Fence Case Research Articles

A turbulent crosswind simulation method at high-speed railway tunnel entrance: Based on field test and geometric turbulence generator

It is common for high-speed trains (HSTs) to abruptly switch between a tunnel and a flat ground along high-speed rail lines. When encountering strong crosswinds, the safety of HSTs in such running scenarios will be severely threatened. The simulation of the turbulent component of an incoming crosswind is very important to restore the real aerodynamic environment of HSTs in tunnel-flat ground-tunnel (TFT) running scenario. The purpose of the present study is to determine which of the two geometric turbulence generators, the spire and the fence, is more suitable for computational fluid dynamics (CFD) simulation of a fluctuating crosswind field in the TFT scene. First, the wind field characteristics in the TFT scene are analyzed based on the field test. Then, the tunnel-flat ground-spire/fence CFD model was established based on the “mosaic” mesh technology. Finally, the difference of wind field fluctuating characteristics under two turbulence generator conditions based on improved delayed detached eddy simulation (IDDES) is discussed. The main results show that the average wind speed of the windward and leeward lines in the fence case are 60% and 43.75% higher than the corresponding values in the spire case, respectively. The main conclusions show that the turbulent crosswind generated by the spire is more consistent with the spectrum characteristics of the natural wind field.

An experimental investigation of a roof-mounted horizontal-axis wind turbine in an idealized urban environment

Wind-tunnel experiments are performed to investigate the effect of minor modifications to the roof edge shape on the power performance and wake characteristics of a horizontal-axis wind turbine sited on a cube-shaped building. Three roof edge shapes are considered: a sharp edge, a rounded edge, and a solid fence. The power performance of the turbine is dependent on its streamwise position, and on the roof edge shape due to the difference in the flow shear induced by different roof edges. The sharp edge and solid fence cases show high variation in power with the turbine position, which is reduced significantly in the rounded-edge case. The turbine shows the worst power performance regardless of its position in the fence case. The roof edge shape is also found to affect the wind turbine wake. Specifically, the wake recovery and expansion rates are found to be greatest for the fence case, and they decrease with the increasing smoothness of the roof edges. This is related to the difference in the base flow turbulence induced by different roof edge shapes. Compared to the base flow, turbulence intensity in the wake is reduced on the building, except at the rotor top tip level.

Investigation of the hazardous area in a liquid hydrogen release with or without fence

Constructing a fence for potential liquid hydrogen leakage is a common protective measure to prevent the unrestricted spread, and critically evaluating the effects of a fence is essential for the safe use of hydrogen energy. Based on NASA's large-scale experiment of liquid hydrogen release, a 3D numerical model considering the existence of fence is proposed to study the dynamic spread behaviors of hydrogen flammable cloud and liquid hydrogen pool. The results show that the liquid hydrogen pool keeps a downwind radius of about 1.75 m most of the time during the release, and the hydrogen flammable cloud has a limit spread distance. Three cases are set to comparatively evaluate the effect of the fence, which are full fence, downwind half fence and no fence. Under the three cases, liquid hydrogen pools all evaporate completely within 5 s. Full fence scenario has the modest spread scale of hydrogen flammable cloud in the atmosphere but the longest duration for 86 s, and the upwind fence causes an easily overlooked hazardous region due to the vortex here, thus constructing a full fence is not an ideal strategy when the spread direction is constant. Just constructing a downwind half fence leads to the greatest spread distance of the flammable hydrogen cloud, which are 33.6 m and 68 m in vertical and downwind directions. No fence case corresponds to the smallest diffusion scale of flammable hydrogen cloud in atmosphere but the longest near-ground spread distance for 43.35 m. Four stages can be divided to summarize the entire life period of the flammable cloud for the cases with and without a fence, while three stages for the case with a downwind half fence.

Numerical Study on Reduction of Ambient NOx Concentration by a Flow-through ACF (Activated Carbon Fibers) Fences

A method to use fences filled inside with activated carbon fibers (ACF) is presented for reduction of high NO2 concentration in urban atmosphere without excess energy use. Polluted air mass in road space moves with natural- and car-induced- winds to contact with- and to flow through- ACF fences, and the ACF layer removes these pollutants. Two parameters determining the performance of the ACF fences in terms of NOx abatement were identified as (1) resistance coefficient of the ACF layer to air flow, and (2) chemical reactivity of ACF layer for NOx removal. By varying these two parameter values in their ranges obtained by laboratory experiments, the reduction of NOx concentration at roadside by the ACF fences was numerically evaluated under an idealized situation in which two cases were considered; one is the double-fences placed at both sides of road and the other is single fence set at downwind side of the road. The results showed that in both cases these “energy-free” equipment can decrease NOx concentration by 15~55% at roadside. Furthermore, it was indicated that in the double-fence case the ACF fence with lower permeability (larger resistance coefficient) shows higher reduction of NOx, while in the single fence case higher permeability reduces NOx more.

