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1.
Numerical optimisation of a waste-to-energy plant's operating parameters using CFD
Miran Kapitler, Niko Samec, Filip Kokalj, 2011, izvirni znanstveni članek

Opis: The combustion process for using municipal solid waste as a fuel within a waste to energy plant calls for a detailed understanding of the following phenomena. Firstly, this process depends on many input parameters such as proximate and ultimate analyses, the season of the year, primary and secondary inlet air velocities and, secondly, on output parameters such as the temperatures or mass-flow rates of the combustible products. The variability and mutual dependence of these parameters can be difficult to manage in practice. Another problem is how these parameters can be tuned to achieving optimal combustible conditions with minimal pollutant emissions, during the plant-design phase. in order to meet these goals, a waste-to-energy plant with bed combustion was investigated by using computational fluid-dynamics approach. The adequate variable input boundary conditions based on the real measurement are used and the whole computational work is updated using real plant geometry and the appropriate turbulence, combustion, or heat transfer models. The operating parameters were optimized on output parameters through a trade-off study. The different operating conditions were varied and the combustible products were predicted and visualized. Finally, the response charts and matrix among the input and output parameters during the optimization process are presented, which monitored the dependence among these parameters.
Ključne besede: municipal solid waste, bed combustion, computational fluid dynamics, numerical optimization, goal driven optimization, trade-off study, parameters correlation
Objavljeno: 01.06.2012; Ogledov: 949; Prenosov: 51
.pdf Celotno besedilo (1,83 MB)
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2.
Intake system design procedure for engines with special requirements
Primož Pogorevc, Breda Kegl, 2006, izvirni znanstveni članek

Opis: Intake manifolds provide fresh air to internal combustion engines and have a major effect on their performance. Therefore, many investigations are related to their design in order to improve the charging efficiency and to achieve theuniform distribution of fresh air among the engine cylinders. This paper deals with the design procedure of a cheap multipoint injection intake system,adapted to a racing car engine. Some special demands had to be taken into consideration. The intake manifold must contain the imposed constraint for the airflow in the shape of a single circular restrictor placed between the throttle and the engine to limit its power. The flow and the pressure lossreduction in the engine intake region were investigated with computationalfluid dynamics software. Two different geometries of the intake manifold were taken into consideration. On the basis of the numerically obtained three-dimensional results, a mathematical model of the engine with a more appropriate intake was made in the engine simulation code in order to anticipate its characteristics. The intake system was designed, practically manufactured, and tested in the laboratory. The experimental results confirmednumerical predictions, justifying the simple and relatively quick design procedure for the intake system.
Ključne besede: internal combustion engines, intake manifold, computational fluid dynamics, experiment
Objavljeno: 30.05.2012; Ogledov: 1012; Prenosov: 43
URL Povezava na celotno besedilo

3.
Combustion simulation in the secondary chamber of a pilot-scale incinerator
Niko Samec, Filip Kokalj, Jyh-Yan Chen, 2007, izvirni znanstveni članek

Opis: A numerical analysis of combustion in the secondary chamber (thermoreactor) ofa two-stage pilot scale incinerator using computational fluid dynamics (CFD)is presented in detail. Various versions of the CFD program package CFX were used, which offer different combustion models for specific types and forms of combustion processes. The present study was focused on those physicalconditions that assure complete combustion, that is, temperature, residence time, and turbulent mixing. The selection of an appropriate combustion model was based on a comparison of the numerical results and experimental values of some combustion macro parameters in a thermoreactor. Combustion models based on one-step bimolecular chemical reaction and models based on multistep reactions were used. These models enabled a more detailed prediction of the combustion process in the secondary chamber of a pilot-scaleincinerator. The products of incomplete combustion that are significantly important for the designing and optimization of combustion devices can be predicted by applying multistep reaction models more accurately, especially in a transient regime of combustion.
Ključne besede: waste incineration, numerical modeling, combustion models, incinerator chamber, CFX, CFD, computational fluid dynamics
Objavljeno: 31.05.2012; Ogledov: 1222; Prenosov: 26
URL Povezava na celotno besedilo

4.
The influence of rotating domain size in a rotating frame of reference approach for simulation of rotating impeller in a mixing vessel
Matej Zadravec, Sani Bašič, Matjaž Hriberšek, 2007, izvirni znanstveni članek

