O presente trabalho descreve e introduz uma metodologia numérica de simulação térmica de trocadores de calor de fluxo cruzado e de casco e tubo. A metodologia computacional é utilizada para simular doze configurações de arranjos de escoamento de trocadores de calor de fluxo cruzado com número de passes e tubos por passe arbitrários, assim como diversas condições de mistura de ambos os fluidos. O procedimento computacional é desenvolvido, baseado em diversos trabalhos da literatura, para calcular a efetividade de temperatura e o fator de correção da diferença média logarítmica de temperatura para trocadores de calor de fluxo cruzado em escoamentos contracorrente e paralelo. Novos dados da efetividade de temperatura e do fator de correção para configurações complexas de trocadores de calor são apresentados em diversas tabelas e figuras. As condições de mistura do fluido interno depois de cada passe são analisadas e caracterizadas por três configurações: misturado, não misturado com uma ordem idêntica das fileiras e não misturado com uma ordem inversa das fileiras. A influência da mistura do fluido externo entre os tubos do trocador de calor também é analisada. A metodologia computacional também é utilizada para trocadores de calor de casco e tubo tipo TEMA E com um passe de ambos os fluidos (fluidos do casco e dos tubos) em escoamentos contracorrente e paralelo de acordo com as entradas do trocador de calor. O algoritmo é baseado em diversas hipóteses e considerações de modelagem adotadas em diversos trabalhos de trocadores de calor de fluxo cruzado e de casco e tubo. Cada seção entre as chicanas é idealizada como um trocador de calor não misturado - não misturado. Além disso, este estudo fornece um sumário de correlações matemáticas exatas e aproximadas para algumas configurações de trocadores de calor de fluxo cruzado e de casco e tubo, que são muito apropriadas para análises computacionais e que facilitam o cálculo de efetividade de temperatura e do fator de correção. Os resultados encontrados são comparados com o algoritmo HETE e com soluções e relações matemáticas disponíveis em outras literaturas e mostram a capacidade dos algoritmos desenvolvidos. / The present thesis describes and introduces the numerical simulation methodologies for thermal modeling of crossflow and shell-and-tube heat exchangers. The computational methodology is used for simulating twelve general flow arrangement configurations of crossflow heat exchangers with arbitrary number of passes and tubes per pass, as well as, several mixture conditions of both fluids. The computational procedures are developed, based on some works from literature, to calculate the temperature effectiveness and the mean logarithm temperature difference (MLTD) correction factor for crossflow and parallel and counter-crossflow heat exchangers. New temperature effectiveness and correction factor data for the treated complex flow arrangements configurations are provided and showed in various tables and plots. Tube fluid mixing conditions after each pass, characterized by three types of configuration: tube fluid mixed; tube fluid unmixed keeping identical order of the rows; and tube fluid unmixed with inverted order of the rows, are analyzed. The influence of external fluid mixing between tube rows along the heat exchanger configurations is also addressed. The computational methodology is also addressed to TEMA E shell-and-tube heat exchangers type with one-pass of both fluids (in-tube and shell side) flowing in counterflow and parallel regarding the heat exchangers inlets. The algorithm is based on various assumptions and modelling considerations adopted in several works of crossflow and shell-and-tube heat exchangers. Each section between two baffles is idealized as an unmixed-unmixed crossflow heat exchanger. In addition, this study provides a summary of exact and approximate correlations for some configurations of crossflow and shell-and-tube heat exchangers, that are very appropriate for computerized analysis and that facilitate the computation of both parameters, the temperature effectiveness and the mean logarithmic temperature difference correction factor. The results found are compared to algorithm HETE and with available relations and solutions of other works and show the capability of the developed algorithm.

