CoA. PhD, EngD, MPhil & MSc by research theses

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Open Access
The application of computational techniques to the design of thermal ice protection systems
(1990-03) Leah, C. W.; Eshelby, M. E.
A bibliography citing 1350 references related to all aspects of aircraft icing is presented. An ice adhesion database has been compiled, and a survey of ice adhesion test rig designs is presented. An ice shear adhesion test rig is designed, manufactured and operated. The results are added to and compared with those in the database. The adhesion of ice accreted on metal and non-metallic composite aircraft propeller blades in flight is assessed. A one-dimensional thermodynamic study of ice accreted on a non-metallic composite propeller blade with ’built-in1 electrothermal de-icing system is effected and compared with a solid metal blade. A two-dimensional aerofoil icing prediction program is modified and executed in series with additionally created software to predict icing on aircraft engine air intake duct lips in flight. Hence a new de-icing system design method is developed to replace and improve upon an existing one. Validation of the new design method is initiated and a programme for its completion is presented. Icing predictions produced using the new method correlate well with expected values derived by several methods. The new design method is incorporated in the sponsoring companies business with an appropriate computer hardware/software system and employed, in parallel with the ’old’ approach (till validation completion), on commercial projects. Market response indicates a definite preference for the new design method. The ’non-technical’ and other related practical topics of implementing the new de-icing system design method, including specification and installation of computer hardware and software are discussed. Marketing, financial and other commercially oriented subjects are addressed in justifying the research and the implications of introducing the new design method into the commercial business of the sponsoring organisation are considered. This research programme forms a part of a large, long term icing research commitment. Continued research subjects and investigative routes including the integration of ice adhesion mechanical characteristics into the de-icing system design method are discussed together with their relationship to this and the overall icing research plan.
Open Access
The application of relative navigation to civil air traffic management
(2000-08) Sangpetchsong, K; Allerton, David J.
This thesis addresses navigation and guidance which will be required for air traffic management in Future Air Navigation Systems (FANS) and Free Flight. In particular, the thesis covers the issues of data fusion and integrity monitoring, to provide an adequate level of aircraft separation assurance, based on relative navigation (RELNAV). The evolution of air navigation systems is described. The principles of Kalman filtering and Joint Tactical Information Distribution System (JTIDS) RELNAV are covered. Sensor models of strapdown Inertial Navigation System (INS), Global Positioning System (GPS), and Automatic Dependent Surveillance-Broadcast (ADS-B) are developed in Matlab and integrated to form a hybrid navigation system. RELNAV algorithms for centralised and decentralised Kalman filtering are formulated, and their respective performances are analysed using Monte Carlo simulations for an airspace containing several aircraft. It is shown that RELNAV, based on the integration of INS and ADS-B, can enable aircraft to maintain safe separation independent of GPS, where it is assumed that an ADS-B datalink provides accurate time synchronisation. An alternative approach that integrates INS, GPS, and ADS-B is developed and analysed. It is shown that this approach is more applicable to civil aviation because it eliminates the needs to establish and manage several navigation communities simultaneously, in effect, exploiting GPS as the navigation controller. The source selection functions used for RELNAV are also developed, and the stability and performance of this technique is evaluated from simulation studies. A failure detection algorithm that monitors the residuals of a Kalman filter is derived and evaluated using Monte Carlo simulations of GPS failures. It is shown that this algorithm combines the use of likelihood functions and chi-squared tests, allowing both a false alarm rate to be selected and a failed sensor to be identified. Finally, an algorithm is developed for separation assurance to determine the probability that aircraft are closer than a pre-determined distance, taking into account flight path prediction errors. It is shown that this algorithm simplifies aircraft conflict detection in three dimensions and allows the conflict probability at a particular time to be determined. This approach is validated using Monte Carlo simulations of aircraft trajectories which include near-misses.
