Cranfield University at Silsoe (1975-2008)

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Open Access
Design of aerobatic aircraft wing
(Cranfield University, 1969-05-19) Potter, J. G.; Howe, D.
The aircraft under consideration in the following text is a swing wing, 50,000 lb. (maximum weight), land based strike aircraft. The various roles of the aircraft are strike operations at a Mach number of 2.0 and height 36,000 feet or Mach number of 0.9 at low level, interceptor operations at a Mach number of 2.0 with a, dash at a Mach number of 2.0 and search and patrol operations at a Mach number of 0.76 and a height of 36,000 feet (with wings unswept). Design of the aircraft was split into several sections each one being investigated by a different student. The section analysed in this report being the forward-centre fuselage. This lies between the rear sloping pressurised bulkhead of the cockpit to the aft bulkhead of number two fuel tank. Time did not allow for the design of all the structural parts but detailed studies were conducted on two different frames (one light fabricated and one heavy machined), the nose undercarriage bay, two sections of fuselage cross-section, and the variable geometry bullet including aerodynamic loading in the intake. A sample fatigue calculations were done on a fuel tank and nose undercarriage together with a complete weight breakdown for the forward-centre fuselage (several approximations being made 'for undersigned structure). From the loading calculations the critical cases defined that the structure in this section of the fuselage was designed on the manoeuvres and landing cases. Use of Concorde material (aluminium alloy) RR. 58 was used wherever possible because of temperature effects in the high speed configuration. However, for some of the view heavily loaded members steel had to be used (with the appropriate temperature reduction factor applied to the allowable stresses) to keep the volume of material to a minimum.
Open Access
A study of simulated weld heat affected zone structures and properties of HY-80 low alloy stee
(Cranfield University, 1969-10) Kellock, G. T. B.; Sollars, A. R.
Single and double cycle simulation techniques have been employed to investigate the structure and properties of the heat affected zone in HY-80 steel due to a single submerged arc weld run and to the deposition of a tempering bead on a pre-existing edge bead heat affected zone. The thermal cycles used for simulation had peak temperatures of 1275°C, 930°C, 7650C and 6500C and corresponded to those experienced in the parent material during the submerged arc welding of 1.5 in. thick plate using a nominal heat input of 54kJ. in and a preheat temperature of 120°C. Double cycling utilized specific combinations of these thermal cycles. Half the total number of simulated specimens received post cycle heat treatment at 650°C. Charpy V-notch impact transition curves and tensile and hardness data have been obtained for each condition studied and structural examination has employed the carbon extraction replica technique in the electron microscope. The results indicate that the properties of the weld heat affected zone in HY-80 steel are superior to those obtained for QT-35 steel but inferior to those of the HY-80 parent material. The tempering bead technique has been shown to have, at best, only a limited tempering effect on the grain coarsened region of an edge bead heat affected zone and can also cause an increase in the susceptibility of this region to brittle fracture. Post weld heat treatment at 6500C is recommended, wherever possible, for HY-80 weldments. The calculation of weld heat affected zone thermal cycles, which correlate well with the practical situation, has been made possible by the development of a series of computer programs. These programs include functions to account for the release of latent heat from the solidifying weld pool and the variation of thermal conductivity with temperature.
Open Access
Parameter identification applied to aircraft
(Cranfield University, 1973-10) Klein, V.; Matthews, N. O.
All three steps in the identification, namely characterization parameter estimation and verification are considered and applied to the determination of aircraft parameters from flight data. The estimation procedure includes the equation error method and the output error method with the weighted least squares, maximum likelihood and Bayesian estimation technique. The problems concerning accuracy and identifiability are also discussed. A general computing algorithm is developed covering all estimation * techniques described. It is applicable to linear as well as nonlinear systems and is flexible enough for the solution of various identifiability problems. Using this algorithm the computing program has been compiled in general terms to enable the user to achieve the objectives mentioned. â R ' As examples, the results of the identification of aircraft parameters and aerodynamic derivatives for four different aircraft are presented. They include the analysis of flight data from the Basset variable stability aircraft and from the M.S. 760 Paris aircraft, the simulated data for a nonlinear model of the F-100 aircraft, and the flight data from the longitudinal motion of the HP-115 slender delta flowing research aircraft. The report is completed by the recommendation for future work in the area of aircraft parameter identification.
