Numerical investigation on the aerodynamic characteristics of high-speed train under turbulent crosswind

Increasing velocity combined with decreasing mass of modern high-speed trains poses a question about the influence of strong crosswinds on its aerodynamics. Strong crosswinds may affect the running stability of high-speed trains via the amplified aerodynamic forces and moments. In this study, a simulation of turbulent crosswind flows over the leading and end cars of ICE-2 high-speed train was performed at different yaw angles in static and moving ground case scenarios. Since the train aerodynamic problems are closely associated with the flows occurring around train, the flow around the train was considered as incompressible and was obtained by solving the incompressible form of the unsteady Reynolds-averaged Navier–Stokes (RANS) equations combined with the realizable k-epsilon turbulence model. Important aerodynamic coefficients such as the side force and rolling moment coefficients were calculated for yaw angles ranging from −30° to 60° and compared with the results obtained from wind tunnel test. The dependence of the flow structure on yaw angle was also presented. The nature of the flow field and its structure depicted by contours of velocity magnitude and streamline patterns along the train’s cross-section were presented for different yaw angles. In addition, the pressure coefficient around the circumference of the train at different locations along its length was computed for yaw angles of 30° and 60°. The computed aerodynamic coefficient outcomes using the realizable k-epsilon turbulence model were in good agreement with the wind tunnel data. Both the side force coefficient and rolling moment coefficients increase steadily with yaw angle till about 50° before starting to exhibit an asymptotic behavior. Contours of velocity magnitude were also computed at different cross-sections of the train along its length for different yaw angles. The result showed that magnitude of rotating vortex in the lee ward side increased with increasing yaw angle, which leads to the creation of a low-pressure region in the lee ward side of the train causing high side force and roll moment. Generally, this study shows that unsteady CFD-RANS methods combined with an appropriate turbulence model can present an important means of assessing the crucial aerodynamic forces and moments of a high-speed train under strong crosswind conditions

Numerical investigation on the aerodynamic characteristics of high-speed train under turbulent crosswind

Increasing velocity combined with decreasing mass of modern high-speed trains poses a question about the influence of strong crosswinds on its aerodynamics. Strong crosswinds may affect the running stability of high-speed trains via the amplified aerodynamic forces and moments. In this study, a simulation of turbulent crosswind flows over the leading and end cars of ICE-2 high-speed train was performed at different yaw angles in static and moving ground case scenarios. Since the train aerodynamic problems are closely associated with the flows occurring around train, the flow around the train was considered as incompressible and was obtained by solving the incompressible form of the unsteady Reynolds-averaged Navier–Stokes (RANS) equations combined with the realizable k-epsilon turbulence model. Important aerodynamic coefficients such as the side force and rolling moment coefficients were calculated for yaw angles ranging from −30° to 60° and compared with the results obtained from wind tunnel test. The dependence of the flow structure on yaw angle was also presented. The nature of the flow field and its structure depicted by contours of velocity magnitude and streamline patterns along the train’s cross-section were presented for different yaw angles. In addition, the pressure coefficient around the circumference of the train at different locations along its length was computed for yaw angles of 30° and 60°. The computed aerodynamic coefficient outcomes using the realizable k-epsilon turbulence model were in good agreement with the wind tunnel data. Both the side force coefficient and rolling moment coefficients increase steadily with yaw angle till about 50° before starting to exhibit an asymptotic behavior. Contours of velocity magnitude were also computed at different cross-sections of the train along its length for different yaw angles. The result showed that magnitude of rotating vortex in the lee ward side increased with increasing yaw angle, which leads to the creation of a low-pressure region in the lee ward side of the train causing high side force and roll moment. Generally, this study shows that unsteady CFD-RANS methods combined with an appropriate turbulence model can present an important means of assessing the crucial aerodynamic forces and moments of a high-speed train under strong crosswind conditions

Methodology of integral analysis and optimization of aircraft structures aerodynamic surfaces

