Wyniki wyszukiwania - BazTech

1

Introduction to coastal HF maritime surveillance radars

Ilcev Dimov Stojce

Polish Maritime Research

|

2019

|

nr 3

153--162

EN

This paper presents the main technical characteristics and working performances of coastal maritime surveillance radars, such as low-power High-Frequency Surface Wave Radars (HFSWR) and Over the Horizon Radars (OTHR). These radars have demonstrated to be a cost-effective long-range early-warning sensor for ship detection and tracking in coastal waters, sea channels and passages. In this work, multi-target tracking and data fusion techniques are applied to live-recorded data from a network of oceanographic HFSWR stations installed in Jindalee Operational Radar Network (JORN), Wellen Radar (WERA) in Ligurian Sea (Mediterranean Sea), CODAR Ocean Sebsorsin and in the German Bight (North Sea). The coastal Imaging Sciences Research (ISR) HFSWR system, Multi-static ISR HF Radar, Ship Classification using Multi-Frequency HF Radar, Coastal HF radar surveillance of pirate boats and Different projects of coastal HF radars for vessels detecting are described. Ship reports from the Automatic Identification System (AIS), recorded from both coastal and satellite Land Earth Stations (LES) are exploited as ground truth information and a methodology is applied to classify the fused tracks and to estimate system performances. Experimental results for all above solutions are presented and discussed, together with an outline for future integration and infrastructures.

2

Numerical study of fuel and turbulence distributions in an automotive-sized scavenged pre-chamber

Bolla Michele, Shapiro Evgeniy, Kotzagianni Maria, Kyrtatos Panagiotis, Tiney Nick, Boulouchos Konstantinos

Combustion Engines

|

2019

|

R. 58, nr 1

61--67

EN

This article presents a numerical study of the fuel and turbulence distributions in a pre-chamber at spark-time. The study has been conducted in the framework of the H2020 Gas-On project, dealing with the development of a lean-burn concept for an automotive-sized gas engine equipped with a scavenged pre-chamber. The test case considered studies a 7-hole pre-chamber with circumferentially-tilted orifices mounted on the cylinder head of a rapid compression-expansion machine (RCEM), consistent with the experimental test rig installed at ETH Zurich. An accurate description of turbulence and fuel distributions are key quantities determining the early flame development within the pre-chamber. Both quantities have an influence on the overall combustion characteristics and therefore on the engine performance. For this purpose, computational fluid dynamics (CFD) is employed to complement experimental investigations in terms of data completeness. The performance of the Reynolds-averaged Navier-Stokes (RANS)-based turbulence model is compared with large-eddy simulation (LES) through ensemble averaging of multiple LES realizations, in which the fuel injection rate evolution into the pre-chamber has been perturbed. Overall, RANS results show that the distributions of the turbulent kinetic energy and fuel concentration at spark-time agree well with the LES ensemble-averaged counterparts. This constitutes a prerequisite in view of the combustion phase and the accuracy reported provides further confidence in this regard.

3

LES study of turbulence intensity impact on spark ignition in a two-phase flow

Stempka J., Kuban L., Tyliszczak A.

Archives of Mechanics

|

2018

|

Vol. 70, nr 6

551--567

EN

The paper presents large eddy simulation (LES) study aiming at investigations of an influence of flow conditions on a spark ignition process in a two-phase shear dominated flow. Implicit LES approach is applied for the combustion modelling and the spark is modelled using the energy deposition model of Lacaze et al. [20]. We examine an impact of turbulence intensities and randomness of initial distributions of velocity fluctuations on a flame development during the spark duration and shortly after it is switched off. It is found that for a strong spark, as used in IC engines, the turbulence intensity has little effect on the ignition and flame kernel growth and no significant differences are seen even if the turbulence intensities differ four times. It is observed that weak turbulent structures cannot affect fast flame propagation mechanism and its development is conditioned by evaporation and rapid thermal expansion. In such regimes, the turbulence seems to be too weak to significantly alter the flame dynamics. It is found that at the initial stage of the flame development it grows toward the fuel-rich region and spread over the fuel-lean side only after the evaporated fuel diffuses and mixes with the oxidizer stream. The flame size and its shape turn out to be equally dependent on the initial distribution of the turbulence fluctuations and turbulence intensity.

