22 results on '"Bogdanović-Jovanović, Jasmina"'
Search Results
2. Control of MHD Flow and Heat Transfer of a Micropolar Fluid through Porous Media in a Horizontal Channel
- Author
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Kocić, Miloš, primary, Stamenković, Živojin, additional, Petrović, Jelena, additional, and Bogdanović-Jovanović, Jasmina, additional
- Published
- 2023
- Full Text
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3. LOW PRESSURE CENTRIFUGAL FANS OPERATING WITH DIFFERENT AIR TEMPERATURES.
- Author
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BOGDANOVIĆ-JOVANOVIĆ, Jasmina B., STAMENKOVIĆ, Živojin M., and PETROVIĆ, Jelena D.
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ATMOSPHERIC temperature , *STATIC pressure , *AIR conditioning , *HIGH temperatures , *ENERGY consumption - Abstract
For normal operating conditions of the centrifugal fan, the manufacturers provide operating curves (total pressure of the fan, static pressure of the fan, power, and efficiency) for standard air conditions. However, when a fan operates with air at different, usually elevated temperatures, their operating curves can significantly differ. As a result, the fan efficiency decreases, and the energy efficiency of the fan may be reduced. Fan operation in such air conditions also affects its acoustic characteristics. This paper investigates two types of centrifugal fans: with forward curved and backward inclined blades. The main goal was to determine how their operating and acoustic characteristics change with the change in air temperature. For this analysis, low pressure centrifugal fans are used, for which we already had measured operating and acoustic characteristics. The influence of the type of impeller and the curvature of the blades play an important role in the operation of the fan. For numerical investigation, ANSYS CFX software was used, and obtained results show excellent agreement with experimental measurements. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
4. NANO- AND MICRO-POLAR MAGNETOHYDRODYNAMIC FLUID-FLOW AND HEAT TRANSFER IN INCLINED CHANNEL.
- Author
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STAMENKOVIĆ, Živojin M., KOCIĆ, Miloš M., BOGDANOVIĆ-JOVANOVIĆ, Jasmina B., and PETROVIĆ, Jelena D.
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MICROPOLAR elasticity ,HEAT transfer ,FLUID flow ,METAL crystals ,MANUFACTURING processes ,LIQUID metals ,NANOFLUIDICS ,MICROCHANNEL flow - Abstract
Magnetohydrodynamic fluid-flows attract a lot of attention in the extrusion of polymers, in the theory of nanofluids, as well as in the consideration of biological fluids. The considered problem in the paper is the flow and heat transfer of nanoand micro-polar fluid in inclined channel. Fluid-flow is steady, while nano- and micro-polar fluids are incompressible, immiscible, and electrically conductive. The upper and lower channel plates are electrically insulated and maintained at constant and different temperatures. External applied magnetic field is perpendicular to the fluid-flow and considered problem is in induction-less approximation. The equations of the considered problem are reduced to ODE, which are analytically solved in closed form. The influence of characteristics parameters of nano- and micro-polar fluids on velocity, micro-rotation and temperature fields are graphically shown and discussed. The general conclusions given through the analysis of graphs can be used for better understanding of the flow and heat transfer of nano- and micro-polar fluid, which have a great practical application. Fluids with nanoparticles innovated the modern era, due to their comprehensive applications in nanotechnology and manufacturing processes, while the theory of micro-polar fluids explains the flow of biological fluids and various types of liquid metals and crystals. [ABSTRACT FROM AUTHOR]
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- 2023
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5. Design and performance of low-pressure reversible axial fan with doubly curved profiles of blades
- Author
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Spasić, Živan, Jovanović, Miloš, and Bogdanović-Jovanović, Jasmina
- Published
- 2018
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6. MAGNETOHYDRODYNAMIC FLOW AND MIXED CONVECTION OF A VISCOUS FLUID AND A NANOFLUID THROUGH A POROUS MEDIUM IN A VERTICAL CHANNEL.