Open Access
An approach to configuration design synthesis of subsonic transport aircraft using artificial intelligence techniques
(1991-12) Pasaribu, H. M.; Fielding, John
This thesis outlines a computer system developed to tackle the configuration design synthesis of subsonic transport aircraft. The system provides an interactive design environment which combines the reasoning process of the aircraft configuration definition and the numerical analyses that lie behind the reasoning. The system applies Artificial Intelligence (AI) techniques to the configuration analysis. This gives the system the capability to reason with the configuration choices. The system is built in modules, with each module is clearly separated to deal with a complete analysis in a specific aspect of design. The integration of the modules is done through an intelligent interface and a common database. The interface also incorporates AI techniques in deciding the sequence of execution of the modules and the processing of the input/output data for a particular module. The interface permits the sharing of information among the modules and supports modularity and flexibility of the system for future development. Since each module is independent, it can be easily modified or replaced without disturbing the balance of the system. An extensive library of application programs is included in the engineering analysis module which enable detailed analysis to be performed. The system is equipped with a simplified database management and a special purpose graphics module which is extensively used for the presentation of the output. The system has been validated and tested. It can handle both propeller driven and jet engined aircraft. An example of the case studies is presented. The improvement of the system for future development is also considered. These include the extension of the knowledge base for dealing with problems in other modules, the enhancement of the application programs in the engineering module, and a possible interface with an established Computer Aided Drafting (CAD) system.
Open Access
Buckling of corrugated core sandwich panels
(1969-09-19) Patel, N. G.; Griffin, K. H.
A computer program is developed to determine the buckling stress and deflections of symmetric corrugated core sandwich panels. In the program freedom for lateral deflections at core to face-plate junction is allowed for. Provision is also made to study the effect of variation of core bend radius. A range of test specimens using four basic core configurations is designed to assess the effect of core bend radius on the buckling stress of the panel. The computer program indicates that above a certain value of core bend radius there is a marked drop in the value of critical buckling stress and a change in buckling Mode. The values of deflections at core to face-plate junctions at low buckling wave-lengths are not reliable* Due to the limited range of the experimental work, it is not possible to draw any conclusions on the effect of core bend radius on the buckling stress. The method used for determining the experimental buckling load is somewhat subjective in application, and its accuracy is difficult to assess. In general, the experimental values of buckling stresses are 15% higher than those predicted by the computer program. These discrepancies are not large when dimensional and material property variations are considered and indicate that the computer results are giving the correct trend and are conservative. Recommendations are made for : (i) Investigation of the buckling deflections at low values of buckling wave-lengths for specimens with high face-plateto-core thickness ratio. (ii) A test programme covering a wider range of specimens than that covered by the test programme in this study. and (iii) Trying out the other two methods of determining the buckling load.
Open Access
A class of upwind methods for conservation laws
(1994-06) Billett, S. J.; Toro, E. F.
Various new methods for the solution of hyperbolic systems of conservation laws in one, two and three space dimensions are developed. All are explicit, conservative timemarching methods that are second order accurate in space and time in regions of smooth flow and make use of local Riemann problems at intercell boundaries. In one space dimension, the Weighted Average Flux (w af ) approach of Toro is extended to generate a scheme that is stable with timesteps twice as large as those allowed by the stability conditions of the original scheme. A Riemann problem based extension of the Warming-Beam scheme is considered. Total Variation Diminishing (t v d ) conditions are enforced for both schemes. Numerical results for the Euler Equations of Gas Dynamics are presented. In two and three space dimensions, finite volume versions of the waf scheme on Cartesian grids are derived for the linear advection equation. Two two dimensional schemes are found that are second order accurate in space and time. One of these is extended for the solution of nonlinear systems of hyperbolic conservation laws in two separate ways. The resulting schemes are tested on the Shallow Water equations. The equivalent three dimensional schemes are also discussed. The two dimensional schemes are then extended for use on structured, body-fitted grids of quadrilaterals and one of these extensions is used to demonstrate the phenomena of Mach reflection of shallow water bores.
Open Access
The design and analysis of a reconfigurable flight control system for advanced civil aircraft
(1994-04) Oliva, A. P.; Cook, M. V.
