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This study concerns an underexpanded jet, issuing from a convergent slot into quiescent air, as it is deflected by a convex surface of constant radius. Emphasis Is placed on the mechanism of breakaway, a phenomenon whereby the jet leaves the surface tangentially. An optical system based on the standard Z-type Schlieren configuration and capable of interferometric, Schlieren and shadowgraph techniques has been designed. The techniques are interchanged simply, a laser source being employed for Interferometry and a Xenon spark source for Schlieren and shadowgraph. Vibrations limit the interferometry and improvements are discussed. Shadowgraph and both spark and continuous Schlieren techniques gave good results. Total pressure traverses and surface oil flow visualization show that the influence of secondary flows on breakaway is small. Measurements of the coefficient of discharge show an increase both as the stagnation pressure Is Increased and as the slot width is reduced. The existence of a separation bubble has been established from surface static pressure measurements and shadowgraph and Schlieren photographs. Surface oil flow visualization shows a region of reversed flow withhin the bubble. The bubble grows as the stagnation pressure Is increased and eventually causes breakaway. A potential flow calculation method using the method of characteristics has been developed. Calculation of a fully attached Jet is inaccurate because the separation bubble is ignored. A calculation using the measured surface static pressures accurately predicts the main features of the first shock cell. Reattachment occurs further downstream of the jet and its breakaway should involve a coupling of the solutions of the outer shear layer, potential core and separated boundary layer, the latter including reversed flow.

Unsteady flow analysis has been gradually introduced in turbomachinery design systems to improve machine performance and structural integrity. A project on computation of unsteady flows in turbomachinery has been carried out. A quasi 3-D time-linearized Euler/Navier-Stokes method has been developed for unsteady flows induced by the blade oscillation and unsteady incoming wakes, hi this method, the unsteady flow is decomposed into a steady flow plus a harmonically varying unsteady perturbation. The coefficients of the linear perturbation equation are formed from steady flow solutions. A pseudo-time is introduced to make both the steady flow equation and the linear unsteady perturbation equation time-independent. The 4-stage Runge-Kutta time-marching scheme is implemented for the temporal integration and a cell-vertex scheme is used for the spatial discretization. A 1-D/2-D nonreflecting boundary condition is applied to prevent spurious reflections of outgoing waves when solving the perturbation equations. The viscosity in the unsteady Navier- Stokes perturbation equation is frozen to its steady value. The present time-linearized Euler/Navier-Stokes method has been extensively validated against other well- developed linear methods, nonlinear time-marching methods and experimental data. Based upon the time-linearized method, a novel quasi 3-D nonlinear harmonic Euler/Navier-Stokes method has been developed. In this method, the unsteady flow is divided into a time-averaged flow plus an unsteady perturbation. Time-averaging produces extra nonlinear "unsteady stress" terras in the time-averaged equations and these extra terras are evaluated from unsteady perturbations. Unsteady perturbations are obtained by solving a first order harraonic perturbation equation, while the coefficients of the perturbation equation are forraed from time-averaged solutions. A strong coupling procedure is applied to solve the time-averaged equation and the unsteady perturbation equation simultaneously in a pseudo-time domain. An approximate approach is used to linearize the pressure sensors in artificial smoothing

The aims of this project were the implementation of Computational Fluid Dynamics (CFD) to the study of supersonic ejectors, and the investigation of the flow processes that occur. The conventional ejector has been in existence for more than a century yet the design has remained largely unchanged and is difficult to optimise. This has been attributed to a lack of understanding of the complex flow processes and phenomena that occur. CFD provides the ability to study these processes, and to rapidly assess geometrical influence upon operational performance. The CFD model was assessed through systematic appraisal of the numerical parameters that influence solution stability and simulation accuracy. Two proprietary CFD codes were utilised; a structured segregated code and an adaptive mesh coupled code. Assessed parameters included; mesh dependency, discretisation schemes, turbulence models, and boundary layer models that are shown highly influential. Simulation was validated through comparison of predicted and experimental entrainment values. Simulations of an ejector that is part of a steam-jet refrigeration cycle were used to assess the influence of geometry and operating conditions. The structured code was found suitable for geometrical studies however the coupled code was required for detailed flow analysis. Geometrical studies showed current ejector design guidelines to be well set. Operational studies highlighted the dominant influence of motive fluid flow rate upon entrainment levels. Shock systems and flow processes could be clearly identified. Simulations of ejectors utilised in vacuum and thrust augmenting applications were also conducted in assessment of the general applicability of CFD. CFD has the potential to be an effective and powerful tool III simulating and understanding ejectors. Qualitative and quantitative results can be obtained dependent upon the optimisation and validation of the mathematical model. This however can only be performed properly if the user fully understands the t10w physics and applied numerics.

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Effects of changing the ratio of the arm length and width, the arm ratio, on the static and dynamic characteristics of cruciform parachute canopies are described. Forces and moments were determined from measurements made when fabric canopies were towed under water in a ship tank as well as from integrated pressure distributions determined by using specially designed pressure transducers fixed in fabric wind tunnel models. These techniques, designed to aid in the examination of general principles concerning the dynamics of bluff bodies in viscous flow, were used to investigate time and acceleration dependent variations in aerodynamic characteristics. Flow visualization techniques were utilised to determine the flow field around cruciform canopies. From numerical analysis of fluctuating aerodynamic forces and the determination of the characteristics of the cruciform canopy flow field, it is shown that strong jets of fluid through the four gaps between adjacent canopy arms cause a gross momentum defect in the canopy wake resulting in a high degree of aerodynamic drag. From consideration of solutions of the equations of motion of a parachute system, the value of the first angle-of-attack derivative of the normal force component function is most significant in determining a given system's dynamic characteristics. Experimental results were input into the current Leicester University parachute performance computer model and the variations of dynamic performance characteristics determined as a function of arm ratio. It is shown that a unique optimum arm ratio, corresponding to the most acceptable compromise between aerodynamic drag and dynamic characteristics does not exist for all canopy-payload configurations but will always be greater than 3:1 for any specific configuration.

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No description available.

No description available.