Search results

The purpose of this paper is to develop a new approach for rapid computation of subsonic and low-transonic rotary derivatives with the available steady solutions obtained by Euler computational fluid dynamics (CFD) codes.

The approach is achieved by the perturbation on the steady-state pressure of Euler CFD codes. The resulting perturbation relation is established at a reference Mach number between rotary derivatives and normal velocity on surface due to angular velocity. The solution of the reference Mach number is generated technically by Prandtl–Glauert compressibility correction based on any Mach number of interest under the assumption of simple strip theory. Rotary derivatives of any Mach number of interest are then inversely predicted by the Prandtl–Glauert rule based on the reference Mach number aforementioned.

The resulting method has been verified for three typical different cases of the Basic Finner Reference Projectile, the Standard Dynamics Model Aircraft and the Orion Crew Module. In comparison with the original perturbation method, the performance at subsonic and low-transonic Mach numbers has significantly improved with satisfactory accuracy for most design efforts.

The approach presented is verified to be an efficient way for computation of subsonic and low-transonic rotary derivatives, which are performed almost at the same time as an accounting solution of steady Euler equations.

The operating conditions of a conventional aerofoil type propeller or helicopter rotor in both subsonic and supersonic regions are separately considered, in the absence of direct shock and blade interference effects and other disturbances. The performance of a propeller or rotor is approximately predicted by applying the conventional strip‐type analysis and the results of the two‐dimensional aerofoil theory.

A review is attempted with the objective to indicate the most promising aeronautical technology for application to future subsonic civil transport aircraft.

A methodology is put forward, according to which direct operating costs (DOC) are examined in order to identify those that can be reduced, and, then, specific technology is assessed in relation to its efficiency in reducing these DOC, operational feasibility and cost‐effectiveness.

This assessment suggests the selection of propfan and powered lift as the leading future aeronautical technology. These findings are supported by a comparison of a number of advanced technology designs.

Provides a starting point for further investigation of advanced aeronautical technology and unconventional configurations for large subsonic civil transport aircraft.

Because of its high overall pressure ratio and good propulsive efficiency, the jet engine is very efficient for supersonic propulsion. A high thrust per unit power plant frontal area and per unit weight are primary requirements and these imply high combustion temperatures. For a Mach 2.0 aircraft, engine design problems other than this are not outside existing experience but additional problems, such as bearing cooling, become more serious at cruise Mach Numbers approaching 3.0. A variable intake is essential and the method of geometry variation and control requirements are described. Variable propulsion nozzle design is also an area of vital importance and it is not claimed that an entirely satisfactory solution, giving good performance with low drag in the transonic phase, has yet been achieved. The ‘sonic boom’ phenomenon can have an important influence on engine design, in that it may determine the maximum altitude at which the aircraft has to fly subsonically. Should this be appreciably above the tropopause, then it will not only influence the amount of thrust installed but may also dictate the fitment of reheat for the transonic acceleration. Take‐off noise is a requirement which can influence both the installed thrust and the choice of engine type. Despite the lack of firm standards for field noise and ‘coast‐over’ noise, there is good reason to believe that the noise levels of a supersonic transport need not exceed those of the quieter long‐range subsonic transports in service at this time.

This paper aims to reveal the influence of selected geometric parameters on the aerodynamic performance of circular variable aero engine inlets in transonic and supersonic civil aviation.

The trade-off in inlet design and aerodynamic evaluation parameters is presented. The approach to investigate the dependencies between the aerodynamic and geometric parameters at different flight conditions by means of a parametric design study is introduced.

The dependencies of inlet drag and efficiency from geometric parameters at flight speeds of Mach 0.95 up to Mach 1.6 are identified. Although entailing additional weight, the inlet length represents the parameter with the highest potential for drag reduction by up to 50% in the selected design space. Ideal geometries for variable pitot inlets are determined. After considering weight, their potential range benefit nearly disappears for subsonic applications, but remains above 20% for supersonic flight at Mach 1.6.

