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1

Location-optimized aerodynamic rotor design studies and development of small wind turbines

Lehser-Pfeffermann Daniel, Hamman Alexander, Rückert Frank Ulrich

Archives of Thermodynamics

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2022

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Vol. 43, no 1

3--19

EN

Local wind conditions can vary strongly depending on the landmark and vegetation, as well as on the skyline of the buildings in an urban surrounding. Weather, season and time of day influence the yield of electric power. In order to promote the use of small wind turbines as an alternative to photovoltaic power generation, design optimization for location-optimized small wind turbines was carried out. In this work, we want to concentrate on vertical axis wind turbines. Experimental studies, as well as numerical simulations, have been conducted. On the one hand, bionically optimized core structures will be integrated and implemented in the hybrid material of the turbine blades. Several optimization attempts have been examined for single blades. Detailed simulative investigations with large eddy simulations improve the aerodynamic behaviour of the new rotor design. Finally, based on the results of the studies and investigations, a new rotor will be manufactured and tested experimentally in the wind tunnel. A comparison with the reference system from the first part of the paper shows the improvements and effectiveness of the measures and processes investigated.

2

Hybrid Artificial Boundary Conditions for the Application of Blunt-Body Aerodynamic Noise Prediction

Ma Ruixian, Liu Zhansheng, Doolan Con J., Moreau Danielle J., Czarnecki Michał

Archives of Acoustics

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2019

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Vol. 44, No. 1

105--116

EN

A hybrid artificial boundary condition (HABC) that combines the volume-based acoustic damping layer (ADL) and the local face-based characteristic boundary condition (CBC) is presented to enhance the absorption of acoustic waves near the computational boundaries. This method is applied to the prediction of aerodynamic noise from a circular cylinder immersed in uniform compressible viscous flow. Different ADLs are designed to assess their effectiveness whereby the effect of the mesh-stretch direction on wave absorption in the ADL is analysed. Large eddy simulation (LES) and FW-H acoustic analogy method are implemented to predict the far-field noise, and the sensitivities of each approach to the HABC are compared. In the LES computed propagation field of the fluctuation pressure and the frequency-domain results, the spurious reflections at edges are found to be significantly eliminated by the HABC through the effective dissipation of incident waves along the wave-front direction in the ADL. Thereby, the LES results are found to be in a good agreement with the acoustic pressure predicted using FW-H method, which is observed to be just affected slightly by reflected waves.

3

Design and Numerical Simulation of the Performance of Acoustic Plenum Chamber of a Marine Gas Turbine Air Supply System

Rasoulimoghadam Mehrdad, Kheradmand Saeid

Archives of Acoustics

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2019

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Vol. 44, No. 4

793--806

EN

In the present work, an approach to obtain a design method for the size of the plenum chamber cross-section of a marine gas turbine air supply system has been investigated. Flow in ducts makes noise which is very high in the turbine inlet part because of the large amount of flow. Therefore, this phenomenon should be considered in the design process. A suitable approach to design the duct is proposed (considering acoustic and aerodynamic performance at the same time). In this method, an air supply channel system of the marine gas turbine has been categorized into three sections according to the requirements of the aerodynamic and acoustic; inlet, plenum chamber, and outlet channels with circular cross-sections. The geometrical dimensions of inlet and outlet channels have been determined using the plane waves theory about a channel, in which the effects of flow is ignored. Space limitations of battleships at the dominant frequency have been considered. Then, the optimized size of the mid-channel section, in terms of both aerodynamic and acoustic requirements, using numerical methods and regarding the effects of flow has been calculated. Various 3D turbulent flows inside the plenum chamber have been considered, in which large eddy simulation turbulence model is utilized. Ffowcs, Williams and Hawkings models are used for the sound propagation process based on the Lighthill integral equation. The validity of the simulation has been checked by comparing results (sound pressure level) with experimental data obtained from a chamber. The comparison revealed the acceptable errors for a variety of frequencies. The results disclosed that the performance of channel system aerodynamic decreased when the fraction of plenum chamber cross-section to inlet/outlet channel cross-section increased. With an increase in the cross-section size at first Acoustic performance is improved and then worsen. Six different cases of marine gas turbine air supply system configurations have been presented, in which the limitation of the battleship space is considered. Examining and comparing the acoustic performance of different cases of the air supply channel system, it was found that the amount of sound pressure level, around the air supply channel system, and the high-pressure sound area can move along the air supply channel system. Additionally, deviations from plane waves considering the effects of flow have been inspected in all cases. The reason for this deviation is the effects of the airflow through the channel system and quadrupole sources in the production of sound in the channel system, which causes higher modes.

