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1

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.

2

Problemy dotyczące modelowania obciążenia wiatrem obiektów budowlanych

Skotniczny Krystyna, Kopernik Magdalena, Rawska-Skotniczny Anna

Materiały Budowlane

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2022

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nr 6

63--65

PL

Im bardziej skomplikowany kształt obiektu budowlanego, tym trudniej prognozować, jak będą na niego oddziaływały masy powietrza podczas przepływu. Problem jest istotny z uwagi na niezawodność obiektów budowlanych. Analizy numeryczne oraz badania doświadczalne pozwolą w przyszłości zmodyfikować wytyczne normowe, przyczyniając się do poprawy bezpieczeństwa obiektów budowlanych.

EN

The more complex the shape of a building object, the more difficult it is to predict how air masses will affect it during flow. The problem is important for the reliability of buildings. Numerical analyses and experimental studies will allow future modification of the standard guidelines, contributing to the improvement of the safety of buildings.

3

Magnetoconvection of nanofluid in a partially heated cavity with isothermal blockage

Nagaraj Suresh, Nagarajan Nithyadevi

Journal of Applied Mathematics and Computational Mechanics

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2022

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Vol. 21, nr 2

77--90

EN

Natural convection characteristics of Al2O3-water nanofluid in a cavity is investigated numerically under the influence of a inclined magnetic field. The bottom wall is partially heated, and the top wall is cooled and the remaining regions of the cavity are kept adiabatic. An isothermally heated square blockage of the different rectangular size is placed at the centre of the cavity. The schematic model is converted into mathematical form, and the non-dimensional equations are discretized by the finite volume method using power law scheme and solved by Semi-Implicit Method for Pressure Linked Equation algorithm. The relevant parameters such as Rayleigh number (104-106), Hartmann numer (10-500), size of blockage ratio (0.25-0.75), length of the heat source (0.25-1.0) and inclination angle of the magnetic field (0°-90° on the flow and temperature fields are examined. Results are presented in terms of streamlines, isotherms, velocity profile, local and average Nusselt number. It was found that for low Hartmann numbers, the average heat transfer rate attained the maximum at the inclined magnetic field of γ = 45°. In addition, the blockage ratio of B = 0.75 enhanced the higher heat transfer rate for all values of γ.

4

On convergence of explicit finite volume scheme for one-dimensional three-component two-phase flow model in porous media

Mostefai Mohamed Lamine, Choucha Abdelbaki, Cherif Bahri

Demonstratio Mathematica

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2021

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Vol. 54, nr 1

510--526

EN

In this work, we develop and analyze an explicit finite volume scheme for a one-dimensional nonlinear, degenerate, convection–diffusion equation having application in petroleum reservoir. The main difficulty is that the solution typically lacks regularity due to the degenerate nonlinear diffusion term. We analyze a numerical scheme corresponding to explicit discretization of the diffusion term and a Godunov scheme for the advection term. L∞ stability under appropriate CFL conditions and BV estimates are obtained. It is shown that the scheme satisfies a discrete maximum principle. Then we prove convergence of the approximate solution to the weak solution of the problem, and we mount convergence results to a weak solution of the problem in L1 . Results of numerical experiments are presented to validate the theoretical analysis.

5

Numerical solutions of steady free convective flow in a rectangular region with discrete wall heat and concentration sources

Ambethkar Vusala, Basumatary Lakshmi Rani

Journal of Applied Mathematics and Computational Mechanics

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2019

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Vol. 18, nr 4

5--18

EN

In this paper, numerical solutions are obtained for steady free convective ﬂow in a rectangular region with discrete wall heat and concentration sources by using the ﬁnite volume method. The governing equations consist of the continuity, momentum, energy and mass transfer. These equations conjointly with suitable boundary conditions are solved numerically by using this method. The novel concept in this work is to generalize the SIMPLE algorithm suitably and thereby compute the numerical solutions of the ﬂow variables such as the temperature (θ) and the concentration (C) in addition to the components of velocity and the pressure. All non-dimensional parameters are chosen suitably in accordance with the physical signiﬁcance of the problem under investigation. With the help of these numerical solutions, we have depicted the proﬁles of the velocity, pressure, temperature and concentration along the horizontal and vertical directions of the geometric centre of the region. The validity of the numerical solutions are ensured by comparing the present solutions with the benchmark solutions. Code validation has been given for the present problem.

