bluuebunny/crossref_metadata_2025_split huggingface dataset:
Wave Action in Diffusers for Exhaust-Pipe Systems, with Special Reference to the Scavenging of Two-Stroke Engines
Authors: Wallace F. J. , Boxer G. 
Published: October 2007

The work described was carried out in the Mechanical Engineering Department of Birmingham University and is an extension of the investigation into air flow in a naturally aspirated two-stroke engine described in an earlier paper (Wallace and Nassif 1954)‡. In that paper the scavenging process of an unblown, opposed-piston engine with simple parallel-pipe exhaust and inlet systems was analysed, and the results were compared with experimental observations. Only a brief reference was made to the very marked increase in air flow resulting from incorporation of a diffuser in the exhaust system. The present paper describes first a theoretical investigation of wave effects in the exhaust system using: (1) The small-wave theory; (2) The method of characteristics; (3) An approximate analytical treatment designed to give better accuracy than (1), but to avoid the extremely laborious computations associated with (2); and, secondly, an experimental programme comprising: (1) Air-flow tests with various diffuser arrangements and over a wide range of speeds, and (2) Tests in which indicator diagrams were taken at salient points of the exhaust system. The general conclusions are: (1) The incorporation of a diffuser in the exhaust system leads to an increase in air flow of up to 85 per cent under favourable conditions. (2) The very complex phenomena occurring in the exhaust system can be dealt with satisfactorily by the approximate analytical treatment with great saving in time over the method of characteristics and very much better accuracy than can be achieved with the small-wave theory.
A Review of the Performance of Exhaust Systems for Gas-Turbine Aero-Engines
Authors: Ashwood P. F. 
Published: October 2007

This paper summarizes published information concerning the aerodynamic performance of exhaust diffusers and propelling nozzles for turbine aero-engines, and extends and supplements this with additional data obtained from tests made at the National Gas Turbine Establishment (N.G.T.E.). The factors influencing the exhaust system design are reviewed and the effects of the type of engine installation and the use of reheat are discussed. The influence of ducting losses on the thrust are then considered in terms of their effect on the performance of a typical turbo-jet engine. The paper continues with a review of some previous work on turbine exhaust diffusers, which was concerned with the effects of the diffuser area ratio and wall shape and with the effect of inlet swirl. This has since been extended by experimental examination of the influence of the bullet support struts on the performance of an engine, and the results of these tests are given. Little published information is available concerning the performance of propelling nozzles over the range of pressure ratio relevant to the turbo-jet engine. The results of tests up to a pressure ratio of 9 on a series of convergent-divergent nozzles are given and the effects of design pressure ratio and divergence angle are illustrated. A one-dimensional theoretical treatment is used to show the relationship between the non-dimensional and specific thrusts and the applied pressure ratio. The test results are then analysed in terms of these thrust parameters and their related coefficients. The paper concludes with reference, in general terms, to some of the more important mechanical engineering considerations which arise in the design of exhaust-duct installations in jet-propelled aircraft.
The Rotating-Beam Channel and 30-Inch Water Tunnel at Admiralty Research Laboratory
Authors: Lever E. H. , Ritter H. , Woolfson M. , Wright C. T. 
Published: October 2007

To meet a programme of research into the behaviour of underwater weapons, major research facilities including a rotating-beam channel and a 30-inch water tunnel have been designed and constructed by the Ministry of Works in collaboration with the Royal Naval Scientific Service. The rotating-beam channel provides for towing submerged bodies in a circular path of 45-55 feet radius at speeds up to 150 ft. per sec. Models up to 20 feet long can be accommodated. The water is maintained at optical clarity by continuous filtration and chemical dosing. The water tunnel has a slotted wall working section 30 inches in diameter and 15 feet long, providing for experiments on models up to 10 inches in diameter at water velocities up to 60 ft. per sec., static pressure can be varied from 0·1 to 3 atm. Ancillary plant maintains the water to within a specified temperature range and air content. Both plants are provided with high-accuracy speed control by means of a Ward Leonard system equipped with electronic speed-holding servo.
Simulated Gear-Tooth Contacts: Some Experiments upon Their Lubrication and Subsurface Deformations
Authors: Crook A. W. 
Published: October 2007

