Research on wind barrier of canyon bridge-tunnel junction based on wind characteristics

Abstract

Due to the acceleration effect of the wind by the special geographical location of the canyon bridge-tunnel junction, the traffic safety and stability of this section are difficult to be guaranteed, resulting in frequent traffic accidents. In order to ensure the safety and comfort of vehicles driving on this section, the numerical simulation method based on CFD is adopted to establish the numerical model of the canyon bridge-tunnel junction. The acceleration of the incoming wind speed in the bridge-tunnel junction with a guardrail that is 0.8 m high is analyzed from different canyon spacings, wind directions and heights from the bridge deck. Based on the characteristics of wind field above the bridge deck, two kinds of gradient wind barriers—trapezoidal and stepped—are proposed, and their wind reduction effects and turbulence intensity changes are analyzed. Then the aerodynamic performances of running vehicle are compared. The results show that the stepped wind barrier with 50% porosity and rectangular section railings has the best wind reduction effects, and can noticeably improve the comfort of driving. The aerodynamic coefficients of vehicle are lower with stepped wind barrier.

Keywords

bridge-tunnel junction CFD numerical simulation traffic safety wind barriers wind characteristics

Introduction

Crosswinds, which cause unstable driving conditions and affect the safety and stability of vehicle driving, impact vehicles traveling in mountainous expressways. This is a common problem encountered in mountainous expressways. Under strong wind, high-speed vehicles are prone to rollover and sideslip, resulting in traffic accidents (Baker and Reynolds, 1992). Because of the narrow pipe effect, the wind speed of the bridge-tunnel junction in the canyon is much higher than that of other sections. When the vehicle is driving out of the tunnel, it will suddenly be impacted by strong wind, which is very harmful to traffic safety. To study vehicle safety under crosswinds, Cheli et al. (2011a, 2011b) conducted a series of wind tunnel tests to evaluate vehicle sensitivity to different road scenes, wind directions, and vehicle geometric dimensions, finding that these factors have an impact on the aerodynamic coefficients of heavy vehicles. In addition, Batista and Perkovic (2014) proposed a static model for determining the critical wind speed for vehicle slip, overturn, and rollover, and derived a new formula for calculating the critical wind speed leading to vehicle accidents. Zhang and Proppe (2019) also used the probabilistic method based on reliability analysis to study the accident modes and accident risks of different types of vehicles under strong crosswinds.

In a strong wind environment, it is necessary to set up wind barriers to ensure the safety of vehicles. Research show that wind barriers can significantly reduce the drag coefficient of vehicles and improve the aerodynamic performance of vehicles under strong wind (Telenta et al., 2015; Xiang et al., 2015). Kwon (2011) proposed that the minimum height of wind barrier to reduce wind speed by 50% is 12.5% of road width through wind tunnel tests. Chu et al. (2013) studied the effects of wind barriers with different heights and different porosity on the vehicles on the bridge. Their results show that the porous wind barrier can significantly reduce the lateral force coefficient of the vehicle. He et al. (2016) proposed an adjustable louvered wind barrier, and systematically studied the aerodynamic characteristics of this new type of wind barrier by wind tunnel test. The results show that the louvered wind barrier has better aerodynamic characteristics than the traditional forms. Liu et al. (2018) used CFD analysis to study the aerodynamic performance of high-speed trains passing through the transition area of wind barrier. They found that there was an obvious yaw phenomenon when trains crossed the area, and proposed the critical wind speed of trains crossing the area based on safety assessment. Guo and Tang (2019) found that if the porosity of the wind barrier is too large, the stability of the train will not be guaranteed, and there will be derailment risk. Therefore, the maximum porosity of the wind barrier should be limited to avoid selecting too high values.

Previous studies have shown that crosswind will pose a threat to vehicle safety and that wind barriers are necessary to reduce the impact of crosswind on vehicles. However, at present, there are few studies on the traffic safety of the bridge-tunnel junction in mountainous expressway. In fact, existing research (Hu et al., 2016; Niu et al., 2018; Wang and Chen, 2012a) shows that, as a special geographical location, the canyon bridge-tunnel junction has a certain acceleration effect on the incoming wind speed, that the acceleration effect over the bridge is the largest, and the maximum acceleration value can reach 30.8%. This has a significant impact on the driving safety of vehicles on the bridge tunnel junction. In studies of the wind characteristics of the complex terrain of the canyon, field measurements (Ledong et al., 2011), wind tunnel tests (Li et al., 2010) and numerical simulations (Li et al., 2011) can be used. With the development of numerical methods and computer technology, the CFD numerical simulation method is widely used in the study of flow field characteristics. Based on the above, the simplified model of the canyon bridge-tunnel junction is established by GAMBIT software, and the wind characteristics of the bridge-tunnel junction are simulated by CFD, in which the acceleration effect of the bridge-tunnel junction on wind is studied by using the common incoming wind velocity (8 m/s) in the actual situation. Then, wind barriers are established to weaken the acceleration effect of incoming wind. According to the characteristics of the wind field over the bridge tunnel connection section, trapezoid wind barrier and stepped wind barrier are designed. The wind reduction effect of trapezoid and stepped wind barriers is then determined to ensure the safety of driving vehicles, and aerodynamic performance of running vehicle is studied, providing a basis for the establishment of wind barriers in the canyon bridge-tunnel junction.