Open Access
The dissemination of information relating to the reliability of aircraft and their equipment
(Cranfield University, 1979-06) Fielding, J. P.; Keith-Lucas, C. B. E.
This thesis describes the investigations that have been carried out to examine the feedback of safety and reliability information from civil transport aircraft in the United Kingdom . Many organisations were visited during the course of the study , including several civil transport aircraft operators, airframe and component manufacturer?, and airworthiness authorities . These visits showed the way in which individuals and companies contribute to the information system. The quality of the feedback produced by the information system was assessed by means of a selective survey of development, reliability, and design engineers, etc . who had previously been interviewed during visits to industry . The response of the information system was also gauged by determining the average times required for rectification action to be taken. Parallel studies were conducted, in a limited fashion , to see how the safety and reliability information system of the United States of America ' s civil air transport industry and that of the Royal Air Force, and its suppliers, compared with the British civil air transport industry ' s system . A series of case studies was also performed to investigate , in some detail , what happened to faulty components that were removed from aircraft . The transmission of information from these components to everyone else in the information system , and the rectification action taken , were examined . These studies confirmed that the procedures determined in the previous investigations were, in general , carried out and also highlighted some problems. All of the above investigations showed that the reliability information system was not always adequate, and that a considerable amount of work may have had to be done m achieve adequate reliability control . There were some areas where there was insufficient information for reliability control, and improvements were necessary. The most important recommendation was that a more detailed investigation should be carried out into the feasability of a National Aerospace Reliability Data Bank . A further suggestion was that the Maintenance Review Board consultation system, and its associated reliability and maintainability analyses, should be encouraged . Some work was done to produce design aids such as reliability prediction formulae , etc . These should go some way towards overcoming the problem of design experience retention.
Open Access
A study of the interaction between a glancing shock wave and a turbulent boundary layer
(Cranfield University, 1980-08) Kubota , H.; Stollery, J. L.
An oblique shock generated by a variable-angle wedge on the side wall of a wind tunnel, has been used to investigate the three-dimensional glancing interaction problem. The shock interacts with the turbulent boundary layer growing along the side wall. Two related test programmes have been completed using a 2.5 x 2.5 inch intermittent tunnel and a 9 x 9 inch continuous-running tunnel. For both the test programmes, the Mach number was approximately 2.5 and the Reynolds number relative to the wall boundary-layer thickness 5 x 10 4 . The experimental results include oil-flow pictures, vapour-screen and smoke photographs,wall pressure distributions, local heat transfers, wall surface temperatures and viscous layer surveys. The experimental results suggest that the interaction reg10n consists of two different viscous layers between which an ordinary separation can take place, (the double viscous layer flow-field model). The three- dimensional separation is found to depend significantly on the pressure rise in the direction normal to the swept shock. In this sense the separation is similar to the two-dimensional case.
Open Access
Multi-equation travel demand models application to the air-rail competition in Great Britain
(Cranfield University, 1981-10) Cherif, T; Black, Ian G.
