Temat: unsteady flow - Prolib Integro

Skocz do pozycji: 1.

Tytuł:: Characterization of different one-stage blower designs using three-dimensional unsteady numerical flow simulation
Autorzy:: Kalmar, L.
Janiga, G.
Fodor, B.
Soltesz, L.
Tematy:: blower
numerical simulation
unsteady flow; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Powiązania:: https://bibliotekanauki.pl/articles/175582.pdf Link otwiera się w nowym oknie
Opis:: This paper deals with the computational fluid dynamics investigation of the flow in a one-stage radial flow blower-aggregate. The main aim of this numerical study is to compute the relevant operating characteristics of the blower and to determine detailed information about the flow characteristics inside it. The distributions of these flow characteristics in the blower determined by the commercial code are available to judge whether the elements of the blower are working properly, or not. The calculated characteristics of operating parameters are compared with measured data given by experimental tests of the blower-aggregate for their validation.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Analysis of unsteady forces acting on a slender cylinder
Autorzy:: Ziółkowski, P. J.
Witkowski, W.
Sobczyk, B.
Tematy:: unsteady flow
FSI
CFD modelling
CSD modelling; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Powiązania:: https://bibliotekanauki.pl/articles/175172.pdf Link otwiera się w nowym oknie
Opis:: Developments in construction engineering (new materials, construction techniques) facilitate the design of very flexible, light structures with low damping which unfortunately results in higher susceptibility of these structures to wind action. It is therefore necessary to use more accurate scientific tools in the engineering phase of these structures. Analytical methods for considering wind effects on structures encounter difficulties with respect to mathematical formulations of aerodynamic forces. In this paper a 2D numerical model has been described which considers the fluid domain with respect to a cylindrical obstacle. This 2D model has been discretized using the finite volume method, and numerical simulations have been undertaken in order to describe the unsteady flow conditions within the analyzed domain. The simulations have been performed with boundary conditions characterizing the flow past a cylindrical obstacle. The results have been compared with the literature data from similar experiments. On the basis of the flow characteristics obtained, as well as the spatial distributions of the flow parameters, a model for further 3D analyses was selected. Next, a 3D numerical study of unsteady flow forces acting on a slender cylinder has been analyzed. Toward the end, a two-way fluid solid interaction approach has been utilized, which incorporates a computational fluid dynamics approach combined with computational solid dynamics.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Analysis of unsteady flow forces on the thermowell of steam temperature sensor
Autorzy:: Kornet, S.
Sławiński, D.
Ziółkowski, P.
Badur, J.
Tematy:: unsteady flow
resonance
CFD modeling
CSD modeling; Pokaż więcej
Wydawca:: Polska Akademia Nauk. Czytelnia Czasopism PAN
Powiązania:: https://bibliotekanauki.pl/articles/175578.pdf Link otwiera się w nowym oknie
Opis:: In this paper, 3D numerical analysis of unsteady flow forces acting on the thermowell of steam temperature sensor is presented. According to that purpose, the CFD+CSD (computational fluid–solid dynamics) approach has been used. The nonstationary of fluid acting on the thermowell such as: Strouhal frequency, amplitude of pressure, structure of vortex, peak of pressure, field of pressure, field of velocity, etc. are studied analytically and numerically. There have been examined two cases of flow with changing both temperature, pressure and mass flow rate (operating daily and night in the unit with capacity of 380 MWe). In accordance with the standards ASME PTC 19.3 TW-2010 the possibility of entry into resonance has been examined.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Analytical expressions for effective weighting functions used during simulations of water hammer
Autorzy:: Urbanowicz, K.
Tematy:: unsteady flow
water hammer
convolution integral
frequency-dependent friction; Pokaż więcej