Numerical model

Simplified model setup

In this paper, the canyon bridge-tunnel junction of mountainous expressway is taken as the research object. In practice, different canyons have different geometry shapes and surface characteristics. Therefore, for the convenience of research, a simplified model of canyon terrain is established by using GAMBIT software, as shown in Figure 1. To make the research valuable, the physical authenticity of the model should be ensured, being able to minimize the simulation error while representing the characteristics of the surrounding environment. Considering the influence of topographic surface roughness on flow field (Shuyang and Tamura, 2006; Tamura et al., 2007), the acceleration of wind flowing through a smooth surface is greater than that of rough surface. For simplicity, the model of trees and mountains on canyon wall is not established, but the friction coefficient of mountain wall is set as 1 to represent its rough surface. In mountainous expressways, the five-level wind is more common, so the minimum wind speed (8 m/s) is chosen as the wind speed at the entrance when studying the wind characteristics of the bridge-tunnel junction.

Figure 1.

Simplified model of bridge-tunnel junction.

Due to the structural form and height of the guardrail, the wind characteristics above the deck of the bridge will be affected. Therefore, it is necessary to study the wind characteristics in the case of the guardrails on the bridge deck firstly. According to “Technical Requirements for Highway Collision-proof Guardrail,” the construction requirements of the concrete guardrail is adopted, and the height is 81 cm.

Computational mesh and boundary conditions

When choosing the computational domain of the flow field, it should be considered that the range of the wind field is large enough to allow the wind to fully develop in the flow field (He et al., 2014). Then, in order to avoid the influence of incoming wind or wake wind on the overhead wind speed on the bridge deck (Niu et al., 2014), the entrance and exit of the computational domain should be far enough from the bridge-tunnel junction. By comprehensively considering the above two factors, the width W of the bridge-tunnel junction, canyon spacing D, and the height H of mountain are taken as the feature size in this paper. The bridge length is taken as 20 m, 30 m, and 50 m, respectively according to different research conditions, and the tunnel entrance is 7.5 m wide, 7 m high, and 50 m long on one side.

The outflow boundary should be positioned far enough behind the model to allow for flow development, and the top of the computational domain should be also far away from the model to prevent an artificial acceleration of the flow over the model (Franke et al., 2004). Referring to Yang et al. (2008) and Hu et al.’s (2016) research, to make the flow develop enough, the computational domain is defined as figure 2: the inlet distance of the flow field is 10W from the center of the model bottom, the outlet distance is 20W from the center of the model bottom, and the side distance is 10D from the center of the model bottom, the top boundary distance is 12H.

Figure 2.

Computational domain.

Hexahedral meshes are usually used in numerical simulation with higher accuracy and fewer mesh numbers. But due to the characteristics of tetrahedral mesh, it has advantages in dealing with complex objects. In a study on the train passing through the wind barrier transition (Liu et al., 2018), the tetrahedral mesh was used to fill the complex geometry of the domain, and the numerical simulation results agree fairly well with the full-scale test results. In some CFD studies of buildings (Lo et al., 2016; Sanyal and Dalui, 2020; Xing et al., 2018), tetrahedral meshes were used around building model and relatively satisfactory results were obtained. Considering the complex geometry of the bridge-tunnel junction, unstructured tetrahedral grids are used to fill the domain. At the same time, numerical simulations are performed with three different meshes of 1 million, 1.5 million, and 2 million, respectively to check the independence of the mesh. The wind speed at the height of 5 m from the bridge center is compared under the condition that the inflow wind is 8 m/s with different meshes. The results show that the wind speed of 1.5 million meshes is 6.2% larger than that of 1 million meshes, and the wind speed of 2 million meshes is 1.3% larger than that of 1.5 million meshes. The results of meshes of 1.5 million closely match the results of meshes of 2 million. Therefore, in order to satisfy the calculation ability while maximizing the accuracy, the number of meshes is about 2 million. The flow field mesh is encrypted around the model and the minimum mesh size of core area is 0.05 m. The mesh gradually becomes sparse away from the model network and the mesh size to area edge up to 1.5 m, as shown in Figure 3. The boundary conditions of the model are as follows: the wind speed condition is set for the inlet, the tangential velocity is 0, the normal velocity is appointed, the incoming wind speed is set to 8 m/s, and the turbulence intensity is 0.5%; the pressure boundary condition is set for the outlet, with an average static pressure of 0. The symmetry boundary condition is set for the upper and lower sides and the front and rear sides. The model surface is set as no slip wall condition.

