The essential limiting factor of the power transmission line transfer capabilities is the maximal allowed temperature of the conductor that should not be exceeded to avoid excessive sags. A commonly used conservative approach is to limit transfer capability to the worst case scenarios, i.e. hot, sunny, windless days. Of course, system operators strive to raise the limit with more sophisticated models that take into account actual weather conditions or even weather forecasts. As a consequence, there has been substantial research done on Dynamic Thermal Rating (DTR) models in the last few decades. Based on accumulated knowledge the leading standards in the field published guidelines for thermal rating for operative use. However, the proposed models rely only on empirical relations for determination of the temperature gradient on the surface of the conductor that dictates the heat flux due to the advection. This heat flux is the most intense cooling mechanism in play, and also the most complex to model. In this paper, we extend the discussion about advective cooling with a direct simulation of temperature and velocity fields near the conductor with the focus on the natural convection regime. The introduced model considers joule heat generation and heat transport within the power line and its vicinity, fluid flow driven by buoyancy force, solar heating, and radiation. The solution procedure uses RBF-FD numerical method combined with Poisson disk sampling nodal positioning algorithm. The results of the simulation are presented in terms of temperature and velocity magnitude contour plots, convergence analyses, and comparison of convective heat losses of simulated results to IEC, IEEE and CIGRE standards.
{"title":"RBF-FD BASED DYNAMIC THERMAL RATING OF OVERHEAD POWER LINES","authors":"G. Kosec, J. Slak","doi":"10.2495/AFM180261","DOIUrl":"https://doi.org/10.2495/AFM180261","url":null,"abstract":"The essential limiting factor of the power transmission line transfer capabilities is the maximal allowed temperature of the conductor that should not be exceeded to avoid excessive sags. A commonly used conservative approach is to limit transfer capability to the worst case scenarios, i.e. hot, sunny, windless days. Of course, system operators strive to raise the limit with more sophisticated models that take into account actual weather conditions or even weather forecasts. As a consequence, there has been substantial research done on Dynamic Thermal Rating (DTR) models in the last few decades. Based on accumulated knowledge the leading standards in the field published guidelines for thermal rating for operative use. However, the proposed models rely only on empirical relations for determination of the temperature gradient on the surface of the conductor that dictates the heat flux due to the advection. This heat flux is the most intense cooling mechanism in play, and also the most complex to model. In this paper, we extend the discussion about advective cooling with a direct simulation of temperature and velocity fields near the conductor with the focus on the natural convection regime. The introduced model considers joule heat generation and heat transport within the power line and its vicinity, fluid flow driven by buoyancy force, solar heating, and radiation. The solution procedure uses RBF-FD numerical method combined with Poisson disk sampling nodal positioning algorithm. The results of the simulation are presented in terms of temperature and velocity magnitude contour plots, convergence analyses, and comparison of convective heat losses of simulated results to IEC, IEEE and CIGRE standards.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132794191","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nanotechnology research has recently been introduced in the mechanical engineering program at West Texas A&M University through undergraduate thermal-fluid science projects. The projects were offered at the junior and senior level in the program as part of either an independent research course or thermal-fluid design course. The projects have been carefully selected to provide the students with an exposure to nanotechnology concepts through experimental studies. Several of those projects were design-oriented in their focus. This paper addresses four of those projects: 1) design of a closed-loop electronics cooling system using nanofluids; 2) performance evaluation of a radiator-type automobile heat exchanger using a circulating nanofluid; 3) evaluation of the energy absorption by alumina nanoparticles in solar vacuumed tubes; and 4) design of a cost effective filter for water purification in developing countries using clay material impregnated with silver nanoparticles for anti-microbial protection capability. The first two projects investigated the effect of using alumina water-based nanofluid compared to distilled water in enhancing the heat transfer performance of the systems. Parametric studies were conducted to investigate the effect flow operating conditions, nanoparticle size and concentration have on the heat exchanger effectiveness. The third project investigated the effect alumina nanoparticles have on the heat gained by an alumina water-based nanofluid in a solar vacuumed tube. In the fourth project, a clay filter was designed for optimal permeability, porosity, filter thickness, daily flow rate, and silver nanoparticles concentration in the clay. An investigation of the effectiveness of the filter was conducted by analyzing certain parameters such as the water turbidity level and presence of bacteria and in the filtered water.