4

LES numerical study on in–injector cavitating flow

Pyszczek R., Kapusta Ł. J., Teodorczyk A.

Journal of Power Technologies

|

2017

|

Vol. 97, nr 1

52--60

EN

In this paper a computational study on hexane flow in a fuel injector is presented. Large Eddy Simulation (LES) was used to capture the turbulent patterns present in the flow. The main aim was to investigate the cavitation phenomenon and its interaction with turbulence as well as the influence of injection pressure and backpressure on fuel mass flow and flow conditions. Analysis of the approach to define the outlet boundary conditions in terms of convergence time and fluid mass outflow oscillations formed a crucial part of the study. Numerical simulations were performed with AVL Fire CFD (Computational Fluid Dynamics) software. The Euler-Euler approach and multifluid model for multiphase flow modelling were applied. Injector needle movement was included in the simulation. Results show that the additional volumes attached to the nozzle outlets improved the convergence of the simulations and reduced mass outflow oscillations. Fuel mass flow at the outlets was dependent on inlet pressure, position of the needle and backpressure, while the influence of backpressure on fuel mass flow was negligible. The presence of the vapor phase at the exit of the nozzles did not affect average fuel mass flow. All the simulations showed interaction between the gaseous phase distribution and the turbulence of the flow.

5

Numerical study of a turbulent hydrogen flame in oxy-combustion regimes

Wawrzak A., Tyliszczak A.

Archives of Mechanics

|

2017

|

Vol. 69, nr 2

157--175

EN

This paper presents the results of large eddy simulation/conditional moment closure (LES-CMC) computations of a turbulent flame in oxy-combustion regimes complemented by 0D-CMC analysis. The fuel is pure hydrogen and it issues into a hot oxidiser stream which is a mixture of oxygen and water vapour. The flame is initiated by a spark, then it spreads and propagates through the domain and eventually stabilises as a lifted or attached one. The present problem offers new challenges to combustion modelling as the observed combustion process is strongly unsteady. In cases of large content of oxygen in the oxidiser stream the flame has very high temperature (≈ 3000 K) and large temperature/density variations. Nevertheless, it is shown that LES-CMC simulations are stable in such conditions and can be successfully applied to oxy-combustion studies. We analyse the dependence of the flame temperatures and lift-off height of the flames LH on the oxidiser composition and chemical kinetics. It is shown that both these factors may affect the flame behaviour. We identified the conditions in which LH exhibits a linear dependence on the oxidiser composition independently of applied chemical kinetics, and the regimes where the LH changes in a non-linear manner and strongly depends on the chemical kinetics.

6

Aktualny status systemu INMARSAT spełniający funkcje GMDSS

Czajkowski J.

Elektronika : konstrukcje, technologie, zastosowania

|

2015

|

Vol. 56, nr 5

19-20

PL

W artykule przedstawiono aktualny stan systemu INMARSAT- spełniający funkcje GMDSS-u. Przedstawione informacje dotyczące okresu od listopada 2013 roku do października 2014. Scharakteryzowano segment kosmiczny, naziemne stacje lądowe standardu cyfrowego INMARSAT-u B, stacji INMARSAT- Fleet77 oraz standardu INMARSAT-C. Przedstawiono również realizowane wywołania dotyczące niebezpieczeństwa oraz pilności.

EN

The article present actual status of the INMARSAT system. The information covers the period from November 2013 to October 2014. The operational status of key elements of the space and ground segments is summarized. The availability of all GMDSS componets, including distress alerting, Maritime Safety Information and general communication is shown in the article.

7

Comparison of Large Eddy Simulations and κ-ε Modelling of Fluid Velocity and Tracer Concentration in Impinging Jet Mixers

Wojtas K., Orciuch W., Makowski Ł.

Chemical and Process Engineering

|

2015

|

Vol. 36, nr 2

251--262

EN

Simulations of turbulent mixing in two types of jet mixers were carried out using two CFD models, large eddy simulation and k-ε model. Modelling approaches were compared with experimental data obtained by the application of particle image velocimetry and planar laser-induced fluorescence methods. Measured local microstructures of fluid velocity and inert tracer concentration can be used for direct validation of numerical simulations. Presented results show that for higher tested values of jet Reynolds number both models are in good agreement with the experiments. Differences between models were observed for lower Reynolds numbers when the effects of large scale inhomogeneity are important.