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PETROVIĆ, Jelena D., STAMENKOVIĆ, Živojin M., KOCIĆ, Miloš M., NIKODIJEVIĆ DJORDJEVIĆ, Milica D. Milica D., BOGDANOVIĆ JOVANOVIĆ, Jasmina B., and NIKODIJEVIĆ, Dragiša D.
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MAGNETOHYDRODYNAMICS ,NANOFLUIDS ,NUSSELT number ,FLUIDS ,TEMPERATURE distribution ,DIFFERENTIAL equations ,POROUS materials - Abstract
This paper analyzes the MHD flow and heat transfer of a pure fluid and a nanofluid through a porous medium in a vertical channel. The right half of the channel contains the pure fluid and the left half contains the nanofluid, which is immiscible with the pure fluid in the right half. Channel walls are impermeable and at constant temperatures. An external homogeneous magnetic field perpendicular to the channel walls is applied on the channel. Darcian approach is used to model the porous medium. Relevant differential equations are solved using the perturbation method. Velocity and temperature distributions are determined analytically and represented graphically, while the values of skin friction and Nusselt number on the channel walls are given in a table for multiple values of the introduced physical parameters. The results are used to draw conclusions about the influence of the said physical parameters on velocity and temperature distributions and on the values of skin friction and Nusselt number on the channel walls. [ABSTRACT FROM AUTHOR]
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- 2023
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7. Electro-Magnetoconvection of Conductive Immiscible Pure Fluid and Nanofluid
- Author
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Petrović, Jelena, primary, Stamenković, Živojin, additional, Bogdanović-Jovanović, Jasmina, additional, Nikodijević, Milica, additional, Kocić, Miloš, additional, and Nikodijević, Dragiša, additional
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- 2022
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8. NUMERICAL INVESTIGATION OF THE INFLUENCE OF THE DOUBLY CURVED BLADE PROFILES ON THE REVERSIBLE AXIAL FAN CHARACTERISTICS
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Spasić, Živan, primary, Jovanović, Miloš, additional, Bogdanović-Jovanović, Jasmina, additional, and Milanović, Saša, additional
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- 2020
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9. EXPERIMENTAL AND CFD ANALYSIS OF MHD FLOW AROUND SMOOTH SPHERE AND SPHERE WITH DIMPLES IN SUBCRITICAL AND CRITICAL REGIMES.
- Author
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BOGDANOVIĆ-JOVANOVIĆ, Jasmina B. and STAMENKOVIĆ, Živojin M.
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LASER Doppler velocimeter , *PROPERTIES of fluids , *REYNOLDS stress , *VORTEX shedding , *UNSTEADY flow , *SPHERES , *FLOW velocity , *DRAG coefficient - Abstract
An overview of previous researches related to the problem of flow around a bluffbody, using experimental and numerical methods, is presented in the paper. Experimental investigation was performed by a laser doppler anemometer, measuring velocity components of the water flow around a smooth sphere, and a sphere with dimples in square channels. Measurement results in subcritical velocity flow field, velocity fluctuation components, lift, drag and pressure coefficients, and 2-D Reynolds stress at quasi-stationary flow are conducted using 1-D laser doppler anemometer probe. The obtained experimental results are compared with numerical simulations, which are performed using the ANSYS-CFX software. For the numerical simulations of quasi-steady-state flow, k-ω turbulent model was used, while for numerical simulation of unsteady fluid-flow and for the comparison of results related to the eddy structures, vortex shedding and Reynolds stresses, detached eddy simulation were used. Since the obtained results of experimental and numerical investigation of flow around smooth sphere and sphere with dimples showed good agreement, the considered flow problem was expanded by introducing the influence of a transverse magnetic field with a slight modification of the electrical conductivity of the working fluid. The other physical properties of the fluid remained the same, which also corresponds to realistically possible physical conditions. Numerical simulations were performed for three different values of Hartmann number and very small values of Reynolds magnetic number (inductionless approximation). Comparisons and analyzes of the results were made for the cases containing a magnetic field and those with an absence of a magnetic field. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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10. DETERMINATION OF AVERAGED AXISYMMETRIC FLOW SURFACES AND MERIDIAN STREAMLINES IN THE CENTRIFUGAL PUMP USING NUMERICAL SIMULATION RESULTS