Figure 3.

Computational mesh.

Numerical method and validation

The air flow around the model is incompressible flow, so the three-dimensional viscous unsteady incompressible Navier-Stokes (N-S) equation is used to simulate the flow of wind. The shear-stress transport (SST) k–ω model is selected as the turbulence model, in which the standard k–ω turbulence model is used in the near wall region of the turbulence model, and transforms to the high Reynolds number k–ε model outside the boundary layer. The finite volume method (FVM) is used to discretize the governing equations. The second-order central difference scheme is used for the diffusion term, and the second-order upwind discretization scheme is used for the convection term. To meet the demands of the κ–ω turbulence model, the adaptive mesh technique is used in this numerical simulation to ensure that the averaged y+ was approximately 10. When the wind speed over the bridge reaches periodic stability and the net flux through the calculation domain is <0.1%, the simulation result is considered to be convergent.

The wind tunnel test was carried out in the CA-1 atmospheric boundary layer wind tunnel of Chang’an University. It is a dual-purpose wind tunnel, which is composed of steel and concrete. The size of the test section is 15 m × 3 m × 2.5 m, the wind speed is 0–53 m/s continuously adjustable, the turbulence intensity is not more than 0.5%. The same conditions are selected for numerical simulation and wind tunnel test. The test point at the bridge deck center of the bridge-tunnel junction with the bridge length of 20 m are taken as the research objects to compare the data of wind tunnel test and numerical simulation under the action of cross wind. The result is shown as Figure 4. It can be observed that the numerical simulation results agree fairly well with the wind tunnel test results.

Figure 4.

Comparison of wind speed profile at the center of bridge.

Selection of study points

In the y-axis direction, the tunnel vertex is taken as the datum point, and one point is taken every other meter downward as the measuring point for quantitative analysis of the wind speed. In the height range of the tunnel, five measuring points can be taken. The nearest point to the bridge deck is 0.226 m away from the bridge deck, so the height of the five points from bottom to top are 0.226 m, 1.226 m, 2.226 m, 3.226 m, and 4.226 m, respectively. Considering that the change of flow field near the tunnel entrance is more obvious, the measuring points in this part of the area should be arranged more densely. Therefore, when the canyon spacing is 20 m, the distance between the measuring points is 1 m in the 4 m range of the tunnel entrance, and that is 2 m outside the 4 m range of the tunnel entrance. When the canyon spacing is 30 or 50 m, the distance between measuring points in the 5 m range of the tunnel entrance is 1 m, and the distance between measuring points outside the 5 m range is 2 m.

Numerical simulation results

In this paper, as shown in Table 1, wind speed ratio is used to study the variation of wind speed at the junction of canyon bridge-tunnel junction; aerodynamic drag coefficient, lift coefficient, and lateral force coefficient are used to study the aerodynamic performance of vehicles.

Table 1.

Different study index.

Wind speed ratio	The ratio of the actual wind speed of the study point to the incoming wind speed
Aerodynamic drag coefficient (C_D)	$C_{D} = D / (q A_{D})$ , D is the aerodynamic drag, q is dynamical wind pressure, A_D is frontal projection area of aerodynamic drag
Lift coefficient (C_L)	$C_{L} = L / (q A_{L})$ , L is the aerodynamic lift, q is dynamical wind pressure, A_L is frontal projection area of aerodynamic lift
Lateral force coefficient (C_S)	$C_{S} = S / (q A_{S})$ , S is the aerodynamic lift, q is dynamical wind pressure, A_S is frontal projection area of lateral force

Wind characteristics of flow field in bridge-tunnel junction without wind barrier

The wind characteristics of the bridge-tunnel junction without wind barrier are simulated, and the acceleration effect of the bridge-tunnel junction on the incoming wind speed is analyzed under different canyon spacing and different height from the bridge deck. The wind speed ratio is taken as the index to measure the acceleration effect. When the wind speed ratio is >1, it indicates that the wind speed of the point is increased by the acceleration effect, and when the wind speed ratio is <1, the point is reduced by the wind reduction effect.

