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1

Numerical Modeling of Sediment Transport and Bed Evolution in Nonuniform Open-Channel Flows

Zerihun Yebegaeshet T.

Archives of Hydro-Engineering and Environmental Mechanics

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2024

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Vol. 71, nr 1

1--26

EN

The shallow-water and multilayer hydrostatic models have been commonly used to analyze the problems of a sediment-laden, plane open-channel flow. The models are adequate to solve a quasi-hydrostatic flow problem, but their accuracy deteriorates as the effects of the vertical acceleration gain in significance. Herein, a higher-order numerical model for treating the problems of unsteady, plane open-channel flow over a movable bed is proposed. In this model, the flow hydrodynamics is governed by the depth-averaged Boussinesq-type equations, and the bed morphodynamics is determined by an Exner-type equation and additional equations describing the non-equilibrium transports of suspended load and bed load. A hybrid finite-volume and finite-difference scheme was used to discretize and solve the governing equations, yielding solutions that are in satisfactory agreement with the experimental data. Overall, the results of the proposed model for the temporal free-surface profile and bed evolution were fairly adequate. For the two particular cases considered, however, the quality of its results was moderately affected by the effects of the three-dimensional characteristics of the dam-break flow and the sliding of the dike body due to sub-surface flow. The results of this investigation highlight the importance of including a higher-order Boussinesq-type correction for refining sediment transport computations.

2

Wpływ modyfikacji orurowania i budowy wymiennika płaszczowo-rurowego na parametry intensyfikacji przepływu ciepła - model i symulacja numeryczna w ANSSYS

Kasowski Szymon, Anwajler Beata

Ciepłownictwo, Ogrzewnictwo, Wentylacja

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2023

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T. 54, nr 6

14--20

PL

W artykule zaprezentowano wymiennik płaszczowo-rurowy małej mocy wraz z analizą przepływowo-cieplną wykonaną dla dwóch wariantów obejmujących rury proste oraz rury przetłoczone będące modyfikacją intensyfikującą proces wymiany ciepła. Oba wymienniki zaprojektowano jako czterodrogowe w celu minimalizacji ich wymiarów. Przeznaczeniem projektowanego wymiennika ciepła jest podgrzewanie wody użytkowej za pomocą ciepła pozyskiwanego z gorącej wody przesyłanej siecią ciepłowniczą. W artykule przedstawiono autorski układ przegród charakteryzujący się stałą liczbą rur oraz stałą powierzchnią przepływu czynnika w każdej z czterech dróg przepływu wody. Przeprowadzono proces obliczeniowy poparty symulacją numeryczną w programie ANSYS, w której zamodelowano przepływ cieczy przez projektowane wymienniki ciepła. W pracy uzyskano wyniki porównujące i oceniające wpływ modyfikacji na proces wymiany ciepła. Wskutek zastosowania w wymienniku płaszczowo-rurowym przetłoczonych rur zwiększono intensywność wymiany ciepła o 34,6% względem wymiennika o rurach prostych o średnicy 16 mm. Znaczna poprawa intensywności wymiany ciepła znacząco wpłynęła na proces miniaturyzacji wymiennika.

EN

The article a low-power shell-and-tube heat exchanger with a flow-thermal analysis performed for two variants including straight tubes and pressed tubes, which are a modification that intensifies the heat exchange process was presented. Both exchangers have been designed as four-way in order to minimize their dimensions. The purpose of the designed heat exchanger is to heat utility water with the use of thermal energy obtained from hot water sent via the heating network. The article an original partition system characterized by a constant number of pipes and a constant medium flow surface in each of the four water flow paths was presented. A calculation process was carried out supported by a numerical simulation in the ANSYS program, in which the flow of liquid through the designed heat exchangers was modeled. The results comparing and evaluating the impact of modifications on the heat transfer process were obtained in the work. As a result of the use of pressed tubes in the shell-and- tube exchanger, the intensity of heat exchange was increased by 34.6% compared to the exchanger with straight tubes with a diameter of 16mm. Significant improvement in heat exchange intensity significantly influenced the process of miniaturization of the exchanger.

3

Analysis of time-averaged secondary flow cells in wide and narrow straight open channels with lateral bed deformation

Chattopadhyay T., Kundu S.