- Author
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Bogdanović-Jovanović, Jasmina, primary, Milenković, Dragica, additional, Stamenković, Živojin, additional, and Spasić, Živan, additional
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- 2017
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11. Određivanje osrednjenog osnosimetričnog strujanja u radnim kolima hidrauličkih turbomašina
- Author
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Bogdanović-Jovanović, Jasmina B., Milenković, Dragica, Babić, Milun, and Nikodijević, Dragica
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Physics::Fluid Dynamics ,hidraulične turbomašine ,niskopritisni ventilatori ,meridional ,Osrednjeno osnosimetrično strujanje ,meridijanske strujnice ,low pressure fan ,hydraulic turbomashine ,Averaged axisymmetric flow ,streamlines - Abstract
The first chapter of the paper is introductory unfolding, where the task of hydrodynamic calculation is presented, as well as the schema of flow in the flow-through part of turbomachine. It also outlines an overview of recent results in this field, limited to the most significant results, as well as those who have paved the way to some new methods of study and recalculation of the hydraulic turbomachinery and low pressure fans. The main task of the turbomachinery hydrodynamic calculation (the design of flow components that provide the required operated parameters, and at the same time achieving its maximum energy efficiency), is a very complex task which requires a unified application of theoretical and experimental research results. In order to achieve practically applicable methodology for the turbomschinery calculation, the simplification of the fluid flow and fluid characteristics is performed: physical flow is simplified as two-dimensional, in some cases even one-dimensional flow, the turbomachinery operates in a steady operating regime, when the flow can be considered invariant with time, and the fluid in hydraulic turbomachinery and low pressure fans can be regarded as incompressible. The basic assumption is that the flow in turbomachinery runners and its stationary parts are axisymmetric, although realistically it is not the case. Also, in the introductory chapter, the basics of determining the shape of the hydraulic turbomachinery blades are represented. At the end of this chapter, the application, development and significance of the numerical simulation of fluid flow regarding turbomachinery design and testing, with emphasis on the most significant achievements in this field and its application to the turbomachinery performance, is showed. In the second chapter of the doctoral thesis a brief overview of the methodology of numerical simulation of flow, turbulence modeling and application a possibility of CFD (Computational Fluid Dynamics) methods to flow in turbomachinery is given. Especially the numerical simulation of flow in hydraulic turbomachinery and low pressure fans runners, but also in the fixed vane and vaneless stationary parts of turbomachinery, is considered. Due to the simple application, but also the required computing resources for the purpose of ix numerical flow simulation, the focus was on solving the Reynolds-averaged equations (i.e. RANS equations). The basic equations of fluid flow (partial differential equation) are given, which are, in the process of the temporal and spatial discretization, transformed into a system of algebraic equations, suitable for numerical implementation. The system of equations is closed by using any of the existing models of turbulent flow (i.e. turbulence models), what was also discussed in this chapter. In the last part of this chapter the principles of numerical solving of fluid flow are given (beginning with discretization, difference schemes, the generation of the computational grid, and ending with the convergence criterion of the obtained solution). Examples of numerical simulations obtained by using commercial software Ansys Flow Dynamics, which consists of turbomachinery module and validation of numerical models, are the subjects of the third chapter. The examples of numerical simulations of different turbomachines are presented, in following order: I) low pressure reversible axial flow fan with plane runner blades, II) axial-flow propeler pump and III) centrifugal pump. For all cases, the physical model is first presented, and then a numerical model is created, while the results of numerical