Classification and comparison of snow fences for the protection of transport infrastructures

Blowing snow or sand transport generates serious problems such as transport infrastructures buried under snow or sand in many parts of the world. Some of the most important problems that snow and sand storms can cause include drivers getting trapped on the roads, traffic being held up indefinitely, accidents occurring and populations being isolated. Snow fences provide a solution to this problem as they can hold back the snow, preventing displacement and wind-induced drifting. In this way, they reduce these problems on transport infrastructures and improve visibility, providing safer driving conditions. In this review, a classification is proposed of snow fences based on three basic types: earth, structural and living snow fences. Among the structural ones, non-porous and porous snow fences are distinguished. The different possibilities in terms of the placement of snow fences are also analyzed. Finally, different types of snow fences have been compared under design, construction and operation criteria. This review can provide initial guidelines for technicians to choose the best snow fence for blizzard conditions

Performance analysis of wind fence models when used for truck protection under crosswind through numerical modeling

This paper is focused on truck aerodynamic analysis under crosswind conditions by means of numerical modeling. The truck was located on the crest of an embankment during the study. In order to analyze the performance of three wind fence models, the truck's aerodynamic coefficients were obtained and compared in two different situations either with or without the wind fences installed. In addition, the effect of both height and porosity of wind fence models on the aerodynamic coefficients acting on truck with respect to separation distance between the truck and the wind fence, was analyzed. A finite volume (or computational fluid dynamic) code was used to carry out the numerical modeling. The Reynolds-averaged Navier?Stokes (RANS) equations along with the k?? SST turbulence model were used to predict the behavior of turbulent flow. With respect to the results, the influence of the distance on the rollover coefficient is soft for all height values studied except for the lowest value (1 m of fence height), where the maximum value of rollover coefficient was obtained for the truck position closer to the fence. Regarding fence porosity, its effect on rollover coefficient is stronger for truck positions on road closer to the wind fence model.This work was supported by the OASIS Research Project that was co-financed by CDTI (Spanish Science and Innovation Ministry) and developed with the Spanish companies: Iridium, OHL Concesiones, Abertis, Sice, Indra, Dragados, OHL, Geocisa, GMV, Asfaltos Augusta, Hidrofersa, Eipsa, PyG, CPS, AEC and Torre de Comares Arquitectos S.L. and 16 research centres. The authors would also like to thank the GICONSIME research group of the University of Oviedo (Spain) for their collaboration in this research

Improvement of a System for Catchment, Pretreatment and Treatment of Runoff Water Using PIV Tests and Numerical Simulation

This paper studies how to improve the efficiency of a new system for catchment, pretreatment, and treatment of runoff water (SCPT). This system is integrated into an urban sustainable gravity settler that can decrease diffusive pollution. This study provides important advantages for the ecosystem by improving new sustainable drainage to clean runoff water. In this paper, an investigation methodology known as hybrid engineering (HE) was used. HE combines experimental tests and numerical simulations, both of them conducted on a 1:4-scale prototype. In this study, numerical simulations by the finite-volume method (FVM) and experimental tests by particle image velocimetry (PIV) were compared. A strong correlation between the numerical and experimental analysis was found. Next, the efficiency of the SCPTwas optimized by design of experiments (DOE). Analysis of experimental and numerical results and their comparison are presented in this paper.The authors wish to express their gratitude to the Spanish Ministry of Economy and Competitiveness for the research project BIA2009-08272 funding