This work is concerned with the design of a pitch-rate-commandattitude-hold Command and Stability Augmentation System in order that the augmented aircraft meets the Gibson dropback criterion, the Gibson phase-rate criterion and MIL-F—8785C requirements. The work shows two methods of design, pole-placement and optimal control, and discusses the design procedures, the advantages and disadvantages of each method. The work is also concerned with the redundancy aspect of the control law design, and so not only a sensor based design but also an observer-based design are investigated. In order to design the observer-based control law, a Doyle-Stein observer was implemented. Two methods showing how to design the observer are discussed and presented, and the special characteristics of this kind of observer are also considered. The performance of the observer-based control law was compared with that of the sensor-based control law. The failure transients and characteristics of the control law are also studied and presented. Finally an evaluation of the control law was carried out with a non-linear model of the B-747 aircraft, and a simple altitude-hold autopilot was designed to work together with the stability augmentation control law.
Open Access
The design and development of high speed externally pressurized air bearings for an internal grinder
(1969-09-20) Ghosh, K.; Leete, D. L.
Briefly, the basic theory of externally pressurized air bearings which provides shaft support, with very low friction in high speed devices, has been discussed in this paper. Some considerations have been given to the various factors such as axial flow, circumferential flow, dispersion effect, compressibility,. effect and hydrodynamic effect. The main objective was to produce an air bearing system capable of running between 45,000 to 80,000 rev/min., driven by a belt, with the radial and axial stiffnesses of 250,000 lb/in. and 150,000 lb/in. respectively. Moreover, the air consumption rate had to be as low as possible, at a maximum supply pressure of 80 lb/in2 • (gauge), while at the same time the manufacturing method had to be as simple as possible. With the aim of satisfying these requirements, an experimental internal grinding head was designed and manufactured. Throughout the manufacturing stages, the most conventional production techniques were used; even the radial clearance of 0.0005:ins. between the shaft and the journal bearing was achieved by grinding and lapping, and also the smallest journal orifice hole diameter of 0.004 ins. was successfully produced by using a small drill. ·The tests consisted mainly of the verification of the predicted values of stiffness, volumetric air flow and free running and the effect of the driving method. The complete tests were carried out in two test rigs one for direct drive and another for belt drive. The test results revealed a satisfactory correlation between predicted an measured values. At the supply pressure of 80 lb/in. (gauge), the stiffnesses of 235,000 lb/in. and 244,000 lb/in. at the centre position of the rear and_ the front journal bearings, and 190,500 lb/in. and 200 7 000 lb/in. for the front and the rear thrust bearings respectively, were obtained. Without any rotation, the total air consumption was 0.95 ft3/min., which was 1{-% higher than the predicted value but, at 60 7 000 rev/min. due to hydrodynamic effects, the reduction of air consumption of 7½f; of the no rotational condition was observed. An actual speed of 75,000 rev/min. was successfully achieved by the experimental head. Further increase of speed was limited by the pull and the vibration induced by the belt.
Open Access
The development and evaluation of an instrument to assess and develop the desirable attributes of RAF Airmen
(2005-03) Johansen, Dawn; Asch, Rachel
The research reported in this thesis related specifically to Royal Air Force (RAF) personnel. The primary aim of the work was to design an instrument to assess and develop the desirable attributes of airmen regardless of rank, trade-group or location. The work comprised three separate but integrated studies that culminated in the successful introduction of the tool to the Recruit Training Squadron (RTS). The first study consisted of a job analysis based on repertory grid technique with data elicited from 128 RAF personnel with experiences of line management of airmen. This stage of the research yielded 117 constructs from which twenty desirable attributes (each illustrated by observable behavioural examples) were generated. The second study was conducted to assess the content validity and generalisability of the list of twenty attributes identified from the first study. Thirty three officers and airmen, who represented all RAF ranks, considered the face validity of the list: ranked the twenty items in order of importance; and rated a ‘good5, ‘average’ and ‘poor’ airmen on each of the attribute items. The results of this study were used to develop the instrument for recruit assessment and development. The final study was designed to examine the reliability and validity of the tool for use at RTS. In this stage of the research, RTS instructors were trained in the use of the tool which they then trialled with four separate recruit groups. In trial recruits were assessed on the development tool on three occasions over seven weeks. At the end of the initial training period development scores were correlated with standard assessment measures. The correlations between development instrument scores and standard training measures were all statistically significant, with some associations being particularly strong.