4

Produkcja kryształów o pożądanych własnościach w reaktorach zderzeniowych - badania doświadczalne i modelowanie CFD

Makowski Ł., Wojtas K., Wojtalik M.

Inżynieria i Aparatura Chemiczna

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2017

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Nr 4

126--127

PL

Praca przedstawia wpływ parametrów procesowych na przebieg procesu precypitacji w reaktorach zderzeniowych. Do rozważań wybrano dwa procesy: testowy, powstawania kryształów siarczanu barn oraz o charakterze praktycznym, produkcja kryształów disiarczku molibdenu. Wyniki doświadczalne porównano z wynikami symulacji przy użyciu obliczeniowej mechaniki płynów z wykorzystaniem modeli wielkowirowych.

EN

Influence of process parameters on precipitation process in jet reactors is presented in the paper. Two processes were considered: test, barium sulphate crystallization and production of molybdenum disulfide crystals of practical character. The experimental results were compared with simulations using computational fluid mechanics especially large eddy simulation models.

5

Modelling of a passive autocatalytic hydrogen recombiner : a parametric study

Rożeń A.

Nukleonika

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2015

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Vol. 60, No. 1

161--169

EN

Operation of a passive autocatalytic hydrogen recombiner (PAR) has been investigated by means of computational fluid dynamics methods (CFD). The recombiner is a self-active and self-adaptive device used to remove hydrogen from safety containments of light water nuclear reactors (LWR) by means of a highly exothermic reaction with oxygen at the surface of a platinum or palladium catalyst. Different turbulence models (k-ω, k-ε, intermittency, RSM) were applied in numerical simulations of : gas flow, heat and mass transport and chemical surface reactions occurring in PAR. Turbulence was found to improve mixing and mass transfer and increase hydrogen recombination rate for high gas flow rates. At low gas flow rates, simulation results converged to those obtained for the limiting case of laminar flow. The large eddy simulation technique (LES) was used to select the best RANS (Reynolds average stress) model. Comparison of simulation results obtained for two- and three-dimensional computational grids showed that heat and mass transfer occurring in PAR were virtually two-dimensional processes. The effect of hydrogen thermal diffusion was also discussed in the context of possible hydrogen ignition inside the recombiner.

6

Modelowanie oraz badania doświadczalne procesu precypitacji w reaktorach zderzeniowych

Wojtas K., Jagłowski J., Makowski Ł.

Inżynieria i Aparatura Chemiczna

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2015

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Nr 6

362--363

PL

Przedstawiono zastosowanie reaktorów zderzeniowych do produkcji kryształów w procesie precypitacji. W celu określenia pożądanych warunków przebiegu procesu wykorzystano dwa procesy testowe. Wyniki doświadczalne porównano z wynikami symulacji przy użyciu obliczeniowej mechaniki płynów z wykorzystaniem modeli wielkowirowych. Uzyskane wyniki posłużyły do określenia warunków prowadzenia procesu produkcji kryształów disiarczku molibdenu.

EN

Application of jet reactors in precipitation processes are presented in the paper. Two test processes were applied to determine the desired process conditions. The experimental results were compared with simulation results using computational fluid dynamics models, especially large eddy simulation ones. The results were used for the determination of process conditions in the production of molybdenum disulphide crystals.

7

Investigation of thermal mixing in the control rod top tube using large eddy simulations

Pegonen R., Edh N., Angele K., Anglart H.

