been found to have a peak-to-peak variation of between 12 deg and 15 deg for all flow coefficients tested. These observations have been confirmed qualitatively by hot-wire-anemometer spectral measurements.

Unsteady Supersonic Cascade in Subsonic Axial Flow

Abstract: This paper presents an analysis for determining the unsteady flowfield produced by an oscillating cascade placed in a supersonic stream which has a subsonic velocity component normal to the cascade. The analysis is based on the assumptions of an inviscid, two dimensional, linearized flowfield. Solutions for the velocity potential and the blade pressure distributions which satisfy the blade-to-blade periodicity condition are developed explicitly in terms of disturbance functions distributed on blade and wake surfaces. The boundary conditions of flow tangency at blade surfaces and continuity of pressure across wake surfaces provide integral relations which can be solved numerically to evaluate the disturbance functions. Predicted blade pressure distributions are in good agreement with results determined from a previous finite cascade solution. Further, in the two limiting cases of sonic axial velocity and zero frequency, the present solution approaches the lower limit of Lane's solution for supersonic axial flow, and it reduces to an Ackeret type of steady-state solution, respectively. The numerical examples indicate that a single~degree- of-freedom torsional instability will exist over a broad range of cascade parameter values.

Turbomachine with removable stator vane

Abstract: An axial flow compressor or turbine includes a stator case with a plug which is removable from outside the case, together with one or more stator vanes attached to the plug, to provide access to an adjacent part of the rotor. Such access may be used to add balance weights to the rotor as part of a rotor balancing procedure, or for inspection of rotor blades.

Multiple section rotor disc

Abstract: A design technique, method and apparatus for containing failure of the rotors of axial flow fluid machines. A rotor disk is constructed of at least three disk sections. Each disk section is shaped such that the loading on that section will be distributed in an optimum manner from the rim to the hub of the disk. To prevent crack propagation from one disk section to another, and to minimize structural weaknesses in the disk sections, the live disk sections are bolted together in a single bolt circle. In order to reduce overall disk weight while maintaining a maximum level of failure containment, the inner disc sections are made thicker than the outer disk sections. Embodiments for the fan, compressor and turbine rotor sections of a gas turbine engine are disclosed.

Stationary power-generating plant

Abstract: A stationary power-generating plant of the type which includes a turboset comprising an axial-flow combustion gas turbine, an axial flow combustion air compressor and a driven machine such as an electrical generator which are all coupled together and mounted for rotation about a common axis. The driven machine is located within a hollow chamber surrounded by an intake duct which provides for a flow of combustion air to the compressor and the intake duct is arranged co-axially with the rotational axis of the turboset and is connected to the air inlet end of the compressor by means of a convergent conical annular duct thereby providing axial flow of air to the compressor inlet.

Stators of axial turbomachines

Abstract: A stator for turbomachines and especially multistage axial compressors is ovided with stationary vanes having peripheral heels secured to a casing. The casing is constituted by a series of coaxial cylindrical annular sections between which are formed annular spaces for inserting and guiding the heels. The sections are rigidly fixed to ring-shaped peripheral webs or flanges which are secured to each other by means of radial longitudinal ribs.

Vaned diffuser and method

Abstract: My invention relates to centrifugal compressors, more particularly to compressors of a known type, in which air enters the compressor rotor parallel to its axis of rotation, engages an inducer portion of the compressor rotor blades which is generally helical, in which the air is accelerated tangentially, and then proceeds through an impeller portion of the rotor formed with substantially radial vanes in which the air is further accelerated tangentially, leaving the rotor periphery with a high tangential velocity. In such a compressor, the air discharged from the rotor is received in a diffuser in which the velocity head of the air is largely converted to static head by a so-called diffusion process of reducing the air velocity. The air is then directed to the outlet or outlets of the compressor. It is to be understood, however, that this invention is concerned not with the rotor but rather with the vaned portion of the diffuser. The principle object of my invention is to increase the compressor efficiency and essentially eliminate surge problems, thereby reducing the power required to drive the compressor which results in various advantages to any machine that requires a continuous flow of high pressure air. This objective is achieved by several features. First, by defining a method to design the shape of the leading edge of the diffuser vanes, thereby reducing the entering shock loss and also the down stream flow separation; second, by defining a method of shaping the vanes and the passage walls such that the shape will cause a suitable rate of pressure rise that will also lessen the causes of flow separation from the passageway, thereby permitting stable operation, without compressor surge, in an operating regime having a higher compressor efficiency.

Gas turbine engine control system

Abstract: A gas turbine engine which comprises a rotary air compressor and a gas turbine, each with a rotor mounted on opposite ends of a rotor shaft, which is journalled in a housing positioned between the compressor and the turbine. The housing includes reduction gears. A combustion chamber is connected between the outlet air duct of the compressor and the hot gas inlet duct of the turbine. The power output is controlled by varying the air inlet to the compressor by means of an axially moving throttle control which limits the air passage into the compressor, either alone or in conjunction with variable angle compressor inlet pre-whirl vanes. It is also controlled by a shroud which surrounds the nozzle blades of the turbine. The shroud can be moved axially to limit the cross-section of flow of hot gas to the turbine blades. Auxiliary blades are mounted on the back of the turbine rotor which serves to draw cool outside air into the space between the housing and the hot gas inlet duct of the turbine, and up along the back surface of the turbine rotor, and through a plurality of axial holes drilled through the hub of the turbine rotor, all of which helps to cool the critical parts of the engine. Improved construction of the turbine rotor and the compressor rotor involves assembling the unit from a plurality of separate pieces which serve to provide a combined radial and axial flow of gases around the rotor blades. The fuel supply is controlled to be a function of the flow of air into the combustion chamber.

