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EN
Along with the increase in computing power, new possibilities for the use of parametriccoupled analysis of fluid flow machines and metamodeling for many branches of industryand medicine have appeared. In this paper, the use of a new methodology for multi-objective optimization of a butterfly valve with the application of the fluid-structure interaction metamodel is presented. The optimization objective functions were to increasethe value of the KV valve’s flow coefficient while reducing the disk mass. Moreover, theequivalent von Mises stress was accepted as an additional constraint. The centred composite designs were used to plan the measuring point. Full second-order polynomials, non-parametric regression, Kriging metamodeling techniques were implemented. The optimization process was carried out using the multi-objectives genetic algorithm. For eachmetamodel, one of the optimization candidates was selected to verify its results. The besteffect was obtained using the Kriging method. Optimization allowed to improve the KVvalue by 37.6%. The metamodeling process allows for the coupled analysis of the fluidflow machines in a shorter time, although its main application is geometry optimization.
2
Content available remote Computational fluid dynamics and experimental hydrodynamic analysis of a solar AUV
EN
In the present study, the effect of free surface on the hydrodynamic forces acting on themotion of an autonomous underwater vehicle (AUV) has been investigated. The AUVis powered by solar energy. Using computational fluid dynamics, the Reynolds averaged Navier Stokes (RANS) equations for the flow around the AUV are solved, and the freesurface effect is simulated using the volume of fluid (VOF) two-phase flow model. Forthis purpose, the commercial code ANSYS FLUENT 18 was used [1]. The results ofthe numerical solution are compared with experimental results of the AUV model in thesurface motion in the towing tank of the Persian Gulf National Laboratory with a scaleof 1:1. The experiment was performed in a fixed draft and the velocity was ranging from 0.2 m/s to 1.4 m/s (according to Reynolds number 2.4 x 105 to 1.7 x 106).
EN
Tortuosity in coronary artery has been found to be greatly related to the potential sites of stenosis in these last years. Many investigations have been carried out based on the tool of Computational Fluid Dynamics (CFD) mainly focusing on the influences of curved artery in blood flow. Within the limited investigations of coupling between stenosis and tortuosity, the stenosis has been considered to be located at the tortuous segment. However, with recent clinical studies, the case of stenosis occurred at non-tortuous segment before tortuosities has been confirmed which has not been paid enough attention yet. Therefore, the present study aims to investigate the disturbed streamlines and hemodynamics in curved and spiral artery considering symmetrical and asymmetrical stenosis upstream these tortuosities. Different stenosis severities, pulse rates and distances between stenosis and tortuosity as controlling parameters have been studied. The distribution of time averaged wall shear stress (TAWSS) and streamlines through tortuous segment have been displayed in order to determine the potential disease sites. Artery surface of TAWSS below critical value has been quantified as well to evaluate the risks of atherosclerosis. The results reveal that larger artery surface of TAWSS below critical value generally goes with smaller pulse rate, larger stenosis severity and distance between stenosis and tortuosity both for curved and spiral artery. However, exceptions were found in the cases of distance of 6 mm in curved artery with symmetrical stenosis and stenosis severity of 50% in spiral artery. Moreover, the spiral tortuosity tends to suppress the potential risks of atherosclerosis compared to curved tortuosity.
