Esta tese se insere na temática da crise dos grandes discursos, reconhecendo que ao contrário do colapso ou do fim das metanarrativas, eles se abriram, possibilitando a reapropriação de uma outra ideia de homem. Uma ideia que traz como base a gramática trágica. Trágico, aqui, é o que vislumbra o real como idiota, simples, aprovador de todos os acontecimentos, suficiente para reconfigurar a imageria contemporânea e identificar, no âmbito de sua gramática, a presença do sujeito idiotès (vulgar e idiota), uma presença que foi negligenciada ao longo de toda modernidade. Para tratar dessa reapropriação do homem e do sujeito , este estudo se desenvolve a partir de três esferas de observação: a) o advento da racionalidade e a construção de um modelo de sujeito forte, que se tornará a base de uma tradição; b) a crise deste modelo e o seu encontro com o pensamento fraco (Vattimo); e c) o reordenamento da gramática moderna que, intensificando-­se idiota, aponta para um outro imaginário. Na primeira, exponho a preferência da racionalidade moderna por um homem e um sujeito fortes e sua consequente reprovação das narrativas que desprezam a noção de natureza ou afirmam o homem vulgar, fruto do acaso e da idiotia humana; na segunda, analiso a época contemporânea apontando para uma reconfiguração conceitual que, a partir da crise das noções de ser e de natureza (impostas por Nietzsche), aponta para o surgimento do pensamento fraco/débil; no terceiro, com foco na filosofia trágica rossetiana, fixo os desdobramentos de suas noções de acaso, de convenção, de aprovação, de um real idiotès, para a constituição do sujeito contemporâneo. Por fim, aponto para a liberação da imageria trágica e sua expressão idiota, que aproximam o homem de sua condição mais humana: essa idiotia. Ou seja, o objetivo é reapropriar-­se de uma gramática e de um homem que nunca apareceram como aspiração no âmbito dos discursos hegemônicos e que agora evidenciam-­se no campo da contemporaneidade. / This theses stands on the theme of the crisis of great discourses, acknowledging that instead of a collapse or an ending of metanarratives, they unfasten, allowing the reappropriation of another idea of man. An idea that brings as groundwork the tragic philosophy. Tragic, here, is seeing the real as idiot, simplistic, an accepter of everything, enough to reconfigurate the contemporary imagery and identificate, on its own grammar, the presence of an idiots subject (vulgar and idiot), a presence that was neglected all through the modernity. To approach such reappropriation of man and of subject , this research develops departing of three spheres of observation: a) the advent of rationality and the construction of a strong subject model, that will became the base of a tradition; b) a crisis of such model and its clash with the weak thought (Vattimo); and c) the reordering of the modern grammar that, becoming more idiot, points to another imaginary. On the first, I Expose the preference of modern rationality for a strong man and a subject and its Consecutive reprobation of narratives that despises the notion of nature or asserts the vulgar man, product of chance and of human idiocy; the second, I analyse the contemporaneity pointing to a conceptual reconfiguration that, departing from the crisis of notions of being and nature (imposed by Nietzsche), points to the emergence of weak thought; on the third, focusing on the rossetian tragic philosophy, assert the developments of its notions of chance, of convention, of approval, of a idiots real, for the constitution of the contemporary subject. Lastly, I point to the liberation of tragic imagery and its idiotic expression that approximates the man to its most human condition: this idiocy. In other words, the aim is reappropriate a grammar and a man that never appear as ambition on scope of hegemonic discourses and now come to light in the field of contemporaneity.

The remarkable efficacy with which normal surface mass transpiration (blowing and suction) alters a given base flow to achieve a desired predefined objective has motivated several investigations on drag reduction, self-propulsion and suppression of separation and wake unsteadiness in bluff body flows. However, the energetic efficiency, a critical parameter that determines the true efficacy and in particular practical feasibility of this control strategy, has received significantly less attention. In this work, we determine the optimal zero net mass transpiration blowing and suction profiles that minimize net power consumption while reducing drag or enabling self-propulsion in typical bluff body flows. We establish the influence of prescribed blowing and suction profiles on the hydrodynamic loads and net power consumption for a representative bluff body flow involving flow past a stationary two-dimensional circular cylinder. Using analysis based on Oseen’s equations, we find that all the symmetric modes, except the first one, lead to an increase in the net power consumption without affecting hydrodynamic drag. The optimal blowing and suction profile that yields minimum power consumption is such that the normal stress acting on the cylinder surface vanishes identically. Furthermore, we show that a self-propelling state corresponding to zero net drag force is attained when the first mode of blowing and suction profile is such that the flow field be-comes irrigational. Based on these findings we employ direct numerical simulation tools to decipher the Reynolds number dependence of the optimal profiles and the associated power consumption for both drag reduction and self-propulsion. For a typical Reynolds number, the time-averaged drag coefficient first decreases due to vortex shedding suppression, then increases and eventually decreases again after attaining a local maximum as the strength of the first mode is increased. The net power consumption continues to decrease with an increase in the strength of the first mode before reaching a minima after which it rises continuously. For a Reynolds number of 1000 over fifteen fold reduction in drag is achieved for an optimal blowing and suction profile with a maximum radial surface velocity that is nearly 1.97 times the free stream velocity. Next, to establish whether or not higher modes play a role in decreasing net power consumption at finite Reynolds number, we perform theoretical analysis of a configuration similar to the one described above for a spherical body. At zero Reynolds number, as a result of mode independence, we show that surface blow-ing and suction of any form that involves second or higher order axisymmetric or non-axisymmetric modes does not contribute to drag and only leads to an increase in total power consumption. However, at finite Reynolds number, using analysis based on Oseen’s equations, we find that the second and higher modes contribute substantially to the optimal profiles. Finally to understand the effects of a change in shape we consider generalization of the above analysis to axisymmetric prolate and oblate spheroidal bodies. We find that for a general axisymmetric body with non-constant curvature, the optimal drag reducing and self-propelling blowing and suction profiles for minimum power consumption contain second and higher-order modes along with the first mode even when the Reynolds number is zero. The net decrease in power consumption with the use of second and higher order modes exceeds 33% for a disk-like low aspect ratio self-propelling oblate spheroid. Moreover, we perform comparisons between blowing and suction and tangential surface velocity based boundary deformation propulsion mechanisms. Below an aspect ratio of 0.56 we find blowing and suction mechanism to be more efficient for self-propulsion of an oblate spheroid. In contrast, for a self-propelling pro-late spherical micro-swimmer, we show that the tangential surface tread milling consumes less power irrespective of the aspect ratio.

