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  • 1
    Electronic Resource
    Electronic Resource
    Bradford : Emerald
    International journal of numerical methods for heat & fluid flow 14 (2004), S. 116-133 
    ISSN: 0961-5539
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Impingement and forced convection are preferable methods for cooling gas turbine components. However, influences of various design parameters like crossflow and surface enlargements (like ribs) are not well understood. Thus there is a request for reliable and cost-effective computational prediction methods, due to the experimental difficulties. Such methods could be based on the numerical solution of the Reynolds-averaged Navier-Stokes equations, the energy equation and models for the turbulence field. This paper describes some recent advances and efforts to develop and validate computational methods for simulation of impingement and forced convection cooling in generic geometries of relevance in gas turbine cooling. Single unconfined round air jets, confined jets with crossflow, and three-dimensional ribbed ducts are considered. The numerical approach is based on the finite volume method and uses a co-located computational grid. The considered turbulence models are all the so-called low Reynolds number models. Our recent investigations show that linear and non-linear two-equation turbulence models can be used for impinging jet heat transfer predictions with reasonable success. However, the computational results also suggest that an application of a realizability constraint is necessary to avoid over-prediction of the stagnation point heat transfer coefficients. For situations with combined forced convection and impingement cooling it was revealed that as the crossflow is squeezed under the jet, the heat transfer coefficient is reduced. In addition, inline V-shaped 45° ribs pointing upstream performed superior compared to those pointing downstream and transverse ribs.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Bradford : Emerald
    International journal of numerical methods for heat & fluid flow 10 (2000), S. 634-648 
    ISSN: 0961-5539
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A three-dimensional numerical study was conducted to assess the hydraulic and heat transfer performance of a primary surface type heat exchanger surface, called the trapezoidal cross wavy (TCW) duct. This duct is similar to the ducts being used in compact recuperators manufactured by Solar Turbines Inc. The governing equations, i.e. the mass conservation equation, Navier-Stokes equations and the energy equation, are solved numerically by a finite volume method for boundary fitted coordinates. Periodic boundary conditions are imposed in the main flow direction. In this particular case laminar convective flow and heat transfer prevail. Owing to the complex geometry a complicated secondary flow pattern appears in the cross-sectional planes. Details of the recuperator ducts and the numerical method, as well as relevant results, are presented. The overall results are also compared with corresponding results (i.e. Nu numbers, friction factors) of straight ducts with various cross-sectional shapes.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Bradford : Emerald
    International journal of numerical methods for heat & fluid flow 11 (2001), S. 642-662 
    ISSN: 0961-5539
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical investigation to determine the velocity and heat transfer characteristics of multiple impinging slot jets in rib-roughened channels in the presence of cross-flow has been carried out. Fluid flow is modeled using an explicit algebraic stress model. A simple eddy diffusivity and a generalized gradient diffusion hypothesis are applied for the modeling of turbulent heat fluxes. The computations are validated against available experimental fluid flow and heat transfer data. Different size and arrangement of jets and ribs are considered in detail, while the Reynolds numbers of a jet and the channel inlet are fixed at 6,000 and 14,000, respectively. Results show that the ratio (B/W) between the size of the jets and ribs is most important. An explanation is that the ribs inhibit the motion of eddies by preventing them from coming very close to the surface when B/W is low, e.g. B/W = 1, although the ribs will increase the turbulence intensity. This blockage limited the heat transfer enhancement effect of the ribs and impinging jets.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Bradford : Emerald
    International journal of numerical methods for heat & fluid flow 11 (2001), S. 699-717 
    ISSN: 0961-5539
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Numerical analysis of the instantaneous flow and heat transfer has been carried out for offset strip fin geometries in self-sustained oscillatory flow. The analysis is based on the two-dimensional solution of the governing equations of the fluid flow and heat transfer with the aid of appropriate computational fluid dynamics methods. Unsteady calculations have been carried out. The obtained time-dependent results are compared with previous numerical and experimental results in terms of mean values, as well as oscillation characteristics. The mechanisms of heat transfer enhancement are discussed and it has been shown that the fluctuating temperature and velocity second moments exhibit non-zero values over the fins. The creation processes of the temperature and velocity fluctuations have been studied and the dissimilarity between these has been proved.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Bradford : Emerald
    International journal of numerical methods for heat & fluid flow 8 (1998), S. 118-141 
    ISSN: 0961-5539