{"title":"INTRODUCING NANOTECHNOLOGY THROUGH UNDERGRADUATE THERMAL-FLUID RESEARCH PROJECTS","authors":"R. Issa","doi":"10.2495/AFM180131","DOIUrl":"https://doi.org/10.2495/AFM180131","url":null,"abstract":"Nanotechnology research has recently been introduced in the mechanical engineering program at West Texas A&M University through undergraduate thermal-fluid science projects. The projects were offered at the junior and senior level in the program as part of either an independent research course or thermal-fluid design course. The projects have been carefully selected to provide the students with an exposure to nanotechnology concepts through experimental studies. Several of those projects were design-oriented in their focus. This paper addresses four of those projects: 1) design of a closed-loop electronics cooling system using nanofluids; 2) performance evaluation of a radiator-type automobile heat exchanger using a circulating nanofluid; 3) evaluation of the energy absorption by alumina nanoparticles in solar vacuumed tubes; and 4) design of a cost effective filter for water purification in developing countries using clay material impregnated with silver nanoparticles for anti-microbial protection capability. The first two projects investigated the effect of using alumina water-based nanofluid compared to distilled water in enhancing the heat transfer performance of the systems. Parametric studies were conducted to investigate the effect flow operating conditions, nanoparticle size and concentration have on the heat exchanger effectiveness. The third project investigated the effect alumina nanoparticles have on the heat gained by an alumina water-based nanofluid in a solar vacuumed tube. In the fourth project, a clay filter was designed for optimal permeability, porosity, filter thickness, daily flow rate, and silver nanoparticles concentration in the clay. An investigation of the effectiveness of the filter was conducted by analyzing certain parameters such as the water turbidity level and presence of bacteria and in the filtered water.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125310684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The current work presents a 1D analytic model for a PV aeromechanical system and compares it with a 3D CFD model. The 1D model is based on the analogy between airflow and electric current. A PV aeromechanical system enables accurate positioning of thin, flexible substrates by creating an air cushion between the substrate and an accurate, rigid surface, having bi-directional aeromechanical spring-like behavior. Nozzle can be described as the relation they allow between flow (Q) and pressure drop (∆p): R ∝ ∆p/Qn where n depends on the characteristic behavior and (in this work) is between 1 and 2. The 1D model is computationally much cheaper than the 3D CFD model. Although the 1D model requires one CFD 3D model analysis for quantifying the exact resistance in the air cushion, it allows very fast calculations of performance when varying the other parameters of air gap, pressure/vacuum supply, and flowrate. The difference between 1D analytic model and full CFD analysis, in terms of air gap stiffness results was approximately 3%.
{"title":"1D ANALYTIC MODEL FOR PV AEROMECHANICAL SYSTEMS","authors":"Ronen S. Lautman, Liron Shani, B. Nishri","doi":"10.2495/AFM180221","DOIUrl":"https://doi.org/10.2495/AFM180221","url":null,"abstract":"The current work presents a 1D analytic model for a PV aeromechanical system and compares it with a 3D CFD model. The 1D model is based on the analogy between airflow and electric current. A PV aeromechanical system enables accurate positioning of thin, flexible substrates by creating an air cushion between the substrate and an accurate, rigid surface, having bi-directional aeromechanical spring-like behavior. Nozzle can be described as the relation they allow between flow (Q) and pressure drop (∆p): R ∝ ∆p/Qn where n depends on the characteristic behavior and (in this work) is between 1 and 2. The 1D model is computationally much cheaper than the 3D CFD model. Although the 1D model requires one CFD 3D model analysis for quantifying the exact resistance in the air cushion, it allows very fast calculations of performance when varying the other parameters of air gap, pressure/vacuum supply, and flowrate. The difference between 1D analytic model and full CFD analysis, in terms of air gap stiffness results was approximately 3%.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126642793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, forced convective heat transfer in a rectangular channel filled with aluminium metal foam and exposed to a constant heat flux is examined numerically with the thermal non-equilibrium assumption. A constant heat flux boundary condition is applied from the upper side of the channel. A numerical model is first validated with the available experimental results. Next, the effects of different configurations of metal foams with different porosities and different PPI values on fluid flow and heat transfer are examined. Results are given by average Nusselt number and pressure drop factor for different Reynolds numbers. A performance factor is also defined and the effect of different configurations on performance factor is comparatively examined. The results show that the heat transfer rate and pressure drop significantly depending upon Reynolds number, configuration and porosity.
