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1

Impact of Tunnel Stern Design on Hydrodynamic Characteristics of Catamarans

Osmanov Osman, Aksu Erhan

Polish Maritime Research

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2025

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nr 1

31--43

EN

The growth in worldwide maritime activities has resulted in the extensive use of catamarans for passenger and cargo transportation. This study investigates the influence of stern tunnel modifications on catamarans, emphasising their unique design and hydrodynamic features. Computational fluid dynamics (CFD) is used to assess resistance and flow around the hull. Initially, the length, depth, and width of the tunnel were determined as design parameters based on the main dimensions of an original NPL 4A model. Single-hull forms are produced based on these parameters, with nine different stern tunnel configurations. The flow behaviour around the hull was determined by solving the Reynolds-averaged Navier-Stokes equations using the Ansys Fluent commercial software within a Froude number range 0.3-1.0. Subsequently, double-hull analyses are conducted using the best-performing model, in terms of resistance from the single-hull analyses. The results demonstrate that all single-hull designs achieve resistance reductions of up to 39% compared to the original model. The optimal hull form, in terms of resistance performance, similarly showed up to 15% reduction in resistance when applied to the double-hull configuration.

2

Development of a computational framework for low-Reynolds number propeller aeroacoustics

Szulc O., Suresh T., Flaszyński P.

Archives of Mechanics

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2025

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Vol. 77, nr 1

67--85

EN

The paper focuses on the development and validation of a new computational framework designed for the prediction of tonal and broadband noise radiation of propellers of unmanned aerial vehicles (UAVs) operating in the low-Reynolds number regime. The depictedworkflowis hybrid, consisting of in-house, academic, and commercial software components intended for automatic pre-processing (block-structured grid generation), efficient flow solution (computational fluid dynamics, CFD), and acoustic post-processing (computational aeroacoustics, CAA). The delayed detached-eddy simulation (DDES) approach constitutes the basis for estimation of mean blade loading and surface pressure fluctuations due to the existence of massive flow separation that are fed as input to an in-house acoustic solver based on Ffowcs Williams and Hawkings (FW-H) linear acoustic analogy (Farassat’s formulation 1A). The initial phase of validation of the acoustic tool is conducted for elementary rotating and oscillating point sources of mass and momentum (forces) using available analytical solutions for reference. Later, a two-bladed model propeller from the Delft University of Technology (TUD) is analyzed with FLOWer (compressible CFD solver from DLR), relying on RANS or DDES approaches and equipped with either 1-equation strain adaptive linear Spalart-Allmaras or 2-equation shear-stress transport k-! turbulence closures. The equations are solved using both classical second-order and modern fourth-order accurate numerical schemes. For a selected rotational speed of 5000 RPM (tip Mach number of 0.23 and tip Reynolds number of 50 • 103) and the range of the advance ratio J of the axial flight, the predicted propeller aerodynamic performance is confronted with the measurements of TUD. Lastly, for exemplary J = 0 (hover conditions, tripped boundary layer), the resolved pressure fluctuations (URANS/k-! SST and DDES/k-!SST) are directly used as input for acoustic analysis of tonal (harmonic) and broadband noise at an in-plane observer location and the resultant propeller sound pressure level signature is compared with the measured spectrum confirming the applicability of the developed framework for such computationally demanding cases of flow-induced noise.

3

Various blowing-suction schemes for manipulating turbulent boundary layers

Shkvar Yevhenii, Shiju E., Kryzhanovskyi Andrii, Redchyts Dmytro

Transactions on Aerospace Research

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2024

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Nr 1 (274)

19--28

EN

The methodology of efficiency analysis of turbulent flow modification by making permeable sections in the streamlined wing surface with the aim to reduce aerodynamic drag is the principal subject of the presented research. The numerical analysis of the effect of laterally and longitudinally located permeable sections on boundary-layer properties showed the following flow features: (1) the most effective place for permeable surface is an upwind side of the wing; (2) multi-sectional blowing can simply be organised as non-uniform (especially in the case of laterally arranged permeable sections) that brings additional flexibility to change the blowing intensity depending on flight mode and, first of all, on angle of attack; and (3) arrays of longitudinal permeable sections allow to intensify turbulent vortical structures exchange in the lateral direction and improve flow stability to stall. Moreover, due to creating the regular anisotropy of the boundary layer in the lateral direction, this modified blowing technique can potentially have some synergistic properties, which can give the additional benefit. All these effects are too delicate and their experimental study cannot be performed with the use of directed measurements of aerodynamic forces. The comparison of the obtained flow properties with the corresponding experimental data demonstrates an appropriate level of agreement.