simulations are given as the display of operating parameters obtained for a defined number of revolutions. The operated parameters of each presented turbo machine obtained by numerical simulations of the flow in the range of operating flow rate, compared with the operating characteristics obtained by experimental tests of appropriate machines under laboratory conditions, therefore performing the validation of the model. When it comes to turbomachinery, with respect to their practical application, it can be considered that the model validation is performed if the relative error of operating parameters in all current regimes does not exceed 5%. The flow parameters in different discrete points of the turbomachinery runner, i.e. in different cross-sections of the runner (position, pressure, and velocity) of all presented examples, which are used for the purpose of averaging, were presented in the form of tables given in the Appendix of this dissertation. The fourth chapter deals with the determination of averaged axisymmetric flow surface according to the results obtained by numerical simulation of flow in hydraulic turbines and low pressure fans. The real flow in the profile cascades of hydraulic turbomachinery and fans is not axially symmetric, and the can be reduced to axisymmetric flow fictively, if the flow parameters in the blade channels are averaged according to a circular coordinate. Values of x flow parameters at discrete points of the considered flow field are obtained by numerical simulations. According to the results of numerical simulations of flow in turbomachinery runner, it is possible to determine the averaged flow parameters accordint to the circular coordinate, and then to determinate the averaged axisymmetric flow surfaces. The methodology of averaging flow parameters according to the circular coordinate and obtained equations are presented in this chapter. The results of determining the meridional flow streamlines of the averaged fluid flow using the integral equations of continuity, for the cases presented in the chapter 3, are presented in the fifth chapter. Guided by the theory and the equations given in section 4, the results of determination of averaged streamlines in hydraulic turbomachinery and low pressure fans runner, respectively averaged axisymmetric flow surface. In addition, the specific works of elementary stages on averaged axisymmetric flow surfaces in the turbomachinery runner are determined, as well as torque and power of the runner. Finally, the calculation of flow rates of the averaged mechanical flow energy through axisymmetric flow control surfaces, at the entrance and exit of the work area of the runner, is performed, leading to the significant information on the fluid energy losses in the turbomachinery runner. At the end of the dissertation the Conclusion is presented, and in the Appendix tables the averaged values of flow parameters in the corresponding sections of the turbomachinery runners are presented. The results of averaging according to the circular coordinate, as defined in section 4, are presented, and these results are used in section 5.
- Published
- 2014
12. Design of small bulb turbines with unequal specific work distribution of the runner's elementary stages
- Author
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Bogdanović-Jovanović, Jasmina, Bogdanović, Božidar, and Božić, Ivan
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Physics::Fluid Dynamics ,Specific Work ,lcsh:Mechanical engineering and machinery ,lcsh:TJ1-1570 ,Axisymmetric Flow Surfaces ,Bulb Turbine ,Elementary Stages - Abstract
Regarding the present state of knowledge in the field of the turbo machinery design, the method for designing small bulb turbines with unequal specific work distribution of the turbine runner's elementary stages near the hub is presented in the paper. The distribution function of specific work of all the elementary stages is obtained, according to which the averaged axisymmetric flow surfaces of the turbine runner have a negligibly small deviation from the cylindrical flow surfaces. The specific work of the near-the-hub elementary stages, in the given distribution function, can be reduced up to 60% of the required (design) specific work, still achieving nearly cylindrical flow surfaces.
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- 2014
13. RISK OF THERMAL POLLUTION OF THE DANUBE PASSING THROUGH SERBIA DUE TO THERMAL POWER PLANTS.
- Author
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LAKOVIĆ, Mirjana S., Stojiljković, Mladen, BANJAC, Miloš J., Laković-Paunović, Mirjana, BOGDANOVIĆ-JOVANOVIĆ, Jasmina B., JOVIĆ, Milica M., and MILOVANOVIĆ, Zdravko N.