Представљени су интегрални процеси пројектовања, нумеричког прорачуна и оптимизације три различите геометрије. Изведене су раванске анализе опструјавања ветротурбине са вертикалном осом обртања нумеричким моделима различитим по физичким основама и сложености имплементације. Извршене су анализе осетљивости параметара и формиране су одговарајуће полуемпиријске зависности оптималног радног режима ветротурбине и поправног фактора којим је могуће кориговати резултате раванске анализе. Спроведена су два независна поступка оптимизације ројем честица параметара ветротурбине, једнокритеријумски и вишекритеријумски. Написана је функција за спровођење вишекритеријумске оптимизације и проналажење Парето скупа оптималних вредности. Развијена је методологија анализе ветротурбине којом се врши симулација њеног реалног рада на терену при изразито променљивим брзинама ветра. На примеру раванског струјања кроз линеарну каскаду дефинисана је и валидирана одговарајућа нумеричка поставка којом се могу проценити перформансе каскаде у опсегу окозвучних радних режима. Формиран је скрипт за генерисање прорачунске мреже око модела профила по чијој горњаци је распоређен одређени број млазева којима је могуће вршити активно управљање граничним слојем. Написане су функције за одређивање места одвајања струјања и активацију одговарајућих млазева. Извршена је процена перформанси каскаде увођењем вештачких неуронских мрежа. Испитиване су неуронске мреже различитих карактеристика, које су потом трениране и тестиране...Integral processes of design, computation and optimization for three different geometries are presented. Two-dimensional analyses of fluid flow around vertical axis wind turbines have been performed with the use of numerical models of different physical basis and complexity. Parameter sensitivity analyses have been conducted and necessary semiempirical relations concerning optimal working regime and a coefficient that enables a correction of the planar analyses have been defined. Two independent optimizations have been performed, single- and multi-objective, by particle swarm optimization method. A function for performing a multi-objective optimization and finding Pareto set has been written. Analysis methodology that enables the simulation of a vertical axis wind turbine field test under time varying wind conditions has been developed. In the investigation into planar fluid flow through linear cascades, a suitable numerical setting for the evaluation of the cascade performances for a range of transonic regimes has been defined and validated. A script for the generation of computational grids around a profile with a certain number of jets positioned along its upper surface, which can be used for boundary layer control, has been written. Functions for determination of the separation point and jet activation have been written. An assessment of the cascade performances has been done by artificial neural networks. Different neural networks have firstly been investigated, and then trained and tested..

WMLES of flows around small-scale propellers - estimating aerodynamic performance and wake visualization

Wall-modeled large-eddy simulation (WMLES) is an advanced mathematical model for turbulent flows which solves for the low-pass filtered numerical solution. A subgrid-scale (SGS) model is used to account for the effects of unresolved small-scale turbulent structures on the resolved scales (i.e. for the dissipation of the smaller scales), while the flow behavior near the walls is modeled by wall functions (thus reducing the requirements for mesh fineness/quality). This paper investigates the possibilities of applying WMLES in the estimation of aerodynamic performance of small-scale propellers, as well as in the analysis of the wake forming downstream. Induced flows around two propellers designed for unmanned air vehicles (approximately 25 cm and 75 cm in diameter) in hover are considered unsteady and turbulent (incompressible or compressible, respectively). Difficulties in computing such flows mainly originate from the relatively low values of Reynolds numbers (several tens to several hundreds of thousands) when transition and other flow phenomena may be present. The choice of the employed numerical model is substantiated by comparisons of resulting numerical with available experimental data. Whereas global quantities, such as thrust and power (coefficients), can be predicted with satisfactory accuracy (up-to several percents), distinguishing the predominant flow features remains challenging (and requires additional computational effort). Here, wakes forming aft of the propeller rotors are visualized and analyzed. These two benchmark examples provide useful guidelines for further numerical and experimental studies of small-scale propellers

Estimation of wind turbine blade aerodynamic performances computed using different numerical approaches

Although much employed, wind energy systems still present an open, contemporary topic of many research studies. Special attention is given to precise aerodynamic modeling performed in the beginning since overall wind turbine performances directly depend on blade aerodynamic performances. Several models different in complexity and computational requirements are still widely used. Most common numerical approaches include: i) momentum balance models, ii) potential flow methods and iii) full computational fluid dynamics solutions. Short explanations, reviews and comparison of the existing computational concepts are presented in the paper. Simpler models are described and implemented while numerous numerical investigations of isolated horizontal-axis wind turbine rotor consisting of three blades have also been performed in ANSYS FLUENT 16.2. Flow field is modeled by Reynolds Averaged Navier Stokes (RANS) equations closed by two different turbulence models. Results including global parameters such as thrust and power coefficients as well as local distributions along the blade obtained by different models are compared to available experimental data. Presented results include fluid flow visualizations in the form of velocity contours, sectional pressure distributions and values of power and thrust force coefficients for a range of operational regimes. Although obtained numerical results vary in accuracy, all presented numerical settings seem to slightly under-or over-estimate the global wind turbine parameters (power and thrust force coefficients). Turbulence can greatly affect the wind turbine aerodynamics and should be modeled with care

