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A unified method of flutter, dynamic stability and response analysis of deformable aircraft is presented. Normal modes and the generalised coordinate approach are used to develop the equations of motion. Strip theory and Theodorsen's expressions for unsteady lift and moment are utilised to generate the generalised aerodynamic forces. Theodorsen's function C(k) for harmonic motion is employed for the flutter analysis. A comparison is made between generalised unsteady aerodynamic forces and flutter quantities obtained from lifting line theory and those obtained from conventional strip theory, for both a rigid and elastic wing undergoing binary flutter. This investigation shows good agreement between the two theories particularly at high aspect ratios and suggests that the lower limit of aspect ratio for good flutter prediction, using strip theory, is about 6. The unified analysis is carried out on three particular aircraft of which two are high aspect ratio sailplanes, the Kestrel 22m, the tailless Ricochet and the Cranfield A1 a moderate aspect ratio aerobatic aircraft. A symmetric flutter analysis, including the effects of rigid body modes is carried out on all three aircraft. The Kestrel is found to suffer from classical wing bending/torsion flutter. The tail plane aerodynamics is seen to have a marginal if not stabilising influence on its flutter behaviour. The Ricochet in the absence of a tail plane is found to suffer from body freedom flutter involving coupling of the short period mode with the first wing bending mode. As the A1 is very stiff and of comparatively low aspect ratio it is found to be virtually flutter free. Making use of the generalised Theodorsen's function for convergent motion and the current body fixed axis system, the analysis is extended to evaluate the short period mode of an aircraft. Stability derivatives using the normal classical rigid body approach are also used for comparison. The introduction of flexibility and unsteady aerodynamics is seen to have a destabilising influence on the short period mode. Close to the flutter speed, classical rigid body assumptions are found to be inadequate in predicting the short period characteristics of the Kestrel and the Ricochet, but not the relatively stiff Al. An unsteady wing wake is then introduced at the tail plane where this is seen to have a negligible effect on flutter of the Kestrel. An analysis of the aircraft response to continuous atmospheric turbulence and discrete gusts is carried out using the Power Spectral Density method (PSD) and Statistical Discrete Gust method (SDG) respectively. The introduction of flexibility is seen to substantially increase the overall aircraft response, especially at subcritical speeds. From the analysis carried out on all the three aircraft, an SDG-PSD overlap does appear to be characterised in this investigation not by a 10.4 factor, but rather by a 10.4 plus or minus approximately 17% factor when rigid body modes are considered. For the flexible case this range is found to be plus or minus 31% factor.

The beneficial application of vortex generators to control boundary layers in the sub- and supersonic flow regime has been shown in the past. In this thesis the use of vortex generators is extended beyond boundary layer control by using them within an ejector-diffuser type augmentor. During the course of the research work it was established that the vortex generators could be used as effective 'mixers' between the primary air stream and the secondary entrained air stream. A previously developed mathematical model of ejector-diffuser flow, incorporating parameters such as pressure ratio, nozzle to duct area ratio and diffuser area ratio, was extended and refined. With the help of that model the above mentioned parameters were defined and according to these parameters a test rig was designed and manufactured. The primary ejector was driven by either a peripheral slit jet or eight individual air jets or the combination of both. The major task of the project was to design a rig which was short but produced a good thrust augmentation based on the bare nozzle thrust. A good thrust augmentation ratio was obtainable by ensuring rapid mixing between the primary and secondary air streams. The test programme was split into two major parts, namely the use of vane vortex generators in conjunction with the peripheral jet and then the application of air jet vortex generators again with the peripheral jet. The vanes and also the air jets were configured either as eight co-rotating vortices or as four contra-rotating vortex pairs. A special case which was also considered involved the air jet vortex generators on their own without peripheral blowing. This test was possible because the eight air jets could be used as primary air injectors and vortex generators at the same time. It emerged that this configuration was particularly revealing because it highlighted the essential difference between co- and contra-rotating vortices. Near the design primary pressure ratio of 5.0 the bare nozzle thrust was augmented by a maximum of 30 per cent with the vanes installed. This was a considerable advance on the augmentation for the bare augmentor, i.e. the same configuration as above but without vortex generators installed, which came to 1.15 at the same pressure ratio of 5.0. The results of augmentation for the air jets were more complex due to the way in which the air was injected. Elevation and skew angle were responsible for the enlarged complexity. As a general trend it can be stated that the augmentation ratios were high for low pressure ratios, as high as 1.7 at a pressure ratio of 2.0, but fell off as the pressure was increased. Dynamic pressure contour plots in the exit plane gave good indications of the vortex movements produced by the co- and contra-rotating vortex generators. This project showed that considerable thrust augmentations could be achieved by using vortex generators.