Open Access
The effects of junction modifications on sharp-fin-induced glancing shock wave/turbulent boundary layer interaction
(1994-06) Koide, S.; Stollery, J. L.
The effects of junction modifications on the glancing shock wave/turbulent boundary layer interaction generated by a sharp fin placed on the wall of a supersonic wind tunnel were examined experimentally at a Mach number of 2.46 and a Reynolds number of 2.59xl06/m. The interactions between a turbulent boundary layer on the wall and shock-wave systems caused by a fin with a fillet and several fins with different strakes were examined individually in order to find an effective modification technique. The flow features obtained by oil flow visualization, surface pressure measurements and liquid crystal thermography were compared with the data from an unmodified fin to evaluate the effects of each modification. The comparisons indicated that a "srake-type" modification had a weakening effect on the interaction-induced separation. To understand the flowfield structures, three-dimensional surveys using laser-light-sheet flow visualization were employed with schlieren photography and oil flow visualization. In addition to these experimental observations, an Euler CFD solver was used to help understand the inviscid flow structures which play important roles in the interaction behaviour. Based on the data experimentally and numerically obtained, a method was proposed for predicting the junction shapes needed to prevent separation.
Open Access
The employment of jet V-STOL aircraft at sea
(1981-01) Kinch, M. J.; Howe, D.
The means by which the Royal Navy will continue to operate fixed-wing aircraft at sea is by employing VTOL or· given an aid to-take-off, STOVL aircraft. The aid being ' brought into service is -the Skijump, which permits a large increase in payload over unassisted VTOL. The effectiveness of skijump increases with its exit angle up to about 40°, but other considerations of size and ungainliness set a practical lim~tation nearer to 20°. The endspeeds required for ballistic launch off a skijump could be achieved or-enhanced by the use of assistance by catapult or rocket motor. Both of these would call for the initiation of programmes of full research and development, while the skijump, capable of conferring. equivalent performance if it is long enough, already exists. The· smallest number of aircraft in an airgroup able to keep up a useable flying task is three. A vessel big enough to mount three aircraft together with the gear necessary to support and arm them would be big enough to mount a skijump as well. Its size is dictated too by the sea conditions in which it is expected to keep operational. The vessel in question should be a displacement ship, either conventional (e.g. large frigate) or unconventional (e.g. Small Waterplane Area Twin Hull). There is no role here for either hovercraft or hydrofoil. Commitment to the skijump.in the ship means commitment to vectored-thrust as a means of propulsion in the next aircraft~ When specified it must be compatible with existing skijump decks, and it should be single-engined. Its targets for Reliability and Maintainability mµst be wholly related to the Availability called for, and must be given equal prominence with performance.
Open Access
An experimental study of an air-blast atomiser
(1967-10) Bryan, R. H.; Lefebvre, A. H.; Norster, Brian
Visual observations and an optical method of measuring the mean droplet size in sprays have been used to assess the performance of a prototype airblast atomiser, particularly at the low fuel and air flow conditions corresponding to engine cranking. The results obtained from this and a shroud version of the same basic atomiser have enabled design modifications to be made which have resulted in a marked improvement in performance, both in terms of the spraying characteristics of the atomiser at low fuel and air flows, and in terms of the measured droplet size produced. The latter for the final design was very close to that predicted by Wiggs for airblast atomisers operating at the test conditions employed. An apparatus has also been designed to enable tests on the atomisation quality of airblast atomisers to be carried out at pressures up to 250 p.s.i.,, using the same optical technique to make mean droplet size measurements.
Open Access
Flame radiation & smoke emissions in gas turbine combustors
(1969-09-19) Russell, D. T.; Lefebvre, A. H.