PL
Zjawiska lewitacji stanowią potencjalnie interesującą alternatywę dla wielu rozwiązań tradycyjnych i są przedmiotem szerokich badań. Istota lewitacji polega na równoważeniu siły grawitacji innym oddziaływaniem, np. magnetycznym. Jako przykład praktycznego wykorzystania tego fenomenu można wymienić chociażby łożyska wykorzystujące zjawisko lewitacji magnetycznej. Inną metodą uzyskania efektu lewitacji jest oddziaływanie falą akustyczną. Powstająca w tym przypadku siła nośna wywołana jest niezerową wypadkową sumarycznego ciśnienia wywołanego oddziaływaniem fali akustycznej na powierzchni lewitującego ciała. W pracy omówiono podstawy fizyczne zjawiska lewitacji akustycznej oraz potencjalny obszar jego zastosowań w energetyce. Przedstawiono również wstępne wyniki badań modelowych, obejmujących wyznaczenie wpływu podstawowych parametrów środowiskowych, w tym względnego położenia lewitującego ciała, częstotliwości fali akustycznej oraz wilgotności gazu roboczego, na wartości charakterystycznych parametrów zjawiska, w tym maksymalnej siły nośnej. Otrzymane wyniki wskazują na możliwość wykorzystania zjawiska przy zmiennych właściwościach fizycznych gazu roboczego, pod warunkiem ograniczenia masy lewitującej drobiny. Rezultaty wykazują jednocześnie graniczne wartości parametrów środowiskowych, które można uznać za akceptowalne w przypadku wykorzystania omawianego fenomenu. Zebrane dane uwidaczniają fundamentalną zależność siły nośnej od położenia lewitującej drobiny w kanale akustycznym oraz częstotliwości fali akustycznej. Wyniki badań prezentują także ograniczony wpływ wilgotności gazu na parametry zjawiska.
EN
Since the levitation phenomena are potentially interesting alternative to many traditional solutions, they state currently a subject of extensive research. The principle of the levitation consists in balancing the force of gravity with another interaction, e.g. magnetic. As an example of the use of this phenomenon, the bearings using the phenomenon of magnetic levitation might be mentioned. Another method of obtaining the effect of levitation is acoustic wave interaction. The lift force generated in this case is caused by a non-zero resultant vector of the total pressure caused by the impact of the acoustic wave on the surface of the levitating body. The paper discusses the physical foundations of the phenomenon of acoustic levitation and the potential area of its applications in energy. Preliminary results of model tests, including determination of the impact of basic environmental parameters, including the relative position of the levitating body, frequency of the wave and humidity of the gas, on the values of the characteristic parameters of the phenomenon, including the maximum lift are presented. The obtained results indicate the possibility of using the phenomenon with variable physical properties of the working gas, provided limited the mass of levitat-ing particles. Simultaneously, the results show the limit values of environmental parameters that can be considered acceptable when the phenomenon in question is used. The collected data show the fundamental dependence of the lift force on the position of levitating particles in the acoustic channel and the frequency of the acoustic wave. The test results also present a limited effect of gas humidity.
EN
Reactive pollutant dispersion in a 3-D urban street canyon is numerically investigated using a computational fluid dynamics (CFD) code (Ansys-CFX), with the k–ε turbulence model and includes transport equations for NO, NO2, and O3 with simple photochemistry. An area emission source of NO and NO2 was considered in the presence of background O3 with an ambient wind perpendicular to the along-canyon direction. The results showed that the magnitude of NOx (NO+NO2) concentrations on the leeward side of the upstream buildings was much larger than the windward side of the downstream building, due to the entrainment and dispersion of traffic emissions by the primary vortex. The reverse is the case for ozone with higher concentrations on the windward side compared to the leeward side. The model has been validated against no-reactive pollutant experimental data of the wind tunnel experiments of Hoydysh and Dabberdt [1].
PL
Wydajność wymiany ciepła w gruntowych wymiennikach ciepła (GHE) w wielu projektach zmniejsza się wraz z długością czasu eksploatacji. Zaobserwowano duże wahania temperatury w trakcie ładowania wymiennika oraz w trakcie naturalnego stygnięcia. Problem wynika głównie z braku pogłębionych badań dotyczących wpływu ogrzewania oraz migracji wilgotności na pracę gruntowego wymiennika w glebie nienasyconej. W pracy wykorzystano model numeryczny ośrodka porowatego z przepływem płynu wieloskładnikowego. Opis matematyczny wyposażono w dodatkowe strumienie, opisujące wymianę ciepła w elementach podsypki oraz szkielecie modelu porowatego. Odwzorowano geometrycznie oraz matematycznie porowatość gruntu. Wprowadzono definicję temperatury całkowitej. Wyniki porównano z symulacjami wykonanymi dla modelu rozwiązującego klasyczne równanie wymiany ciepła. Model weryfikowano na danych pomiarowych odczytanych dla 3 czujników zamontowanych na różnej głębokości jednego otworu oraz przy różnych przedziałach czasowych. Parametry modelu są oparte na lokalnych warunkach klimatycznych w Jabłonnej w okolicy Warszawy. Odwzorowano numerycznie 24 godzinną pracę pojedynczego otworu. Uzyskane wyniki wykazały dużo większą zbieżność z danymi pomiarowymi niż te uzyskane dla klasycznego modelu opisującego wymianę ciepła. Punktem krytycznym przyjętego modelu był dobór współczynników opisujących opory przepływu i-tych składników w ośrodku porowatym oraz poszczególne człony składowe zaproponowanej definicji temperatury całkowitej. Rozszerzoną dyskusje przeprowadzono w punkcie dotyczącym weryfikacji modelu. Wykonano przegląd prac o podobnej tematyce opublikowanych w ostatnim czasie.