{"title":"LOCAL THERMAL NON-EQUILIBRIUM MODELLING OF CONVECTIVE HEAT TRANSFER IN HIGH POROSITY METAL FOAMS","authors":"Ubade Kemerli, K. Kahveci","doi":"10.2495/AFM180301","DOIUrl":"https://doi.org/10.2495/AFM180301","url":null,"abstract":"In this paper, forced convective heat transfer in a rectangular channel filled with aluminium metal foam and exposed to a constant heat flux is examined numerically with the thermal non-equilibrium assumption. A constant heat flux boundary condition is applied from the upper side of the channel. A numerical model is first validated with the available experimental results. Next, the effects of different configurations of metal foams with different porosities and different PPI values on fluid flow and heat transfer are examined. Results are given by average Nusselt number and pressure drop factor for different Reynolds numbers. A performance factor is also defined and the effect of different configurations on performance factor is comparatively examined. The results show that the heat transfer rate and pressure drop significantly depending upon Reynolds number, configuration and porosity.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126649756","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The addition of nanoscale particles into the fluid is recently a common technology used in several industrial processes, since it has been proved that by introducing particles into the working fluid, the heat transfer characteristics can be improved crucially. However, the understanding of fundamental characteristics of nanofluid saturated porous media domains is still limited. The paper presents a numerical study of free convection in a porous enclosure saturated with a nanofluid. A single-phase mathematical model has been employed assuming that the suspension of nanoparticles in fluid can be modelled as a new fluid with effective properties. Fluid flow in porous media is modelled with the macroscopic Navier–Stokes equations, where the governing parameters are averaged over the representative elementary volume. The obtained set of partial differential equations is solved with use of the numerical code based on the Boundary Element Method, which was primarily developed for pure fluid flow applications and was already proved to be efficient for solving several problems of fluid mechanics. Numerical results for different values of governing parameters are obtained, focusing on the effect of different volume fractions of added nanoparticles and different inclination angles of the porous enclosure on the overall heat transfer through porous domain.
{"title":"NUMERICAL STUDY OF CONVECTIVE HEAT TRANSFER IN AN INCLINED POROUS ENCLOSURE SATURATED WITH NANOFLUID","authors":"J. Stajnko, R. Jecl, J. Ravnik","doi":"10.2495/AFM180031","DOIUrl":"https://doi.org/10.2495/AFM180031","url":null,"abstract":"The addition of nanoscale particles into the fluid is recently a common technology used in several industrial processes, since it has been proved that by introducing particles into the working fluid, the heat transfer characteristics can be improved crucially. However, the understanding of fundamental characteristics of nanofluid saturated porous media domains is still limited. The paper presents a numerical study of free convection in a porous enclosure saturated with a nanofluid. A single-phase mathematical model has been employed assuming that the suspension of nanoparticles in fluid can be modelled as a new fluid with effective properties. Fluid flow in porous media is modelled with the macroscopic Navier–Stokes equations, where the governing parameters are averaged over the representative elementary volume. The obtained set of partial differential equations is solved with use of the numerical code based on the Boundary Element Method, which was primarily developed for pure fluid flow applications and was already proved to be efficient for solving several problems of fluid mechanics. Numerical results for different values of governing parameters are obtained, focusing on the effect of different volume fractions of added nanoparticles and different inclination angles of the porous enclosure on the overall heat transfer through porous domain.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126978743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper examines the migration of solid particles in a high-mixing flow inside an inclined annular pipe. An experimental study of non-Newtonian fluids in the layer region through annular tubes with axial flow and rotation of the inner cylinder was carried out. It was demonstrated that the gravitational force acting on the particle stream plays a very important role in directional drilling, cuttings particle movement, and cuttings transport. The pressure drop and the particle velocity of the drilling fluid (CMC and Bentonite solution) corresponding to the inclination and rotation of the drill pipe were measured. The hydraulic pressure drop owing to the mixture flow increased because of the friction between the wall and the solid particles. Further, a high particle feed concentration increased the pressure drop because of the friction between the solid particles in the fluid stream. The advantages of a rotating and an inclined annulus pipe, for the particle transport phenomena, were confirmed in this study.
