bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Experiments on the Alternating Stress Fatigue of a Mild Steel and an Aluminium Alloy at Elevated Temperatures
Authors: Forrest P. G. , Tapsell H. J.
Published: October 2007

Alternating-stress-fatigue tests have been carried out at several speeds of between 10 and 8,000 cycles per min. on a normalized 0.17 per cent carbon steel at air temperature, 400, 450, and 500 deg. C. and on the aluminium alloy R.R. 58, in a fully softened condition, at 200 deg. C. It has been shown that for the mild steel the fatigue strength at air temperature depends mainly on the number of cycles of stress irrespective of the cyclic speed, but at 400–500 deg. C. failure at a given stress range occurs after a certain time which is approximately independent of the speed. For the aluminium alloy at 200 deg. C. there is evidence of a small speed effect, but fatigue failure depends mainly on the number of stress cycles applied and not on the time of the application.

In addition, a study has been made of the dynamic stress-strain relations, and these are shown to be useful as a guide to the variations of fatigue strength with temperature and speed. They also provide a means for the determination of the stress redistribution when plastic strain occurs in bending fatigue, and it is shown how this, together with the effect of size of test piece may account for the difference between bending and direct-stress fatigue strengths.

A description is given of the special apparatus designed for the work.
The Fatigue Strength under Bending, Torsional and Combined Stresses of Steel Test Pieces with Stress Concentrations
Authors: Thurston R. C. A. , Field J. E.
Published: October 2007

In previous investigations (Gough, Pollard, and Clenshaw 1951)§ under the same general research programme, determinations were made of the intrinsic and vee-notched fatigue strengths of the first seven steels here investigated, under various combinations of bending and torsion. The intrinsic fatigue limits were found to fit reasonably to an ellipse quadrant, and the notched fatigue limits to a two-constant displaced ellipse or ‘ellipse arc’.

The bulk of the present paper concerns the behaviour under combinations of bending and torsional stresses of test pieces with transverse holes, for the same seven steels. The fatigue limits under the various stress combinations have been found to fit reasonably to an ellipse arc of the same form as for the vee-Notched Specimens.

The similarity in form of the ellipse arcs for the seven materials supports the theoretical conclusion that the shape of the curve is dependent only on the shape of the hole, and is independent of the nature of the material.

The information given on strength reduction factors under various combinations of bending and torsion, together with the tables of results of supplementary static tests, should be of use in such problems as crankshaft design.

The paper also includes the results of flexural and torsional fatigue tests on an aircraft crankshaft steel, with other forms of stress concentration. These results are compared with those on two other steels of similar composition.
A Correlation of the Resistance to Air Flow of Wire Gauzes
Authors: Grootenhuis P.
Published: October 2007

The resistance to the flow of air through different assemblies of wire gauzes has been correlated to a common basis. Single gauzes, closely-packed assemblies, sintered packs, and assemblies of spaced gauzes have been considered, although the actual correlations have been restricted to square-mesh gauzes with a single-wire diameter, as these are used most in practice. Experimental data for the sintered packs are presented and compared with the published data for the other types of assembly.

The flow of air through a gauze is considered as analogous to flow through passages or pipes, and the resistance as being due mainly to the friction between the flow and the surfaces of the voids in the gauze, in contrast to the previous approaches of treating the resistance of a gauze as being due to a combined drag of the wire cylinders. The range of Reynolds number (based on hydraulic mean diameter) covered by the correlation is from 0.1 to 5,000.
Convective Heat Transfer to Gas Turbine Blade Surfaces
Authors: Wilson D. G. , Pope J. A.
Published: October 2007

Results are given of experiments into the variation, with chordwise position, of the heat transfer between the surface of a typical gas-turbine blade in cascade and in the air stream. The principal variables investigated are the blade's Reynolds number and the incident angle of the air stream, while the air/temperature ratio of the blade is kept near unity. It is shown that, with certain provisions, the results should be broadly applicable to similar blades under normal operating conditions.

The extent of the correlation of the results with values obtained by available theoretical methods is shown. The laminar boundary-layer heat-transfer theory due to Squire (1942)‡ gives good agreement, but the predictions of heat transfer in the regions of turbulent boundary-layer flow, particularly under negative pressure gradients, leave much to be desired. In addition, knowledge of conditions at transition to turbulence and at laminar separation of the boundary layer is scanty, with consequent uncertainty in any overall heat-transfer forecast. Minor suggestions in this respect have resulted in slightly improved correlations.