EN
The efficiency of heat exchange in ground heat exchangers (GHE) in many projects decreases throughout their service life. Large temperature fluctuations were observed during feeding of the exchanger and during its natural cooling. This problem stems mainly from the lack of in-depth studies on the impact of heating and humidity migration on the operation of ground heat exchanger in unsaturated soil. In our work we applied a numerical model of a porous medium with multi-component fluid flow. The mathematical description was expanded with additional streams describing the exchange of thermal energy in the backfill material and the structure of the porous model. Ground porosity was mapped geometrically and mathematically. We introduced the definition of total temperature. The results were compared with the simulations performed for the model solving the classic heat exchange equation. The model was verified on the measurement data read for 3 sensors installed at different depths of one hole and at different time intervals. The parameters of the model are based on local climatic conditions of Jabłonna near Warsaw. 24-hour operation of a single hole has been numerically mapped. The results proved a much greater convergence with the actual data than those obtained for the classic model describing heat exchange. The critical point of the model was the selection of coefficients describing the flow resistance of i-components in the porous medium and the individual components of the adopted definition of the total temperature. Extended discussions were carried out in the section on model verification. We also performed a review of works on similar topics published recently.
EN
Space-time variational methods differ from time-stepping schemes by discretising the whole space-time domain with finite elements. This offers a natural framework for flow problems in moving domains and allows simultaneous parallelisation and adaptivity in space and time. For incompressible flows, the usual approach is to employ the same polynomial order for velocity and pressure, which requires the use of stabilisation techniques to compensate for the inf-sup deficiency of such pairs. In the present work, we extend to the space-time formulation the idea of the popular Taylor-Hood element for the (Navier-)Stokes equations. By using quadratic interpolation for velocity and linear for the pressure, in both space and time, we attain a stable finite element method which provides optimal convergence for pressure, velocity and stresses.
PL
Przestrzenno-czasowe metody wariacyjne wymagają dyskretyzacji metodą elementów skończonych całej domeny przestrzenno czasowej i tym różnią się od metod wykorzystującej schematy kroków czasowych. To podejście dostarcza naturalnych struktur dla problemów przepływu w poruszających się obszarach i pozwala na równoczesne zrównoleglanie i adaptację zarówno w przestrzeni jak i w czasie. Typowym rozwiązaniem dla przepływów nieściśliwych jest zastosowanie tego samego stopnia wielomianu dla prędkości i ciśnienia, co wymaga wprowadzenia metod stabilizacji w celu skompensowania niedoboru infimum-supremum takich par. W niniejszej pracy rozszerzono sformułowanie przestrzenno czasowe o ideę elementu Taylora-Hooda dla równań (Naviera-)Stokesa. Poprzez zastosowanie kwadratowej interpolacji dla prędkości i liniowej interpolacji dla ciśnienia, zarówno w przstrzeni jak i w czasie, uzyskano stabilną metodę elementów skończonych dającą optymalną zbieżność dla ciśnienia, prędkości i naprężeń.