8

Zastosowanie metody symulacji wielkowirowych do analizy przepływu Taylora-Couette’a płynu newtonowskiego

Dylak A., Peryt-Stawiarska S.

Inżynieria i Aparatura Chemiczna

|

2014

|

Nr 3

146--148

PL

W pracy przedstawiono wyniki symulacji wielkowirowych LES dla przepływu Taylora-Couette’a. Symulacje numeryczne wykonano dla jednofazowego przepływu cieczy newtonowskiej (wody) przez układ dwóch współosiowych cylindrów. Cylinder zewnętrzny był nieruchomy, natomiast cylinder wewnętrzny obracał się ze stałą prędkością kątową ω = 1,05; 2,43; 9,42 [rad/s]. Wyniki symulacji CFD przedstawiono w postaci map i proﬁli prędkości osiowej.

EN

Results of the Large Eddy Simulation for Taylor-Couette flow are presented in the paper. The numerical simulations of single-phase flow for Newtonian fluid (water) were carried out. In the Taylor-Couette flow medium passed between two соахіаl cylinders. The outer cylinder was stationary while the inner cylinder rotated at the constant angular speed ω = 1.05; 2.43; 9.42 [rad/s], The final results were presented in a form of ахіаl velocity maps and profiles.

9

Modelling and experimantal validation of fluid velocity and tracer concentration in jet reactors

Wojtas K., Makowski Ł., Orciuch W.

Czasopismo Techniczne. Chemia

|

2014

|

R. 111, z. 2-Ch

147--154

EN

The paper presents a collection of experimental data from particle image velocimetry and planar laser induced fluorescence methods containing local microstructures of fluid velocity and inert tracer concentration in jet reactors. The results of experiments, performed with resolution of the level of several microns, can be used for direct validation of CFD models, especially for timedependent mixing model used in large eddy simulations.

PL

W artykule przedstawiono wyniki badań doświadczalnych przeprowadzonych z wykorzystaniem zaawansowanych technik laserowych, takich jak anemometria laserowa i laserowo indukowana fluorescencja w celu uzyskania informacji na temat pola prędkości i stężenia trasera w wybranych typach reaktorów zderzeniowych. Wyniki eksperymentalne posłużyły do weryfikacji obliczeń numerycznych z wykorzystaniem obliczeniowej mechaniki płynów w szczególności modeli wielkowirowych.

10

CFD simulation of turbulent velocity field in the discharge streem from a standard Rushton turbine impeller

Kysela B., Fořt I., Konfršt J.

Czasopismo Techniczne. Chemia

|

2014

|

R. 111, z. 2-Ch

73--84

EN

The velocity field around the standard Rushton turbine was investigated by the Computational Fluid Dynamics (CFD) calculations and compared with results obtained from the Laser Doppler Anemometry (LDA) measured in a pilot plant baffled cylindrical vessel. For calculations the Large Eddy Simulation (LES) approach was employed. The impeller motion was modeled using the Sliding Mesh technique (SM). The mean ensemble-averaged velocity profiles and root mean square values of fluctuations were compared in the radial discharge jet from the standard Rushton turbine under turbulent regime of flow of agitated liquid. There were found two subregions in the discharge stream and the values of the axial profiles of the radial component of the fluctuating velocity are rather same determined from the LES calculations and from the LDA measurements in the second one ZEF (zone of established flow) of the impeller discharge stream, but they differ in the first region ZFE (zone of flow establishment) in the impeller vicinity, although they exhibit the same shape. The impeller power number derived from calculations shows also good agreement with values introduced in literature with a significant influence of the thickness of the impeller disc.