In recent years, much of the research into aerodynamics performed at the University of Glasgow has considered the behaviour of helicopter and wind-turbine aerofoils in unsteady conditions. Theoretical predictive algorithms have not yet been developed fully and so there is still a great need to examine experimentally-recorded data. The present research was undertaken in an attempt to increase knowledge of the mechanism of trailing-edge dynamic stall at low Mach numbers. Consequently, the NACA 23012 aerofoil section has been modified over the trailing 75% chord to increase camber, and a model of the resulting aerofoil subjected to a series of wind-tunnel experiments.

The aim of this study is to develop and test a physical model of wind blown sand transport. Once established, such a model will lead to valuable insight into the physics of sand transport by wind especially the processes that interact to produce equilibrium transport conditions. The study begins with a review of the physics of wind blown sand, beginning with Bagnold (1941). In particular, four sub-processes are discussed; aerodynamic entrainment, the grain trajectory, the grain/bed collision and the modification of the wind by the grains. The physical model is based on the coupling (or interaction) of the four sub-processes. The grain/bed collision is modelled using experimental data obtained by Willetts and Rice (1985). The wind modification is calculated from the force profile exerted by the grains and the differential fluid shear stresses induced by the grains; a mixing length model is used to calculate these stresses. The results from the model are compared with the observed features of wind flow sand transport and the agreement is encouraging. Realistic wind profiles are calculated. These profiles show a marked deceleration by the grain cloud and an increase in effective roughness due to the additional drag imposed on the wind by the grains. Moreover the horizontal mass flux profile decays exponentially from the surface in accord with experimental measurements and the sand transport rate has a roughly cubic dependence on the shear velocity. Thus, the success of the model in reproducing (spontaneously) many of the observed features of wind blown sand transport encourages confidence that the physics used to construct the model is broadly correct. A further important result emerges from the model. There appears to be two time scales associated with equilibrium saltation. Firstly, the time for the grain cloud to come into equilibrium with the surface wind; this occurs over a time of approximately 1 s. Secondly, there is an increase in the effective roughness of the surface due to the additional drag imposed on the wind by the grain cloud. The atmospheric boundary layer must come into equilibrium with this change in roughness. This second equilibrium takes place over a much longer time scale of several tens of seconds or more. It results in a gradual decay of the shear stress in time after an overshoot of the steady state. It is noted that the response in time of the boundary layer to a change in roughness is analogous to its response in distance found by Jensen (1978). It is suggested, in the concluding chapter, that the spatial and temporal variation of the saltation cloud may be related through the application of Taylor's hypothesis for turbulence. The saltation modified wind is studied with the aid of an analytical wind profile derived from an assumed fluid shear stress distribution. This distribution is chosen for its similarity to the model calculated distribution: the intension being to use the analytical wind profile as a tool to investigate the model generated wind profile. From this analytical wind profile it is shown that the 'kink' in the wind profile (first noted by Bagnold (1941)) is caused by a maximum in the force profile exerted on the wind by the grains. Such a maximum is shown to exist in the force profile generated by the saltation model. Thus, it is concluded, that the 'kink' found in many experimentally measured wind profiles is likely to be caused by a maximum in the force profile exerted by the grains on the wind. This result is important because further understanding of modification of the wind will ensure that experimental measurements made are consistent with the physics of the system: in particular that wind velocity measurements used to calculate the shear velocity should be made above a height of 2-3 cm from the surface (i.e. above the kink). In the concluding section the desirability of a multiple grain size saltation model is discussed as an important step towards more realistic modelling. Further attention is directed towards modelling sand transport in gusty winds and inclusion of interaction with a developing bed.