The objective of this thesis was to investigate flame radiation and smoke emission phenomena in a combustor typical of those in use in aircraft gas turbine engines. One of the primary aspects of the investigation was to compare the performance of airblast atomisers with that of conventional swirl atomisers under as near identical conditions as possible. A brief study of combustion chamber processes and carbon formation and thermal radiation mechanisms was made, with consideration of such experimental data as exists in the literature. An airblast atomiser and combustion chamber was developed to a state whereby testing at rich mixtures at moderate combustion pressures could be performed for short periods. This enabled a preliminary comparison to be made monitoring the following parameters:- (i) Flame total radiation. (ii) Exhaust smoke level. (iii) Weak extinction. Data was collected at three different combustion pressures for various air-fuel ratios and chamber velocities. The results showed that the airblast atomiser offers significant advantages over swirl atomisers with regard to total flame radiation and exhaust smoke emissions whilst suffering from a poor weak extinction. A more detailed analysis was performed for swirl atomisers using the Schmidt Method to establish flame temperatures and emissivities. The object of this work was to assess the effects of droplet size and combustion pressure on flame radiation. Owing to the poor atomisation quality and fuel distribution of the airblast atomiser used for the preliminary work, two new injectors were designed. It was hoped that a detailed analysis for these injectors could be performed via the Schmidt Method in order to provide a comparison with the swirl atomisers. Unfortunately, manufacturing was not completed with sufficient time left for this analysis to be completed.
Open Access
A flexible, subsonic high altitude long endurance UAV conceptual design methodology
(1997-05) Chang, J. M.; Jones, R. I.
High Altitude Long Endurance (HALE) Unmanned Aerial Vehicles (UAVs) have been considered for use in both civil and military applications for some years. Their advantages, such as low cost, high survivability, long endurance, easy maintenance etc. relative to alternatives, make them useful to scientist and military personnel. In this thesis, a flexible conceptual design methodology for HALE UAVs has been developed. This has been implemented as a FORTRAN computer code. However, it is unlike some commercially available general aircraft design software which appears to the user as a ‘black box’. In this case, the code is broken-down into several subprograms which deal with the different aspects such as parametric study, drag, performance etc. Each of these can be either used as it stands, tailored to the user needs in a particular case or by-passed if more accurate methods or known values are available in a particular area. During production of the methodology problems were encountered in a number of areas due to the unusual operating regime and configurations of HALE UAVs. Obtaining engine data for the high altitude of interest was a problem. This was addressed through use of an existing engine modeling code to generate data. The high altitude also leads to low Reynolds numbers and along with the high aspect ratios typical of HALE UAV configurations, these place such vehicles beyond the validity limits of data sheet methods for prediction of a number of important parameters. Improved methods for the prediction of Oswald efficiency and maximum lift coefficient, in particular, are recommended to be sought. Accepting the above difficulties, an analysis of the Tier-II Plus, Global Hawk, was carried out using published data to provide some validation of the methodology and program. The results obtained provide confidence in the usefulness of the program in the analysis and investigation of HALE UAVs.
Open Access
The interaction of an oscillating airfoil and/or flap with a separating flow
(1975-01) Lang, James D.; Christopher, P. A. T.
At present little is known of the dynamics of a separating and reattaching flowfield. This unsteady flow topic relates to a wide range of aerodynamic problems such as dynamic stall and contfol-sürface-buzz. An experiment was performed with the purpose of investigating the dynamics of a separated region and the effect of the region on the motion of a flap-type control surface. A NACA 0012 airfoil section was fitted with a movable spoiler and flap. Measurements were made of the unsteady, non-linear hinge-moment due to spoiler oscillation. Aerodynamic hinge-moment was also investigated with the spoiler fixed and the flap oscillated harmonically. Flap response to spoiler-induced forcing was also observed in addition to observations of coupled spoiler and flap system behavior. The coupled system exhibited limit-eyele oscillations. Flap response to spoiler-induced loading can be predicted well by use of a linear equation for flap motion which is forced by the effect of spoiler motion. The equation of motion includes attached flow values of aerodynamic damping and stiffness. A theory is developed which models separation bubble dynamics. It includes a quasi-steady model for the external shear-layer, and flow of mass within the bubble at a mean reversed-flow velocity. Pressure perturbations along the bubble are modeled also. The theory is used with the method of Beecham and Titchener in order to predict limit-cycle behavior of the coupled system. Good agreement with experimental results is achieved. The instant of instability and of growth of a laminar separation bubble at the leading-edge of an oscillating airfoil is also investigated theoretically. The beginning of dynamic stall is seen to be related to the dynamics of a separation bubble and the inviscid flowfield. The theory is applied also to a study of the phenomena of control-surface-buzz, where separation is induced by shock waves.