Influence of different spacing on wind speed at different heights

Taking the wind speed of the 0° direction angle, the influence of different canyon spacing (20 m, 30 m, and 50 m) on the wind speed of the bridge-tunnel junction at different heights (0.226 m, 1.226 m, 2.226 m, 3.226 m, and 4.226 m) is analyzed. The result is shown as Figure 5.

Figure 5.

Influence of different spacings on wind speed of bridge-tunnel junction at different heights with guardrails: (a) 20 m, (b) 30 m, and (c) 50 m.

As can be seen in Figure 5, the higher the distance from the bridge deck, the greater the wind speed. The wind speed at the height of 1.226 m and 2.226 m from bridge deck at different canyon spacing shows a certain sudden change. This is because the guardrail changes the direction of the action of incoming wind. And because of the low height of the guardrail, the wind speed ratio at the height of 3.226 m and 4.226 m from the bridge deck is >1, indicating that the bridge-tunnel junction still has a certain acceleration effect on the incoming wind.

It should be noted that the results are not completely symmetric. In fact, by comparing the figures, we found that near the height of guardrail (0.8 m), the data asymmetry is obvious. However, at the position far away from the guardrail height and close to the bridge deck, such as 0.226 m and 4.226 m, the data still maintain good symmetry. Some studies have reported the phenomenon of asymmetric flow in symmetric geometry (Herry, 2010; Prevezer et al., 2002; Syms, 2008). They found the unsteady asymmetric results of symmetric flow in CFD simulation and in wind-tunnel measurement. It would be of inviscid origin, related to the unstable character of the flow. The symmetric flow could be unstable or at least a highly fickle one. Therefore, we think that the existence of guardrail changes the wind speed and direction, which makes the results different on both sides near the height of guardrail.

Based on the above analysis, it can be seen that the deceleration effect of the guardrail on the incoming wind speed is not obvious, and the wind speed change is irregular, which is not conducive to the safety of vehicles. So wind barriers should be set in the bridge-tunnel junction to reduce the acceleration effect of incoming wind speed and ensure the safety of vehicles.

Flow fields around the bridge-tunnel junction

From Figure 6(a), it can be seen that the flow enters the tunnel along the direction of the tunnel from the downwind side of the tunnel entrance, forming a “vacuum” area on the windward side of the tunnel entrance. The wind speed in the “vacuum” area is relatively small, the turbulence intensity is relatively large, that is, the wind pulsation is relatively strong.

Figure 6.

Streamline and velocity distributions of different position on the bridge at a spacing of 50 m; (a) general distribution, (b) tunnel entrance, (c) 4 m from tunnel entrance, and (d) the center of the bridge.

Figure 6(b)–(d) present that the wind speed increases along the direction from the tunnel entrance to the bridge center. There are large whirling vortices in the wind speed vector diagram at the entrance of the tunnel, which indicates that the wind speed is small, but the turbulence intensity is high. As the bridge approaches the center of the bridge, the wind speed increases, and the upper and lower vortices decrease. When reaching the bridge center, the wind speed almost has no vortex, which indicates that the wind speed is large, the turbulence intensity is small, and the mixed fluctuating wind in the average wind is small, which has a great impact on the driving safety.

Influence of different inlet velocity and turbulence intensity on the wind speed of study point

The sensitivity of the results for various velocity and turbulent intensity should be studied to. In Sanyal and Dalui (2020)’s study, the effects of velocity and Reynolds numbers on the velocity profile and the force and moment coefficients were examined under different levels of wind velocity, and the results showed that the dependence of air velocity on aerodynamic coefficients was limited. For the bridge-tunnel junction with 20 m spacing under 0° wind direction angle, the effect of different inlet velocities (under 0.5% turbulence intensity) and turbulence intensity (under 8m/s inlet velocity) on the wind speed ratio was examined.

As shown in Figure 7(a), when theinlet velocity changes, the wind speed ratio over the bridge keeps the same trend. The results show that the variation curves of the three inlet velocities are in good agreement, and the variation range is <3.6%. Figure 7(b) presents s the variation of wind speed ratio at low turbulence intensity (0.5%), medium turbulence intensity (5%) and high turbulence intensity (10%). The wind speed ratio increases with the increase of turbulence intensity. But the increase of wind speed ratio did not exceed 9.3%. The results show that the effect of inlet velocity and turbulence intensity on wind speed ratio is limited, and 8 m/s inlet velocity and 0.5% turbulence intensity can be used for the numerical simulation.