EN
The article presents the results of experimental research and their comparison with CFD simulations for the original selective catalytic reduction system and WALKER replacement. The research was performed to develop the WALKER universal mixer. The SCR prototype without mixer and with the proposed mixer were tested and compared with the original VW part. The next step was reverse engineering, which consisted in scanning the tested parts with a laser and processing their point cloud in Leios2 program. Reverse engineering has allowed the reconstruction of 3D geometry of the tested parts in the Catia v5 program and then preparation their models for computational fluid dynamics. Numerical simulations were carried out in the Ansys Fluent program, thanks to which several quantities were determined e.g. uniformity index of gas flow through the monolith and coefficient of variation as a measure of mixing degree, which have a significant impact on the design of the mixer and the SCR system.
EN
Intra-aortic balloon pump (IABP) is a mechanical circulatory support approach used in case of several cardiac diseases and a challenge of IABP therapy is the weaning process accomplished by decreasing the assist ratio. However, the impact of weaning on aortic hemodynamics on organs perfusions is not well known. Aim of this study was to evaluate and compare the global effects of IABP assistance frequencies on hemodynamics and perfusions in a patient-specific geometry by means of the computational fluid dynamics (CFD). A 3D aorta model was obtained from CT images using segmentation and reverse engineering techniques. The balloon was modeled and positioned in the descending aorta as in clinical practice and its inflation/deflation behavior was realized with a parametric study. Four assist ratios have been investigated: full assistance (1:1), partial assistances (1:2 and 1:3) and weak assistance (1:4). To perform the comparison, same boundary conditions were applied. Our results highlighted that the presence of balloon in aorta modifies significantly its hemodynamics and that the four assist ratios generate different perfusions in the human districts. Data suggested also that the biggest difference occurs between 1:2 and 1:3 frequencies and that 1:4 ratio is more suitable for the weaning of counterpulsation treatment than the 1:3 ratio. This first CFD analysis of IABP weaning increases information and knowledge on hemodynamics and organs perfusions.
EN
The work presents a three-dimensional modeling of air flow around the research object. The purpose of this work was to perform numerical calculations to identify the magnitude of the aerodynamic drag force generated on individual elements of a high energy efficiency vehicle body. This vehicle, specially designed for the Shell Eco-marathon competition, needs to show the lowest possible fuel consumption while maintaining the prescribed speed. Minimizing the drag force at an early designing stage plays an important role here. The calculations were performed using the ANSYS Fluent calculation solver. The result of the conducted research is a description of the velocity and pressure distributions around the tested vehicle as well as an identification of the drag force on the external surfaces of the components and a description of the relationship between them. The work also discusses the dependence of the drag force as a function of speed in the range from 0 to 12 m/s. The influence of the ground on the drag force in the case when the object was immobilized in relation to the walls at the flowing medium, as in a wind tunnel, was investigated. On the basis of the calculations performed, no impact of the ground on the generated drag force magnitude was found.
EN
Heterogeneous catalytic recombination of hydrogen with oxygen is one of the methods used to remove hydrogen from the containment of a light-water nuclear reactor (LWR). Inside a passive autocatalytic recombiner (PAR), hydrogen and oxygen molecules are adsorbed at catalyst active spots and they recombine to yield water. Heat released in this exothermic reaction creates natural convection of gas in the spaces between the elements supporting a catalyst. Hot and humid gas fl ows upwards into the PAR chimney, while fresh, hydrogen-rich gas enters the PAR from below. Catalytic recombination should start spontaneously at room temperature and low hydrogen concentration. Computational fl uid dynamics (CFD) has been used to study the dynamic behaviour of a plate-type Areva FR-380 recombiner in a quiescent environment for several test scenarios, including different rates of increase in hydrogen concentration and temporary catalyst deactivation. A method for the determination of pressure boundary conditions at the PAR exits was proposed and implemented into a CFD code. In this way, transient operation of PAR could be simulated without the need to model gas circulation outside the device. It was found that fi rst a slow downward fl ow of gas is developed, which may persist until the temperature of the catalyst foils rises. As soon as the gas inside the PAR absorbs enough heat to become lighter than the gas outside the PAR, it starts to fl ow upwards. Criteria for determining the start-up time of PAR were proposed. Model predictions were also compared with experimental data obtained in tests conducted at the THAI facility.
