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Near wall flow characteristics in jet impingement heat transferBall, Stephen January 1998 (has links)
No description available.
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Turbulence Modeling for Compressible Shear FlowsGomez Elizondo, Carlos Arturo 1981- 14 March 2013 (has links)
Compressibility profoundly affects many aspects of turbulence in high-speed flows - most notably stability characteristics, anisotropy, kinetic-potential energy interchange and spectral cascade rate. Many of the features observed in compressible flows are due to the changing nature of pressure. Whereas for incompressible flows pressure merely serves to enforce incompressibility, in compressible flows pressure becomes a thermodynamic variable that introduces a strong coupling between energy, state, and momentum equations. Closure models that attempt to address compressibility effects must begin their development from sound first-principles related to the changing nature of pressure as a flow goes from incompressible to compressible regime. In this thesis, a unified framework is developed for modeling pressure-related compressibility effects by characterizing the role and action of pressure at different speed regimes. Rapid distortion theory is used to examine the physical connection between the various compressibility effects leading to model form suggestions for the pressure-strain correlation, pressure-dilatation and dissipation evolution equation. The pressure-strain correlation closure coefficients are established using fixed point analysis by requiring consistency between model and direct numerical simulation asymptotic behavior in compressible homogeneous shear flow. The closure models are employed to compute high-speed mixing-layers and boundary layers in a differential Reynolds stress modeling solver. The self-similar mixing-layer profile, increased Reynolds stress anisotropy and diminished mixing-layer growth rates with increasing relative Mach number are all well captured. High-speed boundary layer results are also adequately replicated even without the use of advanced thermal-flux models or low Reynolds number corrections.
To reduce the computational burden required for differential Reynolds stress calculations, the present compressible pressure-strain correlation model is incorporated into the algebraic modeling framework. The resulting closure is fully explicit, physically realizable, and is a function of mean flow strain rate, rotation rate, turbulent kinetic energy, dissipation rate, and gradient Mach number. The new algebraic model is validated with direct numerical simulations of homogeneous shear flow and experimental data of high-speed mixing-layers. Homogeneous shear flow calculations show that the model captures the asymptotic behavior of direct numerical simulations quite well. Calculations of plane supersonic mixing-layers are performed and comparison with experimental data shows good agreement. Therefore the algebraic model may serve as a surrogate for the more computationally expensive differential Reynolds stress model for flows that permit the weak-equilibrium simplification.
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Numerical simulation of flow distribution for pebble bed high temperature gas cooled reactorsYesilyurt, Gokhan 30 September 2004 (has links)
The premise of the work presented here is to use a common analytical tool,
Computational Fluid dynamics (CFD), along with a difference turbulence models. Eddy
viscosity models as well as state-of-the-art Large Eddy Simulation (LES) were used to
study the flow past bluff bodies. A suitable CFD code (CFX5.6b) was selected and
implemented.
Simulation of turbulent transport for the gas through the gaps of the randomly
distributed spherical fuel elements (pebbles) was performed. Although there are a
number of numerical studies () on flows around spherical bodies, none of them use the
necessary turbulence models that are required to simulate flow where strong separation
exists. With the development of high performance computers built for applications that
require high CPU time and memory; numerical simulation becomes one of the more
effective approaches for such investigations and LES type of turbulence models can be
used more effectively.
Since there are objects that are touching each other in the present study, a special
approach was applied at the stage of building computational domain. This is supposed to
be a considerable improvement for CFD applications. Zero thickness was achieved
between the pebbles in which fission reaction takes place.
Since there is a strong pressure gradient as a result of high Reynolds Number on
the computational domain, which strongly affects the boundary layer behavior, heat
transfer in both laminar and turbulent flows varies noticeably. Therefore, noncircular
curved flows as in the pebble-bed situatio n, in detailed local sense, is interesting to be
investigated.
Since a compromise is needed between accuracy of results and time/cost of effort
in acquiring the results numerically, selection of turbulence model should be done
carefully. Resolving all the scales of a turbulent flow is too costly, while employing
highly empirical turbulence models to complex problems could give inaccurate
simulation results. The Large Eddy Simulation (LES) method would achieve the
requirements to obtain a reasonable result. In LES, the large scales in the flow are solved
and the small scales are modeled.
Eddy viscosity and Reynolds stress models were also be used to investigate the
applicability of these models for this kind of flow past bluff bodies at high Re numbers.