Optimization of Snow Drifting Mitigation and Control Methods for Iowa Conditions

TR-626 1 80224 00Blowing and drifting of snow is a major concern for transportation efficiency and road safety in regions where their development is common. One common way to mitigate snow drift on roadways is to install plastic snow fences. Correct design of snow fences is critical for road safety and maintaining the roads open during winter in the US Midwest and other states affected by large snow events during the winter season and to maintain costs related to accumulation of snow on the roads and repair of roads to minimum levels. Of critical importance for road safety is the protection against snow drifting in regions with narrow rights of way, where standard fences cannot be deployed at the recommended distance from the road. Designing snow fences requires sound engineering judgment and a thorough evaluation of the potential for snow blowing and drifting at the construction site. The evaluation includes site-specific design parameters typically obtained with semi-empirical relations characterizing the local transport conditions. Among the critical parameters involved in fence design and assessment of their post-construction efficiency is the quantification of the snow accumulation at fence sites. The present study proposes a joint experimental and numerical approach to monitor snow deposits around snow fences, quantitatively estimate snow deposits in the field, asses the efficiency and improve the design of snow fences. Snow deposit profiles were mapped using GPS based real-time kinematic surveys (RTK) conducted at the monitored field site during and after snow storms. The monitored site allowed testing different snow fence designs under close to identical conditions over four winter seasons. The study also discusses the detailed monitoring system and analysis of weather forecast and meteorological conditions at the monitored sites. A main goal of the present study was to assess the performance of lightweight plastic snow fences with a lower porosity than the typical 50% porosity used in standard designs of such fences. The field data collected during the first winter was used to identify the best design for snow fences with a porosity of 50%. Flow fields obtained from numerical simulations showed that the fence design that worked the best during the first winter induced the formation of an elongated area of small velocity magnitude close to the ground. This information was used to identify other candidates for optimum design of fences with a lower porosity. Two of the designs with a fence porosity of 30% that were found to perform well based on results of numerical simulations were tested in the field during the second winter along with the best performing design for fences with a porosity of 50%. Field data showed that the length of the snow deposit away from the fence was reduced by about 30% for the two proposed lower-porosity (30%) fence designs compared to the best design identified for fences with a porosity of 50%. Moreover, one of the lower-porosity designs tested in the field showed no significant snow deposition within the bottom gap region beneath the fence. Thus, a major outcome of this study is to recommend using plastic snow fences with a porosity of 30%. It is expected that this lower-porosity design will continue to work well for even more severe snow events or for successive snow events occurring during the same winter. The approach advocated in the present study allowed making general recommendations for optimizing the design of lower-porosity plastic snow fences. This approach can be extended to improve the design of other types of snow fences. Some preliminary work for living snow fences is also discussed. Another major contribution of this study is to propose, develop protocols and test a novel technique based on close range photogrammetry (CRP) to quantify the snow deposits trapped snow fences. As image data can be acquired continuously, the time evolution of the volume of snow retained by a snow fence during a storm or during a whole winter season can, in principle, be obtained. Moreover, CRP is a non-intrusive method that eliminates the need to perform man-made measurements during the storms, which are difficult and sometimes dangerous to perform. Presently, there is lots of empiricism in the design of snow fences due to lack of data on fence storage capacity on how snow deposits change with the fence design and snow storm characteristics and in the estimation of the main parameters used by the state DOTs to design snow fences at a given site. The availability of such information from CRP measurements should provide critical data for the evaluation of the performance of a certain snow fence design that is tested by the IDOT. As part of the present study, the novel CRP method is tested at several sites. The present study also discusses some attempts and preliminary work to determine the snow relocation coefficient which is one of the main variables that has to be estimated by IDOT engineers when using the standard snow fence design software (Snow Drift Profiler, Tabler, 2006). Our analysis showed that standard empirical formulas did not produce reasonable values when applied at the Iowa test sites monitored as part of the present study and that simple methods to estimate this variable are not reliable. The present study makes recommendations for the development of a new methodology based on Large Scale Particle Image Velocimetry that can directly measure the snow drift fluxes and the amount of snow relocated by the fence

Numerical Investigation of the Effects of Sand Collision on the Aerodynamic Behaviour of a High-Speed Train Subjected to Yaw Angles