Figure 7.

Wind speed ratio at 4.226 m height of bridge-tunnel junction under different inlet velocities and turbulence intensity: (a) different inlet velocities and (b) different turbulence intensity.

Wind characteristics of flow field in bridge-tunnel junction with wind barrier

According to the previous analysis of the wind field in the canyon bridge-tunnel junction, it can be found that the wind speed in the middle of the bridge is relatively large, while the wind speed is relatively small when it is close to the tunnel on both sides, due to the special geographical location. In view of the characteristic of wind speed change, the corresponding form of wind barrier should also choose gradual change form to meet the wind reduction effect while simultaneously minimizing construction costs.

The smaller the porosity of the wind barrier is, the better the effect of reducing wind speed. However, compared with the wind barrier with larger porosity, the tail of the wind barrier with small porosity will produce a greater turbulence and affect the overall wind protection effect (Kozmar et al., 2014). If the porosity is too large, it cannot get enough wind reduction effect. According to previous studies (Dong, 2007), the wind barrier with 50% porosity has better wind reduction effect and can also slow down the sudden change of wind speed outside the bridge tower. Therefore, the wind barrier with 50% porosity is chosen and studied in this paper.

The form of the wind barrier can be a porous plate or horizontal and vertical railings. Different forms of wind barrier have little influence on the effect of wind reduction. The structure of wind barrier in the form of railings is simple and cheap, and it is accordingly adopted in this paper. The cross-section form of wind barrier railings has a great influence on the wind reduction effect. Generally, there are two forms- circular and rectangular. The energy loss of air flow passing through the rectangular railings is more than that passing through the circular railings (Guo et al., 2009). Therefore, the wind reduction effect of rectangular railings is better.

According to past research and considering the cost and wind reduction effect, the gradient wind barrier with 50% porosity and rectangular shape is selected for the present study. Considering the acceleration effect of the incoming wind and the height of vehicle, a gradient wind barrier with a height of 3.5 m (total height of 4.31 m) is set up on the basis of the guardrail, and its deceleration effect on the incoming wind speed is studied in the form of trapezoidal wind barrier and stepped wind barrier respectively. The model of wind barrier is shown as Figure 8

Figure 8.

Wind barrier model: (a) trapezoidal wind barrier, (b) stepped wind barrier, and (c) structure section of wind barrier.

Trapezoidal wind barrier

Based on the above model, the effects of different spacings (20 m, 30 m, and 50 m) on wind speed at different heights (0.226 m, 1.226 m, 2.226 m, 3.226 m, and 4.226 m) are simulated and analyzed under the condition of 0° wind direction angle. The results are shown in Figure 9.

Figure 9.

Influence of different spacings on wind speed at different heights with 50% porosity trapezoidal wind barrier: (a) 20 m, (b) 30 m, and (c) 50 m.

In Figure 9, it can be observed that the higher the distance from the bridge deck is, the larger the wind speed is when the wind direction angle is 0°. When the canyon spacing is 20 m or 30 m, the wind speed ratio below a height of 4.226 m is lower than 1, which shows the deceleration effect on wind. When the canyon spacing is 50 m, the wind speed above the height of 3.226 m rapidly increases at first, then tends to be steady, and then decreases rapidly, and the steady wind speed is >8 m/s, which shows the acceleration effect on wind. The wind speed below the height of 3.226 m has a sudden change after a certain distance from the tunnel entrance, and the wind speed ratio below height of 2.226 m is <1, with deceleration effect. It can be seen that the trapezoidal wind barrier has no obvious deceleration effect on the incoming wind speed at 4.226 m height.

Stepped wind barrier

The influence of different spacing (20 m, 30 m, 50 m) on the wind speed at different height (0.226 m, 1.226 m, 2.226 m, 3.226 m, 4.226 m) is simulated and analyzed at 0° wind direction angle in case of stepped wind barrier. The results are shown in Figure 10.

Figure 10.

Effects of different spacings on wind speed at different heights with 50% porosity stepped wind barrier: (a) 20 m, (b) 30 m, and (c) 50 m.

According to Figure 10, in the condition of 0° wind direction angle, the wind speed variation of stepped wind barrier is similar to that of trapezoidal wind barrier. However, the wind speed ratio of stepped wind barrier over the whole bridge is lower and more stable than that of trapezoidal wind barrier. Lastly the wind speed of stepped wind barrier is lower than incoming wind speed of 8 m/s, so the deceleration effect of stepped wind barrier is better.