PL

Pole prędkości wokół standardowej turbiny Rushtona przeanalizowano metodą CFD (Computer Fluid Dynamics) i porównano z wynikami uzyskanymi za pomocą laserowej anemometrii dopplerowskiej (LDA) w doświadczalnym zbiorniku cylindrycznym z przegrodami. W obliczeniach wykorzystano technikę LES (Large Eddy Simulation). Ruch mieszadła zamodelowano z zastosowaniem techniki SM (Sliding Mesh). Średnie ważone profile prędkości i średnie kwadratowe wartości fluktuacji porównano z promieniowym strumieniem cieczy wypływającej z turbiny Rushtona w warunkach burzliwego przepływu cieczy mieszanej. W strumieniu wypływającym z mieszadła wyodrębniono dwa podobszary, a przebiegi profili promieniowych składowych fluktuacji prędkości były zbliżone, zarówno otrzymane w wyniku obliczeń LES, jak i z pomiarów LDA w drugiej strefie przepływu ustabilizowanego w sąsiedztwie wirnika, chociaż wykazywały ten sam kształt. Liczba mocy mieszadła, otrzymana w wyniku obliczeń, wykazała dobrą zgodność z wartościami podawanymi w literaturze, przy znaczącym wpływie grubości tarczy mieszadła.

11

A LES numerical approach for investigating the cycle-to-cycle combustion pressure variability in a direct injection gasoline engine

Teodorczyk A., Jaworski P., Priesching P., Tatschl R.

Combustion Engines

|

2013

|

R. 52, nr 3

794--799

EN

The Large Eddy Simulation method (LES) has become a powerful computational tool for the application to turbulent flows. It links the classical Reynolds Averaged Navier–Stokes (RANS) approach and Direct Numerical Simulation (DNS). This means that the large eddies are computed explicitly in a time-dependent simulation using the filtered Navier-Stokes equations. The LES resolves the large flow scales that depend directly on the geometry where the small scales are modelled by the subgrid-scale models. LES is expected to improve the description of the aerodynamic and combustion processes in Internal Combustion Engines. This paper addresses the topic of developing the combustion model GCM (Gradient Combustion model) for the Large Eddy Simulation (LES) method. Another part of this paper presents numerical investigations of cycle-to-cycle combustion pressure variability with comparison to experimental data. The Gradient Combustion model (GCM) based on the Turbulent Flame Speed Closure Model (TFSCM) is validated against the experimental data for a multi-cycle gasoline direct injection research engine (SCRE). It is shown that the introduced combustion model is stable and capable of proper representation of the experimental results which is one of the assets of the LES method.

PL

Metoda LES jest obecnie zaawansowanym narzędziem numerycznym do analizy przepływów turbulentnych. Metoda LES opiera się na połączeniu klasyczej metody uśredniania równań Naviera-Stokes (RANS) z bezpośrednią analizą numeryczną (DNS). Oznacza to, że duże struktury wirowe są rozwiązywane niejawnie poprzez filtrowanie równań Naviera-Stokesa. W metodzie LES oznacza to obliczanie przepływu dużej skali, który zależy od geometrii, podczas gdy przepływ w małej skali jest modelowany modelem podsiatkowym (ang. Sub-grid-scale models, SGS). Uważa się, że metoda LES pozwoli na poprawienie numerycznego opisu aerodynamiki i procesów spalania w silnikach tłokowych. Artykuł przedstawia wyniki prac rozwojowych nad modelem spalania w metodzie LES. Model GCM (model spalania oparty na metodzie gradientu) został zastosowany do obliczeń wielocyklicznych i ich weryfikacji z wynikami eksperymentalnymi. Wyniki eksperymentalne pozyskano z badań na jednocylindrowym silniku badawczym (SCRE) o wtrysku bezpośrednim. W pracy pokazano, że model spalania jest stabilny numerycznie oraz otrzymane wyniki są zgodne z wynikami eksperymentalnymi, co jest jedną z ważniejszych zalet metody LES.

12

Stan aktualny i rozwój systemu INMARSAT

Czajkowski J.

Elektronika : konstrukcje, technologie, zastosowania

|

2012

|

Vol. 53, nr 11

122-124

PL

W artykule opisano aktualny status satelitarnego systemu radiokomunikacyjnego INMARSAT. Przedstawione dane dotyczą okresu od listopada 2010 roku do października 2011 roku. Opisano główne składowe systemu INMARSAT, tj. satelity umieszczone na orbicie geostacjonarnej nad czterema obszarami oceanicznymi, operacyjne centrum zarządzania, naziemne stacje lądowe, stacje koordynacyjne oraz stacje statkowe. Stwierdzono iż system spełnia wszystkie oczekiwania systemu GMDSS - obejmując alarmowanie w niebezpieczeństwie, rozpowszechnianie morskich informacji bezpieczeństwa - MSI oraz zapewniając łączność ogólną.

