Wyniki wyszukiwania - BazTech

1

A new idea to increase the convective efficiency of a solar tower air receiver by creating a controlled vortex

Cheilytko Andrii

Journal of New Technologies in Environmental Science

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2023

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Vol. 7, nr 2

46--55

EN

Concentrated solar energy as a source of renewable energy has a high potential for solving the current energy crisis. The solar tower receiver is a crucial element of solar energy conversion efficiency. To increase the convective efficiency of the solar tower receiver, the idea of creating a vortex is proposed. The vortex is created either in the plane in front of the receiver, for flat receivers, or in the internal volume of the receiver, for cavity-type receivers. The calculation formulas for calculating the parameters of the controlled vortex are proposed and computer modeling is performed to determine the effectiveness of the proposed idea. The results of computer modeling confirmed the physical possibility of the controlled vortex formation in the receiver space and visually show the flow structure. Also, the general dependence of the air return coefficient in the VoCoRec receiver on the flow twist was found. Conclusions are drawn on the satisfactory results obtained and on the improvement of the existing model of the controlled vortex.

2

Scour around spur dike in curved channel: a review

Tripathi Ravi Prakash, Pandey Kamlesh Kumar

Acta Geophysica

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2022

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Vol. 70, no 5

2469--2485

EN

A spur dike is a hydraulic structure, protruding in a river or channel used for several purposes like protection of river-bank erosion and deepening of the main channel. The present paper discusses pre-existing research work on flow pattern and prediction of temporal and maximum scours depth around the spur dikes placed in different locations at 90◦ and 180° curved channels. The equations having approximately 2.367, 4.47, 0.17, and 0.271 (average) times with their corresponding experimental data. The parameters, influencing the scour process and flow pattern, have been identified as the ratio of flow intensity to critical velocity (V/Vc≥1) is below 1 and special kind of bedding material is approximately 10 % greater than under livebed condition and many more. The numerical value of the Froude number and the geometry of the bed surface material are also discussed in this paper. Based on these parameters, the empirical formulations and experimental studies on local scours around the straight, L-shaped, T-shaped spurs, placed at 30°, 45°, 60°, 120°, and 180° azimuthal angles have been discussed. Various numerical schemes proposed in almost seventy-five literatures have been summarized. A critical review of numerical and experimental results found in different works related to temporal and maximum scour depth, flow characteristics, and bed topography around the dike shows that the data and accompanying results are insufficient for the design of spurs used as river structures in curved channels. There are needs to carry out extensive experiments, under various flow conditions, to examine the flow behavior and scouring processes around the spurs. Due to complex flow pattern and scouring processes, taking place around the spur, it becomes difficult to understand the real physics behind these phenomenon and therefore, data-driven models are suggested to arrive at more reasonable relationships required to be used for design purposes.

3

Numerical comparison of two runners for gravitational vortex turbine

Ruiz-Sánchez Alejandro, Guevara-Muñoz Angie, Sierra Del Rio Jorge Andrés, Posada-Montoya Jose-Alejandro

Engineering Transactions

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2021

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Vol. 69, iss. 1

3--17

EN

The main purpose of this study is to compare numerically the torque generated by two runners for a gravitational vortex turbine. One of the runners was an H-Darrieus turbine with the rotational flow into the chamber that helped to decrease its negative torque. The other runner was a standard (straight blade) turbine, which determined the performance in both cases. The study was conducted in ANSYSrCFX, where the model was configured at constant operating conditions in both cases. The standard runner performance was higher (75%) than that of the H-Darrieus runner. The highest torque for the standard and the H-Darrieus runners was 0.76 and 0.16 N m, respectively. The standard runner had a larger fluid contact area than the H-Darrieus runner, which extracted more energy.

4

Study of Tundish Slag Entrainment Using Physical Modelling

Michalek K., Gryc K., Socha L., Saternus M., Tkadlečková M., Pieprzyca J., Merder T., Pindor L.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 1

257--260

EN

This paper deals with the possibilities of using physical modelling to study the slag entrainment in the tundish. A level of steel in the tundish is changing during sequential continuous casting. The most significant decrease in the steel level occurs when replacing ladles. It is generally known that if the height of steel level in the tundish drops below a certain critical level, it may generate vortexes over the nozzles and as a consequence entrainment of tundish slag into individual casting strands can occur. Thus, it is necessary to identify the critical level of steel for specific operational conditions. In this paper, the development of physical modelling methodology is described as well as physical model corresponding to operational continuous casting machine No. 2 in Třinecké železárny, a.s. The obtained results are discussed.