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THERMAL pollution of rivers, lakes, etc. ,OCEAN thermal power plants ,ENVIRONMENTAL impact analysis ,COOLING ,FISHES - Abstract
A thermal power plant (TPP) uses large amounts of fresh water, mostly for cooling purposes. Among different types of cooling systems, once-through cooling is the most water-intensive and has the greatest environmental impacts. From the viewpoint of the steam cycle efficiency, this type of cooling still provides the most efficient electricity production, and therefore is widely used. Water is withdrawn from nearby water bodies, absorbs heat from the steam in a condenser, and then discharged back to its original source at higher temperatures causing severe environmental impacts, including fish killing, disturbing ecosystems, and heating-up natural water bodies. The total installed capacity of almost 1100 MW on the right bank of the Danube in Serbia threatens the ecosystem of this large international river due to thermal pollution. This problem will be even more pronounced in the near future, due to an inevitable increase in production capacity for new 350 MW, currently under construction. Herein, analysis of the legal framework for the protection of water from thermal pollution as well as analysis of the actual situation on the site of the TPP "Kostolac" in Serbia are presented. Based on meteorological and hydrological parameters, configuration and operation parameters of the plant, the numerical simulation of the condenser was carried on. The temperature of the water leaving condenser and amount of heat discharged back to the river are obtained. According to those results, the analysis of the existing thermal pollution of the Danube River in the flow through Serbia is given by numerical simulation using software ANSYS CFX. Analysis of thermal discharge into the Danube for the five-year period has been carried out. The cooling water effluent causes a temperature increase in the area of the right bank of the Danube, and this thermal disturbance extends along the right river bank for kilometers. Note that the flow rate of the Danube is currently large enough to compensate this thermal disturbance, but for a smaller river and/or larger electricity production capacities, this influence would have even more significant consequences on the ecosystem, making those results even more useful for further analysis. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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14. NUMERICAL INVESTIGATION OF CAVITATING FLOW IN VENTURI NOZZLE.
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BOGDANOVIĆ-JOVANOVIĆ, Jasmina, STAMENKOVIĆ, Živojin, SPASIĆ, Živan, PETROVIĆ, Jelena, and KOCIĆ, Miloš
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VENTURI effect , *CAVITATION , *SATURATION vapor pressure - Abstract
Cavitation problems occurs in water flow where the local pressure reaches saturated vapour pressure, due to the sudden increase of local velocity values, forming bubbles and different forms of flow discontinuity. Water flow in the Venturi nozzle is the typical example of potentially cavitation flow. Due to the large importance of Venturi nozzles in engineering practice, it is important to determine their cavitation characteristics, such a cavitation number and loss coefficient of the nozzle. In case we are unable to obtain cavitation characteristics of the nozzle experimentally, there is the possibility to conduct numerical simulations of the flow in the Venturi nozzle. The objective of this study is to present the possibilities of obtaining cavitation characteristics of Venturi nozzles by applying numerical simulations, and to determine the optimal numerical modelling of flow in the case of Venturi nozzle. [ABSTRACT FROM AUTHOR]
- Published
- 2018
15. PERFORMANCE OF LOW-PRESSURE FANS OPERATING WITH HOT AIR.
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BOGDANOVIĆ-JOVANOVIĆ, Jasmina B. and MILENKOVIĆ, Dragica R.