Archives of Mechanics

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2023

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Vol. 75, nr 1-2

169--211

EN

The usual cellular pattern of the time averaged secondary flow circulation in the central section of wide open channels shows a distorted (laterally or vertically) structure due to the changes in bed configurations along lateral direction. The structures of these secondary circulations (under different bed configurations) are crucial for different types of hydraulic modeling. This study presents mathematical models of the time averaged secondary velocities (lateral and vertical components) for a turbulence-induced secondary current at the central section of a wide open-channel flow under different types of elevated and non-elevated bed conditions. Starting with the Reynolds Averaged Navier-Stokes equation and using the continuity equation, at first the governing equation of secondary flow velocity is obtained including the effects of the eddy viscosity and viscosity of the fluid. The model equations is solved using a separation of the variable technique imposing the bed perturbation condition. Full analytical solutions are achieved through mathematical analysis using suitable boundary conditions consistent with experimental observations. Initially the models are derived for a non-elevated bedforms comprised of alternating equal widths of smooth and rough bed strips. These models are modified further for bedforms with unequal widths of rough and smooth bed strips and elevated periodic bed structures. Four different types of elevated bed configurations are investigated and a general approach is suggested for other types of bed forms. All the proposed models are validated with existing experimental results to ensure the applicability and in each cases, improved results are observed. Obtained results show that the centre of circulation of the cellular structure occurs above the junction of the rough and smooth bed strips (consistent with experimental observations) and it gradually shifts towards the smooth strip, when the length of the rough bed strip is increased. The shifting as a function shows a non-linear pattern with the length of the rough bed strip. A least-square model is proposed to identify the circulation center as a function of the ratio of rough to smooth bed strips. It is also found that the vertically distorted secondary cells are generated when the bed slope strictly increase/decrease throughout the length of the one whole circulation. Finally, all the proposed models are compared with an existing model and an error analysis is done. Results of error analysis show that the present study can be more suitable as it yields improved results.

4

Huragan w filiżance, czyli ruch trochoidalny i efekty niestabilności podczas dyfuzji kawy z mlekiem

Cielica Nina, Szymańska-Markowska Barbara

Postępy Fizyki

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2022

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T. 73, z. 1

24--29

PL

W artykule przedstawiono zjawisko dyfuzji kawy z mlekiem rozpatrzone z perspektywy dynamiki formujących się w trakcie procesu wirów. Zilustrowano je przy wykorzystaniu danych uzyskanych za pomocą kamery termowizyjnej. Pomiary pokazały zależność właściwości utworzonych wirów od czynników takich jak temperatura płynów, stosunek objętości płynów, kierunek i prędkość obrotu tarczy, na której umieszczona jest filiżanka. Na podstawie rozpoznanych efektów niestabilności stworzono symulację pokazującą w przybliżony sposób przebieg zjawiska. Analiza wskazała także podobieństwa do zjawisk w większej skali np. mechanizmu formowania huraganów.

EN

The article presents the phenomenon of milk diffusion in coffee, considered from the perspective of the dynamic of vortices forming during the process. hey are illustrated using data obtained with a thermal imaging camera. The measurements showed the dependence of vortices’ properties on the factors such as the temperature of the fluids, the volume ratio or the direction and speed of rotation of the disc on which the cup is placed. On the basis of the identified instability effects, simulation, that shows the approximate course of the phenomenon, was created. he analysis also showed similarities to larger-scale phenomena, such as the mechanism of hurricane formation.

5

Convective Heat Transfer in Heat Exchangers Using Nanofluids: A Review

Reddy Goda Sreenivasulu, Kalaivanan Ramasamy, Kumar Rampelli Uday, Krishna Varma K. P. V.

Ecological Engineering & Environmental Technology

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2022

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Vol. 23, iss. 3

193--201

EN

Enhancing the Convective heat transfer in the carrier fluids, by augmenting the thermal conductivity in fluids, with nano particles is one of the passive techniques. Enhancement in the thermal conductivity in the carrier fluids can be achieved by suspending particles of nano-size into the base fluids, such colloidal suspensions are called as nanofluids. Nanofluids are proven fluids which improve the convective transfer of heat in the base fluids in the heat exchangers. But still, there are lot of challenges that are existing in understanding the mechanisms of enhancement of convective heat transfer for large scale applications. In this work, an attempt is made to summarize recent advancements on augmentation of convective heat transfer in heat exchangers in turbulent flows using various nanofluids and present various setbacks for the development of nanofluids for critical applications.