EN

The article presents actual status of the INMARSAT system. The information covers the period from November 2010 to October 2011. The operational status of key elements of the space and ground segments is summarized. The availability of all GMDSS components, including distress alerting, Maritime Safety Information and general communication is shown in the article.

13

Effects of a fully submerged boulder within a boulder array on the mean and turbulent flow fields: Implications to bedload transport

Papanicolaou A., Kramer C., Tsakiris A., Stoesser T., Bomminayuni S., Chen Z.

Acta Geophysica

|

2012

|

Vol. 60, no. 6

1502-1546

EN

The objective of this coupled experimental and numerical study is to provide insight into the mean and turbulent flow fields within an array of fully submerged, isolated, immobile boulders. Our study showed that the velocity defect law performed well for describing the mean flow around the boulder within the array. A prerequisite, however, was to accurately estimate the spatial variability of u* around the boulder, which was achieved via the boundary characteristics method. The u* exhibited considerable spatial variability within the array and form roughness was shown to be up to 2 times larger than the skin roughness in the boulder near-wake region. Because the boulders bear a significant amount of the flow shear, the available bed shear stress for entrainment of the mobile sediment, τols, near the boulders was roughly 50% lower than the ambient τols. The τols variability induced by the boulders could lead to a threefold overestimation of the sediment transport rate.

14

Combustion of ethanol-air mixtures in closed vessel - comparison of simulations with the use of RANS and LES method

Jaworski P., Żbikowski M., Teodorczyk A.

Silniki Spalinowe

|

2011

|

R. 50, nr 3

EN

Large Eddies Simulations (LES) has become recently a powerful computational tool with application to turbulent flows. It links classical Reynolds Averaged Navier-Stokes (RANS) approach and Direct Numerical Simulation (DNS). This modeling approach computes the large eddies explicitly in a time-dependent simulation using the filtered Navier-Stokes equations. Filtering is essentially a mathematical manipulation of the exact Navier-Stokes equations to remove the eddies that are smaller than the size of the filter. LES resolves the large flow scales that depend directly on the geometry where small scales are modeled by the sub-grid-scale models. LES is expected to improve the description of the aerodynamic and combustion processes in Internal Combustion Engines. With LES it is possible to resolve the essential part of the flow energy, yielding reliable results. Proper predictions depend on the quality of sub-grid-scale (SGS) models. In this paper the results of computational analysis are compared with experimental results for combustion in constant volume chamber. In that way there is a possibility to see the difference in results of initial flame kernel and laminar flame development. Simulations were made with two CFD codes: Fire and Fluent, which allowed to compare the experimental and simulation results for RANS and LES method and make further improvement in LES combustion model for application in full engine simulation.

PL

LES jest znakomitym narzędziem obliczeniowym przepływów turbulentnych łączącym powszechnie używaną metodę RANS (Reynolds Average Navier Stokes Equation) z DNS (Direct Numerical Simulation). W skrócie metoda LES opiera się na zastosowaniu filtru do równań Naviera-Stokesa i wprowadzeniu rozdziału na zjawiska wielko-skalowe (duże wiry) oraz drobno-skalowe. Zjawiska wielko-skalowe są obliczane przez bezpośrednie rozwiązanie przefiltrowanych równań N-S, natomiast drobno-skalowe są modelowane w skali podsiatkowej. Możliwe jest dzięki temu bezpośrednie obliczenie dużych wirów i wirów biorących udział w procesie kaskadowym. Wiry małe, zależne głównie od lepkości są modelowane, ale wymaga to zastosowanie odpowiednio gęstej siatki od której zależy proces filtrowania. Filtrowanie jest matematyczną manipulacją równań N-S polegającą na wyodrębnieniu wirów z turbulentnego pola przepływu, które są większe niż wielkość zastosowanego filtru. Mimo to właściwe wyniki symulacji uzależnione są również od jakości modelowania w skali podsiatkowej. W pracy przedstawiono porównanie wyników badań eksperymentalnych i symulacyjnych procesu spalania mieszanki ethanolu z powietrzem w komorze o stałej objętości. Celem tej pracy jest przedstawienie pierwszych wyników dla tworzonego modelu spalania w LES.

