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1

Mesh suitability for CFD simulations performed on axial compressor airfoil cascades

Tater Adam, Mačák Pavel, Kovář Patrik

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2024

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Vol. 72, nr 2

art. no. e148873

EN

In the presented paper, two different meshing strategies are compared to show the accuracy advantage of properly constructed mesh. For this purpose, it was necessary to automatize simulation process, in order to perform a number of calculations without the necessity of user interaction. Later, a method of results extrapolation as well as a way of judging mesh quality are introduced for more throughout comparison of presented discretization strategies. The latter method, called grid convergence index, is also used to calculate probability range of accurate result. To conclude, outcomes of this study are in agreement with general opinon on pracitces for an accurate CFD result. Structured O-type mesh with refinement at wall boundaries (often referred to as “inflation layers”) performs better than simple free mesh.

2

On the prediction of the effect of bi-ventricular assistance after cardiac explantation on the vascular flow physiology: A numerical study

Marcel Louis, Specklin Mathieu, Kouidri Smaine, Lescroart Mickael, Hébert Jean-Louis

Biocybernetics and Biomedical Engineering

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2024

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Vol. 44, no. 1

105--118

EN

Heart failure is a chronic and progressive condition characterized by the heart’s inability to pump sufficient blood to meet the body’s metabolic demands. It is a significant public health concern worldwide, associated with high morbidity, mortality, and healthcare costs. For advanced heart failure cases not responding to medical therapy, heart transplantation or mechanical circulatory support with ventricular assist devices (VADs) can be considered. In the specific case of bi-ventricular heart failure a replacement of both ventricles is required. In this context a Total Artificial Heart (TAH) may be proposed as a bridge to transplant solution. Additionally, bi-ventricular assist devices (BiVADs) are available to support both ventricles simultaneously. However Bi-ventricular heart failure management is difficult with poor outcomes. New surgical procedures appear to propose solutions after both ventricle failure. One of these intervention uses two continuous-flow VADs as a total artificial heart after cardiac explantation due to myocardial sarcoma. Unfortunately, this procedure makes patient management very difficult as pulmonary pressures and flow rate are no longer measurable after the surgical procedure. The setting of both pumps is hence a complex task for patient management. This article aims at helping clinicians on patient management undergoing double assistance after cardiac explantation by predicting the different outcomes on the vascular grid for all the possible rotational speed combination using a lumped model. Results provide a range of both pump operating conditions suitable for delivering a physiologically adapted flow to the vascular grid when combined with hypotensive treatments.

3

Evaluation of wind effects on buildings using design codes and numerical wind tunnel tests

Hossain Imam, Islam Jahidul, Amin Al

Structure and Environment

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2023

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Vol. 15, no. 2

73--81

EN

The evaluation of wind effect on the regular shape and simple diaphragm buildings and structures due to wind load has been calculated by several international codes and standards where wind gust nature and dynamic effect could not capture. Bangladesh National Building Code (BNBC) provides the tools for engineers to calculate the wind pressures for the design of a regular-shaped structure with a height to width ratio of less than 5.0, a simple diaphragm, and no unusual geometrical irregularity. If these conditions do not satisfy a wind tunnel testing is required. In this study, a comparative study between two codes in Bangladesh (BNBC-2006 and BNBC-2020), and wind tunnel test results are conducted. An investigation is carried out on four typical buildings with variable heights located within Dhaka, Bangladesh. A computational fluid dynamics (CFD) program RWIND is used to calculate the wind loads on buildings and are compared with those obtained by Bangladesh National Building Codes. Storey shear of four different building models is compared. Between BNBC-2006 and BNBC-2020, there is up to a 53% difference in storey shear. Whereas, up to 30% variation in storey shear is observed between the numerical wind tunnel test data and the data calculated using the BNBC-2020 equations. Finally, this study will help in improving BNBC code provisions for wind load calculations.