6

Numerical study on two dimensional distribution of streamwise velocity in open channel turbulent flows with secondary current effect

Mohan S., Kundu S., Ghoshal K., Kumar J.

Archives of Mechanics

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2021

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Vol. 73, nr 2

175--200

EN

For studying mechanism of sediment transport in river flows, open channel flow is a prototype. Flow has always three components of velocity for all types of channel geometry and for a time independent uniform flow along streamwise or main flow direction, all the components of velocity are functions of lateral and vertical coordinates. The present study investigates the two dimensional distribution of streamwise (or longitudinal) velocity starting from the Reynolds averaged Navier–Stokes equation for a turbulent open channel flow which is steady and uniform along the main flow direction. Secondary flows both along the vertically upward direction and along the lateral direction are considered which are also taken as functions of lateral and vertical coordinates. Inclusion of the secondary current brings the effect of dip phenomenon in the model. The resulting second order partial differential equation is solved numerically. The model is validated for all the cross-sectional, transverse and centreline velocity distribution by comparing with existing relevant set of experimental data and also with an existing model. Comparison results show good agreement with data as well as with the previous model proving the efficiency of the model. It is found that the transverse velocity distribution depends on the formation of circular vortex in the cross-sectional plane and becomes periodic as the number of circular vortex increases for increasing aspect ratios.

7

Influence of Geometric Structure, Convection, and Eddy on Sound Propagation in Acoustic Metamaterials with Turbulent Flow

Pak Myong Chol, Kim Kwang-Il, Pak Hak Chol, Hong Kwon Ryong

Archives of Acoustics

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2021

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Vol. 46, No. 4

637--647

EN

The problem of reducing noise in transportation is an important research field to prevent accidents and to provide a civilised environment for people. A material that has recently attracted attention in research to reduce noise is acoustic metamaterial, and most of the research projects so far have been limited to the case of static media without flow. We have studied the sound transmission properties of the acoustic metamaterials with turbulent flow to develop the acoustic metamaterials that are used in transportation. In this paper, the effects of geometrical structure, convection, and eddy on sound propagation in the acoustic metamaterials with turbulent flow are investigated, and the relationships between them are analysed. The effects of convection and eddy reduce the resonant strength of the sound transmission loss resulting from the unique geometry of the acoustic metamaterials, but move the resonant frequencies to opposite directions. In addition, when the convective effect and the eddy effect of the airflow, as well as the intrinsic interaction effect generated from the unique geometrical structure of the acoustic metamaterials cannot be ignored, they exhibit competition phenomena with each other, resulting in a widening of the resonance peak. As a result, these three effects cause the shift of the resonance frequency of the sound transmission loss and the widening of the resonance peak. The results of this study show that even in the case of turbulent flow, the metamaterials can be used for transportation by properly controlling its geometric size and shape.

8

Numerical study of the thermal and hydraulic performances of heat sink made of wavy fins

Bouchenafa R., Mohammed Hussein A., Saim R.

Mechanics and Mechanical Engineering

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2019

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Vol. 23, nr 1

150--161

EN

The aim of this paper is to numerically investigate the thermal and hydraulic performances of the two heat sinks made ofwavy fins (WFHS). The governing equations fitted with boundary conditions were solved using the finite volume method, and the SIMPLE algorithm for the coupling velocity-pressure. The two-equation model k-ϵ was used to describe the turbulence phenomenon. The effects of wave numbers and the amplitude of wavy fins heat sink on the thermal and flow fields are studied and compared with the plate fin heat sink (PFHS). The results show that the use of wavy fins improves significantly the heat transfer rate, accompanied by a pressure drop penalty.