This work investigates how the vibration-transmission characteristics of periodically stiffened plates and shells might be exploited to reduce propfan-induced noise and vibration in the fuselage cabins of civil aircraft. Initially, steady state harmonic wave propagation is considered in stringer-stiffened and frame-stiffened cylinders. Generality of stringer and frame section is allowed. Both types of structure are analyzed as one-dimensional periodic systems. Exact, closed-form relationships are established between the frequency and the propagation constants. Computed values are presented in graphical form, and clearly show the existence of distinct frequency stop and pass bands. The phase constant part of these curves is used to deduce the natural frequencies and normal modes for a number of specific structures. Provision is made for the inclusion of hysteretic damping. Steady state harmonic wave propagation is then considered in orthogonally stiffened plates and shells. Although the vibration modes and waves of these structures do not admit closed-form, exact solutions, approximate modes and frequencies can be deduced using energy methods. Both types of structure are therefore analyzed as two-dimensional periodic systems by using wave propagation techniques in conjunction with the hierarchical finite element method. Results are presented in the form of phase constant surfaces plotted against frequency. In general, wave propagation is found to commence at zero frequency; at higher frequencies a large number of overlapping pass bands are found to occur. However, a small frequency stop band has been identified for the orthogonally stiffened cylinder in which predominantly flexural waves cannot propagate. Experimental work conducted on two differently stiffened cylinders provides additional substantiation to the theoretical analyses.

An experimental investigation was conducted to study rotor pitch damping in hover, axial flight (climb speed to tip speed ratios: 0 - 0.549), and low speed forward flight (advance ratios: 0.05 - 0.088), for a variation in rotor thrust coefficient 0.001 - 0.013, and for the range of flapping frequency ratios squared 1.0 - 1.11. The tests were conducted at the following oscillation ratio frequencies, (frequency of oscillation divided by rotor angular speed), 0.186 for hover and axial flight and 0.1068 for low speed forward flight and in hover for the case of flapping frequency equal to unity. The nature of the damping of the rig was investigated since it was found that frictional effects contaminated the estimates of the rotor aerodynamic damping. To do this a parameter estimation method, based on a nonlinear minimisation procedure, was developed that does not require a large amount of data to identify the viscous and frictional damping coefficients from the free response of the rotor. A theoretical model for low frequency coupled rotor body dynamics was developed and the effects of rotor and inflow degrees of freedom on rotor damping were investigated. Results indicate that both rotor and inflow degrees of freedom are required in the mathematical description of low frequency coupled rotor-body dynamics for the adequate estimation of rotor damping. The dynamic inflow degrees of freedom were described by using momentum theory and by assuming a nonuniform distribution for the steady induced velocity given by a Glauert wake. A blade flexibility study was conducted to define the flapping frequency for blade-linear spring configurations producing both time invariant and time dependent boundary conditions at the spring location. Comparison of theoretical damping estimates with the experimental data in hover and axial flight show that at oscillation ratio frequency 0.186, the no-inflow model is in reasonable agreement with the experimental data and that the inclusion of dynamic inflow theory produces no improvement in the experimental data correlation. In hover and in low speed forward flight at oscillation frequency ratio 0.1068, the inclusion of dynamic inflow theory provides an improvement in the experimental data correlation indicating that for these conditions inflow degrees of freedom are also required for the adequate prediction of rotor pitch damping.