Open Access
Investigation of the application of hybrid laminar flow control and variable camber wing design for regional aircraft
(1998-10) Edi, Prasetyo; Fielding, John
Approximately 65% of the world's commercial jet fleet consists of narrowbody, single-aisle aircraft with a capacity of 70 to 170 seats. The trend since deregulation in the US has been towards hub-and-spoke networks and a reduction in average aircraft size. The liberalization of the European market could exacerbate this trend. Because of congestion and the competitive environment the airlines are forced to buy technology and competitive aircrafts at low cost and to ask to the manufacturers to provide more operational flexibility, without drastic performance losses. In the feasibility phase of an Advanced Technology Regional Aircraft (ATRA) family, a combined HLFC-VCW (Hybrid Laminar Flow Control - Variable Camber Wing) concept was investigated to improve the overall efficiency, flexibility and reduce weight as the weight-growth factor is a critical issue. A methodology of a conceptual design and wing design incorporating a combined HLFC-VCW concept for regional transport aircraft was developed. For the purpose of this study, SWEPTDES was used to initially design the aerofoil sections for ATRA’s wing. RAMPANT was used to analyse ATRA wing aerodynamic performance in the transonic speed regime for both turbulent and laminar flows. A simple transition prediction method was used, based on assumptions that extended regions of favourable pressure gradient would correspond to extended regions of laminar flow. The boundary layer transition is expected to be just in the front of the recovery point. To identify the drag reductions by the applications of combined HLFCVCW system, a simple drag prediction method was used, to show an initial comparison with a turbulent datum design. Relative to a baseline aircraft, with current state-of-the-art technology, a cruise drag improvement potential of more than 10 % was identified. This drag reduction leads to MTOW reductions up to 4 % or increased range by more than 7 %. Variable camber (VC) offers an opportunity to achieve considerable improvements in operational flexibility, buffet boundaries and performance and enable the use of one wing for a regional aircraft family. Although in this work the design lift requirement was not achieved, but the results showed that using VCW the wing lift could be increased or decreased and could be optimized to produce the desired lift range. The introduction of VC could set off a new generation of intelligent airliners which will optimize their camber schedule automatically throughout the entire mission. Variable Camber is a prerequisite for HLFC wing to control the pressure gradients and the off-design behaviour. Before HLFC and VCW technology can be applied to the transport aircraft, a large multidisciplinary research effort is needed in order to master the technology and demonstrate it on flying test-beds and in-service operational tests.
Open Access
Lagrangian hydrocode modelling of hypervelocity impact on spacecraft
(1998-05) Campbell, J.; Vignjevic, Rade
This thesis addresses the problem of modelling hypervelocity impact on spacecraft structures using a Lagrangian hydrocode. Lagrangian hydrocodes offer the advantages of computational efficiency and structural elements, but traditionally have been unable to model large material deformations. Analyses of impact on a thin plate were per¬formed using the finite element code DYNA3D. These analyses highlighted three areas where improvement was necessary: material modelling, element erosion criteria and modelling large deformations. To improve the material modelling the SESAME equa¬tion of state was implemented in the DYNA3D code. Two new element erosion criteria were then developed, one based on total element deformation, the second on element accuracy. The two criterion were then tested for modelling impacts onto semi-infinite and thin plate targets. The deformation criterion produced the best results for crater size and hole diameter, but can not be used to model the debris cloud. The element accuracy criterion allows a sufficient number of elements to survive to measure debris cloud velocities and spread angle. It was concluded that an alternative method for modelling the debris cloud is required. The Smoothed Particle Hydrodynamics (SPH) method was selected as it is a Lagrangian method, and allows modelling of large deformations as it does not use a computational mesh. The most recent SPH developments require the boundary conditions to be rigorously treated. A penalty contact algorithm for SPH was developed and tested in 1D and 2D. The tests revealed that for successful treatment of boundary conditions it was necessary to address the problem of zero-energy modes. A alternative discretisation method that calculates the velocity and stress at different points was proposed as a cure for the zero-energy mode problem. This method was tested in 1D, and was shown to be a solution to the zero-energy mode problem.