PL

Kalkulację wpływu wiatru na budynki i budowle o regularnych kształtach i prostych konstrukcjach pod obciążeniem wiatrem przedstawiono w kilku normach międzynarodowych, w których jednak nie uwzględniono charakteru podmuchów wiatru i efektu dynamicznego. Bangladeska Krajowa Norma Budowlana (BNBC) zapewnia inżynierom narzędzia do obliczania ciśnienia wiatru przy projektowaniu konstrukcji o regularnym kształcie, o stosunku wysokości do szerokości mniejszym niż 5,0, prostej konstrukcji oraz bez nietypowych nieregularności geometrycznych. Jeśli warunki te nie są spełnione, wymagane jest przeprowadzenie testów w tunelu aerodynamicznym. W niniejszym opracowaniu przeprowadzono badanie porównawcze między dwiema normami obowiązującymi w Bangladeszu (BNBC-2006 i BNBC-2020) oraz wynikami testów w tunelu aerodynamicznym. Badanie przeprowadzono na czterech typowych budynkach o różnej wysokości zlokalizowanych w Dhace w Bangladeszu. Program RWIND do obliczeń i symulacji dynamiki płynów (CFD) został wykorzystany do obliczenia obciążeń wiatrem na budynkach i porównany z wynikami uzyskanymi według bangladeskich norm budowlanych. Porównano ścinanie kondygnacji czterech różnych modeli budynków. W tym względzie różnice pomiędzy BNBC-2006 i BNBC-2020 wynoszą do 53%. Natomiast między danymi z numerycznego testu w tunelu aerodynamicznym a danymi obliczonymi przy użyciu równań BNBC-2020 zaobserwowano do 30% różnic w odniesieniu do ścinania kondygnacji. Badanie to pomoże też ulepszyć przepisy norm BNBC dotyczące obliczeń obciążenia wiatrem.

4

CFD and experimental investigation of the impact of dimensional modifications on wind pressure coefficient distribution

Ali Ramjan, Anam Iftekhar, Yoshida Shigeo

Structure and Environment

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2023

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Vol. 15, no. 4

208--216

EN

The sway of tall buildings in the wind is a fascinating and crucial consideration for professionals in the structural, environmental, and architectural fields. Previous research has related wind pressure to building load and natural ventilation, but few studies have looked at how building dimensions impact wind pressure. This study examined wind pressure coefficient distributions within and around several rectangular-shaped high-rise buildings using experimental and computational fluid dynamics approaches. The height-to-width ratio and height-to-thickness (length) ratio significantly affected the wind characteristics of buildings. The windward side with a narrower width experienced higher wind pressure, while the larger leeward side experienced a more negative wind effect. Wind pressure coefficient distribution varies with decrease in the side ratio. However, the side ratio of the building had little influence on positive wind pressure at wind incidence angle of 0°, which was a surprising finding. Pressure coefficients were evaluated and compared with standards by measuring fluctuating wind pressures at pressure points on all surfaces of models, and then calculating the mean, maximum, minimum, and r.m.s. values of these coefficients.

PL

Kołysanie się wysokich budynków pod wpływem wiatru jest fascynującym i kluczowym zagadnieniem dla specjalistów w dziedzinie konstrukcji, ochrony środowiska i architektury. W niniejszym artykule zbadano rozkłady współczynnika parcia wiatru wewnątrz i wokół kilku budynków wysokich o kształcie prostokąta, stosując metody eksperymentalne i numeryczne (obliczeniowa dynamika płynów). Stosunek wysokości budynku do jego szerokości oraz stosunek wysokości budynku do jego grubości (długości) miały znaczący wpływ na charakterystykę oddziaływania wiatru. Większe ciśnienie wiatru odnotowano po stronie nawietrznej o mniejszej szerokości, podczas gdy na większej ścianie od strony zawietrznej oddziaływanie wiatru było bardziej negatywne. Rozkład współczynnika parcia wiatru zmienia się wraz ze spadkiem stosunku boków. Jednak stosunek ten miał niewielki wpływ na dodatnie ciśnienie wiatru przy kierunku wiatru 0°, co było zaskakującym odkryciem. Współczynniki ciśnienia zostały ocenione i porównane z podejściem normowym poprzez pomiar zmiennego ciśnienia wiatru w punktach parcia na wszystkich powierzchniach modeli, a następnie obliczenie średnich, maksymalnych, minimalnych i średnich kwadratowych wartości tych współczynników.

