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Search Results: 1 - 10 of 325417 matches for " S?awomir Dykas "
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The Analysis of the Noise Generation in Gas Turbine Stage  [PDF]
Sawomir Dykas, Dawid Machalica
Open Journal of Acoustics (OJA) , 2014, DOI: 10.4236/oja.2014.44016
Abstract: The aim of this paper is to assess the impact of the mutual positioning of the turbine stage stator and rotor blades on noise generation. The Ansys CFX commercial software package and the Scale-Adaptive Simulation (SAS) hybrid turbulence model are used for numerical analyses. The paper is focused on an analysis that the pressure wave generation resulting from unsteady flow phenomena. In order to present the problem, the Fast Fourier Transformation (FFT) analysis of pressure fluctuation is carried out at selected points of the turbine stage computational domain. A comparison of values of individual components for subsequent control points allows an approximate determination of the place of generation of pressure waves, the direction of their propagation and the damping rate. Moreover, the numerical analyses make it possible to evaluate the justification for the use of the SAS model, which is rather demanding in terms of equipment, in simulations of unsteady flow fields where generation and propagation of noise waves occur.
Numerical Modelling of Aerodynamic Noise in Compressible Flows  [PDF]
Sawomir Dykas, Sebastian Rulik, W?odzimierz Wroblewski
Open Journal of Fluid Dynamics (OJFD) , 2012, DOI: 10.4236/ojfd.2012.23007
Abstract: The solution of the AeroAcoustics (CAA) problems by means of the Direct Numerical Simulation (DNS) or even the Large Eddy Simulation (LES) for a large computational domain is very time consuming and cannot be applied widely for engineering applications. In this paper the in-house CFD and CAA codes are presented. The in-house CFD code is based on the LES approach whereas the CAA code is an acoustic postprocessor solving the non-linearized Euler equations for fluctuating (acoustic) variables. These codes are used to solve the aerodynamically generated sound field by a flow over a rectangular cavity with inlet Mach number 0.53.
Numerical Analysis of the Losses in Unsteady Flow through Turbine Stage  [PDF]
Sawomir Dykas, W?odzimierz Wróblewski, Dawid Machalica
Open Journal of Fluid Dynamics (OJFD) , 2013, DOI: 10.4236/ojfd.2013.34031
Abstract: This paper presents an analysis of the operation of a stage of an aircraft engine gas turbine in terms of generation of flow losses. The energy loss coefficient, the entropy loss coefficient and an additional pressure loss coefficient were adopted to describe the losses quantitatively. Distributions of loss coefficients were presented along the height of the blade channel. All coefficients were determined based on the data from the unsteady flow field and analyzed for different mutual positioning of the stator and rotor blades. The flow calculations were performed using the Ansys CFX commercial software package. The analyses presented in this paper were carried out using the URANS (Unsteady Reynolds-Averaged Navier-Stokes) method and two different turbulence models: the common Shear Stress Transport (SST) model and the Adaptive-Scale Simulation (SAS) turbulence model, which belongs to the group of hybrid models.
Sensitivity Analysis of a 50+ Coal-Fired Power Unit Efficiency  [PDF]
Katarzyna St?pczyńska-Drygas, Sawomir Dykas, Krystian Smo?ka
Journal of Power and Energy Engineering (JPEE) , 2015, DOI: 10.4236/jpee.2015.312003
Abstract:

The coal-fired power unit integration with a CO2 capture and compression installation involves a considerable rise in the costs of electricity generation. Therefore, there is a need for a continuous search for methods of improving the electricity generation efficiency in steam power plants. One technology which is especially promising is the advanced ultra-supercritical (A-USC) power unit. Apart from steam parameters upstream the turbine, the overall efficiency also depends on the efficiency values of individual elements of the plant and the size of energy consumption of the process of CO2 sequestration from the boiler flue gases. These problems are considered herein to emphasize that without specifying the efficiency values of the power plant main elements the information concerning its electricity generation efficiency is incomplete. This paper presents the influence of the efficiency of individual elements of the power plant on its electricity generation efficiency. The lack of information of the efficiencies of the power plant individual elements, by presenting its overall efficiency, may lead to the false conclusions.

