水垫塘冲击区掺气浓度对脉动压强作用的试验研究
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摘要
采用水工模型试验,研究泄流进入水垫塘后在水垫塘底板冲击区内掺气浓度对脉动压强的作用。通过改变掺气量,使水垫塘内水体的掺气浓度发生变化,开展不同的掺气浓度对水垫塘冲击区底板脉动压强影响的研究。结果表明:在保持水垫深度和泄流流量不变的情况下,增加掺气量,水垫塘冲击区同一测点水体掺气浓度值随掺气量的增加而增加。水垫塘冲击区内掺气浓度分布规律为在冲击点处达到最大值,由冲击点向上、下游递减;冲击区底板总动水压强的峰值随掺气量的增加而降低;脉动压强的方差值随掺气量的增加而减小,即脉动变幅减小。脉动压强的概率密度分布为正态分布,分布曲线随掺气量的增加而变陡、变窄,脉动强度系数分布集中,即方差变小,压强峰值减小,脉动强度减小。同一测点脉动压强的频谱分布规律一致,其优势频率集中在低频范围,随掺气量的增加,脉动幅值降低,即脉动压强降低。
The effect of the aeration concentration on fluctuating pressure in the impacted region of plunge pool after water flow being discharged into plunge pool is studied herein with hydraulic model experiment; from which the effects of various aeration concentrations on the fluctuating pressure of the bottom slab in the impacted region of plunge pool are studied through making the aeration concentration of the water body in the plunge pool changed by changing the amount of aeration. The result of the data analysis shows that under the condition of keeping the water cushion depth and the discharge-flow rate unchanged,the value of aeration concentration of water body at a same measuring point in the impacted region of plunge pool is to be increased along with the increase of the amount of aeration through increasing amount of aeration. The distribution law of the aeration concentration in the impacted region of plunge pool is that the aeration concentration reaches to its maximum value at the impacted point and then gradually decreases toward the upstream and the downstream of the impacted point,while the peak value of the total dynamic water pressure on the bottom slab of the impacted region is to be decreased along with the increase of amount of aeration and the variance of the fluctuating pressure is reduced along with the increase of amount of aeration,i. e. the fluctuation amplitude is decreased. The distribution of the probability density of the fluctuating pressure is a normal distribution,while its distribution curve is to be steepened and narrowed along with the increase of amount of aeration and the distribution of the fluctuation intensity coefficient is concentrated,i. e. the variance is decreased with the decreased peak value of pressure and the decreased fluctuation intensity. The law of the fluctuating pressure spectrum distribution at the same measuring point is consistent,of which the dominant frequency is concentrated in a low frequency range and the fluctuation amplitude decreases along with the increase of amount of aeration,i. e. the fluctuating pressure is decreased.
The effect of the aeration concentration on fluctuating pressure in the impacted region of plunge pool after water flow being discharged into plunge pool is studied herein with hydraulic model experiment; from which the effects of various aeration concentrations on the fluctuating pressure of the bottom slab in the impacted region of plunge pool are studied through making the aeration concentration of the water body in the plunge pool changed by changing the amount of aeration. The result of the data analysis shows that under the condition of keeping the water cushion depth and the discharge-flow rate unchanged,the value of aeration concentration of water body at a same measuring point in the impacted region of plunge pool is to be increased along with the increase of the amount of aeration through increasing amount of aeration. The distribution law of the aeration concentration in the impacted region of plunge pool is that the aeration concentration reaches to its maximum value at the impacted point and then gradually decreases toward the upstream and the downstream of the impacted point,while the peak value of the total dynamic water pressure on the bottom slab of the impacted region is to be decreased along with the increase of amount of aeration and the variance of the fluctuating pressure is reduced along with the increase of amount of aeration,i. e. the fluctuation amplitude is decreased. The distribution of the probability density of the fluctuating pressure is a normal distribution,while its distribution curve is to be steepened and narrowed along with the increase of amount of aeration and the distribution of the fluctuation intensity coefficient is concentrated,i. e. the variance is decreased with the decreased peak value of pressure and the decreased fluctuation intensity. The law of the fluctuating pressure spectrum distribution at the same measuring point is consistent,of which the dominant frequency is concentrated in a low frequency range and the fluctuation amplitude decreases along with the increase of amount of aeration,i. e. the fluctuating pressure is decreased.
引文
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[2]刘沛清,李福田,王颖.挑跌流水垫塘内流态结构控制参数与冲击压强变化规律实验研究[J].水利学报,2003,34(3):25-28.
[3]辜晋德.水跃区水流脉动压强相似律[D].天津:天津大学,2007.
[4]田忠.高速淹没射流冲击压强的试验和数值模拟研究[D].成都:四川大学,2003.
[5]焦爱萍,孙五继,周陈超,等.高拱坝分层多股射流水垫塘冲击压强研究[J].水力发电学报,2012,31(1):114-117.
[6]卢艳娜,李龙国,李乃稳,等.射流形状对水垫塘底板冲击动压特性的影响[J].南水北调与水利科技,2014,12(6):89-92.
[7]张铭,尤超,赵荥.高含沙水流脉动特性试验研究[J].水利水电技术,2016,47(11):82-88,98.
[8]吴持恭.明槽自掺气水流的研究[J].水力发电学报,1988,7(4):23-26.
[9]李乃稳,刘超,李龙国.斜向射流入水垫塘淹没射流区的紊动特性[J].水力发电学报,2016,35(3):66-72.
[10]郭航忠.水垫塘底板稳定性判别标准研究[D].天津:天津大学,2004.
[11]李树宁,杨敏.平底板急流区下表面脉动压力试验研究[J].中国农村水利水电,2016(4):123-125,129.