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Numerical Simulation Of Turbine Internal Cooling And Conjugate Heat Transfer Problems With Rans-based Turbulance ModelsGorgulu, Ilhan 01 September 2012 (has links) (PDF)
The present study considers the numerical simulation of the different flow characteristics involved in the conjugate heat transfer analysis of an internally cooled gas turbine blade. Conjugate simulations require full coupling of convective heat transfer in fluid regions to the heat diffusion in solid regions. Therefore, accurate prediction of heat transfer quantities on both external and internal surfaces has the uppermost importance and highly connected with the performance of the employed turbulence models. The complex flow on both surfaces of the internally cooled turbine blades is caused from the boundary layer laminar-to-turbulence transition, shock wave interaction with boundary layer, high streamline curvature and sequential flow separation. In order to discover the performances of different turbulence models on these flow types, analyses have been conducted on five different experimental studies each concerned with different flow and heat transfer characteristics. Each experimental study has been examined with four different turbulence models available in the commercial software (ANSYS FLUENT13.0) to decide most suitable RANS-based turbulence model. The Realizable k-&epsilon / model, Shear Stress Transport k-&omega / model, Reynolds Stress Model and V2-f model, which became increasingly popular during the last few years, have been used at the numerical simulations. According to conducted analyses, despite a few unreasonable predictions, in the majority of the numerical simulations, V2-f model outperforms other first-order turbulence models (Realizable k-&epsilon / and Shear Stress Transport k-&omega / ) in terms of accuracy and Reynolds Stress Model in terms of convergence.
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Analýza proudění kapaliny v otevřené válcové nádobě s hladinovým vírem / Fluid flow analysis in the open cylindrical container with the free surface vortexIllík, Jakub January 2020 (has links)
This master's thesis analyses fluid flow in an open cylindrical tank with vortex using numerical simulation. The theoretical part introduces a set of equations governing fluid flow and relations used to describe vortex motion. A general overview of terms used in computational fluid dynamics is presented. The experimental section consists of three parts. The vortex modelling is performed using ANSYS Fluent software. Data are consequently analysed within ANSYS CFD-Post software tool. Special focus is put on the vortex shape that is fitted with a curve corresponding to a probability density function of the Cauchy distribution. Results are then plotted in MATLAB software.
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Influência da geometria da distribuição de temperatura em um combustor vertical de leito fluidizado a óleo combustível. / Influence of temperature distribution geometry on a fuel oil fluidized bed vertical combustor.CURSINO, Gustavo Gomes Sampaio. 23 March 2018 (has links)
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Previous issue date: 2016-04-18 / Este trabalho teve o propósito de determinar o comportamento dos gases na seção de
radiação de um combustor de ar que pertence a uma planta industrial. O corpo metálico
do equipamento rompeu em seu primeiro ano de operação, devido a um problema
conceitual em sua geometria. A fluidodinâmica computacional (CFD), por meio do
método dos volumes finitos, foi utilizada para desenvolver um modelo tridimensional
que pudesse reproduzir o perfil de temperatura e o comportamento do fluxo do ar de
combustão no equipamento. Na simulação, através do uso do software ANSYS CFX,
foram utilizados: (i) o modelo de turbulência Reynolds Stress Model (RSM); (ii) as
malhas hexaédrica, tetraédrica e prismática; (iii) o modelo de radiação P-1; e (iv) o
modelo de combustão Eddy Dissipation Concept (EDC). Como resultado, foram
apresentadas quatro possíveis mudanças na geometria do combustor de ar que, caso
adotadas, eliminariam os riscos de novas falhas e garantiriam a continuidade
operacional da unidade de processo. / This paper has the objective to describe the behavior of the flow and temperature of the
flue gas in the radiation section of the vessel used to preheat air in a combustor. The
equipment failed in its first operational year, due to a conceptual problem in its
geometry. The CFD code based on finite volume method was applied to simulate the
physical model of combustor using the ANSYS CFX software, reproducing the main
features of the preheater. The simulation had considered: (i) Reynolds Stress Model
(RSM) as turbulence model, (ii) The meshes applied were the hexahedral, tetrahedral
and prismatic, (iii) P-1 was used as the radiation model and (iv) Eddy Dissipation
Concept (EDC) as combustion model. Through the simulation was possible to propose
four different kind of combustor geometry modification, that the application of anyone of
them would eliminate the risk of new failures, ensuring the unit production availability.
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