This paper describes a study which has been concerned with numerical predictions of the airwakes resulting from two simplified ship geometries: the internationally agreed Simple Frigate Shape, SFS1, and its successor, SFS2. Extensive steady-state simulations have been carried out for a wide range of wind conditions using Fluent, a commercially available Computational Fluid Dynamics (CFD) code. The CFD predictions have been partially validated against wind tunnel data produced by the National Research Council of Canada (NRC) and have shown good agreement. The resulting airwake velocity components have been exported from Fluent, interpolated onto suitable grids and attached to the FLIGHTLAB flight-simulation environment as look-up tables; piloted flight trials were then carried out using the Liverpool full-motion simulator. The pilot workload and helicopter control margins resulting from a range of wind-over-deck conditions have been used to develop the Ship-Helicopter Operating Limits (SHOL) for a Lynx-like helicopter and the SFS2. The workload was compared to the pilot’s experiences on a similar aircraft and a Type 23 Frigate and the simulated SHOL compared with SHOLs derived from sea trials. The results are very encouraging and open up further the long awaited prospect of such simulations being used in the future to reduce at-sea trials, and to provide a safe environment for pilot training.

The Dynamic Relaxation (DR) method is applied to the solution of geometrically non-linear, elastic, laminated plate, flexural and stability problems. Two categories of plate are considered, namely, those that are symmetrically and unsymmetrically laminated with respect to the plate middle surface. Whereas the former category exhibits a bending – twisting coupling phenomenon, the latter exhibits an extensional – flexural type of coupling. The effects of these coupling phenomena are evaluated by comparing the plate responses with those of corresponding homogeneous, specially orthotropic plates. With the exception of uniaxially compressed plates of the latter category in the post-buckling regime, it is found that for both flexural and stability problems the coupling phenomena cause a reduction in stiffness and the extent of this reduction is dependent on the lay-up of the laminate.

A time-accurate solution method for the coupled potential flow and integral boundary-layer equations is used to study aerofoils near stall, where laboratory experiments have shown high-amplitude low-frequency oscillations. The laminar-turbulent transition model incorporates an absolute instability formulation, which allows the transition process in separation bubbles to be sustained in the absence of upstream disturbances, in agreement with recent direct numerical simulations. The method is demonstrated to capture large scale flow oscillations with Strouhal numbers and amplitudes comparable to experiments. The success of this particular physical model suggests that bubble bursting is primarily due to a potential-flow/boundary-layer interaction effect, in which relatively simple models of boundary layer transition and turbulence suffice to describe the key phenomena.

A study has been made of the changes that take place in the flow around a square section cylinder as the angle of incidence is increased from 0° to 45°. Measurements of the Strouhal number, S, and the vortex longitudinal spacing, a/d, are presented and used to estimate the vortex strength, , and vortex street spacing ratio, b/a. is found to vary between about 1.2 and 1.7 depending on incidence, and is given approximately by 0.52(1 - Cpb)/2πS, where Cpb is the mean base pressure coefficient. As the incidence is increased from 0°, S at first decreases slightly and then rises sharply to a maximum at 13.5° incidence, which is the incidence where reattachment of the shear layer, in some mean sense, is expected to commence. The spectra of pressure and velocity fluctuations were measured and subharmonic peaks were found in both spectra at 5° and 10° incidence. It is suggested that they may have been caused by an interaction between a vortex and a trailing edge corner. The degree of organisation of the vortex shedding process was estimated by calculating the sharpness factor, Q, of the spectral peaks at the vortex shedding frequency. In general Q fluctuated with changes in incidence. High values of Q occurred at angles of incidence where the rate of change of the mean base pressure coefficient with incidence is very small whereas low values occurred where the flow is changing to a different state.

This paper presents the results of an experimental investigation into the characteristics of boundary layer transition to turbulence in hypervelocity air flows. A series of experiments was conducted using a flat plate model, equipped with static pressure and thin film heat transfer transducers, in a free piston shock tunnel. Transition was observed in the stagnation enthalpy range of 2·35 to 19·2 MJ/kg. The transition Reynolds number correlates well with the unit Reynolds number through a simple empirical relation. The influences of Mach number, pressure and wall cooling are examined. The measured heat transfer rates in laminar and turbulent regions are compared with empirical predictions. Freestream disturbances of the test flow were also measured and analysed.