Implementation and Evaluation of an Embedded LES-RANS Solver

In the current work, we present the development and application of an embedded large-eddy simulation (LES) - Reynolds-averaged Navier Stokes (RANS) solver. The novelty of the present work lies in fully embedding the LES region inside a global RANS region through an explicit coupling at the arbitrary mesh interfaces, exchanging flow and turbulence quantities. In particular, a digital filter method (DFM) extracting mean flow, turbulent kinetic energy and Reynolds stress profiles from the RANS region is used to provide meaningful turbulent fluctuations to the LES region. The framework is developed in the open-source computational fluid dynamics software OpenFOAM. The embedding approach is developed and validated by simulating a spatially developing turbulent channel flow. Thereafter, flow over a surface mounted spanwise-periodic vertical fence is simulated to demonstrate the importance of the DFM and the effect of the location of the RANS-LES interface. Mean and second-order statistics are compared with direct numerical simulation (DNS) data from the literature. Results indicate that feeding synthetic turbulence at the LES interface is essential to achieve good agreement for the mean flow quantities. However, in order to obtain a good match for the Reynolds stresses, the LES interface needs to be placed sufficiently far upstream, which in the present case was six spoiler heights before the fence. Further, a realistic spoiler configuration with finite-width in the spanwise direction and inclined at 30 degrees was simulated using the embedding approach. As opposed to the vertical fence case this is a genuinely (statistically) three-dimensional case and a very good match with mean and second-order statistics was obtained with the experimental data. Finally, in order to test the present solver for high sub-sonic speed flows the flow over an open cavity was simulated. A good match with reference data is obtained for mean and turbulence profile comparisons. Tones in the pressure spectra were predicted reasonably well and an overall sound pressure level with a maximum deviation of 2.6 dB was obtained with the present solver when compared with the experimental data.

A lattice Boltzmann-Saltation model and its simulation of aeolian saltation at porous fences

This paper introduces a 2D lattice Boltzmann-Saltation (LBM-Saltation) model for numerical simulation of velocity profiles of windblown sand particles. The model is based on the LBM equations for transient, incompressible viscous flow. We first introduced a lattice Boltzmann subgrid model, which was used to predict the turbulent wind field. Two-way coupling was then used to describe the interaction between wind and the saltating sand particles. The correctness of the model was verified by comparing the simulated results of several important variables of wind-sand flow with that of experiment over a flat bed surface. To show the feasibility of this model with complex boundary conditions, we used it to simulate the wind-sand flow at porous wind fences and mainly discussed the particle velocity profiles. Single porous wind fence case was computed first and compared with the measurement. Two tandem porous wind fences cases were simulated next. Different distance and porosity of the fences were considered to quantitatively investigate the variation of the shelter effect. The simulated results achieved additional conclusions: The wind speed and the velocity of sand particles are obviously weakened because of the fence; reduction of the particle velocity by porous fence varies with the fence distance and porosity; the larger the distance or the porosity (significantly larger than the 0.3), the worse the shelter effect, and the weaker the reduction of particle velocity.

Numerical comparison of hybridized discontinuous Galerkin and finite volume methods for incompressible flow

SUMMARYIn this study, a hybridizable discontinuous Galerkin method is presented for solving the incompressible Navier–Stokes equation. In our formulation, the convective part is linearized using a Picard iteration, for which there exists a necessary criterion for convergence. We show that our novel hybridized implementation can be used as an alternative method for solving a range of problems in the field of incompressible fluid dynamics. We demonstrate this by comparing the performance of our method with standard finite volume solvers, specifically the well‐established finite volume method of second order in space, such as the icoFoam and simpleFoam of the OpenFOAM package for three typical fluid problems. These are the Taylor–Green vortex, the 180‐degree fence case and the DFG benchmark. Our careful comparison yields convincing evidence for the use of hybridizable discontinuous Galerkin method as a competitive alternative because of their high accuracy and better stability properties. Copyright © 2014 John Wiley & Sons, Ltd.