5

Preliminary analysis of catenoid chimney cooling towers

Wiśniowski Maciej, Walentyński Robert, Cornik Dawid

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2023

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Vol. 71, nr 6

art. no. e147341

EN

Optimization plays an important role in scientific and engineering research. This paper presents the effects of using the catenoidal shape to design the structure of a chimney cooling tower. The paper compares some geometrical variations of the catenoid with the reference existing hyperboloidal structure. It also compares internal forces, deformation and stability of the catenoidal structure. The comparison shows some predominance of the catenoid over the popular hyperboloid structure of the shell. The paper attempts to find an optimal shape of the cooling tower in order to reduce the amount of material and labor. The paper utilizes engineering tools and the designing process for chimney cooling towers.

6

Experimental and numerical analyses of airflow around two cylinders angled to the direction of wind

Padewska-Jurczak Agnieszka, Szczepaniak Piotr, Walentyński Ryszard

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2023

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Vol. 71, nr 1

art. no. e144578

EN

The analyses aim to determine aerodynamic force coefficients in the case of airflow around two smooth or rough cylinders positioned at different angles to the direction of wind velocity. Such systems, for instance, may be part of a tubular water slide. The results were compared with the values of the interference coefficient of the cylinders arranged in a row included in Eurocode EN 1991 part 4. The aerodynamic forces of the cylinder systems were determined on the basis of experimental tests conducted in a wind tunnel. To verify the above results, CFD (computational fluid dynamics) simulations were prepared. An important observation is that for the angle of yaw β = 0◦, the negative component of the lift force (lateral) fy is shown, while for the other cases, the situation is opposite and the lateral force points outside the gap (upward). The second is that the results of aerodynamic drag for rough cylinders arranged in a row and calculated according to EN 1991 part 4 may be underestimated. The flow around the pair of smooth cylinders is quite different from that of the rough ones, because during the experiment the first falls into the critical flow regime, while the second has supercritical characteristics.

7

Influence of the position of the distal pressure measurement point on the Fractional Flow Reserve using in-silico simulations

Agujetas Rafael, Ferrera Conrado, González-Fernández Reyes, Nogales-Asensio Juan M., Fernández-Tena Ana

Biocybernetics and Biomedical Engineering

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2023

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Vol. 43, no. 1

69--81

EN

Coronary stenosis is mainly responsible for myocardial ischemia as the blood supply to a portion of the heart stops or is severely reduced. The Fractional Flow Reserve is the benchmark for the hemodynamic significance assessment of coronary stenoses. Its value is employed as a gatekeeper/planning tool for revascularization in clinical practice. Non-invasive alternatives have been successfully proposed to guide cardiologists. However, simulation values are not accurate enough in the 0.75-0.85 range, so invasive Fractional Flow Reserve should be used. Several authors argue about where distal pressure should be measured. Therefore, our aim is to use simulation to assess how this value changes and to detect the correct measurement region. First, we have adjusted the simulation method to the segmentations of two patients whose invasive Fractional Flow Reserve is known. We then extended our analysis to four patients and obtained the simulated value at multiple points distal to the stenosis. This is an advantage over invasive measurements, whose locations are restricted. The results are also essential for locating the best region for invasive distal pressure measurements. We propose a hybrid invasive and in-silico procedure that would avoid false results and prevent cardiologists from making erroneous clinical decisions.

8

Prediction of cavitation inside mini-sac Diesel injector nozzle using computational fluid dynamics

Bansode Vaibhav, Verma Munna, Pandhare Amar, Shinde Sandip

Journal of Mechanical and Energy Engineering

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2022

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Vol. 6, No 1

7--12

EN

The performance of the internal flow of the fuel injector is impeded by several factors. The nozzle is one of the factors, being typically about a millimeter long and a fraction of a millimeter in diameter. Cavitation inside the diesel injector nozzle is associated with local pressure distribution. At flow areas with sharp corners, the pressure may locally drop below vapour pressure. The aim of this study is to assess the impact of turbulence and cavitation models on the prediction of flow in diesel injection nozzle. In the present study, an analysis of an existing 6 hole mini-sac diesel injector nozzle is carried out using a CFD package. The main objective of the research is to design a nozzle to avoid cavitation and to find out the contribution of different parameters through parametric study. Cavitation is a complex phenomenon whose appearance depends on the physical as well as flow properties of the flowing substance. Thus, for a better visualization of cavitation, a 3D CFD simulation of mini-sac injector nozzle is carried out. An analysis of a single nozzle hole of a mini-sac diesel injector nozzle is considered for the analysis, as the flow is uniformly distributed through each nozzle. As the three-dimensional geometry of mini-sac nozzle is complicated, therefore tet/hybrid element with T-Grid meshing scheme is used, for good surface meshing. The analysis is carried out at injection pressure of 5 00 bar. The CFDresults are validated against test data with the maximum deviation for the mass flow rate of 8.67% at full needle lift.