Journal of Power Technologies

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2014

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Vol. 94, nr 1

67--78

EN

Thermal mixing and thermal fatigue has led to component failures in the nuclear industry. The thermal fatigue phenomenon is intimately linked with the mixing of streams of different temperatures in proximity to a solid wall. Due to conjugate heat transfer, temperature fluctuations are induced in the wall. One of the key issues is to predict the amplitude and the frequency of the fluctuations. This paper presents pre-calculations of the thermal mixing experiments that are under preparation at the KTH Royal Institute of Technology as part of the THEMFE project (Thermal Mixing and Fatigue Experiment). The proposed geometry is a simplification of a reactor control rod and consists of a top-tube and control rod stem, which are modeled as concentric cylinders. In addition there are only two hot inlet jets and two cold inlet jets, whereas in reality there are 8 upper inlets and 4 lower inlets for hot bypass water and the cold flow is annular. Thermal mixing was studied by using a transient Computational Fluid Dynamics (CFD) solver for the incompressible filtered Navier-Stokes equations and employing a Large Eddy Simulation model of turbulence implemented in OpenFOAM. The aim was to verify that the proposed simplified geometry and the flow conditions of the experiment will lead to low frequent temperature fluctuations of the order of 0.1-1 Hz, as seen in previous experiments with the real geometry. Such low frequencies are typical for the thermal fatigue phenomenon. The study was focused on the region near the control rod stem and therefore a refined grid was used in that region. The final mesh consisted of over one million cells. The results did indeed reveal low frequent temperature fluctuations in the lower part of the mixing region near the control rod stem. The results of this paper indicate that the length of the mixing region is 23 cm, which is large enough to be resolved in the experiment. It was also found that the most dangerous region, where the dominant high amplitude temperature fluctuations have a frequency of the order of 0.1 Hz, is 4 cm long. As expected, the instant flow field is asymmetric with large secondary flows. The present results verify that the proposed geometry and flow conditions can be applied in the experiment.

8

Zastosowanie modeli wielkowirowych do przewidywania końcowych cech produktów złożonych reakcji chemicznych

Wojtas K., Makowski Ł., Orciuch W., Bałdyga J.

Inżynieria i Aparatura Chemiczna

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2014

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Nr 4

324--325

PL

W pracy przedstawiono sposób przewidywania przebiegu złożonych procesów chemicznych (przebiegu złożonych reakcji chemicznych i proces precypitacji) przy wykorzystaniu modeli wielkowirowych. Jako reaktory testowe wybrano dwa typy reaktorów zderzeniowych, charakteryzujące się wysoką intensywnością mieszania. Analiza wyników pokazała możliwość wpływania na jakość powstającego produktu poprzez dobór warunków mieszania reagentów i przydatność metody LES.

EN

The paper presents an application of large eddy simulations to predict a course of complex processes (parallel chemical reactions, precipitation process) carried out in selected types of jet reactors. Results of simulations were validated using PIV and PLIF techniques and also by comparing model predictions with experimental data for test reactions. The study showed an example of influence of process conditions on product quality and potential of LES for solving typical chemical and process engineering problems.

9

Large eddy simulation of precipitation process carried out in jet reactors

Makowski Ł., Wojtas K., Orciuch W., Bałdyga J.

Czasopismo Techniczne. Chemia

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2014

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R. 111, z. 2-Ch

95--104

EN

The paper presents an application of large eddy simulations to predict a course of precipitation process carried out in selected types of jet reactors. In the first part of this work the simulations results were validated using PIV and PLIF techniques and also by comparing model predictions with experimental data for fast parallel chemical test reactions. In the second part of this work predictions of modeling are compared with experimental data for BaSO4 precipitation. Precipitation model is tested in this part also by comparing predictions of the model based on LES with results obtained using the multiple-time-scale mixing model combined with the k‒ɛ model.

PL

W artykule przedstawiono zastosowanie modelowania wielkowirowego procesu precypitacji siarczanu baru przebiegającego w reaktorach zderzeniowych. W pierwszej części pracy uzyskane wyniki numeryczne zweryfikowano z wykorzystaniem technik laserowych oraz z wynikami doświadczalnymi dla przebiegu złożonych reakcji chemicznych. W drugiej części pracy rozważano przebieg procesu precypitacji siarczanu baru. Wyniki modelowania wielkowirowego dodatkowo porównano z wynikami symulacji z użyciem modelu k‒ɛ oraz modelu mieszalnik burzliwego.