Open Access
Monotone integrated large eddy simulation of supersonic boundary layer flows
(2001-02) Chong, Yon Han; Qin, N.
For simulations of supersonic flows shock-capturing schemes have to be used. A shock-capturing scheme produces more dissipation than a central difference scheme. In fact, the numerical dissipation produced by shock-capturing schemes is problematic when performing Large Eddy Simulation of supersonic flows with shock-waves. Another train of thought is to turn the numerical dissipation to our advantage. If the numerical dissipation of a numerical method can mimic the dissipation of the subgrid-scale(SGS) eddies, not only is SGS modelling unnecessary, but the numerical dissipation will be a positive contribution to the calculation. This approach is called MILES. As a reference case, a zero-pressure-gradient, flat-plate boundary-layer flow was chosen as there are analytical, experimental, DNS and LES results available. The freestream conditions are a Mach number of 2.25 and a Reynolds number of 1.613 x 104/in or 6.007 x 103 based on the displacement thickness. The central difference scheme, Osher’s scheme and Roe’s scheme are tested for suitability in MILES. The central difference scheme is found to be numerically^ too non-dissipative without SGS modelling. Osher’s scheme is too dissipative so that it hinders the development of turbulence. Roe’s scheme without use of a limiter seems to have the right amount of numerical dissipation to mimic a SGS model. Two popular slope limiters were also tested, but both affected turbulence development when no shockwave was present.
Open Access
Multiple and moving bodies: CFD research in an adaptive environment
(2000-11) Ren, Tingrong; Edwards, John A.
During this study a new solution adaptive scheme was developed which applied the structured Adaptive Mesh Refinement (AMR) algorithm directly into a Chimera grid system. Two new Computational Fluid Dynamics (CFD) methodologies, the Chimera grid method and the AMR algorithm, have been successfully integrated. The originality of this study is outlined below. 1).This new scheme integrated the Chimera grid method with the AMR algorithm. By using the Chimera grid method to mesh complicated configurations and then applying the AMR algorithm in different Chimera sub-domains to resolve complicated flow features the advantages of these two methods are combined. 2). Both Graph data structure and orthogonal list storage are employed in this new scheme to describing the Chimera sub-domain relationship and improve the region and point searching efficiency. These methods make this new scheme more flexible and more efficient than existing Chimera grid schemes and AMR schemes. 3). This study extended the application of the AMR algorithm. The main limitation of the Quirk's AMR code, poor geometric packing ability, has been replaced by a versatile Chimera grid scheme. 4). This study improved the accuracy of the Chimera inter-grid communication when simulating supersonic or hypersonic flows with strong discontinuities due to applying the AMR algorithm. 5). The combination of the versatile geometric packing ability of the Chimera grid method and the efficient computation ability of the AMR algorithm makes the current scheme capable of simulating multiple and moving body flow problem with strong discontinuities using moderate computational resources. The material in this thesis documents this development of the Chimera grid scheme with an existing AMR code, and the validation and applications of this scheme. Firstly, a Chimera grid scheme has been developed. Most of the tasks associated with the Chimera grid scheme are performed in a fully automated mode. The graph data structure and orthogonal list storage are used to describe the domain relationships. This allows the sub-domains to be arranged in an arbitrary manner and increases efficiency. Secondly, in order to properly integrate the Chimera grid scheme with the AMR, some modification work on the original AMR code had to be done. This work allowed the Chimera grid scheme to be successfully incorporated into the AMR code. Thirdly, this scheme has been employed to solve time-dependent and steady state shock hydrodynamics problems at supersonic and hypersonic speed. Various validation and application cases, such as, shock reflection, shock diffraction, shock/boundary interaction and multiple moving body flows at supersonic speeds are presented, analysed and compared with experimental results or numerical solutions either from the literature or obtained by using another CFD code. The simulations demonstrate the flexibility of the grid generation and the high efficiency and capability to resolve complex flow features. Finally, future research work arising from the present study has also been discussed and highlighted.
Open Access
Passive Techniques for Controlling the Flow in Supersonic Wing - Body Junctions
(1994-03) Blank, S. C.; Stollery, J. L.
