Study On The Characteristics Of Low-Frequency Sound Waves Induced By High Dam Flood Discharge And Noise Reduction

Issues such as scouring,cavitation damage,structural vibration and atomization caused by flood discharge of high dams have always been the focus of attention in the field of water conservancy engineering.There have been a lot of researches on these aspects,however,at present,there are few studies on low-frequency sound waves induced by high dam discharge.In recent years,many hydropower stations have appeared the environmental hazards caused by low-frequency sound waves induced by flood discharge.Therefore,it is necessary to carry out research in this field.This paper relies on the Xiangjiaba project,using hydrodynamic acoustic theory,computational fluid dynamics multi-phase flow turbulence numerical simulation,and acoustic numerical calculation to study the turbulent flow field characteristics and the low frequency sound field induced by flood discharge in Xiangjiaba,and finally,the suggestions for reducing the intensity of low-frequency sound waves generated by flood discharge of Xiangjiaba were provided,and it provided experience for noise reduction optimization of other hydropower projects.The main research results of this paper are as follows:(1)The multi-phase turbulence numerical simulation was used to calculate the Xiangjiaba flood discharge flow field.The results show that the flow field velocity distribution law and turbulent kinetic energy distribution law are similar under each calculation condition,the maximum velocity and turbulence energy of the discharge flow under the orifice appear in the bottom area of the spillway.Until the middle area of the stilling pool,the velocity and turbulence energy of the flow are gradually consumed,at the same time,the turbulent energy at the central position of the mainstream tongue is relatively small compared to the turbulent energy around the tongue.(2)Using software co-simulation to calculate the sound field generated in the downstream area due to flooding of Xiangjiaba.The results show that the Xiangjiaba Hydropower Station does generate low-frequency sound waves during the flood discharge process,and the sound pressure level will lose 46 ～ 60 d B when passing through the water-air interface;The distribution of the sound pressure level in the downstream area of Xiangjiaba is roughly circular in the center of the dam area.The closer to the dam area,the greater at the sound pressure level,and the sound pressure level of the area near the dam decays faster,when the discharge flow increases,the frequency of the low-frequency sound waves that have the greatest impact on the downstream area will be reduced.Finally,it is compared with the results of the prototype observation data,which proves the credibility of the acoustic calculation.(3)Using the opening of the gate as a variable in the table,15 noise reduction conditions were established.The results of the noise field calculation were analyzed.The results showed that the intensity of the low-frequency sound waves generated by the flood discharge of Xiangjiaba generally increases with the opening of the gate,but when the surface hole alone discharging or the middle hole alone discharging,the intensity of low-frequency sound waves generated by the flood discharge may be greater than that generated bt the joint of surface hole and middle hole flood discharge.(4)By comparing the sound field data under various noise reduction working conditions,suggestions for noise reduction optimization of Xiangjiaba Hydropower Station were proposed.Joint flooding in the middle hole of the table should be used as much as possible.The gate scheduling method of small gate opening can reduce the intensity of low-frequency sound waves generated by flood discharge,and for floods of the same flow level,the opening of the surface gate is appropriately reduced while the opening of the middle gate is appropriately increased,which is conducive to reducing the intensity of low frequency sound waves generated by flood discharge.