6

Modelling heat flow in a heat storage system with the use of the Finite Volume Method

Sobieski Wojciech

Journal of Applied Computer Science

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2019

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Vol. 27, nr 1

27--49

EN

Non-stationary heat flow was analysed in a heat storage system comprising a flat multilayer structure with different parameters and thickness. Concrete was the heat storage material, and water was the transfer medium responsible for supplying and evacuating heat from the storage medium. It was assumed that the modelled heat storage system may be powered by a solar thermal collector. Data were collected over a period of 24 hours, and they were analysed separately for the heat accumulation phase and the heat recovery phase. Calculations were performed in a program developed by the author based on the Finite Volume Method (FVM). The main aim is to illustrate the basic features of the developed numerical code and to find effective methods for evaluating the applicability of the modelled structures for heat storage. Except that, in the paper the possibilities are discussed for the use of the source component of the diffusion equation to describe various phenomena of physical, chemical and biological nature. The present article was motivated by the observation that FVM is currently not applied in the process of designing heat storage systems.

7

Wpływ parametrów modelu na dokładność wyników symulacji przepływomierza

Jurkowski Sławomir, Janisz Karina

Autobusy : technika, eksploatacja, systemy transportowe

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2019

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R. 20, nr 12

135--139

PL

W artykule przedstawiono analizę wpływu parametrów symulacji przepływu czynnika ściśliwego przez zwężkę Venturiego na dokładność uzyskiwanych rezultatów, z wykorzystaniem programu Ansys 2019 R2. Analiza została przeprowadzona w oparciu o wzorzec za jaki uznano wyniki obliczeń przepływu wg. normy PN-EN ISO 51674:2005. Rozważono wpływ modelu gazu i modelu turbulencji. Symulacji podlegała całość układu pomiarowego włącznie z przewodami impulsowymi.

EN

The article presents the analysis of the impact of the compressor flow simulation parameters through the Venturi tube on the accuracy of the obtained results. The Ansys 2019 R2 program was used for analysis. The analysis was carried out on the basis of the pattern for which the results of flow calculations according to standards PN-EN ISO 5167-4: 2005. The influence of the gas model and turbulence model was considered. The entire measurement system, including impulse lines, was subject to simulation.

8

Numerical study of natural convection in a vertical cylindrical partially annular

Medebber M. A., Retiel N.

Mechanics and Mechanical Engineering

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2018

|

Vol. 22, nr 1

77--92

EN

A study of free convection in a vertical cylinder partially annulus is conducted numerically. Uniform temperature is imposed cross a vertical wall, while the top and bottom walls are adiabatic. The governing equations are solved numerically by using a finite volume method. The coupling between the continuity and momentum equations is effected using the SIMPLER algorithm. Solutions have been obtained for Prandtl numbers equal to 7.0, Rayleigh numbers of 103 to 106 and height ratios of 0 to 1. The influence of physical and geometrical parameters on the streamlines, isotherms, average Nusselt has been numerically investigated.

9

Symulacja prostego silnika magnetohydrodynamicznego

Lipiński Sz., Supińska D.