15

Numerical simulation of turbulent heat and momentum transport in rotating cavity

Tuliszka-Sznitko E., Majchrowski W., Kiełczewski K.

Journal of Theoretical and Applied Mechanics

|

2011

|

Vol. 49 nr 4

1217-1232

EN

The paper gives the results of the Direct Numerical Simulation (DNS) and Large Eddy simulation (LES) which were performed to investigate the 3D transitional non-isothermal flows within a rotor/stator cavity. A Lagrangean version of the dynamic Smagorinsky eddy viscosity model was used. Computations were performed for the cavity of the aspect ratio L=3.0-5.0, curvature parameters Rm=1.8-5.0, for the Reynolds number Re=(1.0-2.5)105 and for defferent Prandtl numbers. The results were obtained for coupled momentum and thermal transport in the rotor/stator cavity flows. The obtained distributions of the turbulent heat flux tensor components, the Reynolds stress tensor components, the turbulent Prandtl numer and other structural parameters coincide with the experimental data (published in the literature).

PL

W atykule przedstawiono wyniki symulacji przepływu (z wymianą ciepła) w obszarze pomiędzy stojanem i wirnikiem oraz dwoma pierścieniami uzyskane z zastosowaniem metod DNS i LES. Badania przeprowadzono dla rozciagłości obszaru L=3.0-5.0 oraz dla współczynnika krzywizny Rm=1.8-5.0. Badano struktury niestabilnościowe występujące w warstwie przyściennej wirnika i stojana oraz profile osiowe naprężeń reynoldsowskich, fluktuacji temperatury, turbulentnej liczby Prandtla, profile parametrów strukturalnych i korelacyjnych. Obliczenia przeprowadzono dla różnych liczb Reynoldsa i Prandtla. Uzyskane rozwiązania porównano z wynikami badań eksperymentalnych Elkinsa i Eatona (2000) uzyskanymi podczas badania przepływu wokół pojedynczego wirującego dysku podgrzewanego jednorodnym strumieniem. Rezultaty badań porównywano również z wynikami uzyskanymi dla dwuwymiarowych turbulentnych warstw przyściennych.

16

Numerical study on flame propagation in n-heptane/air mixture with the use of a gradient LES combustion model

Jaworski P., Teodorczyk A.

Journal of Power Technologies

|

2011

|

Vol. 91, nr 3

114-121

EN

This paper presents the results of numerical simulations with a combustion model using Large Eddy Simulation (LES). The objective is to check whether the proposed combustion model is capable of representing the laminar reacting flow. The numerical results are compared with flame front propagation data gained from experiments. The combustion model is based on the gradient method, which determines flame propagation. The gradient is calculated from the mass fraction of fuel or products. Laminar burning velocity is described by empirical correlation. Flame generated turbulence is used in this study to represent the nonlinear flame propagation effects in the laminar reacting flow. From the results it is concluded that flame generated turbulence can be used for laminar reacting flows and is important for representation of the combustion process in numerical simulations. The gradient combustion model for turbulence reacting flow is capable of proper representation of the flame front in laminar reacting flows. The gradient combustion model for LES did not increase the time needed for calculation, making it an attractive method in full engine cycle simulations.

17

Modelowanie hydrodynamiki oraz procesu mieszania w mieszalniku Kenics

Murasiewicz H., Jaworski Z.