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FANS (Machinery) , *AIR conditioning , *ATMOSPHERIC temperature , *PRESSURE , *AXIAL flow - Abstract
Performance characteristics of fans are generally provided for the normal temperature and pressure conditions (tI = 20 °C, pI = 101.325 kPa, pI = 1.2 kg/m3). Very often, fans operate in different air conditions, occasionally at different air temperatures. In these cases, equations obtained by the law of similarity are usually used for recalculation of the fan operating parameters. Increasing the inlet air temperature causes a decrease in the characteristic of Reynolds number, and may lead to efficiency lowering of the fan. There are also some empirical formulas for recalculation of fan efficiency, when operating at different air temperatures. In this paper, the common way for obtaining fan performance for different operating conditions (air temperature changing) is presented. The results, obtained by recalculation of fan parameters using a law of similarity, are compared to numerical simulation results of the axial-flow fan operating with different air temperatures. These results are compared with results obtained by some recommended empirical formulas, as well. This paperwork is limited to low-pressure and mid-pressure fans, which represents the majority of all fans used in practice, for different purposes. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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16. HEAT TRANSFER IN MICROPOLAR FLUID FLOW UNDER THE INFLUENCE OF MAGNETIC FIELD.
- Author
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KOCIĆ, Miloš M., STAMENKOVIĆ, Živojin M., PETROVIĆ, Jelena D., BOGDANOVIĆ-JOVANOVIĆ, Jasmina B., and NIKODIJEVIĆ, Milica D.
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HEAT transfer ,STEADY-state flow ,MICROPOLAR elasticity ,TEMPERATURE ,COUPLING constants - Abstract
In this paper, the steady flow and heat transfer of an incompressible electrically conducting micropolar fluid through a parallel plate channel is investigated. The upper and lower plates have been kept at the two constant different temperatures and the plates are electrically insulated. Applied magnetic field is perpendicular to the flow, while the Reynolds number is significantly lower than one i. e. considered problem is in induction-less approximation. The general equations that describe the discussed problem under the adopted assumptions are reduced to ordinary differential equations and three closed-form solutions are obtained. The velocity, micro-rotation and temperature fields in function of Hartmann number, the coupling parameter and the spin-gradient viscosity parameter are graphically shown and discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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17. PUMPS USED AS TURBINES.
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BOGDANOVIĆ-JOVANOVIĆ, Jasmina B., MILENKOVIĆ, Dragica R., SVRKOTA, Dragan M., BOGDANOVIĆ, Božidar, and SPASIĆ, Živan T.
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ENERGY consumption research , *TURBINES , *PUMPING machinery , *COMPUTATIONAL fluid dynamics , *SIMULATION methods & models - Abstract
As the global demand for energy grows, numerous studies in the field of energy efficiency are stimulated, and one of them is certainly the use of pumps in turbine operating mode. In order to reduce time necessary to determine pump characteristic in turbine operating mode problem was studied by computational fluid dynamics approach. The paper describes various problems faced during modeling (pump and turbine mode) and the approaches used to resolve the problems. Since in the majority of applications, the turbine is a pump running in reverse, many attempts have been made to predict the turbine performance from the known pump performance, but only for best efficiency point. This approach does not provide reliable data for the design of the system with maximum energy efficiency and does not allow the determination of the head for a wide range of flow rates. This paper presents an example of centrifugal norm pump operating in both (pump and turbine) regime and comparison of experimentally obtained results and computational fluid dynamics simulations. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
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18. DETERMINATION OF AVERAGED AXISYMMETRIC FLOW SURFACES ACCORDING TO RESULTS OBTAINED BY NUMERICAL SIMULATION OF FLOW IN TURBOMACHINERY.
- Author
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BOGDANOVIĆ-JOVANOVIĆ, Jasmina B., BOGDANOVIĆ, Božidar P., and MILENKOVIĆ, Dragica R.