Figure 11 shows that under the action of 50% porosity stepped wind barrier, the wind speed at different wind direction angles does not exceed 8 m/s and has no acceleration effect. Furthermore, the acceleration effect of the incoming wind speed near the center of the bridge is obviously weakened, which has a better deceleration effect on the incoming wind.

Figure 11.

Effects of different wind directions on wind speed in different spacings with 50% porosity stepped wind barrier: (a) 20 m, (b) 30 m, and (c) 50 m.

In summary, the stepped wind barrier with 50% porosity can significantly reduce the acceleration effect of wind speed in the bridge-tunnel junction, and it can be used to improve the influence of wind on vehicles driving in the canyon bridge-tunnel junction.

Influence of wind barrier on aerodynamic performance of running vehicle

The flow field will be disturbed when the vehicle is running in the bridge-tunnel junction. To verify the effectiveness of the stepped wind barrier and ensure the safety of the vehicle, it is necessary to simulate the running state of the vehicle, and analyze its transient aerodynamic performance and the pressure change of the outflow field. In this paper, a simplified three-dimensional model of car is established by 1:1, and user defined function (UDF) is used to describe the motion state of the structure, and dynamic mesh is used to realize fluid-solid coupling. Under the condition that the velocity of dynamic mesh conforms to the law of space conservation, a method of multi-layer dynamic mesh is proposed to solve the problem that the movement of solid model in the flow field is limited by the mesh size and the mesh deformation is easy to be too large and the calculation fails. The spring analogy method, the dynamic layering method and the local remeshing method are used to realize the mesh deformation in the computational domain. The large eddy simulation method is used to solve the N-S equation. Based on the same model algorithm and parameter settings of the first two sections, the vehicle speed is set as the common speed limit value of mountainous expressway (60 km/h), and the change of the related aerodynamic force and the distribution of the external pressure of the vehicle when vehicle running in the 20 m tunnel spacing with or without wind barrier is simulated.

Figures 12 to 14 show the aerodynamic coefficient changes of a car, minivan and a truck with or without wind barrier, which is the same as the trend of wind speed changes. In the center of the bridge, the aerodynamic force is the largest, and it gradually declines along the center to both sides and be the lowest on the tunnel portal. Take the car as example, by comparison of the average value of aerodynamic drag, lift and lateral force coefficient of vehicle at different positions on bridge, after the setup of stepped wind barrier, the average aerodynamic drag coefficient of vehicle decreases from 0.39 to 0.25, the average lift coefficient decreases from 0.2 to 0.12, and the average lateral force coefficient is reduced from 0.56 to 0.25, which shows that the vehicle aerodynamic force is effectively reduced and the driving safety is improved after the stepped wind barrier is set. Similarly, for the minivan and truck, the aerodynamic coefficient is significantly reduced with stepped wind barrier.

Figure 12.

Aerodynamic coefficient changes of a car: (a) without wind barrier and (b) with stepped wind barrier.

Figure 13.

Aerodynamic coefficient changes of a minivan: (a) without wind barrier and (b) with stepped wind barrier.

Figure 14.

Aerodynamic coefficient changes of a truck: (a) without wind barrier and (b) with stepped wind barrier.

By comparing Figure 15(a) and (b), it can be seen that the pressure on both sides and the top of the vehicle is significantly reduced, the change direction of the vehicle wake and the drag phenomenon at the rear of the vehicle are reduced. The change of the drag size and direction will lead to the instability of the flow field, which will have a great impact on the pressure and turbulence characteristics of the flow field, so the effectiveness of the stepped wind barrier proposed in this paper is further verified.

Figure 15.

Distribution of the external pressure of the vehicle: (a) without wind barrier, and (b) with wind barrier.

Wind tunnel verification

In the wind tunnel test, it is simulated that the car runs along the lane extension direction at the center line of the bridge deck. And the car travel direction is perpendicular to the flow side of the wind tunnel. The same conditions are selected for numerical simulation and wind tunnel test. And the bridge-tunnel junction with the bridge length of 20 m as the study object. The aerodynamic coefficient of a car crossing the bridge without stepped wind barrier and with stepped wind barrier are studied in the test and the results are compared with the numerical simulation, as shown in Figure 16.

Figure 16.

The aerodynamic coefficient of the car with or without stepped wind barrier: (a) lateral force coefficient without wind barrier, (b) aerodynamic drag coefficient without windbarrier, (c) lateral force coefficient with stepped wind barrier, and (d) lateral force coefficient with stepped wind barrier.