This thesis aims to assist the development of a multiblock implicit Navier-Stokes code for hypersonic flow applications. There are mainly three topics, which concern the understanding of basic Riemann solvers, the implementing of implicit zonal method, and grid adaption for viscous flow. Three problems of Riemann solvers are investigated. The post-shock oscillation problem of slowly moving shocks is examined, especially for Roe's Riemann solver, and possible cures are suggested for both first and second order schemes. The carbuncle phenomenon associated with blunt body calculation is cured by a formula based on pressure gradient, which will not degrade the solutions for viscous calculations too much. The grid-dependent characteristic of current upwind schemes is also demonstrated. Several issues associated with implicit zonal methods are discussed. The effects of having different mesh sizes in different zones when shock present are examined with first order explicit scheme and such effects are shown to be unwanted therefore big mesh size change should be avoided. Several implicit schemes are tested for hypersonic flow. The conservative DDADI scheme is found to be the most robust one. A simple and robust implicit zonal method is demonstrated. A proper treatment of the diagonal Jacobian and choosing the updating method are found to be crucial. The final topic concerns the calculation and grid adaption of viscous flow. We study the linear advection-diffusion equation thoroughly. The results are unfortunately not applicable to Navier-Stokes equations directly. Nevertheless a suggestion on the mesh size control for viscous flow is made and demonstrated. An attempt to construct a cell-vertex TVD scheme is described in the appendix.

Current wind turbine performance codes are not yet able to predict the rotor aerodynamic behaviour with sufficient certainty. This has led to both the over-design of blades and to operational restrictions in certain wind conditions. Essentially the problem is one of aerodynamic stall. Steady 3-dimensional stall can occur near the blade root in high wind conditions and may produce more power than predicted. Dynamic stall can also be expected due to the effects of yawed operation, turbulence, tower shadow and the earth's boundary layer. The main aim of this work is to provide a coherent set of measured aerodynamic data accounting for both axial/non-axial flow and stall in high winds. These measurements are designed to highlight the effects of both steady and dynamic stall on the rotor aerodynamic performance. In addition, the data will enable current performance prediction codes to be developed and validated. A completely new turbine has been designed and built at Cranfield to make aerodynamic measurements using pressure transducers. The design has been dominated by the requirements of accommodating the transducer signal processing equipment and allowing variation of many of the rotor parameters. Three commercial glass fibre blades were installed and performance curves measured on a conventional field site at a height of 11.5m for three rotor speed settings. These measurements show the turbine to give adequate power performance. A mobile trailer has been used to tow the turbine at a height of 4m along the Cranfield runways. Mobile testing facilitates an accelerated test schedule and allows aerodynamic data to be acquired under controlled wind conditions. A fully instrumented blade, fitted with forty transducers, has been tested under these circumstances and produced a large database of pressure measurements covering operation in winds up to 25 iq/s and yaw angles between -4511 and +55°. Analysis of the data has shown it to be of good quality and allowed some of the effects of yaw and stall to be identified. The use of the data base for performance prediction code validation has also been established.

The use of sailwing aerofoils in vertical axis wind turbines has been investigated. It was anticipated that this could make vertical axis turbines more suitable for water pumping and that this might help to meet the need for a cheap pump for irrigation existing in many parts of the world. A numerical analysis of the theoretical performance of such a turbine, using existing aerodynamic data for simply constructed sailwings, has been made. This gave an improved understanding of the operation of such turbines but showed a need for further aerodynamic data. Some new wind tunnel tests of sailwings are described in which the effect of pre-tension was investigated and four different fabrics were tested. The results are presented for angles of incidence up to 180 degrees and compared with previous data. With the fresh data, new performance predictions were made which led to the design of a two metre diameter prototype turbine. This used an inclined blade configuration with a guyed top bearing. Canvas was used for the sails. It was predicted that the turbine performance would be significantly affected by windspeed. The turbine was built and later tested in the open air. An acceleration test method was used and the tests generally confirmed the predictions. The averaged starting torque coefficient was about 0.07; the averaged peak power coefficient was about 0.1 at a tip speed ratio of 1.4. Consideration has been given to improving windpump system efficiency by improving the gust energy utilisation. Some tests of a diaphragm pump are described in which inertia flow effects were used. A pair of such pumps were later connected to the prototype turbine. A number of problems were encountered and satisfactory operation was not achieved in the time available. The main problem was the cyclic driving torque produced by the three bladed turbine.