9

Modeling of the microclimate in the work environment with the use of numerical methods

Kosiń Mariusz

Budownictwo o Zoptymalizowanym Potencjale Energetycznym

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2022

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Vol. 11

57--63

EN

The article presents modeling of the work environment microclimate using numerical methods. The numerical models adopted for the calculations were based on an office located in the building of the Faculty of Civil Engineering of the Czestochowa University of Technology. Six computational variations were made that differed in the heating method, air supply and ventilation. The results of the numerical analysis for one of the models were compared with the test in the assumed measuring point recording temperature and relative humidity. The per-formed numerical analysis allows for a relatively quick assessment of the influence of the adopted boundary conditions on the formation of the microclimate in the work environment.

10

Influence of cavity edges shape on flow induced noise

Łojek Paweł, Suder-Dębska Katarzyna, Mach Michał

Vibrations in Physical Systems

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2021

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Vol. 32, nr 1

art. no. 2021110

EN

In this paper, impact of the cavity shape on flow-generated noise is analysed. As reference model, the classic rectangular cavity with perpendicular corners was used. The impact of both upstream and downstream edges was analyzed. In this paper, authors used hybrid method, where the flow was computed by means of Spalart-Allmaras Detached Eddy Simulations (DES) model, and the acoustic wave propagation was calculated by Curle acoustic analogy.

11

Using metamodeling and fluid-structure interaction analysis in multi-objective optimization of a butterfly valve

Pałys Laura, Mrzygłód Mirosław W.

Computer Assisted Methods in Engineering and Science

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2021

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Vol. 28, no. 1

17--38

EN

Along with the increase in computing power, new possibilities for the use of parametriccoupled analysis of fluid flow machines and metamodeling for many branches of industryand medicine have appeared. In this paper, the use of a new methodology for multi-objective optimization of a butterfly valve with the application of the fluid-structure interaction metamodel is presented. The optimization objective functions were to increasethe value of the KV valve’s flow coefficient while reducing the disk mass. Moreover, theequivalent von Mises stress was accepted as an additional constraint. The centred composite designs were used to plan the measuring point. Full second-order polynomials, non-parametric regression, Kriging metamodeling techniques were implemented. The optimization process was carried out using the multi-objectives genetic algorithm. For eachmetamodel, one of the optimization candidates was selected to verify its results. The besteffect was obtained using the Kriging method. Optimization allowed to improve the KVvalue by 37.6%. The metamodeling process allows for the coupled analysis of the fluidflow machines in a shorter time, although its main application is geometry optimization.

12

Computational fluid dynamics and experimental hydrodynamic analysis of a solar AUV

Asadi Asrami Ehsan, Moonesun Mohammad, Azizi Abi Farhad

Computer Assisted Methods in Engineering and Science

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2021

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Vol. 28, no. 1

57--77

EN

In the present study, the effect of free surface on the hydrodynamic forces acting on themotion of an autonomous underwater vehicle (AUV) has been investigated. The AUVis powered by solar energy. Using computational fluid dynamics, the Reynolds averaged Navier Stokes (RANS) equations for the flow around the AUV are solved, and the freesurface effect is simulated using the volume of fluid (VOF) two-phase flow model. Forthis purpose, the commercial code ANSYS FLUENT 18 was used [1]. The results ofthe numerical solution are compared with experimental results of the AUV model in thesurface motion in the towing tank of the Persian Gulf National Laboratory with a scaleof 1:1. The experiment was performed in a fixed draft and the velocity was ranging from 0.2 m/s to 1.4 m/s (according to Reynolds number 2.4 x 105 to 1.7 x 106).