Numerical Method for Modeling of Acoustic Waves Propagation
S awomir Dykas , W odzimierz Wróblewski , Sebastian Rulik , Tadeusz Chmielniak
Archives of Acoustics , 2010, DOI: 10.2478/v10168-010-0003-7
Abstract: In this paper, numerical results of modeling of acoustic waves propagation are presented. For calculation of the acoustic fluctuations, a solution of the full non-linear Euler equation is used. The Euler equations are solved with the use of a numerical scheme of third-order accuracy in space and time. The paper shows a validation process of the described method. This method is suitable also for an aerodynamic noise assessment on the basis of unsteady mean flow field data obtained from a CFD calculations. In such case this method is called a hybrid CFD/CAA method. The proposed method is numerically decoupled with CFD solution, therefore the information about the mean unsteady flow field can be obtained using an arbitrary CFD method (solver). The accuracy of the acoustic field assessment depends on the quality of the CFD solutions. This decomposition reduces considerably the computational cost in comparison with direct noise calculations. The presented Euler acoustic postprocessor (EAP) has been used for modeling of the acoustic waves propagation in a cavity and in the flow field around a cylinder and an aerodynamic profile.
Calculation of a 900 MW conceptual 700/720oC coal-fired power unit with an auxiliary extraction-backpressure turbine
Katarzyna St?pczyńska,?ukasz Kowalczyk,Sawomir Dykas,Witold Elsner
Journal of Power Technologies , 2012,
Abstract: This paper presents the calculations for different configurations of a 900 MW power unit for advanced 700/720°C ultra-supercritical steam parameters with a single and double steam reheat. The use of such high parameters, especially the reheated steam temperature, involves thermodynamic and material problems related to high temperature differences in the feed water heaters. In relation to this, a concept of the modification of the feed water heaters system by using an auxiliary extraction-backpressure turbine fed with steam from the cold reheat steam line is presented. The steam from the bleeds and the turbine outlet is directed to regenerative heaters fed in the classical system from the intermediate pressure turbine, which reduces the temperature differences in these exchangers and simplifies the main turbine IP part structure.
Local inverses of Borel homomorphisms and analytic P-ideals
S awomir Solecki
Abstract and Applied Analysis , 2005, DOI: 10.1155/aaa.2005.207
Abstract: We present a theorem on the existence of local continuoushomomorphic inverses of surjective Borel homomorphisms withcountable kernels from Borel groups onto Polish groups. We alsoassociate in a canonical way subgroups of ℝ withcertain analytic P-ideals of subsets of ℕ. Thesegroups, with appropriate topologies, provide examples of Polish,nonlocally compact, totally disconnected groups for which globalcontinuous homomorphic inverses exist in the situation describedabove. The method of producing these groups generalizesconstructions of Stevens and Hjorth and, just as thoseconstructions, yields examples of Polish groups which are totallydisconnected and yet are generated by each neighborhood of theidentity.
Review
S awomir Wacewicz
Poznań Studies in Contemporary Linguistics , 2007, DOI: 10.2478/v10010-007-0010-7
Abstract:
How to Perform Discounted Cash Flow Valuation?
S awomir Janiszewski
Foundations of Management , 2011, DOI: 10.2478/v10238-012-0037-4
Abstract: Within the last few decades the quickly accelerating globalization processes contributed to rapid increase in the value of the global capital markets, and mergers and acquisitions transactions. This implicated the rising importance of methodologies that enable investors to efficiently value the companies. The aim of this elaboration is to present practical approach towards the discounted cash flow company valuation method, considered one of the most effective but simultaneously one of the most sophisticated among all. The article comprises purely theoretical as well as practical knowledge, based on the author's broad professional experiences.
Is the European pond turtle Emys orbicularis strictly aquatic? – Habitats where the turtle lives in central Europe
Sawomir Mitrus
Acta Herpetologica , 2010,
Abstract: Based on ecological characteristics and phylogenetic analysis, it is possible to try to reconstruct the evolution of ecological traits in turtles. However, the European pond turtle is treated by different scientists as aquatic or as semi-aquatic species. The importance of terrestrial behaviour for this species is discussed.
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