Study On Aerodynamic Characteristics And Buffering Measures For The Sound Barrier Of High-speed Railway Bridge With Full/Semi-closed Section

The novel section noise barriers have been widely used in highspeed railway bridges to meet the demand for noise reduction with the rapid development of the high-speed railway in China.As the running speed of the high-speed railway increases,the noise barriers encounter more and more aerodynamic problems.However,there is still a lack of systematic research on the aerodynamic effects of high-speed railway noise barriers.This doctoral thesis used the dynamic model test,numerical simulation,and theoretical analysis to study the aerodynamic characteristics and the flow evolution of the noise barrier under the coupled action of the train wind and crosswind.Besides,the aerodynamic optimization measures of the noise barriers are put forward.The main research work is as follows:(1)A full/semi-enclosed noise barrier test of the high-speed trainway and bridge was constructed to discuss the pressure wave transfer effect and the fluctuating pressure mutation law of the noise barriers,analyze the variation law of the fluctuating pressure of the noise barrier with the running speed,the measurement points location and the section form,and explore the difference of the aerodynamic characteristics of different noise barriers.The results show that there was a significant pressure wave effect when the train was running with the rectangular noise barriers,and the inlet and outlet openings of the noise barriers could suppress the fluctuating pressure in the inlet and outlet sections of the noise barriers.(2)Based on the "Mosaic" moving mesh technology and Large Eddy Simulation(LES)method,the numerical model of the high-speed trainway and noise barriers was established corresponding to the dynamic model test.The flow evolution mechanism of noise barrier with different cross-section forms was analyzed,and the influence of cross-section forms and crosswind velocity on the pressure characteristics of noise barrier was revealed.The results showed that the reliability of dynamic model test results was verified by comparing numerical results.Under crosswind,the inner measuring points of the full/semi-closed noise barriers were mainly affected by negative pressure,while the outer points were mainly affected by positive pressure.The von Karman vortex street appeared on different acoustic barriers,but their difference was obvious.(3)Based on Proper Orthogonal Decomposition(POD)theory and numerical simulation,the aerodynamic characteristics and average flow field of different noise barriers under crosswind were discussed.By analyzing the contribution of each mode to turbulent kinetic energy and the POD modes of the aerodynamic characteristics of the noise barriers,it can be seen that the low order modes of sound barriers had a more significant contribution to turbulent kinetic energy.The sum of the first-order and second-order POD modes accounted for more than 95% of the total energy.The POD mode characteristics of the rectangular noise barrier were as follows: a series of small-scale alternating positive and negative vortices were attached to the outer side of the roof and the leeward side plate,and the modal characteristics of each mode were consistent.(4)Based on numerical simulation,the law and mechanism of the space-time aerodynamic pressure characteristics of the full/semi-closed noise barrier were analyzed.Besides,the countermeasures of the uneven spatial distribution of the pressure amplitude of two kinds of noise barriers without cross-wind and the aerodynamic mutation of the high-speed trainway with crosswind were put forward.Finally,the aerodynamic optimization scheme of different noise barriers was as follows: three-hole depressurization and gradually varied end ventilation rate were adopted for full enclosed noise barriers,and gradually varied end ventilation rate was adopted for semi-enclosed noise barriers.