5

Geometric modelling of turbulent flat jets in accompanying and contrary flows

Gumen O., Dovhaliuk V., Mileikovskyi V.

Budownictwo o Zoptymalizowanym Potencjale Energetycznym

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2015

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nr 1(15)

70--77

EN

We offer an approach to describe turbulent jets in accompanying and contrary flows without using experimental coefficients and additional values (turbulent viscosity, mixing path length etc.). It is based on the theory developed by a professor of Kyiv National University of Construction and Architecture A. Tkachuk. The analogy between an ideal liquid flow and developed turbulent flow allows describing surfaces of tangential velocity rupture by vortex sheets. We continue this research direction by analysis of jet flows with large-scale vortices (puffs) by geometric and kinematic analysis of this macrostructure. The results have good correlation with well-known experimental data. We analytically obtain conditions of the jet existence in contrary flow. This approach may help in efficient development of new air distribution devices of energy-efficient air exchange organization.

PL

Zaproponowano inne podejście do opisu turbulentnych strumieni w towarzyszących i przypadkowych przepływach. Opiera się ono na teorii opracowanej przez profesora Kijowskiego Narodowego Uniwersytetu Budownictwa i Architektury A.Y.Tkaczuka. Przy opracowaniu tego modelu skupiono się na kinetycznej i geometrycznej analizie przepływów o dużych wirach w skali makro. Otrzymane wyniki są zgodne z wcześniej znanymi już w literaturze przedmiotu.

6

Effect of Some Variables on the Fibre Packing Pattern in a Yarn Cross-section for Vortex Spun Yarn

Zou Z., Zheng S, Cheng L, Xi B, Yao J.

Fibres & Textiles in Eastern Europe

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2014

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Vol. 22, no. 2 (104)

40--46

EN

This paper examined the influence of various parameters such as fibre fineness, yarn count, distance from the front roller nip point to the hollow spindle, nozzle pressure and yarn delivery speed on the fibre packing pattern in a yarn cross-section for vortex spun yarn. Cross-section images of vortex spun yarns were used to evaluate the fibre packing pattern. Results from different variables influencing the fibre packing pattern for vortex spun yarn were also analysed. The results indicated that the fibre fineness, yarn count, distance from the front roller nip point to the hollow spindle, nozzle pressure and yarn delivery speed are all significant parameters for yarn hairiness and fibre packing density in a vortex spun yarn cross-section.

PL

Badano wpływ grubości włókien, masy liniowej przędzy, odległości przedniej rolki do wydrążonego wrzeciona, ciśnienia w dyszy i szybkości podawania przędzy na upakowanie włókien w przekroju poprzecznym przędzy przędzionej systemem vortex. Zdjęcia przekrojów poprzecznych przędzy zostały wykorzystane dla oceny upakowania włókien. Wyniki analizy rozkładów włókien wykazały, że wszystkie badane parametry mają wydatny wpływ na upakowanie i włochatość w przędzy przędzionej systemem vortex.

7

The characteristics of two-blade Submersible Mixers’ flow field inner the pool

Fei T., Weidong S., Qihua Z., Hua J., Desheng Z.