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AXIAL flow , *COMPUTER simulation , *TURBOMACHINES , *ENERGY conservation , *ENERGY consumption , *MATHEMATICAL optimization , *POWER plants - Abstract
In the increasing need for energy saving worldwide, the designing process of turbomachinery, as an essential part of thermal and hydroenergy systems, goes in the direction of enlarging efficiency. Therefore, the optimization of turbomachinery designing strongly affects the energy efficiency of the entire system. In the designing process of turbomachinery blade profiling, the model of axisymmetric fluid flows is commonly used in technical practice, even though this model suits only the profile cascades with infinite number of infinitely thin blades. The actual flow in turbomachinery profile cascades is not axisymmetric, and it can be fictively derived into the axisymmetric flow by averaging flow parameters in the blade passages according to the circular coordinate. Using numerical simulations of flow in turbomachinery runners, its operating parameters can be preliminarily determined. Furthermore, using the numerically obtained flow parameters in the blade passages, averaged axisymmetric flow surfaces in blade profile cascades can also be determined. The method of determination of averaged flow parameters and averaged meridian streamlines is presented in this pa-per, using the integral continuity equation for averaged flow parameters. With thus obtained results, every designer can be able to compare the obtained averaged flow surfaces with axisymmetric flow surfaces, as well as the specific work of elementary stages, which are used in the procedure of blade designing. Numerical simulations of flow in an exemplary axial flow pump, used as a part of the thermal power plant cooling system, were performed using ANSYS CFX. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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19. LOW-PRESSURE REVERSIBLE AXIAL FAN DESIGNED WITH DIFFERENT SPECIFIC WORK OF ELEMENTARY STAGES.
- Author
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BOGDANOVIĆ, Božidar P., SPASIĆ, Živan T., and BOGDANOVIĆ-JOVANOVIĆ, Jasmina B.
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FANS (Machinery) ,LOW pressure (Science) ,IMPELLERS ,BLADES (Hydraulic machinery) ,AIR intakes (Jet engines) - Abstract
Low-pressure axial fan impellers designed according to the principle of equal specific work of all elementary stages have blades whose profile near the fan hub is under a significantly larger inclination angle than at the impeller periphery. In order to minimize the spatial curvature of the fan blades and the fan hub length, impeller blades of low-pressure axial fans can be designed with different specific work of elementary stages, so that the specific work of elementary stages is smaller at the hub than at the periphery. This paper presents the operating characteristics of a low-pressure reversible axial fan with straight blade profiles, de-signed with different specific work of elementary stages. The fan was tested on a standard test rig, with air intake loading on the suction side of the fan. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
20. EXPERIMENTAL AND NUMERICAL INVESTIGATION OF FLOW AROUND A SPHERE WITH DIMPLES FOR VARIOUS FLOW REGIMES.
- Author
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BOGDANOVIć-JOVANOVIć, Jasmina B., STAMENKOVIć, Živojin M., and KOCIć, Miloš M.
- Subjects
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SPHERES , *ENGINEERING , *ENGINE cylinders , *HYDRODYNAMICS , *FLUID dynamics - Abstract
Flow over a sphere is a typical bluff-body flow with many engineering applications. However, it has not been studied in depth, as compared to flow over a circular cylinder, because of the difficulties in the experimental set-up as well as in the computational approach for studying flow over a sphere. The main challenges are to understand the flow hydrodynamics and to clarify the flow pattern around a dimpled sphere because the flow pattern complying with the dimple structure on its surface is very complicated. In this paper experimental and numerical investigations of the fluid flow around a sphere with dimples, are represented. The sphere with dimples is placed in a quadratic cross-section duct (measuring section) and numerical simulation results are obtained by solving RANS equations. Furthermore, experimental measurements are carried out using a laser-Doppler anemometer. Experimental and numerical results of flow velocity fields were compared for three different flow regimes (Re = 8.103, 2.104, and 4.104). Numerical investigation was performed for wide range of Reynolds numbers (Re = 270.106). The final purpose of this paper is experimental and numerical determination of velocity field, separation point, pressure and drag coefficient, the length of reverse flow region in the wake and RANS turbulent model which gives the best results for engineering practice. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
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21. Nestacionarna strujanja u sistemima za transport tečnosti i njihova zaštita