In this paper, the aerodynamic performance of the head car of a CRH2 train running in sandstorms was investigated. A numerical simulation method based on Realizable k-ε turbulence model was used to explore the flow features around the high-speed train. The accuracy of mesh resolution and methodology of CFD was validated by wind tunnel tests. A discrete phase model (DPM) was adopted to investigate the effects of sand particle properties (diameter and restitution coefficient) on the aerodynamic performance of the head car. Yaw angle effects with the sand-laden flow on the aerodynamic coefficient were also discussed. The results show that the drag force, lift force, lateral force, and overturning moment of the head car increase significantly due to the sand, and the sand particle properties have dominant effects on the aerodynamic performance of the head car. The impact probability of sand particles on the vehicle increases with the sand particle diameter and the yaw angle increasing. Larger restitution coefficients lead to lager forces of the head car, resulting in more contribution to the aerodynamic coefficients. Owing to the sand collision, a larger yaw angle causes more contribution to the aerodynamic performance of the head car, and the influence of sand properties on the drag force, lateral force and overturning moment are enhanced with the increase of the yaw angle. Using appropriate coatings around the high-speed train can not only reduce the energy consumption, but also improve the lateral stability and the critical operational speed of the high-speed train in the sandstorms

Wind Shielding Analysis for Cold Regions Using Experimental and Numerical Techniques

The thesis presents a systematic experimental and numerical study on the interactions among porous fence, airflow, and windblown snowdrifts, a knowledge that will contribute to optimize the performance of porous wind shielding system in Cold Regions. A comprehensive review of the concepts, theories, techniques, and key findings associated with the research work has been undertaken. The key technical parameters influencing fence performance have been systematically studied by means of wind tunnel experimental investigations and Computational Fluid Dynamics (CFD) simulations. The study has found that porosity is the most influential structural parameter affecting the performance of porous fences in many aspects. Fence height stands a significant positive position in terms of its performance. It was found that fence performance is not sensitive to the changes of approaching atmospheric airflow velocity. Nevertheless, a bottom gap can improve snow fence trap efficiency. All of those findings agree with most of the findings of other researchers, which affirms that the research methodology adopted in this research is sound. Physical experimental work was performed to assess the reliability and credibility of the numerical models. Those models have been intentionally simplified, which made them easier to construct and quicker to obtain numerical solutions at a lower computational cost. Furthermore, the numerical models demonstrate the level of competence acquired through this research that is implemented in the optimisation of fence design. Special attention has been paid to the issues where elaborate research work has not been systematically reached in the open literature, this includes areas such as the effects of arrangement of porous holes, fence surface shear, and directions of wind load with respect to the fence, etc. Correlation between the reattachment length, the shelter distance, and the creation and distribution of fence surface shear is reported, to the author’s knowledge, for the first time in the open literature. General guidelines for the design of shelters based on porous fences have been established through this study. For example, the desirable size of hole range should be identified beforehand, and porous holes with sharp angular corners should usually be avoided in the fence design. It is recommended to place the fence within an angle of 30° to the wind load, where the effective shelter distance can be estimated in a linearized equation, and the normal drag coefficient can be described as a function of cos2θ. Optimal design of the arrangement of porous holes will maximize the fence performance, especially when the close fence environment is of concern. Although the definition of fence effective zone is still vague in the research field, the key factors influencing the fence effective zone have been investigated by evaluating the reduction of wind velocity leeward of the fence in this thesis. It is found that the fence effective zone is not sensitive to the change of approaching airflow velocity, and that increasing fence height will increase the physical size of the fence effective zone, but not in a proportional manner. It is also concluded that fence effective zone will be significantly reduced when the non-normal wind load is inclined at an angle greater than 30° to the fence. The effective zone increases effectively when the fence porosity is optimal. In contrast to the majority of published research work, the transient snow transport model presented in this work considers the snow transport rate as a whole without distinguishing the rate in saltation and suspension layer. The numerical study indicated that the position of the snow crest is mainly determined by the fence height, while porosity and bottom gap mainly affect the downwind deposition length. The optimal porosity for snow fences is in the range of 0.4 to 0.5, which is greater than the one for wind fences, which lies in the range from 0.25 to 0.35. Two snow crests have been observed leeward the fence at the onset of snow deposition, when the fence was placed without a bottom gap to the snow ground. This finding has not been encountered in any of the reported research work. Wind tunnel simulations of snowdrift around the fences have marginally under-predicted the sizes of snow deposition. The numerical predictions were quantitatively and qualitatively in good agreement with the field observations. This incompetence of wind tunnel experiments on porous fences implies that numerical modelling can play a more important role in snow fence research