9

Experimental Studies on the Spatial Structure and Distribution of Flow Velocities in Bolt Fishways

Puzdrowska Marta, Heese Tomasz

Journal of Ecological Engineering

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2019

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Vol. 20, nr 11

82--99

EN

One of more important elements affecting the efficiency of fish passes is a 3D spatial structure of the flow and the flow velocity. The paper presents an analysis pertaining to the deformations of these elements caused by the modification of the fishway’s partition geometry. It has a crucial meaning for the ability of fish to migrate through the fish pass. The research has a key practical significance as it proves the way the apparent modification of the partition geometry affects the hydraulic conditions within the entire the channel of the fishway. It may have very serious consequences for the design assumptions. The presented results of the experimental research were obtained as a consequence of the site and laboratory tests carried outusing a physical model. The measurements were performedfor 3 components of flow’s instantaneous speed within the indicated measurement sections. The results were developed using Matlab software. It was established that the number of whirls produced in the fishway’s pool depends on the quantity of spillway slots and – what seems to have the greatest impact on the flow structure – on the location of slots. The size of whirls is determined by the geometry of spillway slots. The presence of additional spillway slots in the pool, except for the huge main migration slot, contributes to the generation of more whirl structures within the recirculation zone. The more whirls produced in each of the whirl zones, the smaller their diameter. Thisshould create more favourable conditions for the fish migration.

10

Numerical analysis of turbulent flow around twodimensional bodies using non-orthogonal body-fitted mesh

Tarafder M. Shahjada, Mursaline M. Al

International Journal of Applied Mechanics and Engineering

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2019

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Vol. 24, no. 2

387--410

EN

This paper deals with the numerical simulation of a turbulent flow around two-dimensional bodies by the finite volume method with non-orthogonal body-fitted grid. The governing equations are expressed in Cartesian velocity components and solution is carried out using the SIMPLE algorithm for collocated arrangement of scalar and vector variables. Turbulence is modeled by the turbulence model and wall functions are used to bridge the solution variables at the near wall cells and the corresponding quantities on the wall. A simplified pressure correction equation is derived and proper under-relaxation factors are used so that computational cost is reduced without adversely affecting the convergence rate. The numerical procedure is validated by comparing the computed pressure distribution on the surface of NACA 0012 and NACA 4412 hydrofoils for different angles of attack with experimental data. The grid dependency of the solution is studied by varying the number of cells of the C-type structured mesh. The computed lift coefficients of NACA 4412 hydrofoil at different angles of attack are also compared with experimental results to further substantiate the validity of the proposed methodology.

11

Large Eddy Simulation of turbulent flowand heat transfer in a Kenics static mixer

Murasiewicz Halina, Zakrzewska Barbara

Chemical and Process Engineering

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2019

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Vol. 40, nr 1

87–-99

EN

CFD modelling of momentum and heat transfer using the Large Eddy Simulation (LES) approach hasbeen presented for a Kenics static mixer. The simulations were performed with the commercial codeANSYS Fluent 15 for turbulent flow of three values of Reynoldsnumber,Re=5 000, 10 000 and18 000. The numerical modelling began in the RANS model, where standardk−εturbulence modeland wall functions were used. Then the LES iterations started from the initial velocity and temperaturefields obtained in RANS. In LES, the Smagorinsky–Lilly modelwas used for the sub-grid scalefluctuations along with wall functions for prediction of flowand heat transfer in the near-wall region.The performed numerical study in a Kenics static mixer resulted in highly fluctuating fields of bothvelocity and temperature. Simulation results were presented and analysed in the form of velocity andtemperature contours. In addition, the surface-averaged heat transfer coefficient values for the wholeinsert length were computed and compared with the literature experimental data. Good compliance ofthe LES simulation results with the experimental correlation was obtained.

12

Simulation and analysis of a turbulent flow around a three-dimensional obstacle

Benahmed Lamia, Aliane Khaled

Acta Mechanica et Automatica

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2019

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Vol. 13, no. 3

173--180

EN

The study of flow around obstacles is devised into three different positions: above the obstacle, upstream of the obstacle, and downstream of the latter. The behaviour of the fluid downstream of the obstacle is less known, and the physical and numerical modelling is being given the existence of recirculation zones with their complex behaviour. The purpose of the work presented below is to study the influence of the inclined form of the two upper peaks of a rectangular cube. A three-dimensional study was carried out using the ANSYS CFX calculation code. Turbulence models have been used to study the flow characteristics around the inclined obstacle. The timeaveraged results of contours of velocity vectors , cross-stream and stream wise velocity and streamlines were obtained by using K-ω shear -stress transport (SST), RANG K-ε and K-ε to model the turbulence, and the governing equations were solved using the finite volume method. The turbulence model K-ω SST has presented the best prediction of the flow characteristics for the obstacle among the investigated turbulence models in this work.