The experimental method employed involved the manufacture of a wind tunnel having a form of contraction based on the theoretical work of Cheers (1945), which gave excellent results; also a novel process was developed for the manufacture of the cascade blade which, it is considered, possesses certain advantages over the more traditional methods.
Factors Influencing the Continuing Development of the Steam Turbine
Authors: Dollin F.
Published: October 2007

The Parsons Memorial Lecture was instituted in 1935 under the auspices of The Royal Society. It is delivered each year in one of the branches of science to which Sir Charles Parsons contributed, and is sponsored by the Institution or Society appropriate to that subject.

The range of Parsons' activities included marine engineering, naval architecture, civil, electrical, and mechanical engineering, and optics.
Modern Developments in the Use of Large Single-entry Centrifugal Pumps
Authors: Anderson H. H.
Published: October 2007

In parallel with the electric motor and the steam turbine, which provide suitable high-speed power, the centrifugal pump has been developed to a high degree of reliability and efficiency.

This paper describes a recent step in this development, namely, the research manufacture and adoption of single-entry pumps, combined with their driving mechanisms, for medium and large power duties.
Development of the Lost-wax Process of Precision Casting, 1949–53
Authors: Turnbull J. S.
Published: October 2007

The paper describes the limitations of the original lost-wax process (1945–49) and describes improved methods developed in the Precision Casting Shop of the Metropolitan-Vickers Electrical Co., Ltd., by which the process has extended its application in industry.

In the technique of wax injection, methods are described for eliminating ‘draw’ in wax patterns, and for making accurate patterns considerably larger in size. Wax-injection machines are also described.

In the manufacture of moulds, the new Investment X technique of shell moulding is described with full details of its technical and economic advantages.

Methods of improving progressive solidification in castings are discussed.

The application of centrifugal and vacuum casting is discussed.

Attention is drawn to the mechanical properties of S.80 castings with higher consistency resulting from a combination of Investment X and centrifugal casting.

Distortion of patterns and of castings are described and methods of correction suggested.

The economics of lost-wax castings are considered and, finally, the scale of manufacture is reviewed with a view to mechanization.
An Analysis of Turbulent Free-convection Heat-transfer
Authors: Bayley F. J.
Published: October 2007

In this paper a theoretical analysis is made of natural-convection heat-transfer under conditions of turbulent flow. A theory is developed relating the non-dimensional heat-transfer coefficient to the boundary-layer thicknesses which are subsequently determined from solutions of the simplified heat and momentum balance equations. These are applied to fluids of ***Prandtl numbers near unity and to liquid metals having very low Prandtl numbers, which are of importance for cooling gas-turbine blades and nuclear-power sources. It is shown that data obtainable from simple small-scale equipment can be extrapolated without serious error to the highest values of the relevant parameters likely to be met in any practical application.
Pulsating Flow Measurement by Viscous Meters, with Particular Reference to the Air Supply of Internal-combustion Engines
Authors: Kastner L. J. , Williams T. J.
Published: October 2007

The problem of measuring the mean rate of mass flow of a fluctuating stream is one which has attracted the notice of many investigators but, although a limited degree of success has been achieved by more than one method, it may be said that a simple, inexpensive, and compact device which is capable of dealing with flows subject to severe pulsations without loss of accuracy and without ancillary apparatus has yet to be described. Meters of the orifice type, used in conjunction with large smoothing capacities, have been widely employed, in particular for the measurement of the air consumption of reciprocating internal-combustion engines, but the smoothing capacity often requires to be inconveniently great and too small a volume will lead to surprisingly large errors (Watson and Schofield 1912; Kastner 1947)‡ whilst the range of flows covered by a single orifice is rather restricted since the rate of flow is proportional to the square root of the head. Electrical methods, depending on the transfer of heat from an electrically heated wire to the stream, have been tried (Moss 1924) but are also not free from errors when velocity fluctuations are present. Other methods adapted to particular circumstances have had some success (Bailey 1939; Cornelius and Caplan 1952) but do not represent a satisfactory general solution of the problem.

So-called ‘viscous meters’ in which the pulsating stream is directed through a number of narrow passages across which the pressure difference is measured and in which the Reynolds number is kept so low that the flow is laminar (Alcock and Ricardo 1936) may be shown theoretically to have certain advantages, notably that of a straight-line law between head and mass flow even when the instantaneous velocity is subject to fluctuations. Within limits these advantages have been confirmed in practice but under conditions of severe pulsation such meters have shown large and puzzling errors.