The main purpose of this research is to develop a set of econometric Air-Rail competition models which are sufficiently sensitive to measure the effects upon demand of policy decisions, with regard to such variables as frequency of services and fares. Existing Modal Competition Models have, rather uncritically, applied Multiple Regression analysis in considering only one aspect of the market, namely the demand for travel, ignoring therefore the effects of the supply upon the demand. The emergence of the so called "Simultaneous Equations Bias", due to the two-way dependency between the demand and the level of service factor expressing the supply, renders the application of the 015 (Ordinary Least Squares) inappropriate, and hence, yields biased, inconsistent, and inefficient OLS coefficients. The models, developed in this study, depart from all existing Modal Competition Models, and overcome some of their drawbacks. They are formulated as Multi-equation Supply/Demand Modal Competition Models. They introduce the frequency of services variable not only in the demand, but also in the supply equation expressing the level of supply in response to changes in other variables. In order to derive unbiased, more conSistent, and more efficient coefficients, sophisticated statistical techniques, such as 2315 and JSLS (Two-Stage Least Squares and Three-Stage Least Squares) • are applied as a means of calibration. The elasticities obtained are consistent with the Supply and demand Microeconomic Theory. The frequency of services appears as the most powerful explanatory variable in Air demand; whereas fare and income are the most powerful variables in Rail demand equation. This leads to the conclusion that Air mode is mainly higher income groups and/or business oriented market; and Rail mode lower income groups and/or personal oriented market. Furthermore, Air and Rail are competing on a fare basis in short routes; while they do not show close substitutes for each other in longer ones. The high significance of the frequency of services, in Air demand, outlines its importance as a factor influencing the demand, and therefore, provides the Airlines management with the capability of improving the demand by acting upon the endogenous factor. This is of great interest in the scheduling fleet process. Similarly, the significance of Rail fare variable offers the Railways management the possibility of acting upon the demand through this controlable variable, for an efficient pricing policy. Rail journey time elasticities, derived from these models, are very close to the elasticities assumed by British Railways Board, in their Passenger Traffic Model, 1980. The statistical results indicate that the elasticities derived are useful for both analysis and forecasting purposes.
Open Access
The immediate extraction and display of insect flight trajectories from infra-red remote sensing signals
(Cranfield University, 1982) Bent , Graham; Schaefer, G. W.
The increasing need to study insect flight behaviour in the natural environment has led to the development of a relatively inex- pensive remote sensing instrument (IRADIT) . Flying insects dfferentay iumjmted, under a light cmations, in a intense ba of pulsed near infra-red radiation and detected using a gated image intensifier - CIV system at a rate of 5OHz. This thesis details the methods employed for extracting insect oo-ordinates from the' CI video signals, 'using low~oost electronic circuits ad micro computer (Apple II+) , and for the immediate analysis and display of two-dimensional insect flight trajectories, whilst rejecting environmental and system noise. Flight trajectories are often dominated by the immediate local wind. A new low-cost sensitive three dimensional digital anemometer system hs be developed for use with the IRADIT system, providing the data required to allow the vector wind to b immediately subtracted and interesting aspects of flight behaviour to b revealed. The IRADIT - Anemometer system ws tested i the field, on insects above wheat. _ Small insects with membzßanous wing areas as small as 5mm2 were readily detected and tracked over distances of the order of l at ranges up t 15m against a mid-day sky background. Subse- quent computer analysis of stored insect track and wind data oonfirmed that the effects of immediate local wind cn b smdied or canoelled out. Examples of insect flight behaviour are described. The relatively low cost of the IRADIT system and the practical features in its design result in a powerful new tool for use by the field entomologist.
Open Access
The identification of aircraft stability and control parameters in turbulence
(Cranfield University, 1982-07) Foster, G. W.; Christopher, P. A. T.
A technique for the identification of aircraft stability and control parameters from flight test recordings made in either calm or turbulent air is presented. The maximum likelihood output error method is used with a steady-state Kalman filter incorporated to account for atmospheric turbulence. A modified Newton-Raphson search technique, enhanced by a line search, is employed for parameter identification. Separate algorithms are developed for estimating the biases and noise levels in the observations. Some areas of practical problems in the application of such methods are stressed. A computer program for the identification of longitudinal stability derivatives is described and the aircraft instrumentation required is exemplified by that in Gnat XPSOS. The wind tunnel calibration of the flow-direction sensing nose probe assembly of Conrad yawmeters on this aircraft is detailed. The problems of handling the flight observations recorded are covered and some of the troubles experienced with the instruments are noted. The performance of the identification technique is investigated. The data required, the choices open to the analyst and the statistical information produced being highlighted. The identification of the process noise level, in this instance the turbulence intensity, is addressed and it is found that the value specified for this level can influence the other parameters. The longitudinal stability and control derivatives obtained for Gnat XPSOS are presented.