Wydawca:: Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Powiązania:: https://bibliotekanauki.pl/articles/281377.pdf Link otwiera się w nowym oknie
Opis:: For some time, work has been underway aimed at significant simplification of the modelling of hydraulic resistance occurring in the water hammer while maintaining an acceptable error. This type of resistance is modelled using a convolution integral, among others, from local acceleration of a liquid and a certain weighting function. The recently completed work shows that during efficient calculations of the convolution integral, the effective weighting function used does not have to be characterised by large convergence with a classical function (according to Zielke during laminar flow and to Vardy-Brown during turbulent flow). However, it must be a sum of at least two or three exponential expressions so that the final results of the simulation could be considered as satisfactory. In this work, it has been decided to present certain analytical formulas using which it will be possible to determine the coefficients of simplified effective weighting functions in a simple direct way.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: Drag force on a flat plate in cavitating flows
Autorzy:: Seif, M. S.
Asnaghi, A.
Jahanbakhsh, E.
Tematy:: numerical simulation
cavitation
psio algorithm
flat plate
unsteady flow; Pokaż więcej
Wydawca:: Politechnika Gdańska. Wydział Inżynierii Mechanicznej i Okrętownictwa
Powiązania:: https://bibliotekanauki.pl/articles/258824.pdf Link otwiera się w nowym oknie
Opis:: The present study focuses on the simulation of two dimensional unsteady cavitating flows. For simulation of unsteady behaviors of cavitation which have practical applications, the development of unsteady PISO algorithm based on the non-conservative approach is utilized. For multi-phase simulation, single-fluid Navier–Stokes equations, along with the volume fraction transport equation, are employed. The bubble dynamics model is utilized to simulate phase change between vapor and liquid phases of the water. Unsteady simulation of cavitation around NACA66(MOD) and supercavitation around a flat plate normal to flow direction are performed to clarify accuracy of presented model. Numerical results and comparisons with experimental data are provided. The accuracy is good, and it is possible to apply this method to more complex shapes.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Tytuł:: Improved method for simulating frictional losses in laminar transient liquid pipe flow
Autorzy:: Urbanowicz, K.
Zarzycki, Z.
Kudźma, S.
Tematy:: unsteady pipe flow
unsteady friction
weighting function; Pokaż więcej
Wydawca:: Politechnika Gdańska
Powiązania:: https://bibliotekanauki.pl/articles/1943217.pdf Link otwiera się w nowym oknie
Opis:: This paper is devoted to the problem of energy dissipation and it concerns unsteady friction modeling of the liquid flow in hydraulic lines. One dimensional (1D) quasi-steady model of energy dissipation is in common use. It means that the loss of energy is estimated by the Darcy-Weisbach formulae. Such an approximation is close to reality only for slow changes of the velocity field in the pipe cross-section. In case of fast changes, like fast transients, e.g. water hammer, it fails. In this work the wall shear stress (defined as an effect of unsteady fluid friction) is presented as a sum of quasi-steady and unsteady components. The unsteady component of the wall shear stress is modeled as an convolution of the local fluid acceleration and a weighting function w(t). The weighting function, in general, makes an allowance for a relation of the historic velocity changes and the unsteady component of the wall shear stress. Primitive weighting functions have usually very complicated structures, and what is more, they make it impossible to perform an efficient simulation of dynamical runs. In this paper, a new weighting function is presented as a sum of exponential components in order to enable efficient calculation of the unsteady component wall shear stress. A few examples of the new effective method of unsteady wall shear stress simulations, in case of the water hammer, are presented. The results of the calculations are compared with experiments known in literature and satisfying results are obtained.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 7.