The investigation described below was undertaken with the primary aims of studying the performance of viscous meters under the most severe conditions of pulsating flow, with special reference to the measurement of the air consumption of reciprocating internal-combustion engines, and of developing an accurate meter suitable for use under such conditions. It is believed that these aims have been at least partly achieved and, whilst many of the experiments relate to engine air-flow measurements, it is considered that the results are capable of wider application and that they will be of value in a variety of problems concerned with fluctuating flows.
Report on Investigation into the Failure of Two 100-MW. Turbo-generators
Authors: Gibb Claude
Published: October 2007

It has often been said of engineering that ‘Progress is made by solving the problems resulting from the making of progress’.

This paper describes the investigations made following the failure of two generators each of 100 MW. capacity installed in the Richard L. Hearn Generating Station at Toronto of The Hydro-Electric Power Commission of Ontario. The author details some general considerations affecting the design of alternator rotors, the selection of materials used, past troubles which had to be avoided, reasons for certain features incorporated in the original design and modified as the result of the failures, and safeguards introduced into current practice to avoid the possibility of a repetition of the failures.
The Flow of Air through Radial Labyrinth Glands
Authors: Kearton W. J.
Published: October 2007

A theory for the flow of air through a radial gland has been worked out for both outward and inward flow. Expressions are derived for the pressure distribution in each kind of flow, and it is shown that the critical pressure ratio can be reached only in the final constriction. Experiments were made on a gland having a single ring and also on a 20-ring gland of the staggered type. The discharge coefficients in the latter gland were lower than those in the single-ring gland, possibly due to the different approach conditions. The observed pressure distribution in the multi-ring gland agreed well with the theoretical value. Finally, some experiments were made with unstaggered radial glands under various conditions. Discharge coefficients greater than unity were measured.
Investigation of the Mechanics of Wire Drawing
Authors: Wistreich J. G.
Published: October 2007

Round wire was drawn slowly and without backpull through dies with bores in the shape of truncated cones, in a study of the relations between external forces and process parameters. Not only the drawing force but also the mean die pressure and the mean coefficient of friction were measured, so that existing theories of wire drawing could be put to a more exacting test than had hitherto been possible. The investigation has revealed weaknesses in all wire-drawing theories; the use of Hill and Tupper's (1948)† sheet-drawing theory for the prediction of forces in wire drawing is not justified. Semi-empirical formulae for the forces have been devised. A simple relation between tool-stock configuration and non-homogeneity of deformation was discovered, which is also applicable to the mechanics of swaging. The assumption that the deformation is independent of the properties of the wire is not valid for annealed wires drawn with very light reductions, but is acceptable otherwise. The occurrence of thickening of the wire before entering the die and its continued thinning beyond the die deserves attention in bar drawing. There was no correlation between die pressure and coefficient of friction.
Some Further Tests on High-speed Ball-bearings
Authors: Barwell F. T. , Hughes M. J.
Published: October 2007

Friction torque and natural running temperature of ‘Light’ type and ‘Extra Light’ type bearings of bore 5 inches have been measured at speeds ranging from 5,000 to 11,000 r.p.m. Loads up to 2,400 lb. were applied at varying incidence of radial to thrust load. Lubrication was by liquid jet at the rate of 6 pints per min. It is concluded that a large proportion of the friction measured under the conditions of lubricant supply adopted in the experiments is attributable to viscous friction in the lubricant. An analysis of the friction torque based on the work of Poritsky, Hewlett, and Coleman (1947)‡ for varying angles of application of load shows no correlation with the experimental results obtained. Estimates of hysteresis loss based on the work of Tabor (1952, 1954) indicate that this factor represents a comparatively small proportion of the total frictional loss of bearings of this type.
The Reversible Bending of Turbine Shafts with Temperature
Authors: Barker A. , Jones F. W.
Published: October 2007

The reversible bending of certain carbon-molybdenum steam turbine shafts is shown to be caused by expansion coefficient differences existing in the steel from which the shafts were made. This difference is a function of the heat treatment of the steel and it is shown that the magnitude required could be obtained in shafts of the size considered by faulty normalizing conditions. A defective shaft has been cured by a second normalizing treatment in which the uniformity of the austenitizing temperature was improved. The modifications of the expansion characteristics of this steel are associated with different carbide structures.
Experiments on the Effect of Rate of Testing on the Criterion of Failure of Certain Mild Steels When Subject to Dynamic Torsion and Static Tensile Stresses
Authors: Calvert N. G.
Published: October 2007

Torsional impact tests have been carried out on a range of mild-steel specimens subjected in addition to various intensities of axial tensile stress. Tests have been carried out at a low speed (time to yield about 002 second) and at a high speed (time to yield about 0001 second). In each case the stresses observed are compared with those predicted by various of the criteria of failure.