Open Access
Wind tunnel techniques for reducing commercial vehicle aerodynamic drag
(Cranfield University, 1982-09) Garry, K. P.; Stollery, J. L.
Increases in the price of petroleum fuels have significantly affected the importance of aerodynamic drag on commercial vehicle operating costs. The considerable savings to be made have resulted in: (i) the appearance of numerous 'add-on' devices intended to reduce the drag-of existing vehicles, and (ii) an acceptance by vehicle manufecturers of the importance of aerodynamics to their new designs. The majority of drag optimisation programmes are carried out using scale models in a wind tunnel, and the effectiveness of resulting modifications is often confined to the individual vehicle concerned. The relatively crude simulation techniques have been acceptable on the basis that potential errors are small compared to the reductions in drag that can be achieved. If the trend in reducing drag is to be maintained a greater understanding of the flow around commercial vehicle configurations will be needed, especially under simuleted,crosswind conditions, together with improvements to the wind tunnel techniques used to simulate the full scale environmen The experimental programme presented in this report is intended to Illustrate ,the influence of wind tunnel simulation technique, on the methods for reducing commercial vehicle aerodynamic-drag. result in wind tunnel tests over a 'range of simulated crosswind conditions and levels of free stream turbulence are present illustrate the significance of variations in Reynolds number, vehicle geometry, and wind tunnel size on the pressure distribution 2. and resulting diagonal forces on the vehicle. I.Jrfece pressure contours are ceteidgued.t0 give insight into the flowfield, around the vehicle in relation to the problems of body fouling and water spray generation although analysis here specifically concerns aerodynamic drag. Techniques for reducing drag relate primarily to modifications Of the forebody flowfield and results from a number of experimental Programmes are collated to illustrate the effectiveness of various,,, techniques on different vehicle geometries.
Open Access
Flow inside axial pump impellers
(Cranfield University, 1982-12) Resnick, Avi; Goulas, A.
The subject of this work is the flow inside an axial pump impeller, which is studied both numerically and experimentally. The aim of the work is to provide a numerical method to predict the three-dimensional flow field within an axial flow pump impeller. The numerical scheme is divided into three basic parts. The first part involves the matrix through flow method to obtain the mainstream flow profiles on various blade-to-blade stream surfaces distributed from hub to tip and for given boundary conditions. In addition these solutions w to obtain a detailed flow field in the region of the leading edge. Furthermore, the transport equations of vorticity are integrated along each streamline to obtain the normal and stream wise components of vorticity.
Open Access
The effects of exfoliation corrosion on the fatigue and fracture behaviour of thin aluminium alloys
(Cranfield University, 1982-12) Morad, T. A.; Chubb, J.; Hockenhull, B. S.
The present study is concerned with the interaction of stress and corrosion in high strength aluminium a11oys in sheet form used in the aircraft industry. Many of these alloys are susceptible to exfoliation corrosion under service conditions. This type of corrosion was reproduced in the susceptible a11oys using the Exco test method. The fracture toughness of an A1 - Zn - Mg - Cu a11oy (7178 - T6) was assessed using R - curves. The interaction between exfoliation corrosion and the thinning effect of exfoliation on the fracture toughness are discussed. Fatigue crack growth behaviour in two naturally aged A1 - Cu ~ Mg alloys, 2024 - T351 and 3L7O (2014 - T4) was evaluated under conditions of low and high humidity using constant amplitude loading. A similar assessment of the effect of humidity on the propagation rates in the higher strength 7178 - T6 was carried out. Additionally, the effect of the presence of exfoliation corrosion on crack growth in 2024 - T351 and 7178 -- T6 was examined. Both humidity and exfoliation corrosion enhanced fatigue crack growth rates in the alloys, though to differing extents, with 7178 - T6 being affected more. The fatigue resistance of 7178 - T6 diminished even further in the presence of humidity and corrosia together. Finally, a mechanism to explain the way by which exfoliation corrosion affects the fatigue and fracture behaviour of thin aluminium sheets is proposed.
