M.Tech.

Sur une maquette à l’échelle 2/5ième équipée d’un diffuseur et de pneus Michelin. La géométrie du véhicule, basée sur le modèle ASMO, a été modifiée précédemment à ce travail afin d’obtenir un angle d’attaque de l’écoulement sur les roues avant et un équilibre du sillage réaliste en présence de quatre roues tournantes. Cette configuration a servi de référence dans le cadre de cette étude.Il a été mis en évidence que la configuration de base avec un sillage équilibré peut facilement être modifiée d’un point de vue aérodynamique en changeant l’état des roues (en rotation ou pas) et le type de pneumatique, en particulier sur l’essieu arrière. Cela provient d’un effet global et d’une sensibilité importante de l’équilibre du sillage aux changements de débit au soubassement. A contrario, lorsque le sillage du véhicule se trouve déséquilibré, il devient plus robuste par rapport à des perturbations de soubassement comme un changement d’état des roues ou une modification des pneumatiques. Si l’on supprime les quatre roues ou uniquement les deux roues avant, le débit de quantité de mouvement au soubassement est grandement augmenté. Par contre, si l’on supprime le diffuseur (changement important de la géométrie du véhicule), celui-ci s’en trouve nettement réduit. Dans ces deux configurations, le sillage est très fortement déséquilibré vers le sol et devient indépendant aux modifications apportées sur les roues.Il a également été mis en évidence un effet plus local du sillage des roues sur la portance et la traînée du véhicule.En effet, la zone de dépression dans le sillage des roues avant a un effet sur la portance alors que le sillage des roues arrière pilote en partie la pression au culot et donc la traînée. Il a ainsi été observé une augmentation importante de la traînée du véhicule lorsque le sillage des roues arrière, non fermé, venait en interaction directe avec le sillage du véhicule. / The thesis aims to provide a better understanding of the wheel-vehicle interaction, via experimental investigations on a 2/5-th scale vehicle with an underbody diffuser and 2/5-th scale wheels equipped with Michelin tires. The vehicle geometry, based on ASMO model, was modified prior to the PhD work, in order to achieve a reasonable front wheel yaw angle, and a realistic wake balance with four rotating wheels. It is the baseline configuration in the scope of this work.The findings demonstrate that the well-balanced wake of the baseline configuration can be easily modified by different wheel states or tire modifications, especially at the rear axle. This results from a global effect of the underbody momentum modifications, i.e. a high wake sensitivity to the underbody flow. On the contrary, when the vehicle mean wake develops into a non-balanced topology, it is more robust towards underbody perturbations such as different wheel states or tire modifications. By eliminating four wheels or front wheels, the underbody momentum flux is vastly increased; by eliminating the underbody diffuser, which is a vehicle geometry modification, the underbody momentum flux is significantly reduced. In these two circumstances, one can observea robust downwash from the roof, independent of the wheel states or tire modifications. Besides, there is a more local effect of the wheels near wakes on the aerodynamic lift and drag of the vehicle. Low pressure regions in the underbody downstream the front wheels have an effect on vehicle lift. The rear wheels impose pressure conditions on the vehicle base, influencing the vehicle drag. Particularly, the merging of nonclosed mean wakes of the rear wheels with the vehicle wake can give rise to strong penalty in vehicle drag.