Turbulent flow and transition are some of the most important phenomena of fluid mechanics and aerodynamics and represent a challenging engineering problem for aircraft manufacturers looking to improve aerodynamic efficiency. Laminar flow technology has the potential to provide a significant reduction to aircraft drag by manipulating the instabilities within the laminar boundary layer to achieve a delay in transition to turbulence. Currently prediction and simulation of laminar-turbulent transition is con- ducted using either a low-fidelity approach involving the stability equations or via a full Direct Numerical Simulation (DNS). The work in this thesis uses an alternative high-fidelity simulation method that aims to bridge the gap between the two simulation streams. The methodology uses an LES approach with a low-computational cost sub-grid scale model (WALE) that has inherent ability to reduce its turbulent viscosity contribution to zero in laminar regions. With careful grid spacing the laminar regions can be explicitly modelled as an unsteady Navier-Stokes simulation while the turbulent and transitional regions are simulated using LES. The methodology has been labelled as an unsteady Navier-Stokes/Large Eddy Simulation (UNS/LES) approach. Two test cases were developed to test the applicability of the method to simulate and control the crossflow instability. The first test case replicated the setup from an experiment that ran at a chord-based Reynolds number of 390, 000. Two methods were used to generate the initial disturbance for the crossflow vortices, firstly using a continuous suction hole and secondly an isolated roughness element. The results for this test case showed that the approach was capable of modelling the full transition process, from explicitly modelling the growth of the initial amplitude of the disturbances to final breakdown to turbulence. Results matched well with the available experimental data. The second test case replicated an experimental setup using a custom- designed aerofoil run at a chord-based Reynolds number of 2.4 million. The test case used Distributed Roughness Elements (DRE) to induce crossflow vortices at both a critical and a control wavelength. By forcing the crossflow vortices at a stable (control) wavelength a delay in laminar-turbulent transition can be achieved. The results showed that the UNS/LES approach was capable of capturing the initial disturbance amplitudes due to the roughness elements and their growth rates matched well with experimental data. Finally, downstream a transitional region was assessed with low-freestream turbulence provided using a modified Synthetic Eddy Method (SEM). The full laminar-turbulent transition pro- cess was simulated and results showed significant promise. In conclusion, the method employed in this thesis showed promising results and demonstrated a possible route to high-fidelity transition simulation run at more realistic flow conditions and geometries than DNS. Further work and validation is required to test the secondary instability region and the final breakdown to turbulence.

L'objectif de cette étude est de prévoir la transition laminaire/turbulent de la couche limite sur l'avant-corps d'un véhicule hypersonique évoluant à des nombres de Mach compris entre 4 et 8 et à des altitudes variant de 20 à 30km. L'approche utilisée est celle de la croissance modale des perturbations (stabilité linéaire locale) couplée à la méthode du eN.<br />Un code de stabilité a été créé pour cette étude. Il utilise un modèle spécifique pour le calcul des coefficients de transport et de chaleur spécifique de l'air.<br />Un code Navier-Stokes (Fluent) est utilisé pour le calcul des profils de base. Cette approche a été validée sur plaque plane par comparaison avec des résultats de stabilité obtenus à partir de profils Levy-Lees.<br />Les facteurs N sont calculés par la méthode enveloppe, en suivant des chemins d'intégration localement tangents à la vitesse de groupe. Une méthode originale du calcul, en approche spatiale, de la direction de cette vitesse est proposée.<br />Les résultats de stabilité montrent un effet déstabilisant de la couche entropique due à l'émoussement du nez du véhicule. Cependant, l'instabilité majoritaire mise en évidence est de type CrossFlow. Dans certains cas, le premier mode oblique est aussi important. La présence du second mode droit est anecdotique. Une étude paramétrique permet de comparer les facteurs N par rapport au critère NASP (Rd2/Me) lorsque l'altitude puis l'incidence de vol varient. Dans le premier cas, les résultats concordent, dans le second, ils divergent. Ainsi, un nouveau critère basé sur la quantité d'écoulement transverse est développé. Ce dernier est en adéquation avec les résultats du calcul de stabilité pour tous les cas considérés.

Abstract The influence of rotating and cross flow effect on local heat transfer coefficient and flow visualization for a single confined air/water jet with jet-to-wall spacing from 5 to 11.4, jet Reynolds number from 6500 to 26000, rotational Reynolds number from 0 to 112000, curvature ratio from 150 to , ratio of crossflow massflux to jet mass flux from 0 to 2, and the heat flux from 1430 to 12890W/m2 were reported. The local heat transfer coefficient for air/water along the surface is measured and the effect of the rotation, the jet-to-wall spacing, the surface curvature, local and average Nusselt number, are presented and discussed. Furthermore, flow visualization was made in the present study. Based on the experimental result, it is found that the rotation will induce the centrifugal and coriolis force. It also shows that the heat transfer response will be decreased when the impinging direction parallel to the rotating direction, and increased when impinging direction perpendicular to the rotating direction. Crossflow effect will make Nusselt number decrease to 48% when M=2. Moreover, the roughen surface will increase the heat transfer coefficient up to 22% due to the secondary flow. The flow visualization is used to observe the transition of laminar to turbulence flow and to calculate the boundary layer thickness.