13

3D Simulation of Chlorine Dispersion in Rrural Area

Polanczyk A., Salamonowicz Z., Majder-Lopatka M., Dmochowska A., Jarosz W., Matuszkiewicz R., Makowski R.

Rocznik Ochrona Środowiska

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2018

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Tom 20, cz. 2

1035--1048

EN

Prediction of hazardous substances dispersion resulting from accidental leakage in environment is essential for risk analysis and emergency response. Different numerical tools are applied for description of dispersion process. Development of numerical algorithms has enabled the computational fluid dynamics (CFD) models to be used extensively in indoor dispersion studies. Numerical methods based on computational fluid dynamics (CFD) may facilitate the precise investigation of the hazardous substances dispersion. Therefore, the aim of the study was to prepare a transient CFD model describing the phenomena of chlorine dispersion in a dynamic setup including different environmental factors. Reliable computational description of dispersion process still represents one of the most challenging applications. Therefore, we aimed to prepare a transient 2D and 3D numerical models of chlorine dispersion from a ground source in a dynamic setup. For 2D simulation a Degadis model was used, while for 3D approach a multiphase Volume of Fluid model (VOF) was applied. For both analyzed cases area of investigation was equal to 0.1 km2. Furthermore, for 3D simulations height was equal to 50 m. For the reconstruction of atmospheric conditions Pasquill stability classes and one-direction wind were applied. Analysis of chlorine concentration in function of wind intensity indicated extension of chlorine cloud with decrease of concentration. Moreover, comparison of constant and dynamic setup indicated high impact of wind. In case of windless conditions circular profile of chlorine concentration around dispersion source was noticed. Wind directed the chloride cloud which dispersed accordingly to the wind direction. As expected chloride concentration decreased with altitude. 2D model allowed prediction of polluted cloud in horizontal direction, while 3D model allowed description of horizontal and vertical distribution of chlorine. It was observed that with increase of Pasquill stability class the area of chlorine dispersion had similar character for horizontal model as well as for horizontal and vertical model (3D). For the windless case circular profile of chlorine concentration around dispersion source was observed. Additionally, for the wind application the main chlorine concentration moved ahead the source of dispersion. Analysis of chlorine concentration in function of height resulted in decrease of chlorine appearance in upper level of mathematical domain.

PL

Predykcja dyspersji substancji niebezpiecznych z przypadkowych wycieków jest niezbędna w analizie ryzyka. W tym celu do opisu procesu dyspersji stosowane są różne numeryczne narzędzia. Rozwój matematycznych algorytmów umożliwia stosowanie m.in. techniki CFD na szeroką skalę. Tym samym celem niniejszej pracy było opracowanie dwuwymiarowego i trójwymiarowego modelu opisującego zjawisko dyspersji chloru z naziemnego źródła. Dla dwuwymiarowego podejścia zastosowano model Degadisa. Natomiast dla trójwymiarowego podejścia wielofazowy model VOF. Dla obu przypadków powierzchnia analizowanego obszaru wynosiła 0.1 km2. Co więcej, dla trójwymiarowego podejścia wysokość analizowanej domeny obliczeniowej wynosiła 50 m. W celu rekonstrukcji parametrów atmosferycznych uwzględniono klasy stabilności Pasquilla oraz wpływ wiatru. Dwuwymiarowy model umożliwiał analizę procesu dyspersji w płaszczyźnie poziomej, podczas gdy model trójwymiarowy umożliwiał analizę zarówno w płaszczyźnie poziomej jak i pionowej. Analiza obu modeli wskazuje, iż wzrost intensywności wiatru wydłuża zasięg chmury chloru, z jednoczesnym spadkiem jego stężenia. Co więcej, w przypadku nieuwzględnienia przepływu wiatru obserwowano kołowy profil stężenia chloru dookoła źródła dyspersji. Natomiast przepływający wiatr powodował zmniejszenie koncentracji chloru wraz z wysokością. Również zaobserwowano, iż uwzględnienie klas stabilności Pasquilla miało porównywalny efekt w przypadku podejścia dwuwymiarowego i trójwymiarowego. Uwzględnienie wiatru powodowało przemieszczenie maksymalnej wartości stężenia chloru znad źródła dyspersji. Co więcej, analiza stężenia chloru w funkcji wysokości wskazuje na zmniejszenie zawartości chloru w górnej części domeny matematycznej.