Steam turbine extraction system

Abstract: An extraction system for extracting steam from the blade path of an axial flow turbine apparatus in a circumferentially uniform manner. Steam is extracted through an extraction orifice having a circumferentially-varying throat portion, the throat communicating with a diffusing passage leading into a circumferentially-extending extraction manifold. The manifold is connected to an extraction pipe of predetermined cross-section area. Steam extracted from the blade path is conducted through the extraction pipe to an associated user apparatus. The dimension of the throat in the longitudinal plane relative to the axis of the shaft and the radial dimension of the manifold in a plane normal to the shaft axis are sized and cooperatively related such that steam is uniformly extracted from the blade path without creating significant pressure variations at various circumferential locations therewithin.

Method and apparatus for cooling turbomachines

Abstract: An auxiliary blower is connected to the gaseous supply line to the axial compressor to deliver a gaseous medium, such as air, under pressure to the compressor when the rotor has been shut-off and slowed to a reduced speed. The delivered gaseous medium allows the rotor to continue rotating at the reduced speed while cooling of the rotor and vanes takes place in a uniform manner. The drive power for the blower amounts to 0.05% to 0.1% of the useful power in full-load operation of the compressor.

Axial flow blower of high energy transfer - has rotating blades of various angular distribution and separation

Abstract: An axial flow blower has several blades (3, 4) which are separated from each other to varying degrees, and which have profiles of unequal sequence to produce higher energy in the flow which passes the blades in a narrow blade channel, so that an almost equivalent energy output into the blast flow is generated to the energy input to rotate the blades. The blades may be plates of similar shape but with different angles of inclination to each other. This arrangement avoids hydraulic loss and thereby improves the efficiency of the blower. The total noise level can be reduced by matching the number of blades with the revolutions.

Start-up compressed air system for gas turbine engines

Abstract: The system described herein utilizes a constant speed compressor to augment a service compressor that is an integral part of a gas turbine engine to assure that adequate pressure and volume of air is provided for fuel atomization during start-up of the engine. Further, the system is arranged so that the service compressor automatically assumes the load as its speed increases during the acceleration of the gas turbine engine. The system is designed so that the starting compressor will not be overloaded and can be completely isolated from the circuit if desired.

Observations of Separated Laminar Flow on Axial Compressor Blading

Abstract: This paper describes some detailed observations of separated laminar flow regions on the rotating and stationary blading of a single-stage axial compressor operating at low speed. The data covers the “critical” Reynolds number range where “bursting” of laminar separation bubbles causes a sharp increase in blade profile losses. The experimental results are compared with various empirical correlations and theoretical models proposed by other workers. Horton’s semi-empirical model of separation bubble bursting is broadly supported by the present investigation. However, it appears that some aspects of Horton’s theory require significant modification in order to give an accurate description of the separation bubble behavior on the blades in an axial compressor. It is stressed that correlations of the critical Reynolds number for axial compressor cascades in terms of overall performance parameters should be applied with caution, as they are only likely to be valid for a narrow range of conditions.Copyright © 1975 by ASME

Platform seal-tangential blade

Abstract: In an axial flow compressor rotor stage having a tangential slot in the periphery of the rotor to receive the blade roots, a seal is positioned below the blade platforms to seal these platforms against air recirculation The seal extends under the platforms of several blades and is ladder shaped with the rungs sealing the platform spaces and the struts serving to interconnect and hold the rungs in place

Duct liner optimization for turbomachinery noise sources

Abstract: An acoustical field theory for axisymmetric multisectioned duct liners is combined with a numerical minimization algorithm to predict optimal one‐ and two‐sectioned liner configurations producing maximum sound attenuation. Optimal inlet liner impedance properties calculated by this method are presented for a research compressor operating at about 0.4 Mach number. Kemp‐Sears theory is used to describe the rotor/stator viscous wake interaction effects. Comparisons with data presented for point and plane‐wave sources indicate that optimal liners for complex turbomachinery sources cannot be easily inferred from data based on these simpler source models.

Supporting ring for stator vanes in an axial compressor

Abstract: A supporting ring for stator vanes in an axial compressor. The supporting ring permits an adjustment of the angular position of the stator vanes. The adjustment is carried out by removing the stator body while the machine is at standstill. The supporting ring is provided with recesses which are defined by an elastic wall which also defines the bores in which the stator vanes are mounted. Clamping bolts are provided in the elastic wall and by tightening these clamping bolts the stator vanes are held in a predetermined position.

Generating plant and method of starting up a generating plant

Abstract: A generating plant is driven by a gas turbine, which is run with combustion gases from gas coming from a carbon pressure reactor and which obtains the combustion air necessary for its operation from a primary compressor driven by the gas turbine by means of a final compressor connected at the outlet side of the primary compressor. The final compressor is driven by an expansion turbine connected between the pressure reactor and the combustion chamber acting to produce the combustion gases. During starting up of such a plant the pressure reactor is operated with extraneous air which is primarily compressed by a starting compressor and further compressed by the final compressor which is powered by a pony motor, the expansion turbine being disconnected until it reaches operating speed.