Actuator Disk Model 기반의 로터 해석자를 사용한 방풍 구조물 내부의 로터 성능 예측

본 연구에서는 로터 성능 해석을 위한 로터 성능 해석자를 개발하고 이를 사용하여 방풍 구조물 내부의 로터 성능 해석을 수행하였다. 로터 성능 해석자는 깃요소 이론 기반의 actuator disk model을 사용한 해석자를 사용하였다. 또한, 주변의 구조물로 인한 로터 하중의 비대칭성을 고려하기 위해 깃요소 이론에서 블레이드의 flapping 운동에 대한 해석을 수행하여 유효받음각 계산에 적용하였다. 개발된 해석자를 사용하여 바닥면과 벽면에 의한 로터 성능 변화에 관한 연구와 비교 검증을 수행하였다. 방풍 구조물 형상에 따른 로터 성능 해석을 통해 방풍 구조물에 의한 로터 성능 감소 현상을 확인하였다. 이를 통해 방풍 구조물이 없는 경우 대비 95% 이상의 로터 성능 비를 가지는 방풍 구조물의 유출입덕트 면적을 제안하였다. The purpose of current study is to develop the rotor analysis solver and perform a rotor aerodynamic analysis in the wind fence. To this end, the rotor analysis solver based on actuator disk model was employed. To consider the asymmetric effect of the rotor in the wind fence, the flapping motion analysis was conducted with blade element theory for the effective angle of attack calculation. The validation cases which are the rotor with wall and ground were accomplished by developed solver. The decrease of rotor performance by wind fence was confirmed. The wind fence configuration was suggested which guarantees more than 95% rotor performance compared with the no fence case.

VISUALIZATION OF FLOW THROUGH THE TURBINE BLADE CASCADE WITH OPTIMIZED STREAMWISE BOUNDARY LAYER FENCE

The present study focuses on the study of critical points formed on the surfaces of a turbine cascade with and without streamwise endwall fences with the help of flow visualization. A fence whose height varies linearly from the leading edge to the trailing edge and is located in the middle of the flow passage produces the least Coefficient of Secondary Kinetic Energy (CSKE) and is the optimum fence. The reduction in CSKE by the optimum fence is 27% compared to the baseline case. The geometry of the fence is new and is reported for the first time. The objective of the fence is to block the passage vortex from crossing the passage and impinging on the suction surface of the blade. A saddle point is formed near the leading edge on the endwall for baseline and optimum fence cases. There is nearly no change in saddle point location. Distribution of critical points on the endwall near the trailing edge of the blade is symmetrical for the baseline case, while no symmetry exists for the optimum fence case. Based on skin friction line patterns, it is clear that the pressure-side leg of the horseshoe vortex is diverted by the optimum fence, and hence, impinged on the suction surface of the blade with reduced intensity. Skin friction lines on the suction surface show that with application of the optimum fence, the spanwise penetration of the passage vortex is reduced by 33%.

수직벽 전방에서의 흡입/토출을 이용한 후류제어 연구

The effect of periodic blowing and suction of upstream flow on the separated shear flow behind the vertical fence was experimentally investigated. The fence was submerged in the turbulent shear flow and DPIV method was used to measure the instantaneous velocity fields around the fence. Periodic blowing and suction flow was precisely generated by the syringe pump. Spanwise nozzle made 2D planar periodic jet flow in front of the fence and the effect of frequency and maximum jet velocity was studied. From the results, the reattachment length can be reduced by 60% of uncontrolled fence case under the control.

Study on the effect of porous fence on air quality and traffic noise level around a double-decked road structure

Fence for traffic noise control sometimes causes adverse effect on air pollution. Thus in this study, performance of porous fence as a tool for control of both air pollution and noise pollution was evaluated. A two-dimensional numerical model for flow and pollutant concentration and an analytical model for traffic noise were utilized in the analysis of a double-decked road structure with fences only at ground (Case 1) and at both ground and upper deck (Case 2). Porous fences were assumed only at the ground level since the solid fences at the upper deck usually leads to desirable result on air pollution. Effects of the variable porosity on air quality and noise level near road were evaluated. Obtained results showed: (1) flow pattern in leeward of fence was drastically changed at 40-50% porosity in Case 1 and 50% in Case 2. The porosity larger than 40% excluded presence of a circulation behind the fence. (2) Effect of porous fence on air pollution was different in Cases 1 and 2. In Case 1, the porous fence generally resulted in the reduction of air pollution at the ground level; on the other hand, in Case 2, it rather led to increase of the concentration. (3) Traffic noise level was also largely changed by the porosity of the fence; an example of simultaneous evaluation of the effects of porous fence on both air and noise pollution in Case 1 showed that the fence of 60% porosity leads to reduction of air pollution by 20% compared with solid fence case, and reduction of noise pollution by 4-6% in dB compared with no fence case, at 1 m high and 10 m from the road.