PL
Przedstawiono ogólną charakterystykę współczesnych zagadnień inżynierii wiatrowej i śniegowej oraz rolę badań modelowych w tunelach aerodynamicznych. Omówiono wybrane badania modelowe przeprowadzone w tunelu aerodynmicznym Politechniki Krakowskiej.
EN
A general characteristics of contemporary issues of wind and snow engineering and a role of model tests in wind tunnels were presented. Selected model tests carried out in wind tunnel at the Cracow University of Technology were discussed.
EN
The aim of this paper was to demonstrate the feasibility of using a Computational Fluid Dynamics tool for the design of a novel Proton Exchange Membrane Fuel Cell and to investigate the performance of serpentine micro-channel flow fields. A three-dimensional steady state model consisting of momentum, heat, species and charge conservation equations in combination with electrochemical equations has been developed. The design of the PEMFC involved electrolyte membrane, anode and cathode catalyst layers, anode and cathode gas diffusion layers, two collectors and serpentine micro-channels of air and fuel. The distributions of mass fraction, temperature, pressure drop and gas flows through the PEMFC were studied. The current density was predicted in a wide scope of voltage. The current density – voltage curve and power characteristic of the analysed PEMFC design were obtained. A validation study showed that the developed model was able to assess the PEMFC performance.
EN
The paper addresses the issues of quantification and understanding of Solid Oxide Fuel Cells (SOFC) based on numerical modelling carried out under four European, EU, research projects from the 7FP within the Fuel Cell and Hydrogen Joint Undertaking, FCH JU, activities. It is a short review of the main projects’ achievements. The goal was to develop numerical analyses at a single cell and stack level. This information was integrated into a system model that was capable of predicting fuel cell phenomena and their effect on the system behaviour. Numerical results were analysed and favourably compared to experimental results obtained from the project partners. At the single SOFC level, a static model of the SOFC cell was developed to calculate output voltage and current density as functions of fuel utilisation, operational pressure and temperature. At the stack level, by improving fuel cell configuration inside the stack and optimising the operation conditions, thermal stresses were decreased and the lifetime of fuel cell systems increased. At the system level, different layouts have been evaluated at the steady-state and by dynamic simulations. Results showed that increasing the operation temperature and pressure improves the overall performance, while changes of the inlet gas compositions improve fuel cell performance.
15
Content available remote Energy saving rates for a multistage centrifugal pump with variable speed drive
EN
Multistage centrifugal pumps with variable speed drives are currently widely used in a variety of industrial and commercial applications. However, there are limitations to defining the efficiency of variable speed drive pumps. As an alternative method, energy saving rates can be evaluated with flow patterns and mean duty cycles. Computational fluid dynamics (CFD) is being used as a good tool to understand this and is less time consuming in terms of analyzing performances the experimental method. Research attention was focused on the energy saving rates of a multistage centrifugal pump for variable flow with variable speed drive through numerical and experiment methods. For this investigation Reynolds-averaged Navier-Stokes (RANS) equations were discretized by the finite volume method and a two equations SST model was used to account for three dimensional steady state flows. In the experimental system, an experimental set-up of a variable flow system was made to obtain energy saving rates and computational results were validated. The energy saving rates of the pumps depend on the flow patterns and specific mean duty cycles on which the machine or system operates. Mean duty cycles were divided into different flow operating conditions and a weighting for the mean value was given for each segment according to interval time. The pump system was operated at 50_70% of maximum flow rates. The energy saving rates were obtained from input power through CFD simulation and experimentally, and the mean duty cycle was obtained from flow patterns in the field of the pump. Energy saving rates were evaluated as a function of mean duty cycle and input power of the system operation. The total energy consumed for the constant speed drive was 25,922 kWh and for the variable speed drive pump was 17,687 kWh through CFD. The total annual energy saving rates were annually 33.81% through computational and 31.77% through experimental method with the variable speed drive system when compared to the constant speed drive system.