13

Badania numeryczne przepływu wewnętrznego w różnych typach filtrów

Stanik Magdalena, Caban Szymon, Klonecka Marlena, Buczak Mateusz, Wiśniewski Piotr

Chłodnictwo : organ Naczelnej Organizacji Technicznej

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2021

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R. 56, nr 5

17--22

PL

Jakość otaczającego nas powietrza staje się obiektem powszechnego zainteresowania. W ciągu ostatnich dziesięcioleci oczyszczanie powietrza stało się integralną częścią systemów HVAC, inżynierii procesowej, motoryzacji i ochrony dróg oddechowych. Skuteczna separacja mikroi nanocząstek jest powiązana z opracowywaniem nowych, wyrafinowanych materiałów filtrujących, a także tworzeniem i weryfikacją modeli matematycznych opisujących zachodzące w nich zjawiska. Artykuł dotyczy numerycznego modelowania przepływu powietrza wewnątrz różnych filtrów. Autorzy proponują innowacyjne podejście, w którym bezpośrednio modelowana jest reprezentatywna objętość wewnętrznej struktury materiału filtrującego, a następnie wyniki są uśredniane na podstawie geometrii całego filtra. Prezentowana praca ma na celu walidację czterech modeli materiałów filtrujących, tj. filtra HEPA z włókna szklanego, filtra papierowego stosowanego w motoryzacji, metalowego filtra tkanego oraz pianki poliuretanowej. W artykule zbadano spadek ciśnienia uzyskany dla badanych filtrów. Wyniki analizy numerycznej wskazują dobrą zgodność z danymi eksperymentalnymi, co uzasadnia wykorzystanie proponowanego podejścia w celu dalszych badań.

EN

The quality of the air around us becomes an object of general interest. Over the past decades, air purification has become an integral part of HVAC, process engineering, automotive and respiratory protection systems. Effective separation of micro- and nanoparticles is related with the development of new, sophisticated filtering materials, as well as the generation and verification of mathematical models describing the phenomena occurring in them. The article deals with numerical modeling of air flow inside various filters. The authors propose an innovative approach in which a representative volume of the internal structure of the filter material is directly modeled, and then the results are averaged based on the geometry of the entire filter. The presented work aims to validate four models of filtering materials, i.e. a glass fiber HEPA filter, a paper filter used in the automotive industry, a metal woven filter and polyurethane foam. The article examines the pressure drop obtained for the tested filters. The results of numerical analysis show good agreement with the experimental data, which justifies the use of the proposed approach for further research.

14

Energetic efficiency of mixing in a periodically reoriented Dean flow

Rożeń Antoni, Kopytowski Janusz

Chemical and Process Engineering

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2021

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Vol. 42, nr 4

391–-410

EN

The energetic efficiency of mixing is studied numerically in a continuous flow mixer constructed from a sequence of alternately twisted pipe bends. Counter-rotating vortices present in the curved channels and known as Dean vortices narrow the distribution of the residence time of fluid elements and accelerate the generation of a new material surface without obstructing the main flow and increasing the risk of fouling or flow stoppage. Cyclic twisting of the pipe curvature allows for quick reorientation of Dean vortices. The reorientation induces chaotic advection in a stable three-dimensional flow and speeds up mixing. The effect of computational domain discretisation for the low and medium Reynolds numbers (20 < Re < 2000º on the head loss, primary and secondary flow, residence time distribution, and the energetic efficiency of generation of the inter material surface is determined. The energetic efficiency is calculated in the time space, a standard approach in modelling reactive micromixing, and at the reactor exit. The maximum energetic efficiency is determined for Re = 600 : 700. It is also found that the initial orientation of the material surface to the pipe curvature has a significant impact on the energetic efficiency of mixing.