{"title":"A STUDY ON CUTTINGS TRANSPORT IN DRILLING FLUIDS WITH INCLINED ANNULUS","authors":"Sangmok Han, N. Woo, Young-Ju Kim","doi":"10.2495/afm180101","DOIUrl":"https://doi.org/10.2495/afm180101","url":null,"abstract":"This paper examines the migration of solid particles in a high-mixing flow inside an inclined annular pipe. An experimental study of non-Newtonian fluids in the layer region through annular tubes with axial flow and rotation of the inner cylinder was carried out. It was demonstrated that the gravitational force acting on the particle stream plays a very important role in directional drilling, cuttings particle movement, and cuttings transport. The pressure drop and the particle velocity of the drilling fluid (CMC and Bentonite solution) corresponding to the inclination and rotation of the drill pipe were measured. The hydraulic pressure drop owing to the mixture flow increased because of the friction between the wall and the solid particles. Further, a high particle feed concentration increased the pressure drop because of the friction between the solid particles in the fluid stream. The advantages of a rotating and an inclined annulus pipe, for the particle transport phenomena, were confirmed in this study.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130071016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The effects of free-stream turbulence (FST) on the evolution of hairpin vortices during the process of laminar-turbulent transition are investigated by direct numerical simulation. The simulations are conducted for FST intensities of 0–6% and a free-stream Mach number of 0.5. FST changes the symmetry of the hairpin vortex, the arrangement of vortices inside the boundary layer, the location of high friction at the wall, and the scales of the vortices. The relationship between high-friction regions at the wall and hairpin vortices convected downstream is investigated by analyzing the computed flow fields. When FST is introduced along with inlet sinuous disturbances, asymmetric hairpin vortices and numerous secondary hairpin vortices, which are different from the case of no FST, are generated. The boundary-layer transition is characterized by an increase in skin-friction. As a result of vortex creation very close to the wall, high-friction regions are generated. To detect the vortex parts responsible for generating the high-friction regions, a new judgement algorithm for interior points is derived based on the Euler angle. The interior points of the near-wall vortices responsible for generating such highfriction regions are successfully visualized as a group of points in R3. The high-friction regions are the tips of hairpin legs and the regions of near-wall vortices induced beneath a hairpin packet. These regions often correspond to the periphery of the hairpin packets.
{"title":"DNS INVESTIGATION INTO THE EFFECT OF FREE-STREAM TURBULENCE ON HAIRPIN-VORTEX EVOLUTION","authors":"K. Matsuura","doi":"10.2495/AFM180151","DOIUrl":"https://doi.org/10.2495/AFM180151","url":null,"abstract":"The effects of free-stream turbulence (FST) on the evolution of hairpin vortices during the process of laminar-turbulent transition are investigated by direct numerical simulation. The simulations are conducted for FST intensities of 0–6% and a free-stream Mach number of 0.5. FST changes the symmetry of the hairpin vortex, the arrangement of vortices inside the boundary layer, the location of high friction at the wall, and the scales of the vortices. The relationship between high-friction regions at the wall and hairpin vortices convected downstream is investigated by analyzing the computed flow fields. When FST is introduced along with inlet sinuous disturbances, asymmetric hairpin vortices and numerous secondary hairpin vortices, which are different from the case of no FST, are generated. The boundary-layer transition is characterized by an increase in skin-friction. As a result of vortex creation very close to the wall, high-friction regions are generated. To detect the vortex parts responsible for generating the high-friction regions, a new judgement algorithm for interior points is derived based on the Euler angle. The interior points of the near-wall vortices responsible for generating such highfriction regions are successfully visualized as a group of points in R3. The high-friction regions are the tips of hairpin legs and the regions of near-wall vortices induced beneath a hairpin packet. These regions often correspond to the periphery of the hairpin packets.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126455466","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In motorcycle competitions, aerodynamics play a fundamental role. In order to improve the performance of racing motorbikes, different front-wheel geometries have been studied by means of numerical CFD simulations. Different lean angles were analysed for each geometry and the air motionfield were calculated. The considered geometries range from standard spoked design to solid wheels. . ® source free software OpenFOAM state and dynamic simulations were run using the open steady Both This open-source code was selected because, like all the computer programs of this type, it allows a higher flexibility with respect to any close-source commercial software, allowing a customization of the code by implementing specific models for the analysis of the physical problem of interest and also, at the same time, a higher parallelization of the computations. Steady-state simulations were performed using a rotating reference frame (MRF) while, for the transients, a partially-rotating mesh was adopted, thus taking advantage of the internal sliding interfaces (AMI). Drag, lift and force-moments have been calculated with the aim of examining the stability and manoeuvrability of the different configurations.