Opis: This paper presents simulation of rotating impeller in a mixing vessel by means of Computational Fluid Dynamics (CFD). A special emphasis is devoted to the study of influence of the choice of numerical model for simulation of rotation of impeller when mixing a Newtonian fluid in a vessel equipped with Rushton impeller, and operating under turbulent flow conditions. In order to determine the best simulation approach experimental validation of the selected problem is done by means of Particle Image Velocimetry (PIV) system. When using the rotating frame of reference approach, the stirring vessel geometry has to be split into a stationary and rotating part, and the questionarises where to position the interface between both regions in order to avoid numerical errors, originating in numerical approximations at the interface. To answer this question, a comparison between the CFD based numerical results and experimental results, was made.
Ključne besede: fluid mechanics, turbulent flow, Computational Fluid Dynamics, Particle Image Velocimetry, rotating frame of reference
Objavljeno: 31.05.2012; Ogledov: 1143; Prenosov: 30
URL Povezava na celotno besedilo

5.
Aerodynamic analysis of an oscillating airfoil in a power-extraction regime using the compressible Navier-Stokes equations with efficient and accurate low-speed preconditioning
Jernej Drofelnik, 2012, diplomsko delo

Opis: A wing that is simultaneously heaving and pitching may extract energy from an oncoming air flow, thus acting as turbine. The purpose of this study was to analyse the relationship between the aerodynamics and the theoretical performance of this device by means of timedependent laminar flow simulations performed with a research compressible finite volume Navier-Stokes solver COSA. In presented analyses, which confirm the findings of another independent study, the efficiency of the power extraction of this device can be of the order of 35 %, and such an efficient operating condition is characterized due to the favourable effects of a strong dynamic stall. This study is a part of a wider research programme of Dr. Campobasso’s group at University of Glasgow, aiming to develop a general-purpose computational framework for unsteady aerodynamic and aeroacoustic wind energy engineering. In view of aeroacoustic applications, the developed flow solver uses the compressible formulation of the Navier-Stokes equations with carefully optimized low-speed preconditioning. To demonstrate the modeling capabilities, the accuracy and the high computational performance of the developed low-speed preconditioning technology, the unsteady aerodynamics of the energy-extracting device is simulated by using a computationally challenging freestream Mach number of 0.001. A mixed preconditioning strategy that maintains both the nominal accuracy and the computational efficiency of the solver also for time-dependent low-speed problems is presented. A fundamental element of novelty of this study is a thorough assessment of the proposed approach partly based on the challenging and realistic problem associated with the oscillating wing device.
Ključne besede: Low-speed preconditioning, compressible multigrid Navier-Stokes solver, energy-extracting oscillating wing, computational fluid dynamics.
Objavljeno: 06.07.2012; Ogledov: 1647; Prenosov: 78
.pdf Celotno besedilo (2,40 MB)

6.
The wavelet transform for BEM computational fluid dynamics
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2004, izvirni znanstveni članek

Opis: A wavelet matrix compression technique was used to solve systems of linear equations resulting from BEM applied to fluid dynamics. The governing equations were written in velocity-vorticity formulation and solutions of the resulting systems of equations were obtained with and without wavelet matrix compression. A modification of the Haar wavelet transform, which can transformvectors of any size, is proposed. The threshold, used for making fully populated matrices sparse, was written as a product of a user defined factor and the average value of absolute matrix elements values. Numerical tests were performed to assert, that the error caused by wavelet compression depends linearly on the factor , while the dependence of the error on the share of thresholded elements in the system matrix is highly non-linear. The results also showed that the increasing non-linearity (higher Ra and Re numbervalues) limits the extent of compression. On the other hand, higher meshdensity enables higher compression ratios.
Ključne besede: fluid mechanics, computational fluid dynamics, boundary element method, wavelet transform, linear systems of equations, velocity vorticity formulation, driven cavity, natural convection, system matrix compression
Objavljeno: 01.06.2012; Ogledov: 1169; Prenosov: 26
URL Povezava na celotno besedilo

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Numerical analysis of fluid flow in a vial
Žiga Časar, 2019, magistrsko delo

Opis: Lyophilization or freeze-drying is a widely used process in the pharmaceutical and food industry. In the process the solvent will be removed under extreme conditions of low temperature and low system pressures, whereby sublimation happens, the transition from the solid phase to the gas phase, with skipping the liquid phase, which happens bellow the triple point. This study focuses on numerical modeling at the start of the process, the so called primary drying. For this stage the highest mass flow rates of vapor are typical, since the driving force of the process is the pressure difference between the sublimation front and surrounding area. In this stage the non-bonded solvent is removed. Because of the extreme conditions the typical computational fluid dynamics approach is not suitable anymore and has to be corrected. One way to do this is to use additional models for fluid behavior at the solid wall. The study focuses on the influence of different boundary conditions on the solid wall, No-Slip, Free Slip and Maxwell Slip, and their effect on fluid flow inside the vial. A quantitative and qualitative comparison of the results is presented.
Ključne besede: Lyophilization, Knudsen number, computational fluid dynamics, fluid flow, numerical modeling, slip boundary condition
Objavljeno: 09.07.2019; Ogledov: 93; Prenosov: 9
.pdf Celotno besedilo (2,66 MB)

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