15

Numerical study on flow topology and hemodynamics in tortuous coronary artery with symmetrical and asymmetrical stenosis

Song Jianfei, Kouidri Smaine, Bakir Farid

Biocybernetics and Biomedical Engineering

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2021

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Vol. 41, no. 1

142--155

EN

Tortuosity in coronary artery has been found to be greatly related to the potential sites of stenosis in these last years. Many investigations have been carried out based on the tool of Computational Fluid Dynamics (CFD) mainly focusing on the influences of curved artery in blood flow. Within the limited investigations of coupling between stenosis and tortuosity, the stenosis has been considered to be located at the tortuous segment. However, with recent clinical studies, the case of stenosis occurred at non-tortuous segment before tortuosities has been confirmed which has not been paid enough attention yet. Therefore, the present study aims to investigate the disturbed streamlines and hemodynamics in curved and spiral artery considering symmetrical and asymmetrical stenosis upstream these tortuosities. Different stenosis severities, pulse rates and distances between stenosis and tortuosity as controlling parameters have been studied. The distribution of time averaged wall shear stress (TAWSS) and streamlines through tortuous segment have been displayed in order to determine the potential disease sites. Artery surface of TAWSS below critical value has been quantified as well to evaluate the risks of atherosclerosis. The results reveal that larger artery surface of TAWSS below critical value generally goes with smaller pulse rate, larger stenosis severity and distance between stenosis and tortuosity both for curved and spiral artery. However, exceptions were found in the cases of distance of 6 mm in curved artery with symmetrical stenosis and stenosis severity of 50% in spiral artery. Moreover, the spiral tortuosity tends to suppress the potential risks of atherosclerosis compared to curved tortuosity.

16

Submarine Resistance Force Characteristics Determination After Modification of Depth Rudder System

Kiciński Radosław, Jurczak Wojciech

Advances in Science and Technology. Research Journal

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2021

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Vol. 15, no 1

1--9

EN

A submarine, as a technical object, has many systems which are necessary for operation. In addition to the weapon systems, there are many systems required for the safe operation under the water. The submarine steering system is one of them. The article presents the principle of operation and the modification concept of the stern rudders of the project 207 (Kobben class) submarine. On the basis of measurements, the resistance force characteristics were determined. A calculation model was proposed using CFD (Computational Fluid Dynamics) and CAE (Computer Aided Engineering) techniques to determine the resistance force characteristics during the design stage. Then, the measured resistance force characteristics were used to verify the calculation model. Using the proposed method, the resistance force characteristics for an existing submarine were determined, and then its modification was proposed. The simulation results for the modified rudder design allowed determining the reduction of the ship resistance force for the new solution. Lower resistance force means lower demand for electrical power in the engine room, which consequently affects the operational safety by increasing maneuverability and improving the immersion curve. The proposed modification enables to reduce the power consumption by about 8 kW and reduced the resistance force by 2%, which increased the ship’s autonomy.

17

Numerical studies of internal flow in different types of filters

Stanik Magdalena, Caban Szymon, Klonecka Marlena, Buczak Mateusz, Wiśniewski Piotr

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2020

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Vol. 24, No 4

335--344

EN

The quality of ambient air attracts considerable, widespread interest. Over the last decades, air purification has become an integral part of HVAC systems, process engineering, automotive and respiratory protection. Efficient separation of micro- and nano- particles is solidly linked with the development of new, sophisticated filtrating materials, as well as generating and validating mathematical models of such porous structures. The paper regards the numerical modeling of various filters. The presented work aims to validate four virtual filtrating materials – the fiberglass HEPA filter, the paper filter used in the automotive industry, knitted wire mesh and polyurethane foam. The pressure drop obtained for the filters under investigation was examined. The CFD results were validated against the data available in the literature. The agreement of the results of numerical and experimental studies proves the suitability of the proposed methods. At the same time, the simplifications employed in the simulations leave room for further improvement in future works.