14

Modele numeryczne turbulencji – źródła i dostosowanie do specyfiki aerologii górniczej

Krawczyk J., Janus J., Głuch B., Skotniczny P., Ostrogórski P.

Prace Instytutu Mechaniki Górotworu PAN

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2018

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T. 20, nr 4

355--362

PL

W artykule omówiono temat modelowania zjawisk turbulentnych w kopalniach podziemnych. Kopalnie podziemne ze względu na technologię wydobycia posiadają skomplikowaną sieć wentylacyjną. Dotychczas stosowane w wentylacji przemysłowej i nie tylko półempiryczne modele turbulencji posiadają stałe, które zostały określone w wyniku badań podstawowych dla geometrii odbiegających od tych spotykanych w górnictwie. Zastosowanie tego typu modeli umożliwia poszukiwanie rozwiązań dla wielu zagadnień, jednak kosztem konieczności sprawdzenia, czy dany model jest w stanie wystarczająco dobrze opisywać wybrane zagadnienia. Dla wentylacji kopalń podziemnych tego typu walidacje przeprowadzono w bardzo ograniczonym zakresie i nie wystarczają one do pełnej reprezentacji zjawisk występujących w wyrobiskach kopalnianych. W związku z tym pojawiła się potrzeba uaktualnienia lub rozszerzenia istniejących wartości stałych stosowanych w modelach numerycznych odpowiednich do geometrii wyrobisk górniczych. W artykule przeprowadzono przegląd dotychczas stosowanej metodyki określania stałych w wybranych modelach turbulencji na podstawie wyników badań eksperymentalnych typowych zagadnień przepływowych. Określono zarys analogicznego programu badań w zakresie wybranych zagadnień przepływowych charakterystycznych dla wentylacji kopalń.

EN

Paper presents discusses about turbulent phenomena modelling in underground mining which, due to the mining technology, has complicated ventilation network. So far, in industrial ventilation semi-empirical turbulence models have been used. These models use constants, which were determined as a result of basic research on geometries of shapes, which in most cases are different from the shapes of workings of underground mines. The use of this type of models helps in searching solutions for many problems, but results of numerical calculations should be checked if the given model is able to describe to selected issues well enough. For underground mine ventilation systems, the validations have been carried out to a very limited extent and they are not sufficient to fully represent phenomena occurring in mine drifts. Therefore, it is necessary to update or extend the existing constants values used in turbulence models to customize them to specific conditions of trhe flow in the workings of underground mines. Paper conatins a review of used methodology for determining constants in selected turbulence models based on results of typical flow problems investigations and an outline of planned studies.

15

Numerical investigation of the turbulent flow generated with a radial Turbine using a converging hollow blade

Beloudane M., Bouzit M., Ameur H.

Polish Journal of Chemical Technology

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2018

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Vol. 20, nr 4

129--137

EN

The aim of this study is to investigate the effect of the blade shape on the characteristic of the flow patterns in a stirred tank. A new impeller blade design has been proposed. It is characterized by a converging hollow. The investigations of the flow structure generated in the vessel are made by using the computer code ANSYS CFX (version 16.0). The analysis has shown that the converging hollow blade yields highly radial flows which gave an increase in the radial velocity by 35% with less power consumption than the flat blade. Also, the effectiveness of the energy dissipation and the quality of mixing has been obviously noted. A validation test of our predicted results with other literature data was done, and a satisfactory agreement has been found.

16

Prędkość krytyczna przejścia ruchu laminarnego w turbulentny na przykładzie przepływu mieszaniny węglowo-wodnej w rurociągach

Luo R., Xia J., Sobota J.