With this particular type of stressing the effect of increasing the speed of the torsional component is to move the criterion of yield in a direction away from that of constant shear strain energy (Mises-Hencky) toward that of constant maximum tensile stress.

The maximum observed torsional stresses lie between the constant maximum shear stress and the constant maximum tensile stress and they are apparently unaffected by the rate of straining within the range investigated.

The angles endured to fracture diminish progressively as the axial tension is increased and they tend to be slightly reduced by an increase in speed.
Southampton Docks
Authors: Biddle R. P.
Published: October 2007

Since the Institution of Mechanical Engineers last held their Summer Meeting at Southampton in 1928 many important developments at the Docks have taken place, notably the building of the New Docks, one of the largest reclamation schemes ever undertaken in Britain, and the provision of the King George V drydock.

A commentary on the increase in the size of vessels using the Docks is provided by the fact that although in 1954 slightly fewer vessels used the Docks than in 1928 the gross tonnage of shipping has increased by 21 per cent.

In passenger traffic 1928 was at that time a record year but 1954 showed an increase of 23 per cent.
An Investigation into the Accuracy of the Industrial Measurement of Sizes up to 80 Inches
Authors: Harrison P. W.
Published: October 2007

The need to formulate proposals for the extension of the I.S.A. system of Limits and Fits above 500 mm. (20 inches) has required an improved knowledge of the accuracy of industrial measurement of such sizes. In an investigation conducted by the National Physical Laboratory (N.P.L.) this information has been obtained for diameters up to 2,000 mm. (79 inches) from a number of firms who have made measurements upon a special set of work-pieces circulated amongst them, these measurements being compared with those made at the N.P.L.

The industrial measurements tended to be too small, especially at the larger diameters. Both this tendency, expressed as the algebraic means of the measurements, and their standard deviation about this mean, bore an approximately linear relationship with diameter in this range of size. Supplementary information on measuring equipment did not suggest that, among the techniques more commonly used, there was one which provided particularly accurate results, but indicated that some refinement in existing equipment and methods could do much to improve accuracy of measurement.
Flow of a Compressible Fluid through a Sudden Enlargement in a Pipe
Authors: Hall W. B. , Orme E. M.
Published: October 2007

A theory, based on the same assumptions which are applied to incompressible flow, has been developed for the flow of a compressible fluid through sudden enlargements. Experimental measurements, with air as the working fluid, agree well with theoretical predictions for the relation between throat Mach number and the Mach number downstream of the sudden enlargement for the range of enlargement ratios 0.0292–0.255 and for throat Mach numbers up to 1.00.
A Slip Line Field for the Hot Rolling Process
Authors: Alexander J. M.
Published: October 2007

By using a geometrical representation, recently proposed by Prager (1953)†, of the equations defining the flow in plane strain of a plastic rigid material, it is possible to obtain a solution to the statically undetermined problem of hot rolling. The geometrical method facilitates adjustment, by inspection, of the slip line field until both velocity and stress boundary conditions are satisfied. Accuracy of the method is ensured by continual reference to the stress plane, in which an orthogonal family of identical cycloids defines the slopes of both slip lines and hodograph characteristics at corresponding points. To allow for the effect of rotation of the roll surface it has been necessary to consider the effect of rotation on hodographs in detail.

The main assumptions which have to be made are that the yield stress of the material is constant throughout the plastic zone, and that the shear stress along the boundary between roll and material attains the yield shear stress of the material. This latter assumption corresponds with Orowan's condition of ‘sticking’ throughout the complete arc of contact (Orowan 1943), and implies that the slip lines of one family meet the roll surface orthogonally. An interesting feature of the solution is the occurrence of a thin slice of rigid material adjacent to the roll surface at the entry point having a large velocity discontinuity along its boundary.
Performance of a Flat-plate Solar Heat Collector
Authors: Ward G. T.
Published: October 2007

An orthodox flat-plate solar heat collector has been constructed which is capable of being manufactured cheaply on a large scale. A simple relation has been established between the efficiency of the collector, the plate temperature and the rate of insolation for constant rates of flow of circulating water. Performance charts have been constructed enabling an assessment to be made of the practicability of using solar energy in the tropics for the production of heat and power.
The Value of the Notch Tensile Test
Authors: Baker J. F. , Tipper C. F.
Published: October 2007

A History of the development at Cambridge of a notch tensile test for the investigation of brittleness in structural mild-steel is described. The test procedure and the methods of assessing the temperature limit at which the material becomes brittle are outlined in Part I.