4

Numerical Analysis of Aerodynamic Performance of a Fixed-Pitch Vertical Axis Wind Turbine Rotor

Rogowski Krzysztof, Michna Jan, Ferreira Carlos

Advances in Science and Technology. Research Journal

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2024

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Vol. 18, no. 6

97--109

EN

The aim of this study was to assess the accuracy of predicting the aerodynamic loads and investigate the aerodynamic wake characteristics of a vertical axis wind turbine (VAWT) rotor using a simplified two-dimensional numerical rotor model and an advanced numerical approach - the Scale Adaptive Simulation (SAS) coupled with the four-equation γ-Re_θ turbulence model. The challenge for this approach lies in the operating conditions of the rotor, the blade pitch angles, and the very small geometric dimensions of the rotor. The rotor, with a diameter of 0.3m, operates at a low tip speed ratio of 2.5 and an extremely low blade Reynolds number of approximately 22,000, whereas the pitch angles, β, are: -10, 0, and 10 degrees. Validation was conducted based on high-fidelity measurements obtained using the PIV technique at TU Delft. The obtained results of rotor loads and velocity profiles are surprisingly reliable for cases of β=0° and β=-10°. However, the 2-D model is too imprecise to estimate both aerodynamic loads and velocity fields accurately.

5

Feasibility study of RANS in predicting propeller cavitation in behind-hull conditions

Zhang Yuxin, Wu Xiao-ping, Lai Ming-yan, Zhou Guo-ping, Zhang Jie

Polish Maritime Research

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2020

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nr 4

26--35

EN

The propeller cavitation not only affects the propulsive efficiency of a ship but also can cause vibration and noise. Accurate predictions of propeller cavitation are crucial at the design stage. This paper investigates the feasibility of the Reynolds-averaged Navier–Stokes (RANS) method in predicting propeller cavitation in behind-hull conditions, focusing on four aspects: (i) grid sensitivity; (ii) the time step effect; (iii) the turbulence model effect; and (iv) ability to rank two slightly different propellers. The Schnerr-Sauer model is adopted as the cavitation model. A model test is conducted to validate the numerical results. Good agreement on the cavitation pattern is obtained between the model test and computational fluid dynamics. Two propellers are computed, which have similar geometry but slightly different pitch ratios. The results show that RANS is capable of correctly differentiating the cavitation patterns between the two propellers in terms of the occurrence of face cavitation and the extent of sheet cavitation; moreover, time step size is found to slightly affect sheet cavitation and has a significant impact on the survival of the tip vortex cavitation. It is also observed that grid refinement is crucial for capturing tip vortex cavitation and the two-equation turbulence models used – realizable k-ε and shear stress transport (SST) k-ω – yield similar cavitation results.

6

Numerical investigating the effect of water depth on ship resistance using RANS CFD method

Hoa Nguyen Thi Ngoc, Vu Bich Ngoc, Tran Ngoc Tu, Chien Nguyen Manh, Le Tat Hien

Polish Maritime Research

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2019

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nr 3

56--64

EN

On inland waterways the ship resistance and propulsive characteristics are strictly related to the depth of the waterway, thus it is important to have an understanding of the influence of water depth on ship hydrodynamic characteristics. Therefore, accurate predictions of hydrodynamic forces in restricted waterways are required and important. The aim of this paper is investigating the capability of the commercial unsteady Reynolds– Averaged Navier–Stokes (RANS) solver to predict the influence of water depth on ship resistance. The volume of fluid method (VOF) is applied to simulate the free surface flow around the ship. The hull resistance in shallow and deep water is compared. The obtained numerical results are validated against related experimental studies available in the literature.

