| Nowadays,people's living standards are constantly improving,and intensive traffic produces a lot of exhaust pollution,which has a great negative impact on the public health.Air quality has been our main perspective of concern about human settlements ecology.In the beginning of the 14th five year plan,we continue to uphold the new development concept,namely innovation,green,coordination,opening up and sharing.In the road of building a socialist modernization powerful country in an all-round way,it has become one of the hot topics in academic circles to solve our daily living environment.This topic combines the recent research progress at home and abroad,The paper analyzes the advantages and disadvantages of the plane shape of urban intersections in Tianjin,and studies the distribution of wind environment and pollutant diffusion in the intersection by numerical simulation and experimental research.The influence of intersection types,flow direction,intersection angle and width of the street Valley on the ventilation efficiency of the intersection is discussed.The numerical simulation is carried out by ANSYS fluent fluid simulation,and the wind speed distribution and pollutant concentration distribution in 12urban plane forms are simulated.Combined with the research content of the project,the wind environment under the influence of the width of the street Valley is explored and analyzed by using the air volume wind chamber experimental platform and the optimized design scheme.The numerical simulation results are compared with the experimental data,and the following conclusions are drawn(1)Case1(i.e.angle 30°)The R-shaped intersection is the best ventilation layout under four intersections,the pure flow PFR is 463m~3/s,and the PFR value of the best wind direction is 16.6%higher than that of the west south wind;The angle of case intersection of case2 is 45°The results showed that the effect of south wind was better than that of southwest wind,and the PFR value of the best wind direction was 9.1%higher than that of the east south wind;Case intersection angle of case3 is 60°The results showed that the wind effect of south wind was better than that of the southwest wind,and the PFR value of the best wind direction was 18.9%higher than that of the southwest wind;Case intersection angle of Case4 is 90°The results showed that the ventilation effect of the wind was better than that of the south wind,and the best wind direction was 9.5%higher than that of the south wind.The ventilation effect of case1 case is the best under the action of south wind.(2)Case6 case(i.e.45 angle°)The four fork intersection is the best ventilation layout in four cases.The PFR of the intersection under the action of south wind reaches the maximum value,and the PFR value of the best wind direction south wind is 33.4%higher than that of the east south wind.Case intersection angle of case5 is 30°The results showed that the ventilation effect of south wind was better than that of the other two wind directions,and the PFR value of the best wind direction was 15.1%higher than that of the other two.The intersection angle is 30°And 45°When the value of nev is close to that of the south wind,the effective velocity of pollutant dispatch is close.Case7 case,intersection angle is 60°The results showed that the ventilation effect of the east south wind was better than that of the southwest wind,and the PFR value of the best wind direction was 14.4%higher than that of the southwest wind.The best ventilation effect of case6 under the action of south wind is obtained.(3)The angle of the case8 intersection is 90°When the cross intersection is T-shaped and cross,the PFR of cross intersection under the action of south wind reaches the maximum value.Under this condition,the pure flow rate of the intersection is the highest,and the net escape velocity nev value is 14.4%higher than that of the east south wind in the intersection with two different plane forms.Under the effect of south wind,the ventilation effect of T-shaped intersection in Case4 case is 9.3%higher than that of cross intersection in case8 case.Under the action of southeast wind,the ventilation effect of T-shaped intersection in Case4 case is 19.1%higher than that of cross intersection in case case8.When the width of street Valley is 20 m,the overall ventilation performance of T-shaped intersection is better than that of cross-section intersection.(4)When the width of the valley is certain,the ventilation efficiency of the valley is different with the wind direction,and the influence of the convection and diffusion of pollutants transmission is consistent with the ventilation efficiency;When the valley width of case8 case is 20 m,the PFR value of this case is 14.3%higher than that of the east south wind under the action of south wind;When the valley width of case9 case is 25m,the PFR value of this case is 8.9%higher than that of the east south wind under the action of south wind;When the valley width of case10 case is 30m,the PFR value of this case is 4.3%higher than that of the east south wind under the action of south wind;When the width of valley in cas11 case is 35m,the PFR value of this case is 4.1%higher than that of the east south wind under the action of south wind;When the valley width of case12 case is 40m,the PFR of this case is 4.6%higher than that of the east south wind under the action of south wind;When the dominant wind direction is south wind,the ventilation performance decreases with the increase of Valley width.The case of Valley width of 20 m is the most unfavorable environment in five conditions,and the width of street Valley is 40m,which is the best environment in ventilation index.The best ventilation effect is case12 at cross intersection.(5)The experimental results show that under the plane layout of five cross intersections with different Valley width,the temperature of each measuring point of street Valley decreases with the increase of Valley width,and the maximum wind speed appears at the entrance with the width of 20 m,and the wind speed value is 1.79m/s;The minimum wind speed appears at the exit with the width of 40 m in the street Valley,the wind speed is0.22m/s,and the wind is in the wind free state at the end of the vertical branch and the horizontal branch of the intersection.(6)Through the comparative analysis of the numerical simulation and experimental data,it is found that the numerical simulation is in line with the experimental value trend,the error is controlled within 10%,the change trend tends to be consistent,and within the acceptable range. |
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