The purpose of this thesis is to present a study on motorcycle aerodynamics with particular regard to the performance characteristics of faired and unfaired types in use today for road racing and speed record attempts. To achieve this, a wind tunnel procedure for the testing of scale models was developed with emphasis on the problems involved in obtaining valid data from large model-to-tunnel area blockage ratios, (approximately 15'%). Following a review of the results, which included six aerodynamic force and moment coefficients and their variation with Reynolds number and yaw angle, a programme of drag reduction was pursued which approached the problem from two directions: firstly, by using simple bolt-on devices for conventional fairings, designed so as to obviate the need for major machine modifications and secondly, by a complete redesign of the motorcycle.� The latter involved the use of more efficient aerodynamic shapes and also achieved a reduction in frontal area without compromising rider comfort. The final result was a machine which would provide greatly enhanced racing performance through a drag reduction of approximately 40% and also lend itself to the incorporation of radical primary and secondary safety features, beneficial both an the track and public roads. Preliminary studies into a computational flow simulation as a first stage to the full prediction of fairing pressure distribution are also included. The techniques explored attempted to retain a reasonable accuracy of result without recourse to excessive computer power or complicated calculations. This was achieved successfully with the simple models considered, despite the highly separated nature of the simulated flow.

A description of the experimental investigation of the aerodynamic characteristics of variable geometry of an aircraft model is presented. Aerodynamically, the model is tested-for a sweep range of 0°,12.5° 32.5°, and 52.5° and incidence range of 0° to 200° in 4° intervals. All the pressure distributions on the wing, glove, and body are recorded for each wind tunnel test. Aerodynamic forces and moments were also taken through a balance mechanism system which is attached to the model. This is connected to an independent computer terminal and a Teletype printer. Initially, a flow visualization to test the flow separation on the wing model was carried out. A three-dimensional subsonic program, which was already developed by Hawker Siddeley Aviation Limited, was modified for our purposes in order to carry out numerical calculation of the aerodynamic characteristics and investigate the interference of wing and body. This programme has also been developed to include the compressibility effects and compare these results with those for incompressible flow. The three-dimensional numerical solution was a Panel method for the subsonic case. This investigates the three-dimensional flow-field using a distribution of quadrilateral vortex panels, the effects of which are summed to calculate the aerodynamic characteristics of the model. This subsonic theory was applied to calculate the characteristics of the wind tunnel model over a similar range of sweep and incidence to those tested, for Mach numbers of 0 and 0.5. As the only input data required is the configuration geometry and the flight condition, however, the program can be used to calculate the aerodynamics of any wing-body arrangement specified by the user. The program includes the capability of analysing both fixed-wing and variable sweep-wing configurations. This computational method is capable of being applied to general arbitrary subsonic three-dimensional potential flows, including inlet flow fields. In panel methods, the velocity potential at any point in a flow field is expressed in terms of the induced effects of source and doublet (or vortex) sheet distributed on the boundary surfaces. The configuration surfaces are divided into panels, and essentially, this is a general three-dimensional boundary value problem solver that is capable of being applied to most problems that can be modelled within the limitations of potential flow. Compressibility effects are approximated by the Göthert rule. Comparisons were made between the subsonic calculations and the experimental results and some other theoretical results. Hence, an indication of agreement and accuracy among them is seen, which is good up to a certain degree of incidence (about 10°). Owing to viscous effects, the experimental results for lift coefficient show a significant decline in size with respect to subsonic calculated results. Wing-body interference was calculated for subsonic flows and found to be favourable. Similarly, a general supersonic program was developed for numerical analysis of the aerodynamic characteristics of a thin wing. The theory was extended to include wing-body interferences. This extended treatment consists of slender body theory combined with a thin wing solution using a "characteristic box" method for supersonic analysis. Streamwise pressure-distributions on an aircraft wing are presented, and also-some aerodynamic force and moment coefficients of this wing are-presented. Finally, for wing body interaction analysis, the Nielsen method was used. All the relevant computations including centre of pressure position and interferences of wing and body for a combined model are presented. Comparisons of the supersonic results with some theoretical and experimental results shows good agreement. The interference calculations in this case showed favourable effects, which very broadly tend to be lower than those calculated for subsonic flow.