Open Access
Quantification of the interactive motions of the atmospheric surface layer and a conifer canopy
(Cranfield University, 1983-12) Scannell , B; Schaefer, G. W.
Consideration is given to the use of.vane (DVA) and propeller anemometers in the sensing of atmospheric turbulence. Careful experimental measurements of the DVA dynamic response contributes to this consideration. Quantification of the airflow within and above a Sitka spruce canopy then follows. Statistics indicate the non-Gaussianity of the air turbulence Such forms are interpreted through the intermittency of turbulence and investigated by a conditional sampling scheme. Nindspeed spectra have ragged forms, showing them to be vastly modified by the combined effects of the canopy-imposed scales, together with the canopy's elemental vortex shedding frequencies and resonances. Studies of tree motions show the possibility of_a simple connection between the resonances of the separate canopy elements, which could provide the tree with an atmospheric shock-absorbing structure, supportive of its observed response to turbulence The ensuing proposal of a hypothetical qualitative mechanical design principle based on aeroelastic similaritynay bebeneficial to the tree's survivability in conditions of strong atmospheric turbulence.
Open Access
Theoretical analysis of Gas Dynamic disturbances in an explosive atmosphere
(Cranfield University, 1984-02) Ashdown, P. D.; Clarke, J. F.
Various problems, which examine the propagation of gas dynamic disturbances, through an explosive atmosphere, are considered. The first set studies a model relaxing gas, and asymptotic methods are employed. A high frequency expansion is used to investigate piston oscillations in an infinite half space. The first two terms in the velocity perturbation are found in the acoustic case. The amplitude and frequency change on a wavelet are given; the wave number alters from wavelet to wavelet. For an enclosed volume the multi-time method is employed. When a standing wave exists in the vessel the frequency changes: when the vessel oscillates the wave number changes. The situation when forced oscillations at a natural frequency of the container is discussed. Also finite amplitude oscillations in a vessel are considered by using the multi-time method. An integral equation for the amplitude growth is found. A numerical solution of outward wave propagation, in spherical and cylindrical coordinates until shock formation, is given. The second group of problems considers a multi-component gas which can be analysed numerically. The effect of the homogeneous explosion in amplifying or damping a weak ii discontinuity is simulated. Thus proposals for reaction schemes can be analysed. It is found there is a relation- ship between amplification/damping and strong/weak ignition, in a mixture of hydrogen and oxygen in a shock tube. The reactions liberating a significant amount of energy in the chemical reaction, are the reactions causing greatest amplification.
Open Access
The experimental and theoretical aerodynamic characteristics of aerofoil sections suitable for remotely piloted vehicles
(Cranfield University, 1984-03) Render, P. M.; Stollery, J. L.
Using the design requirements of Remotely Piloted Vehicles (RPV's), selected for wind tunnel testing over the Reynolds number range 3 x 105 to 1 x 106. The first aerofoil, NACA 643-418, showed a degradation of performance in terms of lift-to-drag ratio as the Reynolds number was reduced. There was also a laminar separation bubble of notable extent on both the upper and lower surfaces at most incidences throughout the Reynolds number range. The second aerofoil, Göttingen 797, had good performance in terms of lift-to-drag ratio and maximum lift coefficient, even at the lowest Reynolds number. This was attributed to the flat bottom of the aerofoil, which allowed the formation of extensive laminar flow on the lower surface without the formation of a laminar separation bubble. The third aerofoil, Wortmann FX63-137, generally exhibited the best aerodynamic performance in terms of maximum values of both lift-to-drag ratio and lift coefficient, throughout the Reynolds number range considered. Four alternative lower surface geometries for this aerofoil were also tested. The modifications reduced the maximum values of both the lift coefficient and lift-to- drag ratio of the original aerofoil throughout the Reynolds number range, but generally improved the lift-to-drag ratios at low values of lift coefficient. The notable exception was the modification which resulted in a flat bottomed section. This had maximum values of lift-to-drag ratio which were within a few percent of those of the original aerofoil throughout the Reynolds number range. Wind tunnel results were used to evaluate low-speed aerofoil analysis computer programs written by Eppler and Somers (13) and Van Ingen (18). The results were disappointing. However, using the same wind tunnel results it was noted that computer programs using semi-inverse viscous methods show great promise.