10

A large eddy based lattice-Boltzmann simulation of velocity distribution in an open channel flow with rigid and flexible vegetation

Gac J.

Acta Geophysica

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2014

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Vol. 62, no. 1

180--198

EN

The large eddy simulation method, based on a lattice-Boltzmann algorithm, was used to compute the vertical velocity profile in an open channel flow with submerged and emerged vegetation. The numerical method is characterized by the relatively short time of computation and low complexity. On the other hand, it allows a more realistic description of the vegetation properties relative to the methods commonly used in 1-D numerical models. For the proper conditions, the method developed in this work gives results similar to other numerical methods. These results are also in good agreement with the experimental data presented in other papers.

11

Efekty mieszania w wybranych zagadnieniach procesów inżynierii produktu

Makowski Ł.

Prace Wydziału Inżynierii Chemicznej i Procesowej Politechniki Warszawskiej

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2013

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Vol. 36, z. 1

3--166

PL

Praca prezentuje możliwości kontrolowania końcowych cech produktu chemicznego poprzez dobór warunków prowadzenia procesu, a w szczególności warunków mieszania reagentów. Przedstawiono sposoby i wyniki modelowania połączone z doświadczalną weryfikacją wpływu mieszania na przebieg złożonych procesów chemicznych na przykładzie charakterystycznych procesów: realizacji równoległych i procesu precypitacji. W ostatnich latach do modelowania procesów chemicznych wykorzystuje się obliczeniową mechanikę płynów, obserwowany zaś współcześnie wzrost wydajności komputerów pozwolił na zastosowanie zaawansowanych modeli, takich jak modele wielkowirowe. W pierwszej części pracy przedstawiono możliwości modelowania przepływu burzliwego, wykazując ograniczenia modelowania bezpośredniego i pokazując, te modele wielkowirowe są rozsądną alternatywą pomiędzy jakością uzyskiwanych wyników a wymogami co do niezbędnej mocy obliczeniowej. Określono również warunki koniecz.ne do spełnienia dotyczące rozdzielczości przestrzennej i czasowej oraz opisano kryteria zbieżności obliczeń numerycznych. W dalszej części pracy skupiono się na przedstawieniu wybranych modeli podsiatkowych dla przepływu i mieszania pasywnego chemicznie trasera. Modelowanie mieszania burzliwego z jednoczesną reakcją chemiczną oparto na metodzie zamknięcia wykorzystującej funkcję gotowości prawdopodobieństwa aproksymowaną przez funkcję beta. Jako reakcje testowe wybrano układ równoległych reakcji chemicznych zobojętniania zasady sodowej kwasem solnym i zasadową hydrolizę chlorooctanu etylu oraz proces precypitacji siarczanu baru następujący po zmieszaniu wodnych roztworów siarczanu sodu i chlorku baru. Przebieg wybranych procesów w pierwszej kolejności rozważano w reaktorach zbiornikowych z mieszadłem turbinowo-tarczowym o działaniu ciągłym i półokresowym. Obliczenia wykonano z wykorzystaniem modeli opartych na uśrednieniu Reynoldsa połączonych z modelem mieszalnika burzliwego i hipotezą zamykającą. Wyniki modelowe porównano z danymi doświadczalnymi, uzyskanymi zarówno z nieinwazyjnych pomiarów laserowych, takich jak anemometria laserowa, anemometria obrazowa, laserowo indukowana fluorescencja, jak i wartościami określającymi własności końcowe produktów, takimi jak końcowa selektywność reakcji i średni rozmiar cząstek. Następnie przedstawiono zastosowanie modeli wielkowirowych do symulacji przebiegu wyżej wymienionych procesów w dwóch typach reaktorów przepływowych: reaktorze kanałowym z dozowaniem poprzecznym oraz reaktorze rurowym wyposażonym w głowicę zderzeniową typu T-mieszalnik. W pracy zaproponowano nową procedurę modelowania mieszania z reakcją chemiczną z użyciem modeli wielkowirowych. Dobra zgodność wyników teoretycznych i doświadczalnych potwierdziła jej poprawność. Wynikiem niniejszej pracy jest opracowanie metod opisu matematycznego wpływu mieszania na przebieg złożonych procesów w reaktorach chemicznych, co daje możliwość przewidywania własności końcowych produktów, takich jak selektywność reakcji, morfologia i rozmiar cząstek. Wykazano również praktyczne możliwości stosowania modeli wielkowirowych w procesach inżynierii chemicznej i procesowej.