18

Zjawisko lewitacji akustycznej – badania wstępne

Grzywnowicz Krzysztof, Remiorz Leszek

Rynek Energii

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2020

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Nr 1

51--58

PL

Zjawiska lewitacji stanowią potencjalnie interesującą alternatywę dla wielu rozwiązań tradycyjnych i są przedmiotem szerokich badań. Istota lewitacji polega na równoważeniu siły grawitacji innym oddziaływaniem, np. magnetycznym. Jako przykład praktycznego wykorzystania tego fenomenu można wymienić chociażby łożyska wykorzystujące zjawisko lewitacji magnetycznej. Inną metodą uzyskania efektu lewitacji jest oddziaływanie falą akustyczną. Powstająca w tym przypadku siła nośna wywołana jest niezerową wypadkową sumarycznego ciśnienia wywołanego oddziaływaniem fali akustycznej na powierzchni lewitującego ciała. W pracy omówiono podstawy fizyczne zjawiska lewitacji akustycznej oraz potencjalny obszar jego zastosowań w energetyce. Przedstawiono również wstępne wyniki badań modelowych, obejmujących wyznaczenie wpływu podstawowych parametrów środowiskowych, w tym względnego położenia lewitującego ciała, częstotliwości fali akustycznej oraz wilgotności gazu roboczego, na wartości charakterystycznych parametrów zjawiska, w tym maksymalnej siły nośnej. Otrzymane wyniki wskazują na możliwość wykorzystania zjawiska przy zmiennych właściwościach fizycznych gazu roboczego, pod warunkiem ograniczenia masy lewitującej drobiny. Rezultaty wykazują jednocześnie graniczne wartości parametrów środowiskowych, które można uznać za akceptowalne w przypadku wykorzystania omawianego fenomenu. Zebrane dane uwidaczniają fundamentalną zależność siły nośnej od położenia lewitującej drobiny w kanale akustycznym oraz częstotliwości fali akustycznej. Wyniki badań prezentują także ograniczony wpływ wilgotności gazu na parametry zjawiska.

EN

Since the levitation phenomena are potentially interesting alternative to many traditional solutions, they state currently a subject of extensive research. The principle of the levitation consists in balancing the force of gravity with another interaction, e.g. magnetic. As an example of the use of this phenomenon, the bearings using the phenomenon of magnetic levitation might be mentioned. Another method of obtaining the effect of levitation is acoustic wave interaction. The lift force generated in this case is caused by a non-zero resultant vector of the total pressure caused by the impact of the acoustic wave on the surface of the levitating body. The paper discusses the physical foundations of the phenomenon of acoustic levitation and the potential area of its applications in energy. Preliminary results of model tests, including determination of the impact of basic environmental parameters, including the relative position of the levitating body, frequency of the wave and humidity of the gas, on the values of the characteristic parameters of the phenomenon, including the maximum lift are presented. The obtained results indicate the possibility of using the phenomenon with variable physical properties of the working gas, provided limited the mass of levitat-ing particles. Simultaneously, the results show the limit values of environmental parameters that can be considered acceptable when the phenomenon in question is used. The collected data show the fundamental dependence of the lift force on the position of levitating particles in the acoustic channel and the frequency of the acoustic wave. The test results also present a limited effect of gas humidity.

19

Thermal energy storage in rock bed - CFD analysis

Jurczyk Michał, Rulik Sebastian, Bartela Łukasz

Journal of Power Technologies

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2020

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Vol. 100, nr 4

301--307

EN

This article reports on an analysis of the possibility of storing thermal energy in a rock bed. The calculations were made in Ansys CFX 18.0 CFD. The analysis determined the charging time of a packed bed of granite rocks in variable flow conditions for the assumed geometry of the energy storage system. The model was 2-dimensional, consisting of two domains connected by an interface. The packed bed was modelled using a porous model approach. The inlet velocity was varied in the range 0.25-4 m/s. The total charging time was 70 to 1100 min, depending on inlet velocity.

20

Computational fluid dynamics modelling of short timebottle filling process

Jałowiecka Monika, Makowski Łukasz

Chemical and Process Engineering

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2020

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Vol. 41, nr 2

143-–163

EN

Every change in the bottle geometry as well as every change of physical and rheological properties posesa risk of excessive gas entrainment during a filling process. To maintain satisfactory filling efficiencythere is a need to optimise this process with respect to all adverse phenomena which affect the fluidflow, such as spluttering on the bottom, air caverns formation and air entrainment with incoming liquid.This paper comprises numerical simulations of two filling methods. The first method involves dosingwith a pipe placed over the free liquid surface of a fully filled bottle. The second method covers fillingwith a pipe located near the bottom. Moreover, the influence of rheological properties and surfacetension values is considered. The comprehensive analysis of amount of entrained air represented byair volume fraction in dispensed liquid let the authors define the influence of filling speed on themechanism and amount of entrapped air.