Maszyny Elektryczne : zeszyty problemowe

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2018

|

Nr 3 (119)

65--69

PL

Silnik magnetohydrodynamiczny jest maszyną elektryczną, w której elementem bezpośrednio wprawianym w ruch jest płyn znajdujący się w polu magnetycznym. W opisanym przykładzie taką rolę pełni osolona woda przewodząca prąd znajdująca się w zewnętrznym polu magnetycznym pochodzącym od magnesu ferrytowego. W artykule zawarto model matematyczny zjawisk pozwalający na przewidywanie zachowania się płynu oraz wykorzystany model numeryczny, który wstępnie zweryfikowano na modelu fizycznym w laboratorium. Omawiane urządzenie wprawia w ruch obrotowy wodę znajdującą się w szalce Petriego, której zewnętrzna ścianka wyłożona jest taśmą miedzianą. Na dnie szalki położony jest magnes ferrytowy w kształcie pierścienia. Całość zasilana jest prądem stałym przepływającym poprzez płyn z umieszczonej centralnie elektrody wykonanej z miedzianego drutu do znajdującej się na zewnątrz elektrody utworzonej z taśmy miedzianej, którą wyłożona jest zewnętrzna ścianka.

EN

Magnetohydrodynamic drive is a type of electric drive, where force acts directly on fluid without mechanical moving parts. The fluid in most cases conducts electric current in magnetic field creating force. Article includes mathematical model allowing to predict fluid behavior together with incorporated numerical model, which was preliminary verified on physical model on test rig. In described example salty water conducts direct current from central electrode made of copper wire to external electrode made of thin copper sheet covering external wall of Petri dish. External magnetic field is provided by ferrite magnet located on the bottom of the vessel. In result water spins in directions according to forces created in conductor exposed to magnetic field.

10

Stabilność rozwiązania zagadnienia brzegowego niestacjonarnego profilu temperatury w przegrodzie budowlanej

Owczarek M., Radzikowska-Juś W.

Inżynieria Bezpieczeństwa Obiektów Antropogenicznych

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2018

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Nr 3-4

30--34

PL

Jedną z uniwersalnych a zarazem prostych metod dla numerycznego rozwiązywania zadań nieustalonego przewodzenia ciepła w obudowie budynku jest metoda objętości skończonych. Jednak, przy sformułowaniu jawnym konieczne jest dobranie kroku czasowego, gwarantującego stabilność rozwiązania. W tym artykule wartość takiego kroku czasowego została określona z warunku zerowej różnicy pomiędzy teoretycznym a numerycznym rozwiązaniem dla danej geometrii ściany. Rozpatrzono wpływ współczynnika przewodzenia ciepła ściany na długość kroku. Warunki brzegowe przyjęte w artykule odpowiadały obciążeniom ogniowym ściany schronu.

EN

One of the most simple and versatile method for numeric solving of the problems of transient heat conduction in the building envelope is the finite volume method. In explicit scheme however there is a problem of assuming correct time step for solution stability. In this article stable step value was determined from the condition of zero difference between the theoretical and numerical solution for the particular geometry of the wall. The influence of the thermal conductivity on the step length has been evaluated. Condition for the correctness of solutions obtained from the analysis in this article is sharper than the condition of equations stability according to the literature. For the boundary conditions adopted solution can be applied to the study of resistance of buildings shelters to long fire.

11

Modeling of Air Permeability of Knitted Fabric Using the Computational Fluid Dynamics

Puszkarz A. K., Krucińska I.

Autex Research Journal

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2018

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Vol. 18, no. 4

364--376

EN

This article concerns the widespread matter of biophysical comfort. In this work, 10 double-layer knitted fabrics with potential application in multilayer garments addressed to a specific group of users, such as newborns, were investigated. The materials were constructed with the following raw materials: cotton, polypropylene, polyester, polyamide, bamboo, and viscose. The textiles with a comparable geometrical structure and different composition were tested for their air permeability. In the experimental part, the materials were tested in specific constant ambient conditions using an air permeability tester. In the simulation part, 3D models of actual textiles were designed and air permeability based on the performed simulations using finite volume method was calculated. Both measurements and simulations yielded comparable results and showed that the air permeability of the knitted fabric strongly depends on the thickness and geometrical parameters of yarn.