Ochrona Środowiska

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2018

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Vol. 40, nr 1

51--55

PL

Transport hydrauliczny rurociągami należy do najbardziej niezawodnych i ekonomicznie uzasadnionych rodzajów transportu. Z uwagi na jego walory ekologiczne i estetyczne, jest także preferowanym rozwiązaniem w inżynierii środowiska. Przesyłanie rurociągami mieszanin zawierających znaczne ilości zawiesin wymaga określenia ich właściwości reologicznych, na podstawie których można przyjąć odpowiedni model reologiczny. Wyznaczony na podstawie badań model reologiczny pozwala z kolei na poprawne obliczenie strat hydraulicznych podczas przepływu danej mieszaniny w instalacji przemysłowej. Jednym z istotnych problemów występujących podczas przepływu mieszanin w rurociągach jest ustalenie momentu przejścia ruchu laminarnego w turbulentny, bowiem transport odbywający się w zakresie tego ruchu charakteryzuje się znacząco większym zapotrzebowaniem na energię. W pracy przedstawiono rezultaty badań przepływu mieszaniny węglowo-wodnej (pył węgla kamiennego z wodą) o stężeniu objętościowym 43÷53% i gęstości 1 176÷1 217 kg/m3 w rurociągach o średnicy 21÷47 mm. Badana mieszanina miała cechy reologiczne, które opisuje dwuparametrowy model Binghama. Rezultaty badań eksperymentalnych były następnie podstawą do analizy zachowania się mieszaniny w czasie przejścia z ruchu laminarnego do turbulentnego w rurociągach o średnicach 21 mm i 29 mm podczas przepływu mieszaniny węglowo-wodnej o stężeniu objętościowym wynoszącym 43%. W tym celu przeprowadzono analizę porównawcza kilku metod określenia prędkości krytycznej przejścia ruchu laminarnego w turbulentny, przy czym do określenia wartości prędkości krytycznej zaproponowano wykorzystanie różnych definicji liczby Reynolsdsa. Na tej podstawie obliczono wartości prędkości krytycznej ze wzorów różnych autorów oraz przy założeniu, że strefa przejściowa pomiędzy przepływem laminarnym i turbulentnym zawarta jest w przedziale wartości liczby Reynoldsa od 2000 do 4000.

EN

Pipeline hydrotransport belongs to the most reliable and economically justified modes of transport. Due to its ecological and aesthetic values, it is also the preferred solution in environmental engineering. Transport of mixtures with significant amounts of suspensions requires determination of their rheological properties to adopt an appropriate rheological model. The rheological model determined on the basis of research allows then for the correct calculation of hydraulic losses during the flow of a given mixture through industrial installation. One of the major challenges regarding the flow of mixtures through pipelines is determination of transition point at which laminar traffic changes into turbulent, because transport under turbulent flow is characterized by significantly higher energy demand. The flow study results for the coal-water mixture (bituminous coal dust) with volume concentration of 43–53% and 1 176–1 217 kg/m3 density in the pipelines of 21–47 mm diameter were presented. The rheological features of the mixture under testing were described by the Bingham two-parameter model. Results of the experiments were the basis for analyzing the behavior of the coal-water mixture with 43% volume concentration in 21 and 29 mm pipelines during transition from laminar to turbulent flow. For this purpose, a comparative analysis of several methods for determining critical velocity of the laminar-turbulent transition was carried out. In order to determine the critical velocity value, application of various definitions of Reynolds number was proposed. On this basis, the critical velocity value was calculated from the formulas by different authors and with the assumption that transition zone between laminar and turbulent flow was in the range of Reynolds number from Re = 2000 to Re = 4000.

17

Numerical modelling of combustion process with the use of ANSYS FLUENT code

Kowalski M., Jankowski M.

Journal of KONES

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2018

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Vol. 25, No. 4

175--186

EN

The article presents the modelling of the combustion process of liquid fuels using professional ANSYS FLUENT software. This program allows modelling the dynamics of compressible and incompressible, laminar and turbulent flows as well as heat exchange phenomena with occurrence and without chemical reactions. The model presented in the article takes into account the influence of the gas phase on the liquid phase during the fuel combustion process. The influence of velocity and pressure of the flowing gas and the type of flow has a significant impact on the combustion of liquid fuels. The developed model is fully reliable and the presented results are consistent with experimental research. The occurrence of a laminar sublayer in a turbulent flow was confirmed, and the thickness of this layer and the turbulent layer significantly influences the course of the combustion process. The use of the flat flow model reflects the basic phenomena occurring during the combustion of liquid fuels under turbulent conditions. The use of the program for flows with different flow velocity profiles is justified. It gives important information about the processes taking place during the combustion of liquid fuels. The results of numerical tests are presented graphically. The article presents graphs of velocity field, absolute pressure, power lines, temperature and density.

18

Analiza metrologiczna zastosowania przepływomierza ultradźwiękowego w niestandardowych warunkach wykonywania pomiarów za przepustnicą

Piechota P., Synowiec P., Andruszkiewicz A., Wędrychowicz W., Tajchman K.