Open Access
Effects of phase separation in crosslinked resins containing polymeric modifiers
(Cranfield University, 1984-03) Partridge , I. K.; Bucknall, Clive
The study reported in this thesis concerns the relationship between morphology and the properties of multicomponent epoxy and methacrylate resins. The thermodynamic and kinetic aspects of phase separation in reactive, thermosetting, systems are explored and applied to the investigation of blends of 'high performance' epoxy resins with polyethersulphone. The mechanical properties of the same cured blends are shown to be insensitive to considerable variations in composition, cure and the resulting morphology, both in the bulk-resin and in carbon fibre-epoxy laminate forms. Room temperature fracture and yield behaviour of highly cross linked and rubber modified methacrylates, of rubber modified dysfunctional epoxies, as well as of the above mentioned epoxy/polyether sulphone blends, is investigated. Special emphasis is placed on a comparison of the kinetics of tensile creep between the different systems. Loss of ductility in the highly cross linked resins is shown to result in a very limited scope for toughness enhancement by the usual rubber toughening methods.
Open Access
Drainage benefits and farmer uptake
(Severn Trent Water Authority, 1984-07) Morris, J.; Hess, Tim M.; Ryan, A. M.; Leeds-Harrison, P. B.
As part of the Severn Trent Water Authority's need to improve managerial decision on future projects, post appraisals of completed projects have been instigated. These can involve either a comprehensive review of all aspects or the project or, alternatively, can consider key parameters only. In the case of agricultural land drainage schemes key parameters have been identified as the benefits resulting from schemes and the rate of uptake of these benefits by farmers. The investment of public funds in improved agricultural land drainage is normally justified in terms of the resultant net increase in the value of agricultural production.
Open Access
The design and manufacture of a low cost, six axis, industrial robot
(Cranfield University, 1985-01) McMaster , Robert S; Rathmill, K.
The aim of the work presented in this thesis is to investigate the feasibility of producing a low cost, 6 axis, Industrial Robot. The formulation of a design specification based on market trends is shown, and used as a starting point for formal design analysis. A robot conceptual design based on two, series coupled, triangular link mechanisms was devised, following a detailed analysis of various kinematic mechanisms. The purpose of the mechanisms analysis was to find a low cost, inherently stiff, means of driving the robot main axes; in particular, the shoulder and elbow joints. By adopting the novel concept of a hand and wrist mechanism, a "true 3 axes" wrist was devised. A unique feature of this is that the roll, pitch and yaw axes form an orthogonal set with the origin at the wrist point. Although emphasis is placed on the robot mechanical design, a Servo amplifier system, suitable for driving all 6 axes of the robot is presented, and recommendations for a position control system are given. Finally, costs relating to the robot mechanical system, Servo amplifier system and Position control system were investigated. The variation in cost with robot volume is shown for each of the 3 systems. This indicates that a manufacturing cost of E9000 per robot can be achieved providing at least 150 robots are produced. The following papers have been published by the author in connection with this work: (i) The Development and Design of a Low Cost Assembly Robot, Proceedings of the 7th B.R.A. Annual Conference, May 1984. pp 171-182. (ii) Overview of Robotic Manufacture Worldwide, Seminar "Exploiting robot in arc welding fabrication", The Welding Institute, Cambridge, Nov. 1984. pp 1-7
Open Access
The measurement of the size and concentration of fine sand suspensions using scattered ultrasound
(Cranfield University, 1985-09) Lenn, C. P.; Enever, K. J.