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The present investigation is an extension of the authors' previous work on ducts with different cross sections. It concerns application of turbulence models for forced convective heat transfer in three-dimensional corrugated or wavy ducts. Different wavy ducts with fully developed flow and temperature fields are considered. The numerical approach is based on the finite volume technique with a non-staggered grid arrangement. For handling the pressure-velocity coupling the SIMPLEC-algorithm is used. Cyclic boundary conditions are imposed in the main flow direction to achieve fully developed conditions. The non-linear k-e model of Speziale with wall functions is used to calculate the turbulent stresses. The simple eddy diffusivity concept is applied to calculate the heat fluxes, but the GGDH and the WET methods are also used in some cases. The influence of the geometry parameters and comparison between different ducts are presented in terms of the friction factor and average Nusselt number. In particular the secondary velocity field and the cross sectional temperature distributions are investigated.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 16 (1993), S. 525-544 
    ISSN: 0271-2091
    Keywords: Turbulence modelling ; Second-moment closure ; Complex geometries ; Finite-volume method ; Collocated variables ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper addresses the implementation of second-moment closure into a collocated variable arrangement body-fitted-finite-volume scheme in which Cartesian velocity components are used. The methods for avoiding instability in the solution procedure are described. A new method for the treatment of the near-wall regions for the momentum equations, as well as the prescription of the stresses at the wall, is described in detail. The performance of the methodology is assessed by applying it to two flow situations, where experimental data are available: the flow over a backward step, and the flow through a sinusoidal pipe constriction. The results are very promising.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 225-242 
    ISSN: 0271-2091
    Keywords: turbulent flow ; non-linear turbulence modelling ; secondary flow ; rectangular duct ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Details of the turbulent flow in a 1:8 aspect ratio rectangular duct at a Reynolds number of approximately 5800 were investigated both numerically and experimentally. The three-dimensional mean velocity field and the normal stresses were measured at a position 50 hydraulic diameters downstream from the inlet using laser doppler velocimetry (LDV). Numerical simulations were carried out for the same flow case assuming fully developed conditions by imposing cyclic boundary conditions in the main flow direction. The numerical approach was based on the finite volume technique with a non-staggered grid arrangement and the SIMPLEC algorithm. Results have been obtained with a linear and a non-linear (Speziale) k-ε model, combined with the Lam-Bremhorst damping functions for low Reynolds numbers. The secondary flow patterns, as well as the magnitude of the main flow and overall parameters predicted by the non-linear k-ε model, show good agreement with the experimental results. However, the simulations provide less anisotropy in the normal stresses than the measurements. Also, the magnitudes of the secondary velocities close to the duct corners are underestimated. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 13 (1991), S. 537-556 
    ISSN: 0271-2091
    Keywords: Three-dimensional ; Flow and heat transfer ; Trapezoidal duct ; Entrance region ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The laminar convective flow and heat transfer in a duct with a trapezoidal cross-sectional area are studied numerically. The governing equations are solved numerically by a finite volume formulation in complex three-dimensional geometries using co-located variables and Cartesian velocity components. Details of the numerical method are presented. The accuracy of the method was also established by comparing the calculated results with the analytical and numerical results available in the open literature. The Nusselt numbers are obtained for the boundary condition of a uniform wall temperature whereas the friction factors are calculated for no-slip conditions at the walls. The asymptotic values of the Nusselt numbers, friction factors. incremental pressure drops, axial velocity and momentum rate and kinetic energy correction factors approach the available fully developed values. Various geometrical dimensions of the cross-section are considered.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 35 (1992), S. 729-736 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The influence of viscous heating on forced convective heat transfer from a circular cylinder in cross flow is investigated numerically. The Reynolds number is in the range of 5-40 and the Prandtl number is 0.72, corresponding to air. The Navier-Stokes equations and the continuity equations are solved in two dimensions using the streamfunction-vorticity formulation. In the energy equation the dissipation of mechanical energy into thermal energy is taken into account. All equations are cast into a non-dimensional form. The numerical solution procedure is based on second-order finite difference approximations and an implicit formulation is employed. The far field boundary conditions of the flow field are satisfied by matching to asymptotic solutions. The resulting algebraic equations are solved by an iterative relaxation technique. In particular, temperature distributions for an adiabatic wall boundary condition are presented.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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