Tytuł:: Accuracy and parameter estimation of elastic and viscoelastic models of the water hammer
Autorzy:: Weinerowska-Bords, K.
Tematy:: water hammer
unsteady flow in pipelines
parameter estimation
numerical methods; Pokaż więcej
Wydawca:: Politechnika Gdańska
Powiązania:: https://bibliotekanauki.pl/articles/1933158.pdf Link otwiera się w nowym oknie
Opis:: The water hammer problem is considered, one of the most important questions of unsteady flows in pipelines. Although first mentioned in the scientific literature more than a hundred years ago and widely analyzed since in many research centers, the problem is not fully recognized yet. It may be considered on two levels: practical and theoretical. In both cases, several difficulties arise rendering the results less than fully satisfactory. The most important difficulties are the proper mathematical description of the phenomenon, the choice of the solution method, estimation of the model parameters and numerical aspects of solving the equations governing the phenomenon's run. They are presented in the paper and typical approaches to their solution are discussed. Numerical solutions are compared with experimental results.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 8.

Tytuł:: Space-time conservation method appplied to numerical solution of water hammer equations
Autorzy:: Weinerowska-Bords, K.
Tematy:: water hammer
unsteady flow in pipelines
numerical methods
numerical dissipation; Pokaż więcej
Wydawca:: Politechnika Gdańska
Powiązania:: https://bibliotekanauki.pl/articles/1934017.pdf Link otwiera się w nowym oknie
Opis:: This paper is devoted to the space-time conservation (STC) method and its application to a water hammer in steel pipelines. The STC method, due to its numerical properties, in particular its high accuracy, can be an interesting alternative to traditional numerical methods, especially when dealing with problems where the numerical errors have the potential to significantly influence the solution, making interpretation very difficult. As the problem of water hammer is one of such problems, an analysis of the application of the STC method to this case can be very interesting.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 9.

Tytuł:: PIV measurement of tube-side in a shell and tube heat exchanger
Autorzy:: Wang, K.
Zhang, Z.
Liu, Q.
Tu, X.
Hyoung-Bum, K.
Tematy:: shell and tube heat exchanger
tube-side
PIV
unsteady flow; Pokaż więcej
Wydawca:: Zachodniopomorski Uniwersytet Technologiczny w Szczecinie. Wydawnictwo Uczelniane ZUT w Szczecinie
Powiązania:: https://bibliotekanauki.pl/articles/778192.pdf Link otwiera się w nowym oknie
Opis:: In order to improve the performance of the shell and tube heat exchanger, a porous baffle and a splitter bar are employed in this research. Through the arrangement of the porous baffle in the tube-side inlet and the splitter bar in the tube, the flow distribution of liquid in the heat exchanger is improved. PIV technology is used to investigate the unsteady flow in the tube-side inlet and the outlet of different models. The porous baffle significantly improves the flow of fluid in the shell and tube heat exchanger, especially by eliminating/minimizing the maldistribution of fluid flow in the tube-side inlet. The performance of the arc baffle is better than that of the straight baffle. The splitter bar has a minimal effect on the flow field of the tube-side inlet, but it effectively improves the flow in the tube bundle and restrains the vortex generation in the tube-side outlet.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 10.

Tytuł:: Unsteady Shock Wave: Turbulent boundary layer interaction in the Laval Nozzle
Autorzy:: Doerffer, P.
Szulc, O.
Magagnato, F.
Tematy:: unsteady transonic flow
shock waves
nozzle flow; Pokaż więcej
Wydawca:: Politechnika Gdańska
Powiązania:: https://bibliotekanauki.pl/articles/1965143.pdf Link otwiera się w nowym oknie
Opis:: The flow in transonic diffusers and supersonic air intakes often becomes unsteady due to shock wave-boundary layer interaction. Oscillations may be induced by natural separation unsteadiness or forced by boundary conditions. Significant improvements of CFD tools, increased computer resources and the development of experimental methods have again drawn the attention of researchers to this topic. Forced oscillations of a transonic turbulent flow in an asymmetric two-dimensional Laval nozzle have been considered to investigate the problem. A viscous, perfect gas flow was numerically simulated using SPARC, a Reynolds-averaged compressible Navier-Stokes solver, employing a two-equation, eddy viscosity, turbulence closure in the URANS approach. For time-dependent and stationary flow simulations, Mach numbers upstream of the shock between 1.2 and 1.4 were considered. Comparison of computed and experimental data for steady states generally gave acceptable agreement. In the case of forced oscillations, a harmonic pressure variation was prescribed at the exit plane resulting in shock wave motion. Excitation frequencies between 0Hz and 1024Hz were investigated at a constant pressure amplitude. The main result of the work is the relation between the amplitude of shock wave motion and the excitation frequency in the investigated range. Increasing excitation frequency resulted in decreasing amplitude of the shock movement. At high frequencies, a natural mode of shock oscillation (of small amplitude) was observed, which was insensitive to forced excitement.
Dostawca treści:: Biblioteka Nauki

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