Hence, the technology of circular variable pitot inlets for supersonic transport aircraft could be a way to achieve the ambitious ecological, safety and economic goals for future civil aviation.

The effect of increasing lip thickness (LT) and Mach number on subsonic co-flowing Jet (CFJ) decay at subsonic and correctly expanded sonic Mach numbers has been analysed experimentally and numerically in this study. This study aims to a critical LT below which mixing enhances and above which mixing inhibits.

LT is the distance, separating the primary nozzle and the secondary duct, present in the co-flowing nozzle. The CFJ with LT ranging from 2 mm to 150 mm at jet exit Mach numbers of 0.6, 0.8 and 1.0 were studied in detail. The CFJ with 2 mm LT is used for comparison. Centreline total pressure decay, centreline static pressure decay and near field flow behaviour were analysed.

The result shows that the mixing enhances until a critical limit and a further increase in the LT does not show any variation in the jet mixing. Beyond this critical limit, the secondary jet has a detrimental effect on the primary jet, which deteriorates the process of mixing. The CFJ within the critical limit experiences a significantly higher mixing. The effect of the increase in the Mach number has marginal variation in the total pressure and significant variation in static pressure along the jet axis.

In this study, the velocity ratio (VR) is maintained constant and the bypass ratio (BR) was varied from low value to very high values for subsonic and correctly expanded sonic. Presently, commercial aircraft engine operates under these Mach numbers and low to ultra-high BR. Hence, the present study becomes essential.

This is the first effort to find the critical value of LT for a constant VR for a Mach number range of 0.6 to 1.0, compressible CFJ. The CFJs with constant VR of unity and varying LT, in these Mach number range, have not been studied in the past.

A new implementation of the implicit lambda scheme recently proposed by other authors is provided. One‐dimensional compressible non‐isentropic flows inside four different nozzles and Fanno and Rayleigh's subsonic/ supersonic flows are computed, which demonstrate the superior efficiency and accuracy of the present formulation.

Over the years, theories of the forces on bodies moving with purely subsonic or purely supersonic velocities through gases have been evolved as required by current aeronautical practice; the development of such theories has not proved unduly difficult. Moreover, the theories have been monitored and checked by corresponding experimental investigations. In view of the complexity of some of the subsonic work, it might have been expected that supersonic theory would prove intractable; in the event, it has proved that, in some respects at least, supersonic theory is simpler than subsonic. By contrast with these fields, studies of transonic phenomena have lagged badly. For one thing, experimental work at transonic speeds is comparatively recent: until the development of slotted or perforated walls for transonic tunnels, it used to be said that one could only test at M=l a model of infinitesimal size—anything finite choked the tunnel. On the theoretical side the investigator is faced with the study of a region involving mixed flows, different parts of the field obeying different laws, with an unspecified sonic line at the boundary. Clearly, even in steady conditions this is a problem of great complexity.

The first compressible flow solution based solely on the locally analytical method is developed. This is accomplished by developing the flow model and locally analytical solution for inviscid subsonic compressible flow. The stream function for irrotational, compressible flow without body forces was chosen as the governing differential equation. To demonstrate the modelling and locally analytical solution, this analysis is then applied to predict the flow in convergent nozzles, both planar and axially symmetric, for different back pressures. Results are presented which demonstrate the effectiveness of this technique.

A mathematical analysis of the time‐dependent multi‐dimensional Hydrodynamic model is performed to determine the well‐posed boundary conditions for semiconductor device simulation. The number of independent boundary conditions that need to be specified at electrical contacts of a semi‐conductor device are derived. Using the classical energy method, a mathematical relation among the physical parameters is established to define the well‐posed boundary conditions for the problem. Several possible sets of boundary conditions are given to illustrate the proper boundary conditions. Natural boundary conditions that can be specified are obtained from the boundary integrals of the weak‐form finite element formulations. An example is included to illustrate the importance of well‐posedness of the boundary conditions for device simulation.