This paper describes some experiments with disk machines in which the electrical resistance between the disks was measured at various stages of running. It also describes some experiments with mild steel disks run at such loads that considerable plastic deformation occurred. The resistance measurements illustrate the process of ‘running-in’ and show that a state of almost complete hydrodynamic lubrication is eventually reached. It has also been found that the surface temperatures of the disks have a very considerable influence upon the hydrodynamic film. The flow of material in the plastically deformed disks is described and its bearing upon the mutual accommodation of engaging tooth surfaces and their subsequent pitting is discussed. An explanation of the greater propensity to pit of surfaces with the lower peripheral speeds may be provided by one unexpected feature of the flow. It was also found that even at the high loads, which produce gross plastic distortion, the mild steel disks did not scuff, and this is attributed to the persistence of hydrodynamic lubrication even under such extreme conditions.
Self-Excited Vibration of Axial-Flow Compressor Blades
Authors: Carter A. D. S. , Kilpatrick D. A. 
Published: October 2007

Blade vibration, with the possibility of a failure, is one of the major factors controlling the reliability of axial-flow compressors. Self-excited vibration occurring at part load, when some blade rows are stalled, often causes most trouble. In this paper an investigation which has been undertaken into this phenomenon is described. The main objective has been to determine the major factors governing the vibration, and to establish, if possible, some design rules which would reduce the chances of a failure to an acceptable minimum. The self-excited vibration of blades in cascade has been studied, and a simple theoretical correlation attempted. This has been supplemented by single-stage work and by multistage full-scale tests. Both flutter and stall cell excitation have been encountered, and are described. A semi-empirical design rule is suggested, and its interpretation in terms of the normal blade design parameters is included.
Experimental Investigation of the Process of Expanding Boiler Tubes
Authors: Alexander J. M. , Ford Hugh 
Published: October 2007

The objectives of this work were to examine the tube expanding process in relation to as many variables as possible and to determine whether there would be any significant ‘size effect’. For these investigations an apparatus has been constructed which enables detailed observations to be made of the behaviour of a specimen tube-plate joint during expanding. A typical record is given showing how the strains and mandrel torque develop during expanding. No appreciable size effect was found on the three geometrically similar systems tested. It is shown that the residual strains are much greater on the back than on the front of the plate, leading to lack of parallelism in the joint face, and that the plastic-elastic interface can extend much farther into the plate than was previously thought possible. Comparison is made between these experimental results and the predictions of a theory proposed by the authors, and it is concluded that higher seat pressures could be obtained if axial extrusion of the tube could be restricted. This finding was confirmed by axially compressing short lengths of tube into a plate, the axial compression causing the tubes to bulge and expand themselves into the plate seat.
Analogue for High-Intensity Steady-Flow Combustion Phenomena
Authors: Spalding D. B. 
Published: October 2007

In this paper a technique is described which is intended to assist in the preliminary stages of developing a high-intensity combustion chamber for an aircraft gas-turbine or ram-jet. Since the chief unknowns are aerodynamic rather than chemical, an air-flow model is made; the chemical reaction is then simulated by electric heaters distributed through the chamber. External controls regulate the heat input in accordance with the local temperature and the properties of the fuel which is to be simulated. The apparatus used is a prototype intended to demonstrate the principle rather than to make predictions, but good agreement is found between predicted blow-out velocities of baffle-stabilized flames and experiments on these flames reported by other workers. Tests are also reported on two-dimensional combustion chamber designs for burning pre-mixed fuel and air, the efficiency, space utilization, and pressure-drop performance being compared. It is shown by an example that separate injection of fuel to the combustion chamber greatly reduces the blow-out velocity and space utilization, but increases the combustion efficiency and the range of fuel-air ratios over which a flame can be maintained. The analogue does not simulate atomization, heat loss, carbon formation, or gas-dynamic instability.
Measurement of Residual Stresses in Alloy Steel Forgings
Authors: Barker A. , Hardy E. H. 
Published: October 2007