From the comparison between numerical simulation and wind tunnel test, it can be seen that the variation trend of lateral force coefficient and aerodynamic drag coefficient between numerical simulation and wind tunnel test is consistent, and the results of numerical simulation is consistent with that of wind tunnel test. It can be also seen that the vehicle aerodynamic coefficient has been significantly reduced with stepped wind barrier. The wind tunnel test furthur verifies the accuracy of numerical simulation and the effectiveness of adding stepped wind barrier.

Conclusion

In this paper, the CFD model is used to simulate the flow field characteristics of the canyon bridge-tunnel junction, and the flow field variation over the bridge deck with a guardrail of 0.81 m is analyzed. Then, the flow field changes over the bridge deck with trapezoidal and stepped wind barrier with 50% porosity and rectangular cross-section are analyzed. The wind reduction effects are compared. And the aerodynamic performance of running vehicle are analyzed. The main conclusions are as follows.

With the same canyon spacing, the higher the distance from the bridge deck is, the greater the wind speed is.

The deceleration effect of guardrail on incoming wind is not obvious, and the change of wind speed is irregular, which is not good at the safety of vehicles.

Compared with trapezoidal wind barrier, the stepped wind barrier with 50% porosity and rectangular cross section has better deceleration effect, which can significantly reduce the wind speed in bridge-tunnel junction, and overcome the disadvantage of large turbulence intensity at tunnel entrance when there is no wind barrier, providing reference and theoretical support for the design of traffic safety facilities in bridge-tunnel junction. It can also effectively reduce the aerodynamic coefficient of the vehicle, improve the pressure distribution of the vehicle outflow field, and improve the driving safety.

However, this paper makes a lot of simplification to the model of Canyon bridge-tunnel junction, and the actual mountainous terrain is not considered. In addition, many factors can affect the wind field characteristics of the bridge-tunnel junction, including external factors and internal factors, so the acceleration effect on the incoming wind speed needs further study.

Supplemental Material

sj-pdf-1-ase-10.1177_1369433220971730 – Supplemental material for Research on wind barrier of canyon bridge-tunnel junction based on wind characteristics

Supplemental material, sj-pdf-1-ase-10.1177_1369433220971730 for Research on wind barrier of canyon bridge-tunnel junction based on wind characteristics by Lu Wang, Xiaoxin Chen and Hong Chen in Advances in Structural Engineering

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by China National Key R&D Program during the 13th Five-year Plan Period (2017YFC0803906); and Fundamental Research Funds for the Central Universities of Ministry of Education of China (300102219111); and The Project Supported by Natural Science Basic Research Program of Shaanxi (2019JQ-146).

ORCID iD

Xiaoxin Chen

Supplemental material

Supplemental material for this article is available online.

References

Baker

Reynolds

(1992) Wind-induced accidents of road vehicles. Accident Analysis and Prevention 24(6): 559–575.

Batista

Perkovic

(2014) A simple static analysis of moving road vehicle under crosswind. Journal of Wind Engineering and Industrial Aerodynamics 128: 105–113.

Cheli

Corradi

Sabbioni

, et al. (2011a) Wind tunnel tests on heavy road vehicles: Cross wind induced loads-Part 1. Journal of Wind Engineering and Industrial Aerodynamics 99(10): 1000–1010.

Cheli

Ripamonti

Sabbioni

, et al. (2011b) Wind tunnel tests on heavy road vehicles: Cross wind induced loads-Part 2. Journal of Wind Engineering and Industrial Aerodynamics 99(10): 1011–1024.

Chu

Chang

Huang

, et al. (2013) Windbreak protection for road vehicles against crosswind. Journal of Wind Engineering and Industrial Aerodynamics 116: 61–69.

Dong

(2007) Numerical simulation of wind barrier influence on bridge deck wind environment. Master’s thesis, Zhejiang University, Hangzhou, China.

Franke

Hirsch

Jensen

, et al (2004) Recommendations on the use of CFD in wind engineering. In: COST Action C14, 5–7 May. Brussels, Belgium: European Science Foundation COST Office.

Guo

Tang

(2019) Effects of wind barrier porosity on the coupled vibration of a train-bridge system in a crosswind. Structural Engineering International 29(2): 268–275.

Guo

Zhu

Zhou

(2009) Optimum selection of wind barrier for bridges and its effect on aerodynamic performance of bridges. In: 14th national symposium on structural wind engineering, Beijing, China, p.8. Beijing, China: China Civil Engineering Society.

10.