EN

The paper focuses on the methods of testing the influence of mixing on product qualities like selectivity, particle size distribution and morphology of the solid product. The practical aspects of these effects arc related to the fact that many chemical reactions leading to desirable intermediate and end-products are accompanied by side reactions producing undesired by-products. To predict, control and optimize mixing effects on chemical reactions, one needs to apply so-called micromixing models and closure methods, usually in combination with CFD. In recent years, large eddy simulation (LES) has become a very attractive method for simulations of reactive flow for a wide range of Reynolds number. It is an intermediate technique between direct numerical simulation (ONS) of turbulent flow and the solution of Reynolds-averaged equations. To evaluate predictions of models describing reactive mixing, one can employ specially designed mixing sensitive test reactions. In this paper, two characteristic processes were considered: a parallel reaction system that includes competitive neutralization of hydrochloric acid and alkaline hydrolysis of the ethyl chloro-acetate and precipitation of barium sulphate from aqueous solutions of barium chloride and sodium sulphate. Consideration of the effects of turbulent mixing on the course of the complex processes starts from modelling of stirred tank reactor of continuous and semibatch mode. In this case the non-equilibrium multiple-time-scale mixing model combined with a standard k-ɛ model and conditional moment closure were included. The obtained predictions were compared with experimental data, fluid velocity was measured using Laser Doppler Anemometry (LOA) and the Particle Image Velocity (PIV) technique, whilst the passive tracer concentration was measured using the Planar Laser Induced Fluorescence (PLIF) technique; also the final product quality was measured: the final selectivity or mean particle diameter. Next, the large eddy simulation method was applied to model the course of complex processes in two reactors: the square channel reactor with the cross dosing section and a tubular reactor with a T-shaped mixing head. The new procedures of subgrid modelling of the course of chemical reactions and precipitation were presented. The simulation results are compared with PIV and PLIF experimental data and With results obtained using the multiple time-scale mixing model combined with the k-ɛ model. All comparisons show a very good performance of the model based on LES. Practical applications of the presented models to predict the course of chemical reactions in different reactor types were presented.

12

LES-CMC and LES-Flamelet simulation of non-premixed methane flame (Sandia F)

Tyliszczak A.

Journal of Theoretical and Applied Mechanics

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2013

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Vol. 51 nr 4

859--871

EN

In this paper, the Large Eddy Simulation (LES) together with the Conditional Moment Closure (CMC) and flamelet combustion models have been applied for modelling of methane flame Sandia F. In the case of the CMC model, both instantaneous and time averaged values predicted numerically agree well with measurements. Attention was devoted to modelling aspects of the conditional scalar dissipation rate (SDR), which is a key quantity of the CMC approach. The two methods of computing SDR are compared with emphasis on a correct prediction of localised extinctions and on their influence on the mean values. It was found that the method of modelling of SDR has rather minor impact on the instantaneous values, whereas larger differences were observed in statistics. In the case of the flamelet model, although it is not able to predict extinctions and re-ignition, the mean values were in good agreement with the experiment.

13

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

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2013

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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.

14

Hybrid RANS/LES of plane jets impinging on a flat plate at small nozzle-plate distances

Kubacki S., Rokicki J., Dick E., Degroote J., Vierendeels J.