To provide power on a national scale, a large number of windmills will have to be deployed in wind farms or arrays because the output of individual machines is relatively small. Within an array, some windmills will be faced with the wakes generated by others. This interaction leads to a loss of power relative to upwind turbines and changes in the wind loading across the turbine blades.

A large-scale compressor/diffuser test rig has been designed and constructed which,. together with an automated data acquisition system, permits more detailed and more accurate measurements than were previously possible - especially in the region of the compressor OGV's. Results are presented based on experiments carried out using two different single-stage axial-flow compressors operating immediately upstream of a straight-core annular diffuser, each compressor being tested with a conventional stator row and a double-dihedral chevron type of stator row i.e. four main configurations were investigated. In addition to these main tests, the effects of operating the stator row at low Reynolds number, and of operating the stator row with a small hub clearance have been investigated. The chevron OGV shows a clear improvement, compared to the straight OGV, in t=s of diffuser performance and diffuser exit velocity profiles, at the expense of a general tendency for the OGV loss to increase. When hub clearance is used on a straight OGV, a hub corner stall arises, but this can be eliminated by incorporating blade dihedral at the hub. It seems likely that further improvements in diffuser exit conditions could be achieved by . careful design of the blade shape to encourage radial movement of flow. Traversing within the blade passage, for a straight type OGV, has revealed significant vortices rotating in the opposite sense to classical curved duct secondary flows.

The technique of the boundary element method consists of subdividing the boundary of the field of a function into a series of discrete elements, over which the function can vary. This technique offers important advantages over domain type solutions such as finite elements and finite differences. One of the most important features of the method is the much smaller system of equations and the considerable reduction in data required to run a program. Furthermore, the method is well-suited to problems with an infinite domain. Boundary element methods can be formulated using two different approaches called the ‘direct' and the ‘indirect' methods.

A typical aircraft flight consists of three phases, namely climb, cruise and descent. The purpose of this research was to study the control schedules for a transport aircraft which would result in least fuel expenditure in each flight-segment.

A technique has been developed to enable the measurement of the velocity field in the vicinity of a lifting rotor. This involved the use of a triaxial hot-wire probe coupled to a mini-computer. Using this technique extensive flow measurements in one plane (z/R = -0.075) under the rotor were made at advance ratios of 0.1 and 0.067. In addition the rotor thrust, torque and blade bending moments were also measured. The results of the analysis of the time averaged flow show clear evidence that the wake of the rotor rapidly rolls up into 2 `fixed-wing' type vortices. Also indicated is that the value of K in Glauert's induced velocity equation is underestimated by about 50%. It is also shown that results obtained from tests carried out at the same advance ratio, but different tip speeds, do not produce the same non-dimensionalised velocities at all positions. Analysis of the time varying results has shown that the roll-up of the tip vortex is completed within approximately 1 chord length of the blade and that the strength of the tip vortex is equal to the maximum value of the blade bound vorticity. The time varying data also reveals the influence of the turbulent blade wake and this has been used to obtain estimates of the blade profile drag. It is believed that this is the first time this has been observed in helicopter wake measurements and is potentially of great use in investigating the reductions in drag from using advanced blade sections and tip planforms. Aft of the rotor velocity traces showing the intersection of the tip vortex by the probe has been analysed to provide estimates of the vortex core size. These results also show evidence of axial flow in the vortex core.

This study develops analytical methods for the analysis of harmonically forced vibrations of multi-supported beams and stiffened plates. The methods are based on the response of infinite, uninterrupted structures to a single external excitation from which families of waves propagate outwards in all directions. The structures considered are uniform in thickness. The beams have a single-point force. The plates are finite in width with the two opposite parallel edges being simply-supported along the length. A line forcing varies sinusoidally between those edges. The first part of the thesis analyses the dynamics of infinite, uninterrupted structures. Special attention is subsequently paid to three-layered sandwich structures and their dispersion characteristics are also investigated. The second part considers finite structures. An analytical approach is presented for single-bay and multi-bay structures with arbitrary support spacing. Influences of support elastic/inertial characteristics are investigated in detail. Effects of end reflections are fully dealt with. The third part deals with the free and forced vibrations of infinite, periodic structures. Particular attention is focused on the effects of stiffness characteristics and cross-sectional distortion of the stiffeners. Part four outlines experimental work undertaken to validate the above theories. The experimental and theoretical results are compared.