Przegląd Elektrotechniczny

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2013

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R. 89, nr 3b

236--241

EN

To study the flow pattern of submersible mixers inner the pool, the research uses FLUENT6.3 mainframe computational fluid mechanics software as well as RNG k –εturbulent model、SIMPLE algorithm and rigid-lid assumption to numerically simulate the two-blade submersible mixers inner the sewage treatment pool and also analyzes the velocity distribution inner big pool and the distributions of the flow field, pressure and the velocity circulation inner the mixers’ impellers. The results indicate that the fluid flow inner the pool belongs to high Reynolds number with large turbulence intensity; the fluid flow is complex, and there exists obvious big vortex; Coanda Effect and boundary-layer separation is also apparent. Clearly large vortex exists and the flow velocity near the blades is higher while the flow velocity of the pool’s surface and bottom takes the form of double parabolic distribution and is lower. The velocity gradient and pressure gradient are obvious from working face to the blade back; the flow velocity is lower and the pressure is higher near the working face of the blades, moreover, there are high velocity zone and negative zone in the blade back. The velocity in the axis surface inlet and outlet the blades is also parabolic distributed, and its circulation does not vary considerably; the velocity in the axis surface inlet and outlet the blades is distributed similar as the velocity in the isometric axis surface, and its velocity circulation follows a linear law distribution. It can guide submersible mixer hydraulic performance in design study, simulation and engineering application.

PL

W artykule przedstawiono wyniki badań dotyczących przepływu w mieszaczach zatapialnych, znajdujących się w basenie. W celu przeprowadzenia symulacji mieszacza dwułopatowego, wykorzystano m. in. oprogramowanie FLUENT6.3, model turbulencji k-epsilon, algorytm SIMPLE oraz założono sztywność wieka. Analizie poddano także rozkład prędkości i cieśnienia wokół wirnika mieszacza. Wyniki badań zostały omówione i przedstawione wnioski.

8

Effect of Fibre Fineness and Spinning Speed on Polyester Vortex Spun Yarn Properties

Sankara Kuthalam E., Senthilkumar P.

Fibres & Textiles in Eastern Europe

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2013

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Vol. 21, no. 5 (101)

35--39

EN

The properties of vortex yarn made from 100% polyester fibre with different fibre finenesses and spinning speeds were studied. Four different fibre finenesses (0.9, 1.1, 1.3 and 1.5 dtex) were used to produce yarns of 20 tex polyester vortex yarn with five different delivery speeds (320, 340, 360, 380 and 400 m/min), and these yarns were then tested for their unevenness, tensile and hairiness related properties. Linear multiple regression methods were used for the estimation of the yarn quality characteristics. It is found that fibre fineness and spinning speed did not influence the tenacity of the vortex yarn. The yarn unevenness was found to be maximum for coarser (1.5 dtex) fibre and minimum for finer (0.9 dtex) fibre. Minimum thin places were noticed for 0.9 dtex fibre. The hairiness index (H) found decreases when the fibre becomes finer up to 1.1 dtex and then increases when the fibre becomes finer than 1.1 dtex. However, Zweigle hairiness (1 mm) decreases as the fibre becomes finer. The vortex spinning speed does not influence any of the yarn properties except the hairiness values.

PL

Badano właściwości przędzy typu vortex wytworzonej w 100% z włókien poliestrowych o różnych masach liniowych i prędkościach przędzenia. Zastosowano włókna o czterech różnych masach liniowych (0.9-1.5 dtex) do wytworzenia przędzy poliestrowej typu vortex 20 tex, stosując pięć różnych prędkości przędzenia (320, 340, 360, 380 i 400 m/min), a następnie oceniono właściwości fizyczne otrzymanych przędz: nierównomierność masy liniowej, parametry wytrzymałościowe oraz włochatość. Do oceny statystycznej zastosowano metody wielokrotnej regresji liniowej. Wykazano, iż masa liniowa włókien i prędkość przędzenia nie wpływają na wytrzymałość przędzy typu vortex. Stwierdzono, że większa nierównomierność przędzy występuje dla przędz grubszych o włóknach 1.5 dtex, a mniejsza dla cienkich przędz o włóknach 0.9 dtex. Pocienienia przędzy występowały dla przędzy o włóknach 0.9 dtex. Wskaźnik włochatości (H) ulegał zmniejszeniu do 1.1 dtex a następnie wzrastał. Włochatość wg Zweigle’a zmniejszała się przy zmniejszaniu masy liniowej. Prędkość wirowania nie wpływała na parametry przędzy za wyjątkiem włochatości.

9

Effect of some design parameters on the flow fields and power consumption in a vessel stirred by a rushton turbine

Youcefi S., Bouzit M., Ameur H., Kamla Y., Youcefi A.