EN
The aim of this study was to investigate a possibility of using gaseous fuels of a low calorific value as a fuel for internal combustion engines. Such fuels can come from organic matter decomposition (biogas), oil production (flare gas) or gasification of materials containing carbon (syngas). The utilization of syngas in the barrel type Opposed-Piston (OP) engine arrangement is of particular interest for the authors. A robust design, high mechanical efficiency and relatively easy incorporation of Variable Compression Ratio (VCR) makes the OP engine an ideal candidate for running on a low calorific fuel of various composition. Furthermore, the possibility of online compression ratio adjustment allows for engine the operation in Controlled Auto-Ignition (CAI) mode for high efficiency and low emission. In order to investigate engine operation on low calorific gaseous fuel authors performed 3D CFD numerical simulations of scavenging and combustion processes in the 2-stroke barrel type Opposed-Piston engine with use of the AVL Fire solver. Firstly, engine operation on natural gas with ignition from diesel pilot was analysed as a reference. Then, combustion of syngas in two different modes was investigated – with ignition from diesel pilot and with Controlled Auto-Ignition. Final engine operating points were specified and corresponding emissions were calculated and compared. Results suggest that engine operation on syngas might be limited due to misfire of diesel pilot or excessive heat releas which might lead to knock. A solution proposed by authors for syngas is CAI combustion which can be controlled with application of VCR and with adjustment of air excess ratio. Based on preformed simulations it was shown that low calorific syngas can be used as a fuel for power generation in the Opposed-Piston engine which is currently under development at Warsaw University of Technology.
EN
The present study deals with modelling and validation of a planar Solid Oxide Fuel Cell (SOFC) design fuelled by gas mixture of partially pre-reformed methane. A 3D model was developed using the ANSYS Fluent Computational Fluid Dynamics (CFD) tool that was supported by an additional Fuel Cell Tools module. The governing equations for momentum, heat, gas species, ion and electron transport were implemented and coupled to kinetics describing the electrochemical and reforming reactions. In the model, the Water Gas Shift reaction in a porous anode layer was included. Electrochemical oxidation of hydrogen and carbon monoxide fuels were both considered. The developed model enabled to predict the distributions of temperature, current density and gas flow in the fuel cell.
EN
Small-scale vertical-axis wind turbines can be used as a source of electricity in rural and urban environments. According to the authors’ knowledge, there are no validated simplified aerodynamic models of these wind turbines, therefore the use of more advanced techniques, such as for example the computational methods for fluid dynamics is justified. The paper contains performance analysis of the small-scale vertical-axis wind turbine with a large solidity. The averaged velocity field and the averaged static pressure distribution around the rotor have been also analyzed. All numerical results presented in this paper are obtained using the SST k- ω turbulence model. Computed power coefficients are in good agreement with the experimental results. A small change in the tip speed ratio significantly affects the velocity field. Obtained velocity fields can be further used as a base for simplified aerodynamic methods.
EN
A computer program for topological optimization of a rotor for vertical axis wind turbines of various type is presented. The tool is based mainly on two external modules: the GMSH mesh generator and the OpenFOAM CFD toolbox. Interpolation of rotor blades geometry and computational model of the airflow through a turbine are briefly discussed. Moreover, a simple optimization algorithm is described. Exemplary results for a H-type rotor are presented. Finally, potential directions for the software development are indicated.
20
Content available remote Performance Evaluation of Multipurpose Solar Heating System
EN
In order to increase the heat transfer and thermal performance of solar collectors, a multipurpose solar collector is designed and investigated experimentally by combining the solar water collector and solar air collector. In this design, the storage tank of the conventional solar water collector is modified as riser tubes and header and is fitted in the bottom of the solar air heater. This paper presents the study of fluid flow and heat transfer in a multipurpose solar air heater by using Computational Fluid Dynamics (CFD) which reduces time and cost. The result reveals that in the multipurpose solar air heater at load condition, for flow rate of 0.0176 m3/s m2, the maximum average thermal efficiency was 73.06% for summer and 67.15 % for winter season. In multipurpose solar air heating system, the simulated results are compared to experimental values and the deviation falls within ± 11.61% for summer season and ± 10.64% for winter season. It proves that the simulated (CFD) results falls within the acceptable limits.
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