7

Numerical investigation of the drag force reduction for homogeneous column of vehicles

Hamiga Władysław, Ciesielka Wojciech

New Trends in Production Engineering

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2019

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Vol. 2, Iss. 1

524--531

EN

This paper presents simulation studies on the aerodynamics of vehicles moving in an organized column. The object of research is a column that consist of three vehicles of the same type (homogeneous column). In this research geometry of Ford Transit was used. As a part of the studies, the air drag forces acting on individual vehicles were calculated. The results are presented in dimensionless drag coefficient. The influence of the distance between cars on the generated force was also determined. In the first stage of the work, a numerical model was developed based on the Ahmed body reference structure. The calculations were carried out for 9 different velocities. The obtained results of the drag coefficient were compared with the work of other authors. The applied turbulence model and parameters of the boundary layer were used to create a numerical model of a moving column of vehicles. Mesh independence for numerical model of van was verified. The Finite Volume Method was implemented in the ANSYS Fluent program and used for the calculations. The use of supercomputers was necessary due to the large size of the grid.

8

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

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2019

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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.

9

Numerical study of step forward swept angle effects on the hydrodynamic performance of a planing hull

Nourghasemi H., Bakhtiari M., Ghassemi H.

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2017

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nr 51 (123)

35--42

EN

One of the most effective methods to diminish the drag of a planing craft is to use a step at the bottom of the hull. A stepped hull causes a reduction of the wetted area and, as a result, a decrease in the drag. The step may be designed as a straight line through the entire width of the hull or may be V-shaped with a forward or backward swept angle. In this paper, the effects of the step forward swept angle on the hydrodynamic performance of a hard chine planing vessel are investigated by finite volume method (FVM). Reynolds-Averaged Navier Stokes (RANS) equations with a standard k-ε turbulence model coupled with volume of fluid (VOF) equations are solved in order to simulate a transient turbulent free surface flow around the hull with the help of Ansys CFX software. In order to predict hull motions, equations of rigid body motions for two degrees of freedom (2-DOF) are coupled with fluid flow governing equations. To validate the presented numerical model, first the numerical results are compared with available experimental data, and then the obtained numerical results of the drag, dynamic trim, sinkage, wetted keel length, wetted chine length, pressure distribution on the hull, wetted surface and wake profile at different Froude numbers and step angles are presented and discussed.

10

3d mesh model for rans numerical research on marine 4-stroke engine

Kowalski J., Jaworski P.

Journal of Polish CIMAC

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2014

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Vol. 9, no 1

87--94

EN

The article consist the 3d mesh analysis prepared for simulation of the processes in combustion chamber of marine compression ignition engine. The three moving meshes models where prepared: A–mesh for engine cycle work simulation; B –mesh of combustion chamber volume for work stroke simulations, no valves included; C-mesh of combustion chamber including mountings screw whole for work stroke simulations , no valves including. Prepared mesh where used for numerical simulations of injection and combustion processes in engine combustion chamber. Type C model, even if the total number of cells is lower in comparison to B model, result in calculation time increase. B and C models are solution for fast and robust validation of injection and auto ignition model parameters. Type A model is only one suitable for full cycle simulation. Only with accurate initial and boundary conditions the qualitative results of the injection, mixing and combustion process can be obtain on mesh type B and C.

11

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

Dziubińska A., Kiszkowiak Ł.

Mechanik

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2013

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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.

12

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

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2011

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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.

13

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

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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.

14

Evaluation of piping erosion by means of temperature analysis

Radzicki K., Bonelli S.

Studia Geotechnica et Mechanica

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2009

|

Vol. 31, nr 2

17-34

EN

Piping is the most serious menace to the safety of an earth hydraulic work. We present the study of the piping erosion identification by means of temperature analysis. Extensive steady and unsteady numerical computations for the coupled heat and water transport in the porous domain, with the downstream side pipe opening, are described. Choice of the numerical RANS (Reynolds-averaged Navier-Stokes) model is explained to take into account mixed laminar and turbulent water flow in the pipe. Computation covered the range of hydraulic diffusivity from 10-7 to 10-4 m2/s and made use of the finite volume method with the FLUENT numerical modelization platform. The basic principles of the pipe thermal influences are presented with the evaluation of the possibilities of identifying piping parameters with temperature measurements. Correct identification of the pipe thermal influence was found to be important in interpretating thermal data measured that are necessary for hydraulic earthworks.