No description available.

O presente trabalho descreve e introduz uma metodologia numérica de simulação térmica de trocadores de calor de fluxo cruzado e de casco e tubo. A metodologia computacional é utilizada para simular doze configurações de arranjos de escoamento de trocadores de calor de fluxo cruzado com número de passes e tubos por passe arbitrários, assim como diversas condições de mistura de ambos os fluidos. O procedimento computacional é desenvolvido, baseado em diversos trabalhos da literatura, para calcular a efetividade de temperatura e o fator de correção da diferença média logarítmica de temperatura para trocadores de calor de fluxo cruzado em escoamentos contracorrente e paralelo. Novos dados da efetividade de temperatura e do fator de correção para configurações complexas de trocadores de calor são apresentados em diversas tabelas e figuras. As condições de mistura do fluido interno depois de cada passe são analisadas e caracterizadas por três configurações: misturado, não misturado com uma ordem idêntica das fileiras e não misturado com uma ordem inversa das fileiras. A influência da mistura do fluido externo entre os tubos do trocador de calor também é analisada. A metodologia computacional também é utilizada para trocadores de calor de casco e tubo tipo TEMA E com um passe de ambos os fluidos (fluidos do casco e dos tubos) em escoamentos contracorrente e paralelo de acordo com as entradas do trocador de calor. O algoritmo é baseado em diversas hipóteses e considerações de modelagem adotadas em diversos trabalhos de trocadores de calor de fluxo cruzado e de casco e tubo. Cada seção entre as chicanas é idealizada como um trocador de calor não misturado - não misturado. Além disso, este estudo fornece um sumário de correlações matemáticas exatas e aproximadas para algumas configurações de trocadores de calor de fluxo cruzado e de casco e tubo, que são muito apropriadas para análises computacionais e que facilitam o cálculo de efetividade de temperatura e do fator de correção. Os resultados encontrados são comparados com o algoritmo HETE e com soluções e relações matemáticas disponíveis em outras literaturas e mostram a capacidade dos algoritmos desenvolvidos. / The present thesis describes and introduces the numerical simulation methodologies for thermal modeling of crossflow and shell-and-tube heat exchangers. The computational methodology is used for simulating twelve general flow arrangement configurations of crossflow heat exchangers with arbitrary number of passes and tubes per pass, as well as, several mixture conditions of both fluids. The computational procedures are developed, based on some works from literature, to calculate the temperature effectiveness and the mean logarithm temperature difference (MLTD) correction factor for crossflow and parallel and counter-crossflow heat exchangers. New temperature effectiveness and correction factor data for the treated complex flow arrangements configurations are provided and showed in various tables and plots. Tube fluid mixing conditions after each pass, characterized by three types of configuration: tube fluid mixed; tube fluid unmixed keeping identical order of the rows; and tube fluid unmixed with inverted order of the rows, are analyzed. The influence of external fluid mixing between tube rows along the heat exchanger configurations is also addressed. The computational methodology is also addressed to TEMA E shell-and-tube heat exchangers type with one-pass of both fluids (in-tube and shell side) flowing in counterflow and parallel regarding the heat exchangers inlets. The algorithm is based on various assumptions and modelling considerations adopted in several works of crossflow and shell-and-tube heat exchangers. Each section between two baffles is idealized as an unmixed-unmixed crossflow heat exchanger. In addition, this study provides a summary of exact and approximate correlations for some configurations of crossflow and shell-and-tube heat exchangers, that are very appropriate for computerized analysis and that facilitate the computation of both parameters, the temperature effectiveness and the mean logarithmic temperature difference correction factor. The results found are compared to algorithm HETE and with available relations and solutions of other works and show the capability of the developed algorithm.