Investigations of material from an oil storage tank and from ships which fractured in service show that this notch tensile test gives good correlation with these casualties whatever the nominal stress in the plates at the time of the fracture. The results of Charpy V-notch and Izod tests are given for comparison, and it is shown that the energy absorption criterion used in these tests may be misleading (Part II).

In Part III experiments are described in which the tensile test has been used to predict performance in test-pieces of more complicated geometric form.

Criticisms of the notch tensile test are dealt with in Part IV.

In the conclusions, attention is drawn to the fact that the designer of orthodox fabricated structures must be provided with material which is ductile at all operating temperatures and at all stress levels.
An Experimental Study of Air-Entraining Vortices in Pump Sumps
Authors: Denny D. F.
Published: October 2007

The factors affecting the formation of air-entraining vortices in sumps are enumerated, and their relative importance assessed from experiments with a number of different sumps. It is established that vortices are caused by rotation of the mass of water within the sump arising primarily from the entry conditions. Their severity, measured in terms of the minimum safe submergence to avoid air entrainment was also found to depend greatly on the velocity in the suction inlet; air entrainment rarely occurred below a velocity of 2 ft. per sec., and above 15 or 20 ft. per sec. the severity of the vortices did not increase substantially.

The shape and disposition of the suction inlet only slightly affected the vortices, but sump boundaries were found to reduce appreciably the tendency for vortex formation when closer than 8 diameters to the suction pipe: with the walls very close to the pipe, vortices did not occur. Small sumps may thus be more satisfactory than spacious ones.

Tests with scale models of existing or proposed pump installations are described, and for one sump, where vortices formed within the working range, it is demonstrated that suitably placed boundary walls would be considerably more effective in preventing vortices than modifications to the suction inlets.

Measurements of the quantity of air drawn into the pump through a vortex showed that air entrainment of this type could seriously impair pump performance. Severe vortices could lead to depriming of pumps operating with suction lift.
A Criticism of the Technical Education of Recently Qualified Engineers
Authors: Love P. P.
Published: October 2007

The author submits that current technical education falls far short of requirements in training the student engineer in the skills of applying knowledge and using his mind, and he proposes how the means to remedy the situation may be sought.
The Vibrations of Radial-Drilling Machines under Test and Working Conditions
Authors: Tobias S. A. , Fishwick W.
Published: October 2007

Machine-tool chatter is essentially a problem of dynamic instability. A drilling machine under working conditions can be regarded as a dynamic system which for certain values of its system parameters becomes unstable and bursts into oscillations. The system parameters are determined by the static and dynamic characteristics of the machine-tool structure, the geometric shape of the drill, certain features of the work-piece material and the working conditions, and it is the interrelation of these which results in chatter or chatter-free machining. The paper commences with a discussion of the dynamic characteristics of radial-drilling machines. This is followed by an experimental investigation of the behaviour of these machines under working conditions, and finally a theory of drilling chatter is developed. The results of this theory are presented in the form of a stability chart which shows those drill speeds at which, for given values of the system parameters, chatter-free drilling is ensured. Although the theory presented is based on an experimental investigation of radial-drilling machines drilling into solid material, it is directly applicable to drilling operations carried out on any other type of machine and yields also results concerning chatter occurring at drill break-through and when drilling up pre-drilled holes.
The Use of Sodium and of Sodium-Potassium Alloy as a Heat-Transfer Medium
Authors: Hall W. B. , Crofts T. I. M.
Published: October 2007

The applications of liquid metals in heat-transfer problems are discussed, and comparisons are drawn between those metals whose melting points are sufficiently low to make them of interest in this respect. A number of sodium and sodium-potassium circuits which have been built and operated over the past three years are described; some of these were built in order to gain experience in handling the liquid metals, whilst others were for heat-transfer experiments. A general discussion on the design and construction of liquid metal circuits and the components which are commonly used in them is given. A brief discussion of forced-convection heat-transfer with liquid metals follows, and the results of some work on cavitation in sodium-potassium eutectic flowing through a constriction in a pipe are summarized.
The Dynamics of the Ball Mill: Part I: Power Requirements Based on the Ball and Shell System
Authors: Rose H. E. , Evans D. E.
Published: October 2007

In Part I the relation between the relevant dynamic variables and the power requirements to drive a ball mill, containing the ball charge but without powder charge, has been investigated by means of experiments upon small-scale models.