Junction flows are common to all flight speeds and they are associated with undesirable features such as increases in drag, limitations on performance and at supersonic speeds high heat transfer rates. Junction flows are associated with performance losses in turbomachinery (around 30% of the total pressure losses in an axial turbine) and they can lead to premature detection of military underwater vessels. Junction fairings are widely used at subsonic speeds and correct fairing of the C-141 wing alone, could have resulted in potential fuel savings of approximately US $ 40,000 per year per aircraft which can be roughly translated into a $ 600,000 saving during the lifetime of each airframe. Typically, for a modern transport type of aircraft the wing juncture accounts for between 1 and 2 % of cruise drag and therefore, careful design of the wing junction is necessary. At supersonic speeds, by far the most disadvantageous feature associated with juncture design is high heat transfer rates due to shock / shock interaction. These heat transfer rates are sufficient to cause severe structural damage leading to component burn-off. Typical leading edge temperatures during re-entry for an aerospaceplane, like HOTOL, are around 2000 K, exclusive of increases in temperature caused by the interaction. Although drag reduction may not be so relatively critical at these flight speeds, the potential loss of control components, like stabilising fins, needs to be carefully examined and some configuration re-design may be necessary as a consequence. This research project is aimed at developing a technique through which the disadvantageous features associated with supersonic junction designs can be alleviated. It was found that through re-design of the wing / body junction the maximum mean static pressure local to the fin leading edge could be halved, the strength of the junction vortices could be lowered and the amount of separated flow reduced. The applications of the technology span all vehicles operating within the supersonic flight regime and therefore, the markets to which the technology is applicable are military aircraft, defence systems, aerospaceplanes and commercial supersonic transports. As the technology is, in principle, applicable to the design of commercial supersonic transport aircraft (HSCT) and the market for these vehicles is forecast to be worth up to $ 200 billion (FY 1987) an examination of the issues behind marketing this type of vehicle is presented in the non¬technical section. The presently available data produced by the major manufacturers were found to be lacking in the following areas (a) evaluations of market elasticity, (b) distribution techniques, (c) the availability of acquisition finance and financing techniques, (d) political sensitivity analysis (d) product life cycle analysis and (f) the relationship marketing of the venture.
Open Access
Some effects of transpiration on the boundary layer at the leading edge of a swept wing
(2000-03) Smith, A.; Poll, D. I. A.
The effect of transpiration on the boundary layer near the leading edge of a swept wing has been investigated using a large swept cylinder model with a laser-drilled titanium leading edge to model the leading edge of a swept wing. In the region near the leading edge, boundary layer transition due to crossflow instability has been examined. Natural transition on a porous surface was compared with that on a non-porous surface, and it was found that transition occurred at lower R ’s on the porous surface (ie there was a performance penalty due to the porous surface). The effect of suction on transition due to crossflow instability was then studied. It was found that only moderate amounts of suction were required to delay the onset of crossflow-induced transition and a simple algebraic model has been derived, in terms of R , Rex, and Cq, to describe transition on the porous surface with or without suction. It was also found that two-dimensional trip wires had a negligible effect on crossflow transition, except where they caused attachment-line contamination. On the attachment-line, several subjects were addressed. The effect of attachment-line blowing was considered, and good agreement was obtained with previous work. The effect of spanwise blowing length was also addressed, and a simple algebraic model was derived, in terms of R , s/rj, and Cq, to describe attachment-line transition due to blowing. A comparison has also been made with linear stability theory. The effect of suction at the wing-fiiselage junction was examined as an alternative to suction on the attachment-line. However, it was found that applying suction on the attachment-line when the boundary layer had attained infinite swept conditions was much more efficient than applying suction in the junction region. Suction was successfully used to relaminarise a turbulent attachment-line at R values between 600 and 950, the magnitude predicted for the next generation of large transport aircraft. During the experiments, no sign of critical oversuction was found. Finally, the behaviour of a relaminarised attachment-line flowing onto a non-porous surface was studied. The conditions for natural transition on the non-porous surface were measured, and it was found that they were the same as those predicted by previous work on an entirely non-porous attachment-line.