The wake behind a rectangular forebody with variable inlet conditions is investigated. The perforated surface of the two-dimensional rectangular forebody, with a smooth leading edge and a blunt trailing edge, allows for boundary layer modification by means of wall suction. The test section, of which the rectangular forebody is the main part, is experimentally evaluated with a series of hot-wire and Prandtl tube measurements in the boundary layer and the wake. For a suction coefficient of Γ&gt;9, corresponding to 0.9% suction of the free stream velocity, the asymptotic suction boundary layer (ASBL) is obtained at the trailing edge of the forebody for laminar boundary layers (Rex=1.6×105−3.8×105). The key feature of the ASBL, a spatially invariant boundary thickness which can be modified independent of the Reynolds number, is used to perform a unique parametrical study. Turbulent boundary layers (Rex=4.5×105−3.0×106) subject to wall suction are also investigated. For a critical suction coefficient Γcrit, which depends on Rex, the boundary layer relaminarizes. Strong evidence is found to support the hypothesis that turbulent boundary layers will ultimately attain the ASBL as well, provided that the wall suction is strong enough. The effect of the modulated laminar and turbulent boundary layers on the wake characteristics is studied. The shape of the mean wake velocity profile, scaled with the velocity deficit U0and the wake half width ∆y1/2, is found tobe independent of x/h, for x/h&gt; 6 and Reh &gt;6.7×103. The wake width is shown to scale with the effective thickness of the body h+2δ1, where the ratio is expected to vary with the downstream location. A decrease of the displacement thickness leads to a decrease of the base pressure, with Cp,b = −0.36 in the ASBL limit. The Strouhal number based on the effective thickness becomes Sth+2δ1 ≈ 0.29 in the ASBL limit and independent of the plate thickness (h) Reynolds number, in the range Reh = 2.9×103 − 6.7×103. For the turbulent boundary Sth+2δ1 is found to be 25% lower, which shows that the wake characteristics depend on the state of the boundary layer at the trailing edge. The total drag is found to be reduced by as much as 30% for Reh = 2.7×104 when a wall normal velocity of only 3.5% of the free stream velocity is applied. Wall suction successively reduces the total drag with increasing wall suction, at least in the Reynolds number rangeReh = 8.0×103−5.5×104. / <p>QC 20140312</p>

A bluff-body has been employed as the flame stabilization scheme for many combustion devices such as gas turbines and aviation engines. Although the bluff-body flame holder has a key advantage of generating a hot gas recirculation zone behind it and assist in stable combustion, it also induces flow field and combustion instabilities such as unstable vortex shedding, which can adversely affect the flame stability and lead to blow-off. The understanding of the physical mechanism of flame stabilization and blow-off processes has been one of the critical subjects in premixed combustion systems under highly turbulent conditions. As considering this, the present dissertation presents insight of flame stabilization and blow-off mechanisms using several series of computational studies and detailed analysis using diagnostic approaches. Two-dimensional direct numerical simulations are conducted to examine flame/flow and blow-off dynamics in lean premixed hydrogen-air and syngas-air flames stabilized on a meso-scale bluff-body in a square channel. Several distinct effects on flame stabilization and blow-off dynamics are investigated, such as reduced confinement, hydrodynamic instability, flame time scale, and differential diffusion effects. For the analysis, a proper time scale analysis is attempted to characterize the flame blow-off mechanism, which turns out to be consistent with the classic blow-off theory of Zukoski and Marble. The combined approach of computational singular perturbation and tangential stretch rate is applied to examine chemical characteristics in blow-off dynamics. As an extension from Eulerian to Lagrangian viewpoint, Lagrangian particle tracking analysis of post-processing the pre-computed results is performed to examine the local characteristics during the critical transient event of local extinction and recovery.

No description available.

No description available.

This thesis presents an experimental investigation of drag reduction devices on a bluff body in ground effect. It has previously been shown that the addition of end-plate tabs to a rectangular based bluff body with an aspect ratio of 4 is effective in eliminating vortex shedding and reducing drag for low Reynolds number flows. In the present study a square based bluff body, both with and without tabs, will be tested under the same conditions, except this time operating within proximity to a ground plane in order to mimic the properties of bounded aerodynamics that would be present for a body in ground effect.

No description available.

No description available.

No description available.