Chemical and Process Engineering

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2013

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Vol. 34, nr 2

293--307

EN

Knowledge of the fluid dynamic characteristics in a stirred vessel is essential for reliable design and scale-up of a mixing system. In this paper, 3D hydrodynamics in a vessel agitated by a Rushton turbine were numerically studied (with the help of a CFD computer program (CFX 13.0)). The study was carried out covering a wide Reynolds number range: 104 – 105. Computations, based on control volume method, were made using the k-. model. Our main purpose was to investigate the effect of vessel configuration and agitation rates on the flow structure and power consumption. Three types of vessels were used: unbaffled, baffled and a vessel with slots placed at the external perimeter of its vertical wall. The effect of slot length has been investigated. The comparison of our predicted results with available experimental data shows a satisfactory agreement.

10

Effect of the draft ratio on the properties of vortex spun yarn

Erdumlu N., Ozipek B.

Fibres & Textiles in Eastern Europe

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2010

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Vol. 18, no. 3 (80)

38--42

EN

In this study, the effects of draft ratios on the properties of vortex spun yarns were investigated. 100% viscose drawing slivers of three different counts (3.94 ktex, 3.19 ktex and 2.68 ktex) were spun into yarns with a count of 14.76 tex while keeping all other spinning conditions constant. The yarn samples were evaluated on the basis of yarn irregularity and imperfections, as well as hairiness and tensile properties. In addition, a 3rd passage draw frame sliver with a yarn count of 3.19 ktex was spun into yarns of 14.76 tex using two different delivery speeds: 350 and 400 m/min. The significance of independent variables and their interactions for the physical properties of the yarn were tested statistically at a 95% level of confidence.

PL

Do badań wybrano taśmy z włókien wiskozowych o trzech masach liniowych: 3,94 ktex, 3,19 ktex, 2,68 ktex wytwarzając przędze o masie liniowej 14,76 tex. Wytworzone próbki badano analizując ich nierównomierność, ilość zgrubień pocienień i nopów oraz włochatość. Dodatkowo zastosowano trzeci stopień rozciągu dla wyprzędzenia z taśmy 3,19 ktex przędzy o masie liniowej 14,76 tex stosując dwie prędkości zasilania: 350 m/min i 400 m/min. Wpływ poszczególnych parametrów procesu badano statystycznie na poziomie ufności 95%.

11

Unsteady loads evaluation for a wind turbine rotor

Chkir S., Dobrev I., Kuszla P., Massouh F.

Diagnostyka

|

2009

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nr 4(52)

17-22

EN

This paper presents a method for calculating the flow around a wind turbine rotor. The real flow is replaced by a free stream past a vortex model of the rotor. This model consists of lifting vortex lines which replace the blades and a trailing free vorticity. The vorticity shed from the blade is concentrated in two vortices issued from tip and root. To compute the unsteady forces exerted on the rotor, a free wake method is used. The evolution of the wake is obtained by tracking the markers representing the vortices issued from the blade tips and roots. To solve the wake governing equation and to obtain the marker positions, a time-marching method is applied and the solution is obtained by a second order predictor-corrector scheme. To validate the proposed method a comparison is made with experimental data obtained in the case of a model of wind turbine where the flow field immediately behind the rotor is measured by means of PIV. It is shown that the numerical simulation captures correctly the near wake development. The comparison shows satisfactory accuracy for the velocity field downstream of the rotor.

12

Detection of the vortices signs in the scalar fields

Galushko Y., Mokhun I.

Optica Applicata

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2008

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Vol. 38, nr 4

705-713

EN

The technique for determining the vortex sign in the scalar fields (including the statistical ones) under conditions when the use of the regular reference beam is impossible is described. The elaborated approach is based on the shift-interferometry technique. The conditions of the optimal vortices identification are formulated. The results of the computer simulation and experimental confirmation are presented.

13

The behavior of the Poynting vector in the area of elementary polarization singularities.

Mokhun I., Khrobatin R., Mokhun A., Viktorovskaya J.