{"title":"COMPARATIVE STUDY OF THE AERODYNAMIC PERFORMANCES OF MOTORCYCLE RACING WHEELS USING NUMERICAL CFD SIMULATIONS","authors":"F. Concli, M. Gobbi, C. Gorla","doi":"10.2495/AFM180181","DOIUrl":"https://doi.org/10.2495/AFM180181","url":null,"abstract":"In motorcycle competitions, aerodynamics play a fundamental role. In order to improve the performance of racing motorbikes, different front-wheel geometries have been studied by means of numerical CFD simulations. Different lean angles were analysed for each geometry and the air motionfield were calculated. The considered geometries range from standard spoked design to solid wheels. . ® source free software OpenFOAM state and dynamic simulations were run using the open steady Both This open-source code was selected because, like all the computer programs of this type, it allows a higher flexibility with respect to any close-source commercial software, allowing a customization of the code by implementing specific models for the analysis of the physical problem of interest and also, at the same time, a higher parallelization of the computations. Steady-state simulations were performed using a rotating reference frame (MRF) while, for the transients, a partially-rotating mesh was adopted, thus taking advantage of the internal sliding interfaces (AMI). Drag, lift and force-moments have been calculated with the aim of examining the stability and manoeuvrability of the different configurations.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116258514","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Flexible structures, such as cable-supported bridges, are prone to suffer from vortex-induced vibrations (VIV) under wind flow, as their span lengths are steadily growing in the last decades. VIV is a phenomenon that takes place at reduced wind speeds. The movements of the structure at VIV are self-limited and their frequency corresponds with the natural frequency of the structure (lock in). Therefore, VIV affects the structure’s serviceability and can cause fatigue related damage. Hence, the need for identifying and avoiding this phenomenon at the early design stages is a key issue in long-span bridges design. In the present study a rectangular cylinder of width to depth ratio 4:1, which is a common simplification of a bridge deck cross section, is analysed for the static case as well as undergoing free vibration in the vertical direction under wind flow. These analyses have been carried out by 2D URANS CFD simulations, adopting two different turbulence models: the k − ω SST, which is based upon the Boussinesq eddy-viscosity approximation, and the Reynolds Stress Model, which directly calculates the components of the specific Reynolds stresses. For the static case the force coefficients, Strouhal number and the pressure coefficient distributions were calculated and compared with the available experimental data. In the case of the free-to-oscillate 4:1 rectangular cylinder, the oscillation amplitudes are compared with wind tunnel data reported in the literature. In addition, the frequencies and phase-lags between the time-dependent lift coefficient and the vertical oscillations are studied.