The paper describes the application of a recently developed numerical scheme to the computation of the flow in a curved duct. The flow situation is partially-parabolic in nature as there are significant elliptic effects, which are transmitted through the pressure field. The turbulence model used comprises two differential equations, one for the kinetic energy of turbulence and the other for its dissipation rate. It has been observed that the predictions using the new procedure agree very satisfactorily with the experimental data. Comparisons are also made with the predictions of a fully-parabolic calculation procedure.

This paper describes power requirements for micro air vehicles, flying in the Reynolds number regime of -lO*. Three flight modes have been researched: fixed wing, rotary wing and flapping wing. For each mode, the literature in the public domain has been reviewed to obtain appropriate lift and drag coefficient data at these low Reynolds numbers. Energy and power requirements for the three flight modes have been calculated and an optimisation procedure has been utilised to evaluate the most efficient flight mode and configuration for a variety of specified missions. The effect of wind-speed on the optimal solution has been examined. It has been discovered that when there is no hover requirement, fixed wing flight is always most energy efficient for the micro air vehicle. However, if there is a hover requirement, the suitability of flapping or rotary wing flight is dependent on the mission profile and ambient windspeed.

If the definition that hysteretic damping is proportional to displacement but in phase with velocity be accepted, then the free vibration of a simple oscillator may be treated, without ambiguity, using this concept. The apparent anomaly which Dr. Bishop points out in his paper “ The Treatment of Damping Forces in Vibration Theory ” (November 1955 Journal) arises through confusing three distinct possible mathematical representations of some unspecified vibrating system.

Lower bounds for the intensity of the sonic bang of a slender aircraft configuration with various constraints are given in this note which is a condensed version of Ref. 1. Although these lower bounds cannot be achieved in practice the method of obtaining them demonstrates how low values can be obtained. Special emphasis is given to a possible supersonic transport.

Analytical and experimental studies of the effect of geometric and aerodynamic variables on the performance of the Wells self-rectifying air turbine are presented in this paper. Two approaches to the prediction of the Wells turbine performance are described, both of which are based on the two dimensional cascade theory and isolated aerofoil data. Experimental results are based on the investigations in Unidirectional and oscillating airflow rigs.

Comparisons are made on the analytical and experimental results.

The paper deals with the behaviour of three shock waves meeting at a point in a perfect gas. It is shown that the equations of motion can be reduced to a single polynomial equation of degree 10. The real roots of this equation are studied to determine their physical significance. In addition, the appearance of degenerate shock systems is shown to be associated with the formation of certain multiple roots of the polynomial equation.

Numerical methods are used to study the growth of waves of finite amplitude on a pair of parallel infinite vortices. The vortices are treated as lines except in so far as the detailed structure of the core is needed to remove consistently the singularity in the line integrals for the velocities of the vortices. It is shown that the vortices eventually touch and the shape of the wave at this instant is calculated. The wave is quite distorted at this instant, but it is shown that its gross properties are given roughly by linear theory.

With the increasing need for fuel economy all possible areas of drag reduction need investigating. One form which offers considerable promise is lift-dependent drag which for most transport aircraft is approximately 30% of the total drag in the cruise and more at lower speeds. A reduction in lift-dependent drag at a given flight speed would directly reduce the operating costs of existing aircraft. Even greater savings might be obtained for twin-engined airliners where the wing loading is fixed by the high lift-dependent drag at climb-out from the airfield. A method of increasing the effective aspect ratio of a wing would allow new aircraft of this type to have lower wing areas and weights in addition to higher cruise lift-drag ratios.

Experiments performed on a low-speed circulation-controlled aerofoil are described. The aerofoil was of elliptic section with the circulation controlled by means of a jet blowing around the blunt trailing edge. Results for the lift, drag and pitching moment on the aerofoil are presented as functions of the blowing momentum coefficient and the angle of incidence. The results are for a two-dimensional aerofoil. Possible applications of this type of aerofoil are briefly discussed.