Optica Applicata

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2007

|

Vol. 37, nr 3

261-277

EN

The behavior of the Poynting vector in the area of elementary polarization singularities withone or two C-points, which are bounded by regular shape s-contour is considered. It has been shown that C-points are associated with the "vortex" kind singularities of the averaged transversal component of the Poynting vector if the handedness factor and topological charge of C-point are characterized by different signs. "Passive" Poynting singularities arise in the area if the signs are the same. It has been shown that the positions of the Poynting singularities shift relatively to the C-points under the phase and amplitude asymmetry of orthogonal components of the resulting field. The results of the computer simulation are presented.

14

Fine structure of heterogeneous vector field and its space averaged polarization characteristics

Brandel R., Mokhun A., Mokhun I., Viktorovskaya J.

Optica Applicata

|

2006

|

Vol. 36, nr 1

79-95

EN

Interrelation between the fine structure of the vector field and its averaged polarization characteristics is considered. It is shown that space averaged Stokes parameters are defined by dispersion of the phase difference (or dispersion of the polarization azimuth) at its saddle points. At the same time the dispersion of the phase difference is directly related to averaged space between the nearest adjacent component vortices of the same sign, which are associated with the different orthogonal linearly polarized components. The dependence between the dimensions of areas where considerable polarization changes occur and averaged space between the nearest adjacent component vortices of the same sign is obtained. The results of computer simulation and the experimental investigation are presented.

15

Modelowanie dwuwymiarowych przepływów w obszarach o złożonej geometrii metodą cząstek wirowych

Kudela H., Malecha Z.

Inżynieria Chemiczna i Procesowa

|

2006

|

T. 27, z. 3/1

707-719

PL

Przedstawiono wyniki badań nad wykorzystaniem metody cząstek wirowych typu "wir w komórce" (WiK) na siatce nieprostokątnej. Elementem składowym metody WiK jest rozwiązywanie równania Poissona na siatce numerycznej dla funkcji prądu w celu wyznaczenia prędkości cząstek wirowych. Zastosowano nieregularną siatkę strukturalną, dopasowaną do kształtu opływanego ciała. Opracowano nowy algorytm redystrybucji cyrkulacji cząstek na oczka siatki w nieregularnych komórkach. Obliczenia testowe przeprowadzono dla opływu walca i profilu lotniczego z różnymi kątami natarcia. Uzyskano dobrą jakościowo zgodność z obrazami przepływów otrzymanymi eksperymentalnie.

EN

Vortex in the cell method was investigated for solution of the flow problem in an arbitrary domain. The Poisson equation was solved on a non-rectangular body-oriented structural grid. Such a grid allows one to cover precisely a complex geometry and offers a great flexibility in the choice of the software for the mesh generation. A new method for redistribution of the vortex particles intensity (circulation) onto irregular mesh nodes was worked out. Test computation was made for a flow around a cylinder and airfoil with various angles of attack. A good qualitative agreement was obtained with the pictures of the flow presented in literature.

16

Flow Analysis through Axial-Flow Pumps by Means of the Lattice Vortex Method

Kaniecki M.

Zeszyty Naukowe. Cieplne Maszyny Przepływowe - Turbomachinery / Politechnika Łódzka

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2005

|

nr 128, vol. 1

273-280

EN

The paper presents results of numerical flow computation through axial-flow pumps. The calculation method (lattice vortex method) is one of the variety of boundary elements methods, based on the potential flow equation. Brief characteristics of the method and the calculation results of global characteristics of two selected axial-flow pumps are presented.

17

Streamwise vortices induced by semi-circular rods submerged in turbulent boundary layer.

Szumowski A., Wojciechowski J.

Archive of Mechanical Engineering

|

2005

|

Vol. LII, nr 4

353-360

EN

Two semi-circular rods set up in V-shape form were used to generate streamwise vortices in a turbulent boundary layer. The vortices, due to induced helical flow, supplement the streamwise momentum of retarded air particles at the body surface with the momentum of the external flow. In this experimental study it was found that vortices are at their most intensity if the Reynolds number of the flow over generator, based on the diameter of rods is within the range 10 to the 4 - 1.5 x 10 to the 4. Several semi-circular rods set up in a tooth line were examined in delaying the separation of the turbulent boundary layer at a convex cylindrical surface. It has been noted that delay of separation is at its most efficient when the height of the generator is equal to at least half of the boundary layer thickness.