Elektronika : konstrukcje, technologie, zastosowania

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2018

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Vol. 59, nr 10

44--47

PL

Artykuł dotyczy ultradźwiękowej metody pomiaru przepływu cieczy. Metoda ta w ostatnich latach zyskała dużą popularność z uwagi dużą dokładność pomiarów oraz bezinwazyjność. Problemem w zastosowaniu tej metody często jest brak możliwości zachowania wymaganych w normach odcinków prostych rurociągu – zwłaszcza wtedy, gdy pomiary wykonywane są na rurociągach o dużych średnicach. Wykonane pomiary mają na celu określić jakiego rzędu błędy pomiarowe będzie generowało zainstalowanie przepływomierza ultradźwiękowego za przeszkodą bez zachowania wymaganych w normach odległości. Otrzymane wyniki badań wykonywanych za przeszkodą w postaci przepustnicy pozwoliły wyciągnąć wnioski dotyczące wpływu odległości miejsca pomiarowego od przeszkody na dokładność otrzymanych wyników.

EN

The article concerns the ultrasonic method of measuring the flow of liquids. This method in recent years has gained great popularity due to the high accuracy of measurements and non-invasive. The problem in using this method is often the lack of the possibility of maintaining the required straight sections of the pipeline – especially when measurements are made on pipelines with large diameters. The measurements were to answer the question of whether you can perform flow measurements in non-standard measurement conditions (without observing the distance required in the standards)? Obtained results of tests performed behind an obstacle in the form of a throttle allowed to draw conclusions regarding the influence of the distance of the measuring place from the obstacle on the accuracy of the obtained results.

19

Numerical study of an air plane solar collector with the baffle in zigzag form

Guendouz N., Bibi-Triki N., Didi F., Zidani C.

Archives of Thermodynamics

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2018

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Vol. 39, no 4

141–-156

EN

The production of thermal energy from solar energy by flat collectors finds nowadays many applications due to their innumerable economic and environmental interests. Currently, conservation of energy resources has become a global priority. On the other hand, given the dizzying demand for energy, has led specialists to find new techniques, such as renewable energies (solar, wind and geothermal). The present work is a contribution, by numerical simulation, to the study of heat transfer in flat solar collectors. On the basis of some experimental data, several simulation calculations have been carried out in order to determine the influencing parameters allowing better performance of the sensors and ensuring a good homogeneity of the temperature distributions. Based on the observation that, due to the low thermophysical properties of the air used as heat transfer fluid, solar air collectors rather give poor yields. It has been found very useful to have ‘baffling’ obstacles of various shapes and forms in the solar collector duct. This increases the thermal transfer of a coolant, which clearly improves the thermal efficiency of the solar air collector. This article consists mainly of studying the effects on heat transfer of turbulent forced convection by baffles of zigzag shapes, placed in a rectangular channel, using the finite volume method. The pressure-velocity coupling has been processed by the SIMPLEC algorithm. The results are presented in terms of the average Nusselt number and temperature field for different positions.

20

A Numerical Study of Non-hydrostatic Shallow Flows in Open Channels

Zerihun Y. T.

Archives of Hydro-Engineering and Environmental Mechanics

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2017

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Vol. 64, nr 1

17--35

EN

The flow field of many practical open channel flow problems, e.g. flow over natural bed forms or hydraulic structures, is characterised by curved streamlines that result in a non-hydrostatic pressure distribution. The essential vertical details of such a flow field need to be accounted for, so as to be able to treat the complex transition between hydrostatic and non-hydrostatic flow regimes. Apparently, the shallow-water equations, which assume a mild longitudinal slope and negligible vertical acceleration, are inappropriate to analyse these types of problems. Besides, most of the current Boussinesq-type models do not consider the effects of turbulence. A novel approach, stemming from the vertical integration of the Reynolds-averaged Navier-Stokes equations, is applied herein to develop a non-hydrostatic model which includes terms accounting for the effective stresses arising from the turbulent characteristics of the flow. The feasibility of the proposed model is examined by simulating flow situations that involve non-hydrostatic pressure and/or nonuniform velocity distributions. The computational results for free-surface and bed pressure profiles exhibit good correlations with experimental data, demonstrating that the present model is capable of simulating the salient features of free-surface flows over sharply-curved overflow structures and rigid-bed dunes.