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A posteriorní odhady chyby pro řešení konvektivně-difusních úloh / A posteriori error estimates for numerical solution of convection-difusion problemsŠebestová, Ivana January 2014 (has links)
This thesis is concerned with several issues of a posteriori error estimates for linear problems. In its first part error estimates for the heat conduction equation discretized by the backward Euler method in time and discontinuous Galerkin method in space are derived. In the second part guaranteed and locally efficient error estimates involving algebraic error for Poisson equation discretized by the discontinuous Galerkin method are derived. The technique is based on the flux reconstruction where meshes with hanging nodes and variable polynomial degree are allowed. An adaptive strategy combining both adaptive mesh refinement and stopping criteria for iterative algebraic solvers is proposed. In the last part a numerical method for computing guaranteed lower and upper bounds of principal eigenvalues of symmetric linear elliptic differential operators is presented. 1
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On some models in linear thermo-elasticity with rational material lawsMukhopadhyay, S., Picard, R., Trostorff, S., Waurick, M. 27 September 2019 (has links)
In the present work, we shall consider some common models in linear thermo-elasticity within a common structural framework. Due to the flexibility of the structural perspective we will obtain well-posedness results for a large class of generalized models allowing for more general material properties such as anisotropies, inhomogeneities, etc.
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Experimental Aerothermal Performance of Turbofan Bypass Flow Heat ExchangersVillafañe Roca, Laura 07 January 2014 (has links)
The path to future aero-engines with more efficient engine architectures requires advanced
thermal management technologies to handle the demand of refrigeration and lubrication. Oil
systems, holding a double function as lubricant and coolant circuits, require supplemental
cooling sources to the conventional fuel based cooling systems as the current oil thermal
capacity becomes saturated with future engine developments. The present research focuses on
air/oil coolers, which geometrical characteristics and location are designed to minimize
aerodynamic effects while maximizing the thermal exchange. The heat exchangers composed
of parallel fins are integrated at the inner wall of the secondary duct of a turbofan. The
analysis of the interaction between the three-dimensional high velocity bypass flow and the
heat exchangers is essential to evaluate and optimize the aero-thermodynamic performances,
and to provide data for engine modeling. The objectives of this research are the development
of engine testing methods alternative to flight testing, and the characterization of the
aerothermal behavior of different finned heat exchanger configurations.
A new blow-down wind tunnel test facility was specifically designed to replicate the engine
bypass flow in the region of the splitter. The annular sector type test section consists on a
complex 3D geometry, as a result of three dimensional numerical flow simulations. The flow
evolves over the splitter duplicated at real scale, guided by helicoidally shaped lateral walls.
The development of measurement techniques for the present application involved the design
of instrumentation, testing procedures and data reduction methods. Detailed studies were
focused on multi-hole and fine wire thermocouple probes.
Two types of test campaigns were performed dedicated to: flow measurements along the test
section for different test configurations, i.e. in the absence of heat exchangers and in the
presence of different heat exchanger geometries, and heat transfer measurements on the heat
exchanger. As a result contours of flow velocity, angular distributions, total and static
pressures, temperatures and turbulence intensities, at different bypass duct axial positions, as
well as wall pressures along the test section, were obtained. The analysis of the flow
development along the test section allowed the understanding of the different flow behaviors
for each test configuration. Comparison of flow variables at each measurement plane
permitted quantifying and contrasting the different flow disturbances. Detailed analyses of the
flow downstream of the heat exchangers were assessed to characterize the flow in the fins¿
wake region. The aerodynamic performance of each heat exchanger configuration was
evaluated in terms of non dimensional pressure losses. Fins convective heat transfer
characteristics were derived from the infrared fin surface temperature measurements through a
new methodology based on inverse heat transfer methods coupled with conductive heat flux
models. The experimental characterization permitted to evaluate the cooling capacity of the
investigated type of heat exchangers for the design operational conditions. Finally, the
thermal efficiency of the heat exchanger at different points of the flight envelope during a
typical commercial mission was estimated by extrapolating the convective properties of the
flow to flight conditions. / Villafañe Roca, L. (2013). Experimental Aerothermal Performance of Turbofan Bypass Flow Heat Exchangers [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/34774 / TESIS
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