Experimental study on surface pressure and flow structure around a triangular prism located behind a porous fence

Flow structure around porous wind fences and the rear coal stockpile model embedded in an atmospheric boundary layer was investigated experimentally by measuring the surface pressure and flow velocity. The experiments were carried out in a closed-return type subsonic wind tunnel with various oncoming atmospheric boundary layers. Various front fences with different porosity and a back fence of porosity ε=40% were tested. The fence and prism models were both 40 mm high; the Reynolds number based on the model height ( h) and free stream velocity was about Re=3.9×10 4. The velocity field around the prism model and surface pressures were measured using the single-frame double-exposure particle image velocimetry system and an electronic pressure scanner, respectively. As a result, the mean pressure and pressure fluctuations on the model surface were strongly affected by the porosity of front fence. The wind fence with porosity ε=40–50% seems to be effective for attenuating the pressure fluctuations on the prism surface. A back fence behind the prism model reduces pressure fluctuations largely on the leeward surface of the prism, compared with the single front fence case. When a wind fence of porosity ε=40% is installed in front of the prism, the speed of bleed-flow behind the fence is largely reduced down to 1/3 compared with no fence case.

Verification of the shelter effect of a windbreak on coal piles in the POSCO open storage yards at the Kwang-Yang works

The use of windbreaks to reduce wind-blown coal dust at the POSCO Kwang-Yang open storage yards was studied using wind simulations on a scale model of the yards. Based on these simulation results, a full-scale wind fence was constructed on two sides of the yard. Here, we present results on the wind behavior both for the real yard and for the simulation results that guided its construction. Wind-tunnel simulations were used to study the effect of a porous wind fence of porosity ε=30% on the surface pressure and shear stress on coal piles using a 1/1200 model of the POSCO Kwang-Yang open storage yards. In addition, the shelter effects found in the model system were verified in field measurements on the full-scale system. The storage yard model was fully embedded in an atmospheric surface boundary layer over open terrain. The fence and coal pile model had the same height (12.2 mm) and Reynolds number ( Re=1.6×10 4, based on the model height). The mean and fluctuating surface-pressure distributions on the coal piles, which are closely related to the dust emission from the surface, were measured for several directions of the oncoming wind. The wind directions pertinent to the study were determined by statistical analysis of seasonal wind data over the storage yard. A porous wind fence of porosity ε=30% was found to be useful for reducing the wind speed without the formation of a recirculating bubble behind the fence. In addition, the fence caught the wind-borne particles when it was located behind the coal piles. The wind fence reduced the pressure fluctuations and surface shear stress on the coal piles to less than half of the levels observed in the no fence case. To verify the effectiveness of the porous wind fence installed around the Kwang-Yang open storage yard, the local wind speed and the concentration of suspended particles were measured directly. Full-scale porous fences installed around the Kwang-Yang open storage yard greatly decreased the turbulence intensity of the wind over the coal piles and reduced the total suspension particles by 70–80%.

The shelter effect of porous wind fences on coal piles in POSCO open storage yard

Abstract The shelter effect of porous wind fences on surface pressure and wall shear stress acting on the consecutive coal piles of 1/800 scale POSCO open storage yard model was investigated experimentally. The storage yard model was fully embedded in a neutral atmospheric surface boundary layer over open terrain. Reynolds number based on the coal pile height was Re=18,000. The mean and fluctuating surface-pressure distributions on the coal piles, which were directly related to the dust emission from the surface, were measured for several oncoming wind directions. The daily and monthly wind data over the storage yard during two years were statistically analyzed. As a result, a fence of porosity e =40% was found to be effective for decreasing the mean pressure and pressure fluctuations on the coal piles. In addition, the wall shear stress on the windward surface decreased more than half of that for the no fence case. In order to get a good shelter effect for a large-scale open storage yard, the porous fence should be installed along all peripheral sides of the storage yard, and an additional middle fence is needed for every five consecutive piles to prevent the decreasing shelter effect from descending shear flow separated from the wind fence.

Velocity field measurements of flow around a triangular prism behind a porous fence

The shelter effect of a porous wind fence on a triangular prism was experimentally simulated in a circulating water channel. A porous wind fence of porosity ε =38.5% was installed in front of the prism model. The fence and prism model were embedded in a turbulent boundary layer at Reynolds number of about 3460. The instantaneous velocity field around the fence and prism model was measured using a two-frame Particle Tracking Velocimetry (PTV) technique. In addition to the well-known mean velocity reduction, the fence decreases the turbulent intensity and turbulent kinetic energy around the prism. Especially, at the top of the prism model, the turbulent kinetic energy is about half of that without the fence. By installing the fence in front of the prism, the length of the re-circulation region also decreases compared with that of the no fence case.