Minimizing numerical dissipation without compromising the robust shock-capturing attributes remains an outstanding challenge in the design of numerical methods for high-speed compressible flows. The conflicting requirements of low and high numerical dissipation for accurate resolution of discontinuous and smooth flow features, respectively, are the principal reason behind this challenge. In this work we pursue a recently proposed novel strategy of combining adaptive mesh redistribution with conservative high-order shock-capturing finite-volume discretization methodology to overcome this challenge. In essence, we perform high-order finite-volume WENO (weighted essentially non oscillatory) reconstruction on a continuously moving grid the nodes of which are repositioned adaptively in such a way that maximum spatial resolution is achieved in regions associated with sharpest flow gradients. Moreover, to reduce computational expense, the finite-volume WENO discretization strategy is combined with the midpoint quadrature so that only one reconstruction along each intercool location is necessary. To estimate a monotone upwind flux, a rotated HLLC (Harten-Lax-vanLeer-contact resolving) Riemann solver is employed at each intercool location with the state variables estimated from the high-order WENO reconstruction procedure. The effectiveness of this adaptive high-order discretization methodology is assessed on the well-known double Mach reflection test case for reconstruction orders ranging from five to eleven. We find that the resolution of the intricate flow features such as the wall-jet improves progressively with the reconstruction order, which is indicative of the reduced dissipation level of the adaptive high-order WENO discretization. The adaptive discretization methodology is applied to simulate a flow configuration consisting of a Mach 3 supersonic jet injected in a Mach 2 supersonic crossflow of similar ideal gas. It is found that the flow characteristics and especially features that are formed as a result of the Kelvin-Helmholtz instability are strongly influenced by the reconstruction order. The influence of the jet inclination angle on the overall flow features is analyzed.

Rotating-disk flow has been investigated not only as a simple model of cross flow instability to compare with swept-wing flow but also for industrial flow applications with rotating configurations. However the exact nature of laminar-turbulent transi- tion on the rotating-disk flow is still major problem and further research is required for it to be fully understood, in particular, the laminar-turbulent transition process with absolute instability. In addition the studies of the rotating-disk turbulent boundary- layer flow are inadequate to understand the physics of three-dimensional turbulent boundary-layer flow. In present thesis, a rotating-rotating disk boundary-layer flow has been inves- tigated experimentally using hot-wire anemometry. A glass disk with a flat surface has been prepared to archieve low disturbance rotating-disk environment. Azimuthal velocity measurements using a hot-wire probe have been taken for various conditions. To get a better insight into the laminar-turbulent transition region, a new way to describe the process is proposed using the probability density function (PDF) map of azimuthal fluctuation velocity. The effect of the edge of the disk on the laminar-turbulent transition process has been investigated. The disturbance growth of azimuthal fluctuation velocity as a function of Reynolds number has a similar trend irrespective of the various edge conditions. The behaviour of secondary instability and turbulent breakdown has been in- vestigated. It has been found that the kinked azimuthal velocity associated with secondary instability just before turbulent breakdown became less apparent at a cer- tain wall normal heights. Furthermore the turbulent breakdown of the stationary mode seems not to be triggered by its amplitude, however, depend on the appearance of the travelling secondary instability. Finally, the turbulent boundary layer on a rotating disk has been investigated. An azimuthal friction velocity has been directly measured from the azimuthal velocity profile in the viscous sub-layer. The turbulent statistics normalized by the inner and outer sclaes are presented. / QC 20120529

A focus has been put on the stability characteristics of different flow types existing on air vehicles. Flow passing over wings and different junctions on an aircraft face numerous local features, ranging from different pressure gradients, to interacting boundary layers. Primarily, stability characteristics of flow over a wing subject to negative pressure gradient is studied. The current numerical study conforms to an experimental study conducted by Saric and coworkers, in their Arizona State University wind tunnel experiments. Within that framework, a passive control mechanism has been tested to delay transition of flow from laminar to turbulence. The same control approach has been studied here, in addition to underling mechanisms playing major roles in flow transition, such as nonlinear effects and secondary instabilities. Another common three-dimensional flow feature arises as a result of streamlines passing through a junction, the so called corner-flow. For instance, this flow can be formed in the junction between the wing and fuselage on a plane. A series of direct numerical simulations using linear Navier-Stokes equations have been performed to determine the optimal initial perturbation. Optimal refers to a perturbation which can gain the maximum energy from the flow over a period of time. Power iterations between direct and adjoint Navier- Stokes equations determine the optimal initial perturbation. In other words this method seeks to determine the worst case scenario in terms of perturbation growth. Determining the optimal initial condition can help improve the design of such surfaces in addition to possible control mechanisms. / <p>QC 20130604</p> / RECEPT

No description available.