Archives of Mechanics

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2013

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Vol. 65, nr 2

143--166

EN

A k-ω based hybrid RANS/LES (Reynolds-averaged Navier-Stokes/large eddy simulation) model is tested for simulation of plane impinging jets at various nozzle-plate distances (H/B, where H is the distance and B is the slot's width) and various Reynolds numbers (based on the slot's width and the velocity in the symmetry plane). The studied combinations are H/B=2 for Re=10000, H/B=4 for Re=18000 and H/B=9.2 for Re=20000. The focus is on small distance of the nozzle exit to the plate. In LES mode, the hybrid RANS/LES model uses two definitions of the local grid size, one based on the maximum distance between the cell faces in the destruction term of the turbulent kinetic energy equation and one based on the cube root of the cell volume in the eddy-viscosity formula. This allows accounting for flow inhomogeneity on anisotropic grids. In RANS mode, the hybrid model turns into the newest version of the k-ω model by Wilcox.

15

Assessment of implementation variants of conditional scalar dissipation rate in LES-CMC simulation of auto-ignition of hydrogen jet

Tyliszczak A.

Archives of Mechanics

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2013

|

Vol. 65, nr 2

97-129

EN

In this paper the large eddy simulation (LES) and conditional moment closure (CMC) combustion model have been applied for modelling of auto-ignition of hydrogen jet issuing into a hot ambient co-flow. Most of the attention was devoted to modelling aspects of the conditional scalar dissipation rate which is a key quantity of the CMC model. Two models are compared with emphasis on differences in distributions in mixture fraction space. Analysis of mutual relations between the terms of CMC equations confirms importance of the conditional scalar dissipation rate. It is also shown that model constants are crucial from the point of view of an auto-ignition location and a flame lift off height. The numerical results are compared with experimental data and both the mean and the root mean square fluctuating values of the temperature and species mass fraction agree well with measurements.

16

Zastosowanie modeli wielkowirowych do symulacji przebiegu precypitacji siarczanu baru w reaktorach zderzeniowych

Makowski Ł., Orciuch W., Bałdyga J.

Inżynieria i Aparatura Chemiczna

|

2012

|

Nr 6

352-353

PL

W pracy przedstawiono sposób modelowania wpływu mieszania na przebieg procesu precypitacji siarczanu baru przy wykorzystaniu modeli wielkowirowych. Jako reaktory testowe wybrano dwa typy reaktorów zderzeniowych, charakteryzujące się wysoką intensywnością mieszania. Analiza wyników pokazała możliwość wpływania na jakość powstającego produktu poprzez dobór warunków mieszania reagentów i przydatność metody LES.

EN

The method of Large Eddy Simulation (LES) is applied in this work to simulate a course of complex processes in the non-premixed, turbulent reactive flows of incompressible fluids. Effects of mixing on various scales on the quality of final products are investigated for precipitation processes. To achieve the high intensity of mixing, two impinging jet reactors are employed. The study has shown an example of influence of process conditions on product quality and potential of LES for solving typical chemical and process engineering problems.

17

Thermal Boundary Condition Influence on Bi-Periodic Channel Flow with High Thermal Gradient

Aulery F., Baux Y., Toutant A., Bataille F.

Machine Dynamics Research

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2011

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Vol. 35, No. 1

19-28

EN

This study focuses on TLES (Thermal Large Eddy Simulation). We study the influence of thermal boundary conditions on mean and fluctuating profiles for a turbulent bi-periodic channel with a thermal gradient. TLES simulations show that mean profiles of longitudinal velocity, transversal velocities and their fluctuations are not affected by the therm 1 boundary conditions (flux or temperature imposed at wall). Profiles of mean temperature and mean vertical velocity are slightly changed by the thermal boundary conditions. The thermal gradient at wall is stronger and temperature slope in the middle of channel is lower with imposed temperature boundary conditions. Although there are the same in the middle of the channel, temperature fluctuations profiles are very different near to the wall according to thermal boundary conditions. In fact, with flux boundary conditions, the temperature fluctuation profile is similar close to the wall than in the middle of channel; with imposed temperature boundary conditions, theses profiles tend to zero close to the wall. This result is very important for industrial process because thermal fatigue due to thermal fluctuations at wall can damage it.