Dimensional analysis is used to obtain the equations in the form of dimensionless groups, and the functional relations between the groups are given analytically, or by means of graphs.

This analysis indicates that, so far as power input is concerned, the mill with lifters and the mill without lifters are best treated as separate cases, since the motion of the ball charge is different in the two systems, but that the variation in the number and size of the lifters has little effect upon the power required to drive the mill.

By means of the results of this work, the power input required to drive a mill grinding powder may be calculated with reasonable accuracy, and examples of the application of these calculations to large mills are given.
Part III: An Investigation into the Surging of Ball Mills
Authors: Rose H. E. , Blunt G. D.
Published: October 2007

The problem of surging in ball mills has been investigated by the use of small-scale models and, although a complete analysis of all the variables has not been made, a criterion has been obtained by use of which it is possible to determine, whilst the design is still on the drawing board, whether the charge of a proposed mill is likely to surge.

The validity of the proposed criterion has been demonstrated by comparison with the published results relating to industrial mills; this comparison showing that all the mills considered are operated under conditions which are in accordance with those laid down in the present work.

So far as is known, such a criterion has not previously been propounded, and it is believed that it is of considerable value to the designer and to the mill operator.

For the purpose of predicting the existence or non-existence of surging in a mill, it is only necessary to establish within which of two possible zones on a certain graph the point corresponding to the operating conditions of the mill falls; the relevant graph having for the abscissae the value of the ratio of the mill diameter to the ball diameter and for the ordinate the product of the mill filling and the mean coefficient of friction of the ball and powder charge of the mill. Thus, in order that a mill shall not surge, it is necessary that the mill filling and the ratio of mill diameter to ball diameter shall be so chosen in relation to the coefficient of friction, which is fixed by the nature of the material being ground, that the operating point for the mill shall fall within the non-surging zone on the graph mentioned.

It is suggested that if a mill can be operated under ‘non-surging’ conditions, then, for lower first costs and maintenance costs, plain liners should be adopted, but if the mill cannot be operated under these conditions, then heavy lifters should be provided to suppress surging—even though the cost is thereby increased.
Bending of Plating with Widely Spaced Stiffeners
Authors: Chapman J. C. , Slatford Jean E.
Published: October 2007

This paper is concerned with stiffened plating to which a bending moment is applied in the plane of the stiffener webs. Owing to the initial or imposed curvature there is a radial component of force which tends to deflect the plating from its original position, and the effects of this deflexion may be considerable. There is a change in the distribution of longitudinal stress across the plate, and a transverse bending stress is induced which may exceed the longitudinal stress. The effects of initial deflexion of the plating, and of lateral load, are also considered.

A numerical example illustrates the application of the analysis to the transverse bending of a ship's side. An experiment is described which confirms the theoretical conclusions for an initially flat plate.
Effect on the Local Heat-Transfer Coefficient in a Pipe of an Abrupt Disturbance of the Fluid Flow: Abrupt Convergence and Divergence of Diameter Ratio 2/1
Authors: Ede A. J. , Hislop C. I. , Morris R.
Published: October 2007

The effect of an abrupt convergence, diameter ratio 2/1, on the local heat-transfer coefficient for water flowing in a straight pipe has been determined for Reynolds numbers from 800 to 100,000 in the smaller pipe, which had an internal diameter of 1 inch. The pipe was heated by the longitudinal passage of a heavy direct current through the wall. The variation in local coefficient, which was comparatively small, is presented and discussed; it does not differ greatly from the variation found in the entry regions of pipes under more normal entry conditions.

The effect of an abrupt divergence, diameter ratio 1/2, has also been determined for Reynolds numbers from 3,700 to 45,000 in the larger (2-inch) pipe. The variation in local coefficient was considerable.
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.
Principles and Applications of Spark Machining
Authors: Rudorff D. W.
Published: October 2007

The historical background of electro-erosion technique is briefly outlined and the difference between spark and arc*** discharges is defined. The underlying principle of the relaxation-type spark circuit as employed in industrial machines is explained, and development trends are discussed. The various factors bearing upon the efficiency of spark-erosion operations are enumerated. The mechanical features of a typical spark-erosion machine are described, and the range of machining operations for which spark cutting machines can be designed, is outlined. Typical samples of work produced on a commercial unit are described and illustrated, and the properties of spark-machined surfaces are discussed.
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.