The measurement of residual stresses with particular reference to alloy steel forgings by a trepanning method and by Sachs method is discussed. The precautions necessary are investigated experimentally. The possibility of plastic yielding during the machining operations in the Sachs method is demonstrated and the effect of this on the residual stress distribution in water-quenched mild-steel cylinders is investigated. The determination of residual stresses in an induction-hardened roll is given as an example of the use of some of the refinements described.
Rotary Shaft Seals: The Sealing Mechanism of Synthetic Rubber Seals Running at Atmospheric Pressure
Authors: Jagger E. T. 
Published: October 2007

The paper describes an investigation to establish the mechanism by which sealing is achieved in the conventional synthetic rubber oil seal when used on a rotating shaft. After demonstrating that the contact between the seal and the shaft cannot be dry contact—that there is in fact what appears to be a coherent film of oil between the sealing lip and the rotating shaft—further experiments are described to find out why the oil in the film does not flow out past the seal. The conclusion is reached that there is a meniscus at the oil/air interface and that retention of the oil in the oil film is effected by the surface tension of the oil.
Free Undamped Non-Linear Vibrations of Imperfect Circular Disks
Authors: Tobias S. A. 
Published: October 2007

Previous investigations of the vibrations of circular disks confined themselves to small amplitudes when it can be assumed that the strain energy of the disk is due to pure bending only. At large amplitudes this assumption ceases to be valid and the stretching of the middle surface has to be taken into consideration. As a result, the equations of motion become non-linear. The investigation is concerned with the vibration of ‘real’ disks, that is, disks which contain small imperfections. It is shown that, in general, the imperfections eliminate the indeterminancy of the angular position of the radial nodal lines which is characteristic of perfect disks. For those modes which contain at least one radial nodal diameter, there are two fixed nodal configurations which possess slightly different natural frequencies. At small amplitudes these nodal configurations are normal modes of vibration which vibrate independently of each other. At large amplitudes, when the equations of motion become non-linear, these configurations become coupled. The coupling is unsymmetrical in the sense that the configuration with the higher natural frequency can vibrate on its own at all amplitudes. On the other hand, above a certain amplitude, the configuration with the smaller natural frequency cannot vibrate on its own since it also excites, by parametric excitation, the other configuration. Under such conditions the phase difference between the two configurations is fixed to 90 deg. and as a result the motion of the disk corresponds to a beating travelling wave.
Control Equations of Multistand Cold Rolling Mills
Authors: Lianis G. , Ford Hugh 
Published: October 2007

For the practical assessment of the operating behaviour of a multistand cold rolling mill, it is necessary to know how gauge, speed and interstand tensions are affected by screw and speed-setting changes. This paper sets out the control equations governing the response of each stand to any combination of the external disturbances, that is, how the interstand thicknesses, tensions and final output change due to changes of ingoing gauge, coiler tensions, roll gap settings and roll speeds. The partial derivatives of the roll force, roll torque and forward slip, which enter as factors in the governing equations, are evaluated mathematically, and then expressed in nomographic form. Examples of the use of the nomographs are given.
Gyroscopic Loading Tests on a Gas-Turbine Rotor
Authors: Wilson W. Ker , Harris W. J. 
Published: October 2007