- Author
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Nikodijević, Milica, Bogdanović-Jovanović, Jasmina, Mihajlov, Darko, Karadžić, Uroš, and Spasić, Živan
- Subjects
unsteady fluid flow, water hammer, hydraulic valves, valve closing laws, water hammer modelling, Pelton turbine, Francis turbine, leakage flow, leakage location ,Nestacionarno strujanje fluida, hidraulički udar, hidraulički zatvarači, zakoni zatvaranja zatvarača, modeliranje hidrauličkog udara, Pelton–ova turbina, Francis– ova turbina, curenje tečnosti, lokacija curenja - Abstract
The subject matter of this dissertation is a general analysis of unsteady flows in hydraulic transport pipelines with a special focus on small hydropower pipelines and the determination of dynamic properties of control valves and the stator. The determined dynamic properties of governors and system behavior are verified through comparison with the measured results. The research subject and aims are defined based on the analysis of previous relevant literature. Mathematical modelling of unsteady fluid flow in pipelines is conducted. The speed of pressure disturbance during water hammer is determined and some basic cases of this phenomenon are presented. Based on the review of available methods that significantly contributed to the study of this phenomenon, the method of characteristics is deductively selected to solve the relevant differential equations with boundary and initial conditions, after which different representations of the friction factor are given. Based on market availability of different valve types, three of them are selected; calculations and analyses of the three valves yielded results that were then used to propose the best valve type water hammer mitigation. Afterward, the basic parameters of water turbines are described and a classification is provided for the turbines, for which linear and universal characteristics are then determined according to the main universal characteristic and the use of universal characteristics to obtain Suter curves is demonstrated. Water hammer is modelled for systems containing a Pelton and a Francis turbine and the results for specific small hydropower plants are then verified against the modelling results. The dissertation also discusses potential static and hydrodynamic methods of leakage detection in hydraulic transport systems, with special focus on the method of pressure gradient analysis, which is then supplemented with unsteady analyses for intentionally created pressure disturbances in the system. Based on the developed models for establishing the dynamic properties of transients, a procedure is proposed for identifying leakage and leakage locations in a hydraulic system. The obtained results will be used to formulate recommendations for improved reliability and system protection.
- Published
- 2022
22. Istraživanja magnetno hidrodinamičkih strujanja i prenosa toplote mikropolarnih fluida
- Author
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Kocić, Miloš, Stamenković, Živojin, Savić, Slobodan, Jovanović, Miloš, Bogdanović-Jovanović, Jasmina, and Spasić, Živan
- Subjects
Physics::Fluid Dynamics ,ANSYS ,fluid flow ,prenos toplote ,micropolar fluids ,MHD ,heat transfer ,mikropolarni fluidi ,strujanje fluida ,CFD ,EMHD - Abstract
The basis of the doctoral thesis is the analysis of flow and heat transfer of one or two electrically conducting micropolar fluids in the presence of magnetic and electric fields. The first part of the dissertation is the development of mathematical models for described problems of MHD flow and heat transfer of micropolar fluid, where the research is conducted in inductionless approximation and for the case of coupled equations. After that, in the next chapters, the problem of walls conductivity of the channel is considered, also the effects of induced magnetic field and interface boundary conditions for the flow of two fluids. Special attention is paid to the flow of two fluids between inclined plates where one fluid is micropolar and the other one is Newtonian. Analytical solutions are given for momentum, microrotation, energy and magnetic induction equations for the problems of MHD flow of one and two fluids. Next part of the dissertation has a detailed analysis of physical phenomena that occur in MHD and EMHD flow of micropolar fluids, and comparison of analytical solutions obtained in closed form with the results obtained by numerical simulations. Using the numerical simulations the case of the flow of micropolar fluid in the horizontal and vertical channels under the influence of magnetic and electric fields are solved. At the end, within the dissertation detailed analysis of results are given for micropolar fluids, which is significant in the technical practices, for different values characteristic dimensionless numbers that describes MHD and EMHD problems of flow and heat transfer of micropolar fluids. Special attention is also given to the applicability of the research in the development of new technologies.
- Published
- 2019
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