The possibility of obtaining two-dimensional turbulent jet flow from a series of closely-spaced uniform holes in line has been investigated both theoretically and experimentally. The case studied was that of a jet discharging into still fluid of similar density at incompressible speeds. Such a quasi-two-dimensional jet is a particular example of a multiple-interfering jet group.

Reversed direct stress and rotating bending fatigue tests have been carried out on Vee-notched specimens of aluminium alloy, nickel chromium steel and mild steel.

Diagrams are presented showing the relationship between the geometric stress concentration factor Kt and the strength reduction factor Kt. It was found that non-propagating cracks formed in the roots of the sharper notches. These cracks formed at or above some critical value of Kt, the value depending on the specimen material. Below the critical value of Kt, cracks did not form unless the applied nominal stress exceeded that at the fatigue limit, and a crack, once formed, continued to propagate until the specimen failed. Above the critical value of Kt, non-propagating cracks formed at nominal stresses less than the fatigue limit, the stress having to be increased to the latter value in order to propagate the crack. This critical value of Kt coincided with the maximum Kf value realised. It would appear that Kf equals Kt up to a certain value of Kt; there is then a transition where Kt reaches a maximum at the critical value of Kt. Increasing the value of Kt above the critical value causes no further increase and may tend to decrease the value of Kt.

The conclusions drawn apply only when the fatigue stresses are completely reversed, i.e. the mean load is zero.

A “dual-time” method for solving the three-dimensional Euler equations describing the compressible flow about wings undergoing arbitrary motions and deformations is presented. A finite-volume formulation is chosen where the volumes distort as the wing moves or deforms. Independent motion of the inner and outer boundaries of the grid is permitted with a sequence of grids generated using transfinite interpolation.

An implicit real-time discretisation is used, and the equations are integrated in a fictitious pseudo time. This approach allows the real-time step to be chosen on the basis of accuracy rather than stability. It also permits the acceleration techniques commonly used to speed up steady flow calculations to be used when marching in pseudo time, without compromising real-time accuracy. A two-dimensional version of the method has also been developed and results for both two and three-dimensional transonic flows are presented and compared with experimental data where available.

In presenting experimental results on turbulent wall jets, most workers have adopted as basic scales the slot height b and jet exit velocity Uj. Although this is a natural choice, experience with other flows like jets and boundary layers, where the details of the initial conditions are eventually (if not always rapidly) forgotten by the flow, prompts the question: cannot a gross parameter like the jet momentum flux Mj rather than Uj and b separately, suffice to determine the flow, at least in some region where the wall jet may be said to have attained a “fully-developed” state? If the answer to the question is yes, it would give a more compact and practically useful description of the flow than is currently available.

This paper will examine the prospects for propulsion systems for large civil transport aircraft over the next two decades, to the year 2020. This period is likely to see the market drivers for future propulsion system development change from the more traditional ones of fuel consumption and weight, to also include those that affect the impact of civil aviation on the environment, and the continuing pressure to reduce the cost of ownership of civil engines, namely, product unit cost, maintenance costs and reliability. Fifty years of civil aero-engine development are reviewed and trends showing the likely limits to the main engine performance parameters are provided. The paper concludes with consideration of a number of new civil aircraft and engine concepts that may emerge in the next 20 years

A computational analysis is performed of self-sustained oscillatory flow over a cavity driven by a shear layer at Mach 1·5. The unsteady flow is studied through solutions of the Reynolds-averaged Navier-Stokes equations with turbulence modelled by a two-equation k-ω model. The trailing edge (face) of a baseline rectangular cavity is modified using wedge and ramp shapes to investigate means for the suppression and attenuation of the self-sustained oscillation. Through modification of the shear layer impingement, both wedge and ramp are effective in reducing the level of oscillation. The time-averaged pressure (form) drag coefficient of the cavity is also reduced significantly. The main cause of the drag reduction is the elimination or reduction of the high pressure area near the downstream corner of the cavity due to the presence of a vortex. Two types of unsteady flow exist when a curved ramp is employed: ‘regular’ and ‘random’. The use of a h= 0·6D ramp generates a random type pressure fluctuation with lower rms pressure compared with the h= 0·2D and 0·4D ramps.