Inżynieria i Aparatura Chemiczna

|

2011

|

Nr 4

28-29

PL

Przedstawiona praca poświęcona jest badaniom numerycznym hydrodynamiki przepływu oraz procesu mieszania układu dwufazowego typu ciecz-ciecz w mieszalniku Kenics. W badaniach CFD wykorzystano symulacje wielkowirowe LES z dwoma modelami burzliwości: modelem dynamicznym kinetycznej energii burzliwości skali podsiatkowej (Dynamie Kinetic Energy Subgrid-Scale Model) oraz model Smagorinsky-Lilly. Symulowano łącznie 18 przypadków, w tym trzy poziomy liczby Reynoldsa. Stwierdzono, że wraz ze wzrostem liczby Re zmniejsza się wartość CoV oraz im wyższy stosunek L/D tym większy spadek CoV, co powoduje wzrost poziomu jednorodności układu. Prezentowana analiza pozwala stwierdzić, iż oba modele burzliwości mogą być z powodzeniem wykorzystywane do przewidywania zmian hydrodynamiki wewnątrz mieszalnika.

EN

Numerical results of hydrodynamics and mixing process of two-phase liquid-liquid system in the Kenics static mixer are presented. CFD simulations were carried out using Large Eddy Simulation with two turbulent models: Kinetic Energy Dynamic Subgrid-Scale Model and the Smagorinsky-Lilly Model. Eighteen cases were simulated, including three Reynolds numbers. The results showed that increasing of the Reynolds number decreases the CoV; the larger L/D ratio, the greater decrease of CoV. This caused an increase of homogeneity level in the system. Presented analysis proved that both turbulent models can be successfully applied in the prediction of hydrodynamics changes inside the mixer.

18

Local distributions of fluid velocity and tracer concentration in a tank reactor

Makowski Ł., Orciuch W.

Chemical and Process Engineering

|

2011

|

Vol. 32, nr 1

33-40

EN

The aim of the project was to collect experimental data regarding local distributions of fluid velocity and inert tracer concentration in a tank reactor with turbulent flow. The experiments were performed in a microscale in a region of tracer fluid injection. The results of experiments can be used for direct validation of currently developed CFD models, particularly for time-dependent mixing models used in LES.

19

Combustion of ethanol-air mixtures in closed vessel comparison of simulation with the use of RANS and LES method

Jaworski P., Żbikowski M., Teodorczyk A.

Archivum Combustionis

|

2011

|

Vol. 31 nr 4

223-232

EN

Large Eddies Simulation method (LES) has become a powerful computational tool with application to turbulent flows. It links classical Reynolds Averaged Navier-Stokes (RANS) approach and Direct Numerical Simulation (DNS). This modeling approach computes the large eddies explicitly in a time-dependent simulation using the filtered Navier-Stokes equations. LES resolves the large flow scales that depend directly on the geometry where small scales are modeled by the sub-grid-scale models. LES is expected to improve the description of the aerodynamic and combustion processes in Internal Combustion Engines. With LES it is possible to resolve the essential part of the flow energy, yielding reliable results. Proper predictions depend on the quality of sub-grid-scale (SGS) models. In this paper the computational analysis is compared with experimental results in constant volume chamber. In that way there is a possibility to see the difference in results of initial flame kernel development and laminar flame speed. The calculations were made for two different combustion models. This allows to compare the experimental and simulation results for RANS (Fire ECFM combustion model) and LES (Fire) method and make further improvement in LES combustion model for application in full engine simulation.

20

LES of Converging-Diverging Channel Flow with Separation

Kuban L., Elsner W., Tyliszczak A.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2010

|

Vol. 14, No 3

283-295

EN

The paper presents the results of LES simulation of two different turbulent channels with inlet conditions corresponding to the Reynolds number Re =395. In both cases a varying pressure gradient was obtained by an adequate curvature of one of the walls. The first case is treated as a benchmark and is used to validate the numerical procedure. This case is characterized by the same cross-section area at the inlet and outlet and a bump of a smooth profile located on one of the walls designed to be identical to the one used in the experiment conducted at Laboratorie de Mecanique de Lille (LML) (Marquillie et al., 2008). The second case corresponds to the geometry which reproduces the real geometry of the turbomachinery test section of the Czestochowa University of Technology. The test section was created in such a way as to produce the pressure gradient which would correspond to the conditions present in the axial compressor blade channel. The shape of both channels produced initially favorable (FPG) and then adverse pressure gradients (APG), and in this way created conditions for boundary layer separation. Due to a reverse flow where the turbulence transport is dictated by the dynamics of the large-scale eddies such a case is well suited to demonstrate predictive features of the LES technique.