Since the fuel crisis of the 1970s, aerodynamic design has become essential to the vehicle design process in order to reduce fuel consumption and lower emissions as well as (in more recent years) increase the range on vehicles with alternative powertrains. Production car manufacturers have developed shape optimisation techniques that have generated significant improvements over the years however, in order to achieve further gains, a deeper understanding of the fundamental flow structures around vehicles must be achieved. This thesis reports the findings of three studies that aim to understand how the base pressure is manipulated on vehicle like geometries by applying shape optimisations. The base pressure typically contributes approximately 30% of the overall vehicle drag on production vehicles and so presents an opportunity for significant drag saving. A fundamental One-Box model was used to investigate how changing fore-body drag can effect the base pressure and wake topology at varying ground clearances. It was found that at high ground clearances the total drag changes were generated by base pressure changes however when the model was lowered into ground effect the fore-body and skin friction drag produced significantly larger changes than the base pressure. Analysis of the unsteady results showed that with a thinner boundary layer over the model the unsteadiness in the wake was increased. A second study was then conducted on a generic vehicle geometry, the Windsor model, where the lower separation was manipulated through the use of different underbody profiles . As the lower boundary layer on the model was thickened the lower recirculation region grew and lowered the pressure on the base. This was also seen to increase the unsteadiness of the pressures recorded on the base when the upper and lower shear layers were of significantly different strengths. Finally, a rear end optimisation was conducted on the Windsor model using high aspect ratio tapers on the top and bottom trailing edges. It was seen that the amount of downwash or upwash created by the tapers acted on the wake balance which moved the impingement region on the base. This changed the near wall velocities of the wake flow and resulted in changing base pressures. Overall the work has shown that, by controlling the flow conditions at separation, the base pressure can be modified, particularly by altering the relative strengths of the upper and lower shear layers and the impingement location on the base.

Granular materials are in abundance both in nature and in industry. They are of considerable interest to both the engineering and physics communities, due to their practical importance and many unsolved scientific challenges. This thesis is concerned with the “pressure dip” phenomenon underneath a granular pile (commonly known as the “sandpile problem”) which has attracted great attention in the past few decades. Underneath a sandpile that is formed by funnel feeding, a significant minimum (dip) in the vertical base pressure is often found below the apex where a maximum pressure is intuitively expected. Despite a large amount of work undertaken, a comprehensive understanding of this phenomenon remains elusive. This thesis presents an extensive study investigating the underlying mechanism of this phenomenon and also its implications on pressures in silos. The study started with a laboratory test programme of conical mini iron pellet piles. The results confirmed that the pressure dip is a robust phenomenon. It was shown that, under certain deposition radius with uniform deposition across the deposition area, a dip emerges firstly in a ring shape when the radius of the formed pile is small and comparable to the deposition radius. With the increase of the pile radius upon further deposition, the dip ring gradually evolves to a central dip as the pressure at outer radius eventually overtakes that in the centre. The magnitude of the dip was found to be significantly affected by the deposition rate but almost unaffected by the deposition height.

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The thesis contains information about the design of pressure vessels and describes their individual parts. It is mentioned production of individual parts and the process including assembly parts in one unit. The thesis includes options of control and testing of pressure vessels. It is described kinds of built-ins of distillation column and the basic principles and types of distillation. It is created stress analysis of pressure vessels parts according to ČSN EN 13 445 – 3, and also stress analysis of the selected part of column by using FEM. Mechanical drawing of distillation column is part of the thesis.

Splitter plates are passive flow control devices for reducing drag and suppressing vortex shedding from bluff bodies. Most studies of splitter plates involve the flow around an “infinite” circular cylinder, however, in the present study the flow around a surface-mounted finite-height circular cylinder, with a wake-mounted splitter plate, was studied experimentally in a low-speed wind tunnel using a force balance and single-component hot-wire anemometry. Four circular cylinders of aspect ratios AR = 9, 7, 5 and 3 were tested for a Reynolds number range of Re = 1.9×10^4 to 8.2×10^4. The splitter plates had lengths, relative to the cylinder diameter, of L/D = 1, 1.5, 2, 3, 5 and 7, thicknesses ranging from T/D = 0.10 and 0.15, and were the same height as the cylinder being tested. The cylinders were partially immersed in a flat-plate turbulent boundary layer, where the range of boundary layer thickness relative to the cylinder diameter was δ/D = 1.4 to 1.5. Measurements were made of the mean drag force coefficient, the Strouhal number at the mid-height position, and the Strouhal number and power spectra along the cylinder height. For all four finite circular cylinders, the splitter plates were effective at reducing the magnitude of the Strouhal number, and weakening or even suppressing vortex shedding, depending on the specific combination of AR and L/D. Compared to the case of an infinite circular cylinder, the splitter plate is less effective at reducing the mean drag force coefficient of a finite circular cylinder. The largest drag reduction was obtained for the cylinder of AR = 9 and splitter plates of L/D = 1 to 3, while negligible drag reduction occurred for the shorter cylinders.