Strong blast waves, such as those associated with gun fire or rocket exhausts, can cause serious physiological and/or structural damage. It is necessary, therefore, to develop ways in which to minimise this damage whilst still allowing the system that produces the blast waves to function normally. In an effort to develop such a system this study has examined, both theoretically and experimentally, the interaction that occurs when a shock wave is passed along a free unconstrained liquid tube before emerging into the surrounding atmosphere. In the theoretical analysis the problem was confined to the two-dimensional case and involved dividing the liquid sheet up into infinitesimal sections that were then regarded as small piston-cylinder systems, which were driven by the high pressure shocked gas behind the shock wave. The results from these one-dimensional systems were then used as input into a two-dimensional solution of the wave equation which predicted the gross changes in the remainder of the space. The experimental investigation involved laboratory experiments that examined, visually and with pressure transducers, the result of the shock/liquid interactions in two-dimensional and axi-symmetric cases, both between and external to the liquid sheets. The experimental investigation also included field trials that examined the pressure profiles of blast waves that were produced when a shock wave, which resulted from the ignition of a rocket motor, was passed along a liquid tube. From this work it was found that the high pressure gas, behind the shock wave, caused the liquid sheets to move perpendicularly from the line of travel of the shock wave which in turn caused expansion waves and compression waves to propagate out from the face of the water sheets, into the shocked gas and the surrounding atmosphere, respectively. These compression waves were then found to interact with the weak blast (produced when the shock, which had been weakened by the expansion waves, emerged into the atmosphere) in such a way that they produced a weaker blast field than would have been the case had the shock wave emerged directly into the atmosphere; the maximum observed reduction in the strength of the blast wave was 16.4 dB. Experiments were also performed that examined the effect of using rigid sheets in place of liquid sheets. From these experiments it was found that the differences between the liquid and rigid sheet cases was a function of the size of the inertial barrier (i.e. the mass of the water sheet) that the water presented to the shocked gas. Consequently, it was noted that, in terms of attenuating the blast wave, the rigid sheets proved to be inferior to the thicker water sheets and superior to the thinner water sheets. However, when the spectra of the pressure disturbances were examined it was found that, with regard to the attenuation of the 2-4 kHz region of the spectra, all the liquid sheet results showed an improvement in relation to the rigid sheet results.

The modelling of a Coaxial Contrarotating Twin Rotor (CCTR) system has been developed from single rotor modelling techniques. Particular attention has been paid to the characteristics of the tip vortex, namely, vortex strength, structure and decay. Equations are presented which describe both the vortex core and the complete structure of a rolled-up tip vortex. These equations are utilised with., conventional strip theory to enhance the predictive accuracy, and replace the arbitrary application of a tip loss factor. Using this combined approach, named Vortex-Strip theory, the full interference effects between the two rotors of a hovering CCTR have been successfully modelled. By a similar approach, a Vortex-Glauert theory has been developed to model the wake of a CCTR in forward flight. Comparisons between theory and experimental results from model and full scale rotors are shown over a variety of hovering and forward flight conditions. Both wake models have been written in Fortran IV computer language with a flexible input procedure. This feature allows a user to Investigate a wide range of rotor parameters including different rotor radii, number of blades, CCTR rotor spacing, with variations in blade twist, taper and effective hinge offset. The computer program, named ROTOR, was used in a preliminary optimisation study of a hovering CCTR. The results show that a conventional CCTR is a more efficient layout in hover than an equivalent single rotor; a finding which has been endorsed by experimental results. Although the presented models have been developed for a CCTR, it should not be overlooked that they are equally applicable to single rotor configurations.