Two-dimensional numerical analysis of active flow control by steady blowing along foil suction side by different urans turbulence models

The effects of active separation control by steady blowing jets were investigated numerically on three different examples: subsonic flow past Aerospatiale A airfoil at 13 degrees angle-of-attack, transonic flow past NACA 0012 airfoil at 4 degrees angle-of attack, and transonic flow in linear compressor/turbine cascade. Performed analyses are two-dimensional, flow is turbulent (or transitional) while fluid is viscous and compressible. Jets are positioned along the suction sides of the foils, the first one being located just upstream of the separation point, and modeled by source terms added to flow equations. Several different jet diameters and intensities are investigated. As the choice of turbulence model affects the final solution of Reynolds equations, turbulence is modeled by four different models: Spalart-Allmaras, realizable k-epsilon, k-omega SST, and gamma-Re-theta, and a comparison of obtained results is performed. Goals of the study include definition of an adequate numerical setting that enables sufficiently correct simulation of the problems in question as well as evaluation of the possible increase in aerodynamic performances. Lift coefficients, lift-to-drag ratios or relative pressure differences are improved for all controlled cases

Aerodynamic characteristics of high speed train under turbulent cross winds: A numerical investigation using unsteady-RANS method

Usled trenda povećanja brzina i smanjenja mase modernih vozova velikih brzina neophodno je razmatrati dejstvo jakih bočnih vetrova na njihovu aerodinamiku. Jaki bočni vetrovi mogu uticati na stabilnost ovih vozova usled povećanja aerodinamičke sile i momenta. U ovoj analizi sprovedene su numeričke simulacije turbulentnih bočnih vetrova koji duvaju preko prvog i poslednjeg vagona brzog voza ICE-2 pri različitim uglovima skretanja. Problemi stabilnosti voza su blisko vezani za strujno polje oko voza. Okolni fluid smatran je nestišljivim, a strujno polje oko voza dobijeno je rešavanjem nestacionarnih Rejnoldsovih jednačina (RANS) u kombinaciji sa realizable k-epsilon turbulentnim modelom. Aerodinamički koeficijenti važni za ovu analizu, koeficijent sile klizanja i momenta skretanja, izračunati su za uglove skretanja u opsegu od -30° do 60° i upoređeni sa rezultatima dobijenim u aerotunelu. Kvalitativna analiza zavisnosti strujnih struktura od ugla skretanja je takođe sprovedena i prikazana.Increasing velocity combined with reduced mass of modern high speed trains poses the question of influence of strong cross winds on its aerodynamics. Strong cross winds may affect the running stability of high speed trains via the amplified aerodynamic forces and moments. In this study, simulations of turbulent cross wind flows over the leading and end car of ICE-2 high speed train have been performed at different yaw angles The train aerodynamic problems are closely associated with the flows occurring around train. The flow around the train has been considered as incompressible and was obtained by solving the incompressible form of the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations combined with the realizable k-epsilon turbulence model. Important aerodynamic coefficients such as the side force and rolling moment coefficients have been calculated for yaw angles ranging from -30° to 60° and compared to results obtained from wind tunnel tests. The dependence of the flow structure on yaw angle has also been presented

Current state and future trends in boundary layer control on lifting surfaces

Successful flow control may bring numerous benefits, such as flow stabilization, flow reattachment, separation delay, drag reduction, lift increase, aerodynamic performance improvement, energy efficiency increase, shock delay or weakening, noise reduction, etc. For these purposes, many different flow control devices, which can be classified as passive, semi-active and active, have been designed and tested. This review paper aims to highlight the most promising and commonly employed boundary layer control methods as well as outline their potential in specific applications in aerospace and energy engineering. Referenced studies, performed on various geometries (flat plates, channels, airfoils, wings, blades, cylinders), are primarily numerical or experimental. Although enhanced aerodynamic performance is achieved in many cases, further research is required to draw general conclusions. This paper aims to demonstrate that, in the future, we may expect further developments of flow control actuators, as well as their increased application