Design of small bulb turbines with unequal specific work distribution of the runner's elementary stages

Uzimajući u obzir dosadašnja saznanja iz oblasti projetovanja turbomašina, u ovom radu je prikazan metod projektovanja malih cevnih turbina sa različitim jediničnim radovima elementarnih stupnjeva turbinskog kola u okolini glavčine. Data je funkcija raspodele jediničnih radova elementarnih stupnjeva turbinskog kola, pri kojoj osnosimetrične strujne površine u turbinskom kolu zanemarljivo malo odstupaju od cilindričnih strujnih površina. U datoj funkciji raspodele, jedinični rad elementarnog stupnja turbinskog kola može se, uz glavčinu, smanjiti i na 60% proračunskog jediničnog rada turbinskog kola, a da strujne površine u obtnom kolu budu priližno cilindrične.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

Determination of averaged axisymmetric flow in hydraulic turbomachinery runner

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

DESIGN OF SMALL BULB TURBINES WITH UNEQUAL SPECIFIC WORK DISTRIBUTION OF THE RUNNER’S ELEMENTARY STAGES

Regarding the present state of knowledge in the field of the turbomachinery 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

NUMERICAL INVESTIGATION OF THE INFLUENCE OF THE DOUBLY CURVED BLADE PROFILES ON THE REVERSIBLE AXIAL FAN CHARACTERISTICS

Abstract. In reversible axial fans a change in the direction of the impeller rotation is accompanied with a change in the direction of the working fluid flow. To satisfy the flow reversibility, the impeller blades are usually designed with straight symmetrical profiles. The flow reversibility may also be achieved by using asymmetrical blade profiles in which, to satisfy the equality of the leading and trailing angle of the profiles, the mean line of the profile has to have a double curvature in the shape of the stretched letter 'S'. The paper numerically investigates the influence of the doubly curved blade profiles on the reversible axial fan characteristics. Numerical simulations are carried out on an axial fan only with the impeller, with the blades that have double-curved mean line profiles for different values of the angles at the profile ends. For numerical simulation the ANSYS CFX software package is used. Results of the numerical simulation are shown in diagrams Δp(Q), h(Q) and P(Q) at different angles of the profile ends. On the basis of the simulation and analysis of the characteristics, appropriate conclusions are proposed, along with the most advantageous profile of the blades

Experimental and numerical investigation of flow around a sphere with dimples for various flow regimes

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 (LDA). 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

DETERMINATION OF AVERAGED AXISYMMETRIC FLOW SURFACES AND MERIDIAN STREAMLINES IN THE CENTRIFUGAL PUMP USING NUMERICAL SIMULATION RESULTS

One of the most important aims in the turbo pump design is to achieve an optimal design of the pump impeller. The basic assumption in the design procedure of the impeller is that of the axisymmetric fluid flow. It can be confirmed or disputed by using the method presented in the paper, which uses the results of numerical simulation of fluid flow in the pump impeller. The method is actually a procedure for determining averaged axisymmetric flow surfaces and meridian streamlines. Furthermore, according to the obtained streamlines, a correction of the impeller blade geometry can be made (if the streamlines deviate significantly from the assumed axisymmetric ones). It is also possible to calculate the specific works of the elementary stages and compare them with the previous assumptions. The pump impeller torque can be calculated as well

DETERMINATION OF AVERAGED AXISYMMETRIC FLOW SURFACES AND MERIDIAN STREAMLINES IN THE CENTRIFUGAL PUMP USING NUMERICAL SIMULATION RESULTS

One of the most important aims in the turbo pump design is to achieve an optimal design of the pump impeller. The basic assumption in the design procedure of the impeller is that of the axisymmetric fluid flow. It can be confirmed or disputed by using the method presented in the paper, which uses the results of numerical simulation of fluid flow in the pump impeller. The method is actually a procedure for determining averaged axisymmetric flow surfaces and meridian streamlines. Furthermore, according to the obtained streamlines, a correction of the impeller blade geometry can be made (if the streamlines deviate significantly from the assumed axisymmetric ones). It is also possible to calculate the specific works of the elementary stages and compare them with the previous assumptions. The pump impeller torque can be calculated as well

Electro-Magnetoconvection of Conductive Immiscible Pure Fluid and Nanofluid

This paper discusses the magnetohydrodynamic flow and heat transfer in a horizontal channel whose top and bottom halves have different or the same permeability. The top half of the channel is saturated with oil and the bottom half with a water-based nanofluid. The channel is under the influence of an external homogeneous vertical magnetic field and an external homogeneous electric field perpendicular to the vertical longitudinal plane of the channel. The Darcy model is used to determine the fluid flow and heat transfer. Expressions for velocity and temperature distributions are defined and presented graphically for different values of the dimensionless parameters. The Nusselt numbers are determined and given in a table. The paper also investigates the influence of the Hartmann number, the porosity factor, the electrical load factor and the volume fraction of the nanofluid on velocity and temperature distributions in the channel as well as the Nusselt numbers. It has been shown that an increase in the volume fraction of nanoparticles leads to a decrease in the temperature in the channel. Increasing the porosity factor reduces the fluid velocity in the channel and increases the temperature. The Hartmann number increases the temperature in the channel. Higher absolute values of the load factor correspond to higher temperatures. By changing the value of this factor, the direction of fluid flow can also be changed

Risk of thermal pollution of the danube passing through Serbia due to thermal power plants

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 view-point 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

MHD micropolar fluid flow in porous media

The analysis of mass and heat transfer in magnetohydrodynamic (MHD) flows has significant applications in heat exchangers, cooling nuclear reactors, designing energy systems and casting and injection processes of different types of fluids. On the other hand, extraction of crude oil, the flow of human or animal blood, as well as other polymer fluids or liquid crystals are just some examples of micropolar fluid flows. Due to the broad application spectrum of the theory of micropolar fluid flows, and the significance the impact the external magnetic field has on the flow of these fluids, this paper considers the stationary flow of a micropolar fluid between two plates under the influence of an external magnetic field which is perpendicular to the direction of the flow. Stationary plates are maintained at constant and different temperatures, while the whole problem is considered in the non-inductive approximation. The equation system used to define the physical problem under consideration is reduced to the system of differential equations that have been solved analytically and the solutions of which are of general nature. In addition to the solutions for velocity, microrotation and temperature, the paper gives solutions for shear stress at plates, the Nusselt number and flow rate. The provided solutions have been applied in order to reach some general conclusions about the influence of the magnetic field and physical characteristics of a micropolar fluid and the characteristics of porous media on the nature of micropolar fluid flows in porous media by means of chart analysis. General conclusions, obtained in the result analysis in this paper, give us the opportunity to understand the flows of micropolar fluids and highlight their significance