{"title":"STUDY OF A STATIC AND VERTICALLY FREE-TO-OSCILLATE 4:1 RECTANGULAR CYLINDER BY MEANS OF 2D URANS SIMULATIONS","authors":"A. J. Álvarez, F. Nieto, S. Hernández","doi":"10.2495/AFM180051","DOIUrl":"https://doi.org/10.2495/AFM180051","url":null,"abstract":"Flexible structures, such as cable-supported bridges, are prone to suffer from vortex-induced vibrations (VIV) under wind flow, as their span lengths are steadily growing in the last decades. VIV is a phenomenon that takes place at reduced wind speeds. The movements of the structure at VIV are self-limited and their frequency corresponds with the natural frequency of the structure (lock in). Therefore, VIV affects the structure’s serviceability and can cause fatigue related damage. Hence, the need for identifying and avoiding this phenomenon at the early design stages is a key issue in long-span bridges design. In the present study a rectangular cylinder of width to depth ratio 4:1, which is a common simplification of a bridge deck cross section, is analysed for the static case as well as undergoing free vibration in the vertical direction under wind flow. These analyses have been carried out by 2D URANS CFD simulations, adopting two different turbulence models: the k − ω SST, which is based upon the Boussinesq eddy-viscosity approximation, and the Reynolds Stress Model, which directly calculates the components of the specific Reynolds stresses. For the static case the force coefficients, Strouhal number and the pressure coefficient distributions were calculated and compared with the available experimental data. In the case of the free-to-oscillate 4:1 rectangular cylinder, the oscillation amplitudes are compared with wind tunnel data reported in the literature. In addition, the frequencies and phase-lags between the time-dependent lift coefficient and the vertical oscillations are studied.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124335983","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. Nieto, M. C. Montoya, A. Fontán, S. Hernández, C. Rapela, A. J. Álvarez, J. Á. Jurado, Alejandro Casteleiro, V. Garcia
Twin-box decks have recently been introduced in long-span bridges because this type of slotted crosssection provides flutter critical wind speeds higher than mono-box streamlined decks for flexible structures. The two parallel girders are linked together by means of transverse beams with a central gap between them. Experimental and CFD studies have shown that the length of this central gap plays a key role in the aerodynamic and aeroelastic responses of the deck. In this work, the geometry of the Stonecutters Bridge in Hong Kong (China) has been chosen as an application case to conduct a series of parametric studies based on wind tunnel tests. The tests have been conducted under smooth flow, for a 1:80 geometric scale sectional model able to modify its slot length. For an ample range of gap lengths, the force coefficients and the flutter derivatives have been obtained. It has been found that the slopes of the lift and moment coefficients suffer important changes with the gap length. In the same manner, it has also been found that the gap distance modifies the values of flutter derivatives. Finally, for a longspan bridge example, the critical flutter speeds for different gaps are obtained, aiming to identify the gap length that provides a safer threshold for the flutter phenomenon. The results reported herein permit the assessment of the impact caused by the gap length in the aerodynamic and aeroelastic responses of twin-box decks.
{"title":"WIND TUNNEL STUDY ON THE EFFECT OF THE GAP WIDTH IN THE AERODYNAMIC AND AEROELASTIC RESPONSES OF TWIN-BOX DECKS","authors":"F. Nieto, M. C. Montoya, A. Fontán, S. Hernández, C. Rapela, A. J. Álvarez, J. Á. Jurado, Alejandro Casteleiro, V. Garcia","doi":"10.2495/AFM180071","DOIUrl":"https://doi.org/10.2495/AFM180071","url":null,"abstract":"Twin-box decks have recently been introduced in long-span bridges because this type of slotted crosssection provides flutter critical wind speeds higher than mono-box streamlined decks for flexible structures. The two parallel girders are linked together by means of transverse beams with a central gap between them. Experimental and CFD studies have shown that the length of this central gap plays a key role in the aerodynamic and aeroelastic responses of the deck. In this work, the geometry of the Stonecutters Bridge in Hong Kong (China) has been chosen as an application case to conduct a series of parametric studies based on wind tunnel tests. The tests have been conducted under smooth flow, for a 1:80 geometric scale sectional model able to modify its slot length. For an ample range of gap lengths, the force coefficients and the flutter derivatives have been obtained. It has been found that the slopes of the lift and moment coefficients suffer important changes with the gap length. In the same manner, it has also been found that the gap distance modifies the values of flutter derivatives. Finally, for a longspan bridge example, the critical flutter speeds for different gaps are obtained, aiming to identify the gap length that provides a safer threshold for the flutter phenomenon. The results reported herein permit the assessment of the impact caused by the gap length in the aerodynamic and aeroelastic responses of twin-box decks.","PeriodicalId":261351,"journal":{"name":"Advances in Fluid Mechanics XII","volume":"298 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134286679","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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