12

Coupled finite volume and finite element method analysis of a complex large-span roof structure

Szafran J., Juszczyk K., Kamiński M.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 4

995--1017

EN

The main goal of this paper is to present coupled Computational Fluid Dynamics and structural analysis for the precise determination of wind impact on internal forces and deformations of structural elements of a longspan roof structure. The Finite Volume Method (FVM) serves for a solution of the fluid flow problem to model the air flow around the structure, whose results are applied in turn as the boundary tractions in the Finite Element Method problem structural solution for the linear elastostatics with small deformations. The first part is carried out with the use of ANSYS 15.0 computer system, whereas the FEM system Robot supports stress analysis in particular roof members. A comparison of the wind pressure distribution throughout the roof surface shows some differences with respect to that available in the engineering designing codes like Eurocode, which deserves separate further numerical studies. Coupling of these two separate numerical techniques appears to be promising in view of future computational models of stochastic nature in large scale structural systems due to the stochastic perturbation method.

13

Conservative finite volume element schemes for the complex modified Korteweg–de Vries equation

Yan J. L., Zheng L. H.

International Journal of Applied Mathematics and Computer Science

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2017

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Vol. 27, no. 3

515--525

EN

The aim of this paper is to build and validate a class of energy-preserving schemes for simulating a complex modified Korteweg–de Vries equation. The method is based on a combination of a discrete variational derivative method in time and finite volume element approximation in space. The resulting scheme is accurate, robust and energy-preserving. In addition, for comparison, we also develop a momentum-preserving finite volume element scheme and an implicit midpoint finite volume element scheme. Finally, a complete numerical study is developed to investigate the accuracy, conservation properties and long time behaviors of the energy-preserving scheme, in comparison with the momentum-preserving scheme and the implicit midpoint scheme, for the complex modified Korteweg–de Vries equation.

14

Estimating rapid flow transients using extended Kalman filter

Uilhoorn F. E.

Silesian Journal of Pure and Applied Mathematics

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2016

|

Vol. 6, iss. 1

97--110

EN

Theoretical and numerical modeling of ﬂow transients in pipelines is a challenging ﬁeld of research. The governing ﬂow equations constitute a system of nonlinear hyperbolic partial diﬀerential equations enforcing the conservation laws for mass, momentum and energy. The application of these mathematical models might be limited due to the absence of complete knowledge about the physical phenomena and uncertainties. Information about the initial and boundary conditions is usually obtained from measurements. The presence of noise and inaccuracies, as well as inexactness of the ﬂow model and numerical approximations for solving the full model can lead to predictions that diﬀer from reality. In this paper, we deal with the problem of extracting information about states of the system in real time given noisy measurements. We solved the isothermal ﬂow model during a hydraulic shock while using the extended Kalman ﬁlter to estimate the hidden state variables. To avoid spurious oscillations in the solution, the ﬂow model in conservative form was solved using Roe’s ﬂux limiter within the ﬁnite volume framework to ensure the total variation diminishing property. Numerical approximation of the Jacobian was done with an adaptive routine and showed that most entries in the matrix are zero and therefore sparse. The robustness of the extended Kalman ﬁlter was examined by varying the noise statistics. In most of the situations, we can conclude that the extended Kalman ﬁlter was successful in estimating the rapid transients of natural gas.

15

Study of Multilayer Clothing Thermal Insulation Using Thermography and the Finite Volume Method

Puszkarz A. K., Krucińska I.

Fibres & Textiles in Eastern Europe

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2016

|

Vol. 24, no. 6 (120)

129--137

EN

The article concerns the wide issue which is thermal comfort. In the paper investigations on the textile thermal insulation problem are presented. Materials tested were multi-layer systems with potential application in uniforms addressed to firefighters. Thermal insulation was tested both experimentally (using a thermal imaging camera) and by modelling (by means of simulations of heat transfer phenomena on 3-D models of real textiles). The materials investigated were constructed with the following raw materials: Kevlar, Nomex, ePTFE, PU and carbon fiber. Textiles with a comparable geometric structure and similar composition were tested for their thermal insulation. In the experimental part temperature, the change in specific constant ambient conditions was obtained using a thermal imaging camera. In the simulation part 3-D models of actual textiles were designed and the temperature change was calculated on the basis simulations of the real experiment performed . For each multi-layer system two models were designed, with varying degree of mapping the structure of the yarn in the fabrics. The main goal of the work was experimental verification of both models. As a result of the simulation performed on a model characterised by a more accurate mapping of the yarn structure, comparable results were obtained with experimental data and a strong relationship of thermal insulation textiles from the composition of raw materials and the geometric structure was confirmed.