PL

Wiry, których oś wirowania pokrywa się z głównym kierunkiem przepływu (wiry wzdłużne) powodują ruch śrubowy elementów płynu. Tym samym, jeżeli wiry te generowane są w warstwie przyściennej, powodują intensyfikację transportu pędu w kierunku ścianki, a przez to uzupełnianie strat pędu warstwy przyściennej i opóźnianie jej oderwania. W pracy badano na drodze eksperymentalnej wiry wzdłużne generowane przez pręty półwalcowe zestawione w kształcie litery V, umieszczone na płaskiej ściance. Stwierdzono, że intensywność wirów jest największa dla liczb Reynoldsa w zakresie 10 do potęgi czwartej - 1.5 x 10 do potęgi czwartej i kąta rozwarcia między prętami ok. 60 stopni. Efekt działania wytworzonych w ten sposób wirów na opóźnienie oderwania warstwy przyściennej badano przy opływie wypukłej powierzchni walcowej. Uzykane wyniki świadczą, że skuteczność generatora wirów rośnie ze zwiększeniem promienia półwalca aż do wartości tego promienia równego w przybliżeniu połowie grubości warstwy. Dalsze zwiększenie promienia nie powoduje istotnego wzrostu opóźnienia oderwania.

18

Numerical simulation and modification of 3D flow phenomena in an axial flow fan

Elhadi E. E., Keqi W.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2003

|

Vol. 7, No 2

199-213

EN

This work aims to study and analyze the behavior of flow in an axial flow fan using numerical simulation based on solving Reynolds-averaged Navier-Stokes equations coupled with a modified Spalart-Allaras turbulence model. In the present work, different flow phenomena occuring in an axial flow fan were presented and interpreted at different design conditions and at different regions, with special concern to the rotor exit and stator regions. Large vortices and reverse flow at the stator suction side were observed under high loading conditions. These are mainly due to radial and centrifugal effects in the fluid due to a decreasing flow rate. To avoid this type of flow, the stator flow pattern has been modified using a new stator blade. This blade was designed by changing the stator stagger angle by 10o in the radial direction. This study indicates that the flow in the modified stator region behaves well and gives better performance than that obtained when using a baseline stator, especially under high loading conditions. This study also indicates that the stator stagger angle has a significant effect on modifying the fan performance.

19

Drgania masztów z odciągami wywołane opływem wiatru

Bar A., Nizioł J.

Zeszyty Naukowe. Mechanika / Akademia Techniczno-Rolnicza w Bydgoszczy

|

2002

|

Z. 53(241)

7-18

PL

Praca przedstawia przybliżoną analizę na podstawie prostego modelu drgań masztu wzmocnionego odciągami. Drgania te wywoływane są odrywaniem się od masztu wirów Karmana. Wykazano, że zjawisko drgań ma charakter samowzbudno-parametryczny. W pracy zamieszczono charakterystyki amplitu-dowo-częstotiiwościowe, amplitudowo-fazowe oraz przebiegi czasowe drgań uzyskane dzięki analizie numerycznej.

EN

The paper presents an approximate analysis based on a simple model of vibrations of a mast supported by stay cables. The vibrations of the mast are excited by the separation of the Karman vortex. It has been demonstrated that the vibrations in the discussed structure has the self-excited parametric character. The paper includes the frequency and phase characteristics well as the time plots obtained by means of numerical analysis.

20

Remarks on Plane, Steady, Creeping Flows Generated by Singularities

Klonowska-Prosnak M.E., Cześnik P.

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2002

|

Vol. 50, Nr 1

45--69

EN

Two properties of plane, steady, creeping flow generated in the infinite domain around a given contour by a single singularity are investigated in the paper. The first property concerns velocity field. It is shown, that stream uniform at infinity must occur automatically in this case, and formulae for velocity of the stream are derived. The second property concerns similarity of streamline pattern of such flow, and the potential one, generated around the same contour by the same singularity. Investigation of the both properties concerns - in particular: a disc, an ellipse and the airfoil sections NACA 0012, RAE 2822.