Yang

(2014) Strategies for creating good wind environment around Chinese residences. Sustainable Cities and Society 10: 174–183.

11.

Shi

, et al. (2016) Aerodynamic performance of a novel wind barrier for train-bridge system. Wind and Structures 23(3): 2–20.

12.

Herry

(2010) Aerodynamic study of a 3D backward facing double step applied to safer launch and recovery of helicopters on ships. Theses. Université de Valenciennes et du Hainaut-Cambresis.

13.

Han

, et al. (2016) Numerical simulations of the mean wind speeds and turbulence intensities over simplified gorges using the SST k-omega turbulence model. Engineering Applications of Computational Fluid Mechanics 10(1): 361–374.

14.

Kozmar

Procino

Borsani

, et al. (2014) Optimizing height and porosity of roadway wind barriers for viaducts and bridges. Engineering Structures 81: 49–61.

15.

Kwon

Kim

Lee

, et al. (2011) Design criteria of wind barriers for traffic. Part 1: Wind barrier performance. Wind and Structures 14(1): 55–70.

16.

Ledong

ZHU

Pengjie

REN

Wei

, et al. (2011) Investigation on wind profiles in the deep gorge at the Balinghe bridge site via field measurement. Journal of Experiments in Fluid Mechanics 25(4): 15–21.

17.

Chen

Zhang

, et al. (2010) Wind tunnel modeling of flow over mountainous valley terrain. Wind and Structures 13(3): 275–292.

18.

Cai

Tang

, et al. (2011) Study of spatial distribution feature of wind fields over bridge site with a deep-cutting gorge using numerical simulation. China Civil Engineering Journal 44(2): 116–122.

19.

Liu

Chen

Zhou

, et al. (2018) A CFD analysis of the aerodynamics of a high-speed train passing through a windbreak transition under crosswind. Engineering Applications of Computational Fluid Mechanics 12(1): 137–151.

20.

Kim

(2016) Downstream interference effect of high-rise buildings under turbulent boundary layer flow. Journal of Wind Engineering and Industrial Aerodynamics 159: 19–35.

21.

Niu

Zhou

Wang

(2018) Numerical comparison of aerodynamic performance of stationary and moving trains with or without windbreak wall under crosswind. Journal of Wind Engineering and Industrial Aerodynamics 182: 1–15.

22.

Niu

Zhou

, et al. (2014) Research on aerodynamic performance of high-speed train through canyon wind zone. Journal of the China Railway Society 36(6): 9–14.

23.

Prevezer

Holding

Gaylard

, et al. (2002) Bluff body asymmetric flow phenomenon-real effect or solver artefact? Wind and structures 5(2–4): 359–368.

24.

Sanyal

Dalui

S. K.

(2020) Effect of corner modifications on Y plan shape tall building under wind load. Wind and Structures 30(3): 145–160.

25.

Shuyang

Tamura

(2006) Experimental study on roughness effects on turbulent boundary layer flow over a two-dimensional steep hill. Journal of Wind Engineering and Industrial Aerodynamics 94(1): 1–19.

26.

Syms

(2008) Simulation of simplified-frigate airwakes using a Lattice-Boltzmann method. Journal of Wind Engineering and Industrial Aerodynamics 96(6): 1197–1206

27.

Tamura

Okuno

Sugio

(2007) LES analysis of turbulent boundary layer over 3D steep hill covered with vegetation. Journal of Wind Engineering and Industrial Aerodynamics 95(9–11): 1463–1475.

28.

Telenta

Batista

Biancolini

, et al. (2015) Parametric numerical study of wind barrier shelter. Wind and Structures 20(1): 75–93.

29.

Wang

Chen

(2012a) Cross-wind environment numerical simulation of connection section between tunnel and bridge. Journal of Chang’An University. Natural Science Edition 32(5): 52–57.

30.

Xiang

Wang

(2015) Aerodynamic interaction between static vehicles and wind barriers on railway bridges exposed to crosswinds. Wind and Structures 20(2): 237–247.

31.

Xing

Mohotti

Chauhan

(2018) Study on localised wind pressure development in gable roof buildings having different roof pitches with experiments, RANS and LES simulation models. Building and Environment 143: 240–257.

32.

Yang

Quan

Jin

, et al. (2008) Influences of equilibrium atmosphere boundary layer and turbulence parameter on wind loads of low-rise building. Journal of Wind Engineering and Industrial Aerodynamics 96(10–11): 2080–2092.

33.

Zhang

Proppe

(2019) The influence of strong crosswinds on safety of different types of road vehicles. Meccanica 54(9): 1489–1497.

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