PL

Przebicie hydrauliczne jest najpoważniejszym zagrożeniem dla bezpieczeństwa ziemnej budowli piętrzącej. Zanalizowano możliwości rozpoznania przebicia hydraulicznego, stosując metodę analizy termicznej. Opisano szczegółowe modelowanie ustalonego i nieustalonego sprzężonego transportu wody i ciepła w ośrodku porowatym z otworem otwartym na granicy odpowietrznej. Wyjaśniono wybór modelu numerycznego RANS (Reynolds-averaged Navier-Stokes), który umożliwia równoczesne modelowanie laminarnego i turbulentnego przepływu cieczy, gdy korzysta się z metody objętości skończonych i platformy obliczeń numerycznych FLUENT. Analiza objęła zakres współczynnika dyfuzji hydraulicznej od 10-7 do 10-4 m2/s. Zaprezentowano kluczowe parametry termicznego wpływu otworu oraz ocenę możliwości identyfikacji parametrów przebicia hydraulicznego przez pomiary temperatury. Stwierdzono, że poprawna identyfikacja wpływu termicznego otworu istotnie wpływa na właściwą interpretację pomiarów temperatury ziemnych obiektów hydrotechnicznych.

15

Some remarks on modelling and simulation of turbulence

Drobniak S., Bogusławski A., Tyliszczak A.

Journal of Theoretical and Applied Mechanics

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2008

|

Vol. 46 nr 2

243-256

EN

The paper presents contemporary developments in the field of deterministic description of turbulence with special reference to Large Eddy Simulation (LES) methods. The limitations of conventional turbulence modelling based on stochastic methodology have been discussed, and reasons for development of deterministic approach outlined. It has been shown that the computational power of the fastest available computers restrict possible DNS (Direct Numerical Simulation) solutions to the range of small Reynolds numbers. Finally, basic assumptions have been formulated for the LES formalism that seem to offer a reasonable compromise between the tendency towards the deterministic solution to Navier-Stokes equations and the existing computational resources.

PL

Praca przedstawia współczesny stan wiedzy w dziedzinie numerycznego modelowania turbulencji ze szczególnym uwzględnieniem metody LES (ang. Large Eddy Simulation). Przedstawiono ograniczenia modeli turbulencji typu RANS, opartych o uśrednione w czasie równania Reynoldsa oraz wskazano perspektywy deterministycznego ujęcia turbulencji z użyciem metod DNS (ang. Direct Numerical Simulation). Wykazano również, że możliwości najszybszych dostępnych obecnie komputerów ograniczają możliwe obszary aplikacji DNS do przepływów o stosunkowo niskich liczbach Reynoldsa. Następnie sformułowano podstawowe zależności dla metod LES i wskazano ich perspektywiczne znaczenie dla inżynierskiego modelowania przepływów turbulentnych.

16

Modelowanie numeryczne RANS i URANS przepływu burzliwego typu ciecz-ciecz w mieszalniku Kenics

Jaworski Z., Murasiewicz H.

Czasopismo Techniczne. Mechanika

|

2008

|

R. 105, z. 5-M

187-201

PL

Przedstawiono wyniki modelowania przepływu burzliwego dwufazowego typu ciecz-ciecz w mieszalniku statycznym z dziesięcioma wkładkami Kenics. W badaniach numerycznych wykorzystano technikę RANS i URANS dla liczby Reynoldsa, Re równej 10 000. W modelowaniu CFD przepływu dwóch płynów newtonowskich zastosowano podejście pseudohomogeniczne. Porównano wyniki symulacji uzyskanych dla metody RANS i URANS i sformułowano wnioski.

EN

Results of turbulent, two-phase flow simulations in a static Kenics mixer formed by ten inserts are presented. The computational fluid dynamics study was carried out using both the RANS and URANS approaches. Reynolds number was 10 000. The simulation results obtained for the RANS and URANS methods were compared and conclusions drawn.