PL

Artykuł dotyczy szeroko pojętego problemu jakim jest komfort cieplny. W pracy zostały przedstawione wyniki badań dotyczące termoizolacyjności tekstyliów. Przedmiotem analiz były układy wielowarstwowe (składające się z tkanin, włóknin i folii) o potencjalnym zastosowaniu w odzieży ochronnej przeznaczonej dla straży pożarnej. Termoizolacyjność materiałów została przebadana zarówno eksperymentalnie (za pomocą kamery termowizyjnej) jak i teoretycznie (w wyniku symulacji zjawiska transportu ciepła przeprowadzonych na trójwymiarowych modelach rzeczywistych tekstyliów). Przeanalizowane układy tekstylne (wykonane z następujących surowców: Kevlar, Nomex, ePTFE, PU, włókno węglowe) charakteryzowały się porównywalnym składem oraz strukturą geometryczną. W części eksperymentalnej dla wszystkich układów został wyznaczony gradient temperatury w ściśle określonych stałych warunkach otoczenia. W części teoretycznej gradient temperatury został obliczony na podstawie symulacji rzeczywistego eksperymentu. Dla każdego układu zostały zaprojektowane dwa modele, o różnym stopniu odwzorowania struktury przędzy w tkaninach. Głównym celem pracy była weryfikacja eksperymentalna obu modeli. W wyniku symulacji przeprowadzonych na modelu charakteryzującym się dokładniejszym odwzorowaniem struktury przędzy zostały otrzymane rezultaty porównywalne z danymi eksperymentalnymi i potwierdziły silny związek termoizolacyjności tekstyliów z ich składem surowcowym oraz strukturą geometryczną.

16

Influence of hydrogen volumetric flow rate on temperature distribution in CVD reactor based on epi-growth of SiC

Skibinski J., Wejrzanowski T., Teklinska D., Kurzydlowski K. J.

Journal of Power Technologies

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2015

|

Vol. 95, nr 2

119--125

EN

In the present paper the quantitative relationship between the heat and mass transfer in the Aixtron VP508 hot wall CVD reactor and the epitaxial growth of silicon carbide is determined. The aim of this study was to estimate optimal process conditions for obtaining monocrystalline silicon carbide epi-layers with the most homogenous thickness. Since there are many parameters influencing reactions on the crystal area, such as temperature, pressure, gas flow and reactor geometry, it is difficult to design an optimal process. Detailed 3D modeling was used to gain insight into the process conditions, as it is problematic to experimentally determine the exact distribution of heat and mass transfer inside the reactor during epitaxial growth. Numerical simulations allow one to understand the process by calculating the heat and mass transfer distribution during the epitaxial growth of silicon carbide. The present approach was applied to enhance the performance of the Aixtron VP508 reactor.

17

Numerical modelling of thermal phenomena in Yb:YAG laser welding process

Piekarska W., Kubiak M., Saternus Z., Domański T., Stano S., Radcenko M. V., Ivanov S. G.

Journal of Applied Mathematics and Computational Mechanics

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2014

|

Vol. 13, nr 3

175--186

EN

This paper concerns numerical modelling of the Yb:YAG laser beam welding process. Numerical algorithms are developed for the analysis of thermal phenomena in a laser welded joint taking into account the motion of the liquid material in the welding pool. The model describing the laser beam heat source power distribution is developed on the basis of the kriging method. The heat source model uses the real laser beam profile obtained from experimental measurements of the beam emitted from a Trumpf D70 laser head performed on UFF100 analyzer. On the basis of developed numerical algorithms computer simulations of a Yb:YAG laser beam welding are carried out used to analyze the influence of the thermal load model on the shape and size of the weld.

