No description available.

No description available.

The objectives of the present investigation are to determine the nature of the flow field around bluff parachute canopies, considering the effects of canopy shape parameters on this flow field and hence on the resulting aerodynamic forces and moments which are developed on the canopy surface. In order to relate the flow field developed around bluff parachute canopies to their aerodynamic characteristics, a series of experiments in the Leicester University wind tunnel has been conducted on a family of particularly significant canopy shapes. These cross-shaped canopies have excellent drag and stability characteristics if arm ratios of about 4:1 are selected. Flow visualisation, using both helium bubbles and wool tufts, was used to determine the flow field around the canopy. The most probable description of the wake flow is chains of irregularly-shaped vortex loops which move at about 0.7 times the undisturbed free stream velocity. Aerodynamic forces and moments measured on the various canopies correspond with the observed flow characteristics. Statistical correlation analyses made with hot wire anemometers in their wake indicate the periodic structure of the wakes formed behind these bluff bodies and reveal their basic similarities. Strouhal numbers of about 0.15 were obtained in the wake formed behind an imporous rigid hemispherical canopy. These are increased as canopy porosity is made larger. A useful comparison between a semi-theoretical blockage correction applied to aerodynamic forces and test results was obtained from an ancillary test programme conducted under water in a large cross-sectional area ship tank.

At present a large number of fluid dynamics applications are found in aerospace, civil and automotive engineering, as well as medical related fields. In many applications the flow field is turbulent and the computational modelling of such flows remains a difficult task. To resolve all turbulent flow phenomena for flow problems where turbulence is of key interest is a priori not feasible in a Computational Fluid Dynamics (CFD) investigation with a conventional mesh. The use of a Dynamic Grid Adaptation (DGA) algorithm in a turbulent unsteady flow field is an appealing technique which can reduce the computational costs of a CFD investigation. A refinement of the numerical domain with a DGA algorithm requires reliable criteria for mesh refinement which reflect the complex flow processes. At present not much work has been done to obtain reliable refinement criteria for turbulent unsteady flow. The purpose of the work presented in this thesis is to use both a DGA algorithm and Large Eddy Simulation (LES) turbulence model for predicting turbulent unsteady flow. The criteria for mesh refinement used in this work are derived from the equation for turbulent viscosity in the LES turbulence model. By using a modification to the turbulent viscosity as a refinement variable there is a link between both DGA algorithm and turbulence model. The smaller scale turbulence is modelled via the LES turbulence model, while the larger scales are resolved. In comparison with the simulations using a conventional mesh, substantial reduction in mesh size has been obtained with the use of a DGA algorithm. The reduction in mesh size is obtained without a decay in the quality of the prediction. It is shown that the use of a DGA algorithm in the context of turbulence modelling is a suitable tool which can be used as a next step in an attempt to resolve turbulence more realistically.

Passenger cars are bluff bodies and are prone to unsteady phenomena with scales comparable to the scale of the vehicle itself. This type of large-scale, self-excited unsteadiness is the subject of the present work. Aerodynamic unsteadiness can be important for two reasons. It can cause unsteady pressures and forces on the car and it can impact the time-averaged flow through the generation of Reynolds stresses. A range of parametric two-dimensional bodies have been used in the development of novel experimental techniques and analyses and for CFD validation. Detailed investigations have been undertaken on the Ahmed model and on models of a Rover 200 passenger car in wind tunnels at Durham and at MIRA at scales of up to 40%. A method was developed which makes it possible to visualise periodic flow structures from measurements made sequentially in the wake or on the model surface. Unsteady flows for fastback passenger cars were found to be much less periodic than for two-dimensional vortex shedding cases. Pressure fluctuations were significantly lower on the model surface than in the wake resulting in limited unsteady forces. Unsteady flow structures, Strouhal numbers and levels of unsteadiness were similar for the Rover 200 model with and without a backlight spoiler and for the Ahmed model, indicating that sharp corners do not have a dominant effect on unsteadiness. Two principal unsteady structures were observed in the wake of the fastback shapes. A structure was observed at Strouhal numbers around 0.1 involving the alternate strengthening of the two c-pillar vortices in an antisymmetric mode. At Strouhal numbers in the range 0.3 to 0.6 an unsteady structure was observed consisting of the oscillation of the strength of the two c-pillar vortices in a symmetric mode. At the same time the location of the vortices oscillates in the vertical direction.

This work focuses on an investigation of multi-modality in typical aerodynamic shape optimization problems and development of optimization algorithms that can find a global optimum. First, a classification of problems based on the degree of multi-modality is introduced. Then, two optimization algorithms are described that can find a global optimum in a computationally efficient manner: a gradient-based multi-start Sobol algorithm, and a hybrid optimization algorithm. Two additional algorithms are considered as well: a gradient-based optimizer and a genetic algorithm. Finally, we consider a set of typical aerodynamic shape optimization problems. In each problem, the primary objectives are to classify the problem according to the degree of multi-modality, and to select the preferred optimization algorithm for the problem. We find that typical two-dimensional airfoil shape optimization problems are unimodal. Three-dimensional shape optimization problems may contain local optima. In these problems, the gradient-based multi-start Sobol algorithm is the most efficient algorithm.

No description available.

No description available.

The literature concerning bluff-body flows in two-dimensional, incompressible, sheared and unsheared streams is reviewed. It is found that no theory yet exists which can predict the form drag of a bluff body without some recourse to experimental data, even for the simple case of an isolated bluff-plate in an unsheared stream. In the present state of knowledge, and considering the complexity of turbulent shear flows, a theory for the form drag of bluff-plates immersed in turbulent boundary-layers seems remote. A correlation scheme is proposed to relate the form drag of a bluff-plate which is attached to a smooth-wall with the mean-flow characteristics of the naturally-developed, turbulent boundary-layer in which it is immersed. The investigation is limited to smooth-wall flows of the type described by Coles (1956). It is suggested that, for bluff-plates which are small compared with the boundary-layer thickness, the drag might depend only on the “wall variables”: wall shear-stress, fluid density and viscosity, and the plate height.

The performance of current open wheeler race cars depends heavily on the effectiveness of the aerodynamic package of which the front wing and wheels make a significant contribution. Previous investigations have focused on the aerodynamic characteristics of each of these bodies in isolation. Investigations that have considered both working in unison have conflictingly reported that the wheel presence aids or hinders the wing???s performance while the wheel???s aerodynamic performance has been neglected. In order to obtain a more thorough understanding of the interaction of a wing and wheel, experimental results were used to validate a computational model used to investigate a wing and wheel in isolation and in combination. The combined wing and wheel investigation demonstrated that three main interactions can occur, depending on the selection of wing span, angle of attack and height used, while the wheel width and track were found to have little influence. The three interacting states differ in the path that the main and secondary wing vortices take around the wheel and the subsequent variation in the combined wake structure. In general, the wing in the presence of the wheel reduced the wing???s ability to generate downforce by up to 45% due to the high pressure regions generated forward of the wheel. This was also found to alleviate the adverse pressure gradients experienced by the wing, and also reduce the drag by up to 70%. For this reason, the downforce loss phenomenon was observed to occur at a height 0.08c to 0.32c lower in comparison to the same wing in isolation, dependant on the wing span. Wheel lift and drag values were also observed to reduce in the presence of a wing by up to 65% and 38% respectively due to the influence of the wing???s flow structures have on the wake of the wheel. As a result,it was shown that the combined wing and wheel downforce and drag optima differed by up to 75% and 25% respectively to those which would be estimated if the two bodies were investigated individually and the results summed highlighting the importance of investigating these two bodies in unison.