Amongst the important matters investigated after the accident to a ‘Comet’ aircraft at Elba in 1954 and the recovery of the wreckage from the sea, was the severe damage which had been sustained by the turbine rotor hub-shafts. Three of the four engines were recovered with the turbine rotor disks intact, though extensive cracking was discovered in the spigot recess radii of the hub-shaft flanges. In the case of the fourth engine, the turbine rotor disk was missing, through fracture of the hub-shaft flange. A careful step-by-step examination of all the evidence enabled it to be stated quite definitely that the damage sustained by the engine hub-shaft assemblies was a consequence of abnormally severe gyroscopic bending moments imposed during disintegration of the aircraft. Nevertheless, it was considered desirable to determine by practical tests the actual magnitude of the gyroscopic bending moment which the hub-shaft assembly could sustain and the manner in which fracture would occur. The paper describes the special gyroscopic test-rig constructed for this purpose and discusses the results obtained. The results of supplementary investigations of the bending fatigue behaviour of hub-shaft assemblies and plain and notched laboratory specimens, with special reference to the high-stress low-endurance portion of the fatigue diagram, usually called the ‘high-level’ fatigue region, are also included.
Behaviour of Compressed Asbestos-Fibre Gaskets in Narrow-Faced, Bolted, Flanged Joints
Authors: Donald M. B. , Salomon J. M. 
Published: October 2007

In an attempt to establish the conditions necessary to maintain ‘tightness’ in narrow-faced, bolted, flanged joints, experiments were carried out on standard 300 lb. per sq. in., 900 deg. F. screwed-on and welded-on flanges fitted to 2 1/2-inch bore pipes. ‘Klingerit’, rubber-bonded asbestos, gaskets of various dimensions were tested. Stresses in the bolts were measured by means of electrical resistance strain-gauges. The pressure fluid used was water. The screwed-on flanges were later turned down to approximately half their original thickness to determine the effect of flange thickness on leakage pressure. Photo-elastic studies were carried out to determine the distribution of axial stress in the gasket due to bolting up. The following points were established: (1a) The gasket factor, m, of compressed asbestos jointing increases practically linearly with gasket thickness. This is the opposite of the trend of the values given in the A.S.M.E. Unifired Pressure Vessel Code of 1952 (A.S.M.E. 1952). (1b) The gasket factor of compressed asbestos jointing increases with decreased gasket width. (2) The gasket yielding pressure, y, of compressed asbestos jointing is, for water as pressure fluid, independent of gasket dimensions. (3) Bolt stress may increase, decrease, or remain constant during increase in internal pressure, in one and the same joint, depending only on the initial bolt stress. (4) The centre of gasket reaction is situated closer to the outer edge of the gasket than to the inner; the exact position depending on the relative stiffness of the flange and gasket material. (5) Increasing thickness or decreasing width or external diameter of the gasket reduces the pressure which the joint is capable of containing. (6) Reducing the thickness of the flange ring increases the gasket stress necessary to contain any particular internal pressure.
Dynamic Loads on the Teeth of Spur Gears
Authors: Harris Stephen L. 
Published: October 2007

In a theoretical analysis of a single pair of high-class gears three internal sources of vibration are considered: (1) Periodic variations in the velocity ratio due either to running the gears above or below the designed load, or to small manufacturing errors. (2) Period variation in the tooth stiffness. (3) Non-linearity in tooth stiffness. The amplitudes of vibrations caused by (1) depend on damping, while those caused by (2) or (3) will only occur if the damping is below a limit estimated at 0.07 of critical damping. Damping currently reported for tests on steel gears is about 0.1 of critical, but might well be less. Dynamic tooth forces and amplitudes of vibration were found from photo-elastic stress patterns of model gears with both small and large errors. The more accurate gears showed only vibration caused by (1), variation in the velocity ratio, because the damping was too great for the other modes. Information on damping is insufficient for satisfactory prediction of dynamic increments. If the damping in any gears fell to 0.07 of critical the increment, instead of having a small value, might equal the applied load, irrespective of any errors, and this might prove disastrous.
First Year of Operation of a Cyclone-Fired Boiler
Authors: McCulloch R. P. , Willetts J. R. , Richardson A. 
Published: October 2007