This work is concerned with the development of an instrument capable of measuring simultaneously both the size and concentration . of suspended fine sands in the presence of silt. A review of the literature of the measurement of suspended solids showed that the most promising approach to develop such an instrument would use ultrasonic methods. A theoretical study of the scattering of ultrasound for suspensions is presented and this shows that an appropriate choice of frequency and scattering geometry will give reduced sensitivity to silt size particles whilst yielding information on the size and concentration of the suspended particles. Laboratory experiments were conducted using a vertical sedimentation test facility and single angle scattering from suspensions of sand and glass balls. The experiments showed that the theory is adequately modelled in practice. A laboratory model of a field instrument, employing analogue and digital signal processing, was then constructed and tests were performed on a range of suspended sediments with different mean size, The ratio of ultrasound scattered through 10° and 170° was found to be concentration independent, being a function of size only. The ultrasound scattered through 10°. suitably processed, was a measure of concentration. A measure of agreement between theoretical predictions and experimental results was obtained and design recommendations for the manufacture of a field instrument are given.
Open Access
A study of the interaction between a glancing shock wave and a turbulent boundary layer : the effects of leading edge bluntness and sweep
(Cranfield University, 1985-11) Hussain, S.; Stollery, J. L.
The effects of leading edge bluntness and sweep angle on the three dimensional glancing shock wave - boundary layer interaction have been investigated. A large number of hemi-cylindrically blunted fins with leading edge diameter ranging from 0 to l.Oin, with leading edge sweep angles between 0° and 75° were tested. The incidence angle was varied from 0° to 21°. The shock wave from each configuration interacted with a fully developed turbulent boundary layer growing along the tunnel side wall. The free stream Mach number in the 9in x 9in continuous flow supersonic wind tunnel was 2.4 and the Reynolds number based on boundary layer thickness was 5 x 10^. Experimental investigations included oil smear tests, surface pressure surveys, schlieren pictures of the inviscid shock envelopes and shock structure in the plane of symmetry. The study highlighted the significant effects of bluntness and sweep on the scale and character of the interaction. While bluntness intensified the interaction, sweep alleviated its intensity. The most dramatic effect of sweep angle was observed when the leading edge was swept from 0° to 30°. Sufficiently outboard of the plane of symmetry, the features of blunt and sharp fins became similar. The boundary between the inner "bluntness dominated" and the outer "viscous dominated" regions shifted inboard at the higher incidence and sweep angles. The characteristic surface oil flow patterns showed little change for sweep angles up to A = 60°. Leading edge bluntness increased the scale of the interaction almost linearly while leaving its character unchanged. The multiplicity of the separation and attachment lines on the side wall and the fin surface, suggested a system of vortices in the interaction region. Flow field models have been proposed over the range of sweep angles considered in the present study. The number and strength of the vortices is seen to depend on the leading edge bluntness, sweep and the incidence angle. The important parameters governing the primary separation distance and the peak pressure in the plane of symmetry have been identified. Correlation formulae suggest a strong interdependence of the various parameters concerned.
Open Access
Welding C-Mn steels using the pulsed current MIG welding process
(Cranfield University, 1986-03) Foote, W. J.; Apps, R. L.
The welding of C-Mn steels using the pulsed current MIG welding process was investigated. Following initial work on the basic fusion characteristics, the process was applied to the production of closed butt joint linepipe welding and narrow gap welding (in the flat and H-V positions). The initial stage of the work covered the determination of pulse parameters for controlled metal transfer with a variety of wires and shielding gases. Basic bead-on-plate fusion characteristics were investigated 1n all welding positions and quantified in terms of the major welding variables of current and travel speed. Welding position was shown to have no effect on fusion behaviour. Successful full penetration closed butt root welds were produced in all welding positions. Heat input was shown to be the factor controlling bead dimensions. Close control over welding parameters are needed to maintain consistent bead sizes. Complete joint simulations were also made. The vertical-up technique was shown to give superior fusion characteristics with the process producing excellent quality results in all positions. Narrow gap MIG welding was shown to be feasible without wire manipulation at gap widths below 12 mm in the flat position. A wire manipulation technique gave excellent fusion characteristics with gap widths greater than 12 mm. A computer program was devised as a guide to the selection of process parameters and possible fusion behaviour. Modelling considerations showed that H-V position narrow gap welding would be feasible only with gap widths less than 10 ... A short experimental programme validated the predictions of fusion behaviour by the model and indicated the direction for future development work.

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