18

Numeryczna symulacja wyciskania profili nieosiowosymetrycznych

Ryzińska G., Skrzat A.

Hutnik, Wiadomości Hutnicze

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2014

|

Vol. 81, nr 7

421--424

PL

W pracy przedstawiono symulacje numeryczne wyciskania profili nieosiowosymetrycznych. Ze względu na bardzo duże zmiany kształtu obrabianego materiału podejście Lagrangea, typowe dla zadań mechaniki ciała stałego, nie jest efektywne. W obliczeniach numerycznych zastosowano podejścia bazujące na sformułowaniu Eulera: metodę objętości skończonych oraz sprzężoną analizę Eulera-Lagrangea. Jako kryterium poprawności obliczeń numerycznych przyjęto siłę wyciskania, której wartość porównano z wynikami badań eksperymentalnych.

EN

Numerical simulations of extrusion of non-axisymmeric profiles is presented in this paper. Extreme changes of the shape of processed material exclude application of Lagrangian approach typical for solving the solid mechanics problems. In the numerical simulations two approaches based on Eulerian approach are applied, namely: finite volume method and coupled Eulerian-Lagrangian. The punch force is chosen as the criterion of numerical computations reliability – numerically derived punch force was compared to the results of experimental investigations.

19

Steady-state and transient heat transfer through fins of complex geometry

Taler D., Taler J.

Archives of Thermodynamics

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2014

|

Vol. 35, no. 2

117--133

EN

Various methods for steady-state and transient analysis of temperature distribution and efficiency of continuous-plate fins are presented. For a constant heat transfer coefficient over the fin surface, the plate fin can be divided into imaginary rectangular or hexangular fins. At first approximate methods for determining the steady-state fin efficiency like the method of equivalent circular fin and the sector method are discussed. When the fin geometry is complex, thus transient temperature distribution and fin efficiency can be determined using numerical methods. A numerical method for transient analysis of fins with complex geometry is developed. Transient temperature distributions in continuous fins attached to oval tubes is computed using the finite volume - finite element methods. The developed method can be used in the transient analysis of compact heat exchangers to calculate correctly the heat flow rate transferred from the finned tubes to the fluid.

20

Analiza wpływu podwieszeń na obciążenia aerodynamiczne samolotu F-16C BLOCK 52 Advanced

Dziubińska A., Kiszkowiak Ł.

Mechanik

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2013

|

R. 86, nr 7CD

165--176

PL

W artykule przedstawiono wyniki obliczeniowej analizy stacjonarnego opływu samolotu F-16C Block 52 Advanced wraz z podwieszanym uzbrojeniem. Rozpatrywano wariant uzbrojenia składający się z dwóch podskrzydłowych zbiorników paliwa, dwóch bomb GBU-31 oraz dwóch pocisków rakietowych AIM-120 AMRAAM na końcówkach skrzydeł. Wyniki porównano z konfiguracją bez podwieszeń. Symulacje wykonano w warunkach odpowiadających atmosferze wzorcowej na wysokości 0 m n.p.m. Dla tych warunków wyznaczono charakterystyki aerodynamiczne w funkcji kąta natarcia. Wyniki obliczeń przedstawiono w postaci wykresów współczynnika siły oporu, siły nośnej oraz momentu pochylającego. Analizy pola przepływu oraz sił i momentów aerodynamicznych działających na bryłę samolotu dokonano za pomocą specjalistycznego oprogramowania FLUENT.

EN

In following paper the results of CFD steady flow analysis around F-16C Block 52 Advanced with external stores were presented. Store configuration consisting of two external wing tanks, two GBU-31 JDAM smart bombs, and two AIM-120 AMRAAM missiles on wingtip launchers has been considered. Configuration without external stores has been also calculated for comparison. The boundary conditions used in simulation corresponded with those for international standard atmosphere (ISA) at sea level. For those conditions the aerodynamic characteristics as functions of angle of attack have been determined. To analyze flowfield and then extract aerodynamic forces and moments, a specialized FLUENT code has been used.