18

Evaluation of high order smooth filter in large eddy simulation of fully developed turbulent channel flow with explicit filtering

Nouri N. M., Motlagh S. Y., Yasari E.

Journal of Theoretical and Applied Mechanics

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2011

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Vol. 49 nr 4

1101-1114

EN

Explicit filtering with a smooth shape is one of approaches adopted in large eddy simulations (LES). The present work investigates the application of an explicit high order smooth (HOS) filter for the LES of a fully developed turbulent channel flow. The Crank-Nicolson scheme for time marching and second-order finite-volume schemes for spatial derivatives were implemented in this investigation. Implicit filtering, together with the Smagorinsky sub-grid scale (SGS) model, and explicit filtering, along with a HOS filter were studied in a fully turbulent channel flow. In this study, explicit HOS filtering with an explicit filter width to grid size ratio of 2.0 was in agreement with the available direct numerical simulation (DNS) data. However, the mean velocity profile in the streamwise direction was underestimated, and the turbulence intensity in the streamwise direction improved compared to other directions. Moreover, turbulence stresses were well predicted using the mixed SGS and sub-filter stress (SFS) models and applying the HOS filter as an explicit filter.

PL

Jawne filtrowanie typu gładkiego jest jedną z metod stosowanych w symulacjach wielkowirowych (tzw. LES). W pracy opisano zastosowanie filtra wysokiego rzędu o charakterystyce gładkiej (HOS) do symulacji wielkowirowej w pełni rozwiniętego turbulentnego przepływu w kanale. W badaniach wykorzystano metodę Cranka-Nicolsona oraz techniki przyrostów czasowych i objętości skończonych drugiego rzędu do wyznaczania pochodnych zmiennych przestrzennych. Przeanalizowano filtrowanie niejawne łącznie z podsieciowym modelem skalowym Smagorynskiego (SGS) oraz filtrowanie jawne HOS w pełni turbulentnego przepływu w kanale. W badaniach wy- kazano, że filtrowanie jawne za pomocą filtra HOS, którego stosunek długości do rozmiaru siatki wynosił 2, dało zgodne wyniki z dostępnymi rezultatami bezpośrednich symulacji numerycznych (DNS). Nieco niedoszacowany okazał się średni profil prędkości w kierunku wzdłużnym przepływu, natomiast poprawiły się wyniki dotyczące intensywności turbulencji właśnie w tym kierunku w porównaniu do kierunków pozostałych. Zaobserwowano ponadto, że zastosowanie kombinacji SGS z użyciem modeli subfiltrów naprężeń (SFS) oraz HOS jako filtru jawnego pozwoliło na poprawne wyznaczenie wartości naprężeń turbulentnych.

19

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

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2011

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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.

20

Modelowanie numeryczne LES burzliwego przepływu dwufazowego ciecz - ciecz w mieszalniku statycznym SMX

Pianko-Oprych P., Jaworski Z.

Inżynieria i Aparatura Chemiczna

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2010

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Nr 1

85-86

PL

Przedstawiono modelowanie przepływu dwufazowego ciecz-ciecz w mieszalniku statycznym SMX za pomocą numerycznej dynamiki płynów metodami LES i RANS. Uzyskano dobrą zgodność pomiędzy przewidywanymi i doświadczalnymi wartościami spadku ciśnienia i współczynnikami rozkładu stężeń w przestrzeni mieszalnika. Dla liczby Reynoldsa Re = 18 000 segregacja mieszanych cieczy o różnej relacji gęstości wskutek oddziaływania siły odśrodkowej charakteryzuje się podobnymi wartościami dla wyników LES i RANS.

EN

The CFD modelling of two-phase flow of liquid - liquid mixture in a SMX static mixer is presented. Two types of numerical approach were used in simulations: Large Eddy Simulations and the Reynolds averaged Navier-Stokes. A good agreement between the experimental and predicted values of pressure drop and concentration coefficient at the cross-sections of static mixer were obtained. The homogenization level reached in LES for cases 1 and 3 was similar with that obtained in RANS technique.