This paper is intended to give an account of experiences during the first year's operation of the first cyclone-fired boiler to be commissioned in Britain. The reasons for the choice of a cyclone-fired boiler are given and its relation to the plant previously installed is described. The early operational difficulties and the actions taken to overcome them are discussed. The results of official tests are given which show that the boiler efficiency is over 88 per cent on the gross calorific value and efficiencies of this order are being regularly attained in commercial operation. The performance of several widely differing coals in the cyclone are described and various factors which affect their suitability for burning in a cyclone are discussed. The conclusion is reached that after some ‘teething troubles’, the boiler is now giving even a better commercial performance than was envisaged at the time of its inception and that the choice of such a unit has been completely justified.
Theoretical Analysis of the Stresses Induced in a Spherical Pressure Vessel Due to the Constraining Effect of a Cylindrical Skirt
Authors: Hicks Raymond 
Published: October 2007

This discussion deals with the stresses induced in a spherical pressure vessel due to the constraining effect of a cylindrical skirt. The skirt is taken as being made of two sections having different thicknesses, one section being located inside the vessel and the other directly underneath on the outside of the vessel. Expressions are obtained for the bending moments and shear forces induced in the vessel and its skirts when (1) the vessel is stressed by a uniform radial pressure and (2) the skirts are loaded in an axial direction. The general case of an arbitrary load system is also considered and expressions are obtained for the induced moments and shear forces in terms of a set of constants which can be evaluated readily when dealing with any particular problem. In an appendix the general solution is used to consider briefly the particular cases ( a) Temperature gradient in the bottom skirt. ( b) Self weight of the vessel, ( c) Axial load on the vessel.
Transverse Gauge Variation in Strip and Sheet Rolling
Authors: Saxl K. 
Published: October 2007

Large forces acting on the working surfaces of rolls in a mill producing strip or sheet will deform these rolls and, in an endeavour to obtain products of uniform thickness, the roll surfaces are ground to a shape which would compensate for this deflection. Unsupported rolls deform by bending and local compression of the surface, and the latter results in edge thinning. Work rolls of backed-up mills, in addition, deform owing to the effect of the elastic support afforded by the backing roll. The mechanism of deflection is investigated and remedies suggested. Variation of thickness across the strip and particularly its redistribution is shown to be responsible for a number of troubles such as locked-up stresses in the rolled strip, buckling and waviness of strip, edge cracking, lateral deflection of rolls, etc. The performance of a wide four-high mill can be much increased, particularly when rolling narrow strip, provided the secondary deflection of the work roll is controlled. This enables use of more slender rolls which, in turn, makes it possible to roll harder metals to smaller gauges.
The Fatigue Strength of Pin-Jointed Connections in Aluminium Alloy B.S. L65
Authors: Low A. C. 
Published: October 2007

The purpose of this paper is to report investigations into the improvements in fatigue strength of pin-jointed assemblies that could be obtained by the use of interference fits between pin and lug, and the effect on the strength of variations in pin diameter. Direct-stress tension-tension-fatigue determinations were made on assemblies, consisting of an aluminium-alloy lug joined to a steel fork by means of a hardened-steel pin, using one overall size of lug, and varying first the pin size (using a constant percentage interference) and then the degrees of interference (using a constant pin size). Tests were also made on lugs fitted with interference-fit steel bushes and sliding-fit pins. For the overall size of lug tested (2 3/4 in. X 3/4 in., pin centre 1 1/2 in. from the end) the optimum pin size was found to be 1 in. diameter, and the optimum interference on a 1-in. pin was found to be 0.007 in. Joints with such a pin had a fatigue strength at 10 million cycles of about 1/4–9 1/2 tons load as compared with 1/4–1 1/2 tons load using a sliding-fit pin. Bushed lugs gave similar results.