17

Gas-solid particle mixture in vertical duct by rans approach

Kartushinsky A., Michaelides S., Pihlak U.

Inżynieria Chemiczna i Procesowa

|

2005

|

T. 26, z. 3

411-426

EN

In the paper, two-phase turbulent current in the duct is under consideration with implementation of 2D Reynolds Average Navier-Stokes equations (RANS approach) to validate and study manifold processes that may include particle-particle, particle-fluid, particle-wall interactions occurring in the flowfield. Predictions of the model are particle-particle collision accounted by original model of closure of driving equations of dispersed solid phase, particle-fluid interaction determined by Crowe.s two-way coupling approach together with the viscous drag force, the lift Magnus and Saffman forces arisen from the motion of inertial rotated particles in non-uniform velocity field of the gas phase and the particle gravitation. The particles slip along the walls while non-slip boundary conditions are set for the gas phase. As numerical calculations show the RANS method reasonably describes velocity of the carrier fluid (gas phase) and velocity of the particles as well as the influence of the solid particles on a distribution of the turbulent energy. The profiles of the particle mass concentration are also presented.

PL

Rozważano dwufazowy przepływ burzliwy w kanale dwuwymiarową metodą uśredniania równań różniczkowych Reynoldsa (RANS) do opisu i badania różnych procesów, w których mogą występować oddziaływania typu cząstka ciała stałego-cząstka ciała stałego, cząstka ciała stałego-płyn i cząstka ciała stałego-ściana. W rozważaniach zderzeń typu cząstka-cząstka wykorzystano model zamknięcia równań ruchu cząstek rozproszonych. Dla układu cząstka-płyn oddziaływania określano metodą Crowe.a dwuwymiarowego przybliżenia z uwzględnieniem sił oporu lepkiego oraz sił unoszenia Magnusa i Staffmana. W przypadku bezwładnie rotujących cząstek w niejednorodnym polu prędkości w fazie gazowej uwzględniano poślizg cząstek wzdłuż ściany, podczas gdy w warunkach granicznych poślizg nie występuje. Na podstawie obliczeń numerycznych stwierdzono, że metoda uśredniania Reynoldsa dobrze opisuje prędkość płynu nośnego (faza gazowa) i prędkość cząstek, jak również wpływ cząstek ciała stałego na rozkład energii burzliwej.Przedstawiono również rozkłady stężenia cząstek ciała stałego.

18

Numerical analysis of cavitated flows in mixed-flow pump impellers

Sedlar M., Marsik F., Safarik P.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

|

2003

|

Z. 77

57-64

EN

This paper deals with the flow model based on the Navier-Stokes computation and the simulation of bubble dynamics in the flow field, solving the Rayeigh-Plesset equation alongflow characteristics. No interaction between bubbles is considered. The initial bubble sizedistribution is based on a precribed distribution law and the initial void fraction. The flowpast the blades of mixed-flow pump impellers is investigated including the tip leakage flowsfor three different impeller configurations, aimed to predict the impeller configuration influence on cavitation phenomena, especially the blade surface regions endangered with the cavitation phenomena, especially the blade surface regions endangered with the cavitation erosion.

19

The Modeling of unsteady turbulent flows in turbomachines

Magagnato F.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2001

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Vol. 5, No 4

477-494

EN

The suitability of existing models for the simulation of flow through turbomachines is investigated and compared with a recently proposed adaptive turbulence model. Discussed are the improvements in accuracy that can be achieved by using non-linear turbulence models and unsteady calculations. The adaptive turbulence model is based on two equation turbulence modeling. It uses the temporal and spatial scales of the flow field to automatically adapt itself to the unresolved turbulent fluctuations. At its asymptotic limits it reduces either to a Direct Numerical Simulation – when the turbulent scales are in the order of the Kolmogorov micro scale – or to a standard two equation model – when the fluctuations are not resolved at all. In order to compare the quality of the presented models two cases have been considered: the flow past a cylinder and a subsonic as well as transonic flow past the VKI turbine blade. Calculations have been performed for each case using all the models and the results have been compared with measurements. The unsteady calculations gave better agreement with the experimental data demonstrating the superiority over steady state calculations for turbomachines.