Experimental and numerical description of rapid granular flows and some baseline constraints for simulating 3-dimensional granular flow dynamics

Accurate prediction of rapid granular flow behavior is essential to optimize protection measures from hazardous natural granular flows like snow avalanches and landslides and to design efficient production facilities for granulate processing industries. So far, most successful models for rapid granular flow descriptions employ depth-averaging, assuming an essentially constant velocity over depth. This assumption greatly reduces calculation power but can lead to incorrect predictions in regions of strong velocity shearing in the flow depth direction, e.g., during the impact on an obstacle. To overcome these limitations, this study introduces a novel type of non-depth-averaged fluid dynamics simulations for rapid granular flows of cohesionless material. A series of small scale experiments with industrial (polyvinyl chloride (PVC)) and natural (sand) granular material was performed (i) to select and refine the appropriate rheological model, (ii) to yield a better insight into velocity profiles and (iii) to obtain parameters for comparison with numerical simulations. Based on these experiments, Coulomb-type friction was selected as rheological model. A Poly(methyl methacrylate) channel set-up with variable inclination angle in combination with high-speed image recording and an open source particle image velocimetry (PIV) software developed in this study allowed detailed observation of velocity profiles during flow inception, undisturbed flows, flows encountering obstacles, and shock scenarios. The PIV measurements revealed considerable changes in velocity between layers of the granular flow and thus underpin the necessity to perform non-depth-averaged simulations in order to accurately describe the flow behavior in all aspects. Comparison of the depth-averaged simulation model of the Savage-Hutter type and the non-depth-averaged simulation method introduced here with the experiments revealed that certain quantities, like the flow height and shape could only be accurately predicted using the non-depth-averaged simulations. Furthermore, the non-depth-averaged simulations were well capable of predicting the observed velocity profiles and produce accurate predictions of associated quantities like strain rates and slip velocities for both materials in most experiments. Nevertheless, this study also revealed cases where both depth-averaged and non-depth-averaged methods generate similar predictions, e.g., the height of an undisturbed flow and deposition shapes. A detailed summary of parameters and dynamic variables in different experiments, and their predictability by both methods is provided. This serves as a guideline to decide when to employ the reduced but faster depth-averaged methods and when more calculation power intensive, but more accurate, non-depth-averaged methods must be employed. The non-depth-averaged method developed in this study was further validated to measure its predictive power in three dimensional experiments with obstacles. Also here, accurate predictions were observed. Furthermore, a method for the introduction of complex topographies into the simulation process was developed, allowing the direct integration of real mountain topographies. As pilot tests, simulations of granular flows on a complex experimental topography and a real case snow avalanche described in the literature were performed. The results demonstrated that the new method can be transferred to complex topographies and yields good predictions. These findings can serve as a basis for further refinement of the model and its expansions to describe more complex events, e.g., the entrainment of snow mass. Taken together, the novel, non-depth-averaged model and simulation technique build in this study based on the experimental observation are a suitable tool to predict important flow dynamical quantities in non-cohesive granular flows of both natural and industrial origins. Furthermore, it can serve as a basis for the development of a non-depth-averaged predictive model for real scale hazardous granular flows and is thus an important step towards the correct prediction of granular flow behavior for risk assessment in endangered regions

5 European & African Conference on Wind Engineering

The 5th European-African Conference of Wind Engineering is hosted in Florence, Tuscany, the city and the region where, in the early 15th century, pioneers moved the first steps, laying down the foundation stones of Mechanics and Applied Sciences (including fluid mechanics). These origins are well reflected by the astonishing visionary and revolutionary studies of Leonardo Da Vinci, whose kaleidoscopic genius intended the human being to become able to fly even 500 years ago… This is why the Organising Committee has decided to pay tribute to such a Genius by choosing Leonardo's "flying sphere" as the brand of 5th EACWE

Aeronautical engineering: A continuing bibliography with indexes (supplement 253)

This bibliography lists 637 reports, articles, and other documents introduced into the NASA scientific and technical information system in May, 1990. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics