高流速明流泄洪洞气流场特性及泄洪洞需气量研究

Results of prototype observation for Jinping, Nuozhadu, ertan projects indicate that, defective design of ventilation facilities of spill tunnel could seriously affect the safe operation of the tunnel. The fundamental reason of which is lack of systematic research for air flow characteristics of the discharge tunnel. At high flow rates, the flow pattern of the spill tunnel has changed, there is no clear interface between water and air, and the air carrying capacity of the spill tunnel has also increased dramatically. There is a significant scale effect based on research results at low flow rates. Aiming at the problem, the applicant intends to carry out the following research works: A generalized model for a spillway tunnel will be established based on a high speed jet experiment platform with highest speed of 50m/s. Air flow field in the tunnel will be measured by High-speed photography system, wind speed measuring system and by flow display device using colored smoke, so as to reveal the mechanism of interaction between water and air in discharge tunnel under mesoscale, and reveal the variation of airflow field characteristics and ventilation volume in discharge tunnel at the prototype flow velocity scale. Based on the results of systematic tests and prototype observations, aerodynamic balance equations for ventilation system and theoretical calculation methods for the air demand of discharge tunnel will be established. Research results can provide theoretical basis for the design of the ventilation system of the spillway tunnel.

锦屏一级、糯扎渡、二滩等工程泄洪洞泄流期间，出现了高分贝啸叫声、泄洪洞出口间歇性喷水、爆震等现象。上述问题是由于泄洪洞补气不足、通气设施设计不当造成的，其根本原因是对高流速泄洪洞气流场特性研究不够系统深入。在高流速条件下，泄洪洞水流形态发生变化，已无清晰的水气交界面，泄洪洞携气量也急剧增加，基于低流速条件下的研究成果存在明显的比尺效应。针对这一问题，本研究在50m/s高速射流试验平台上建立明流泄洪洞概化模型，采用高速摄影系统、全断面风速风压测试系统及彩色发烟流动显示装置，对泄洪洞气流通道内的气流场进行精细测量，揭示细观尺度下，泄洪洞洞顶余幅内水体与气体相互作用机制，揭示原型流速尺度下，泄洪洞气流场特性及通气量的变化规律，基于系统试验及原型观测成果，建立泄洪洞通气系统气体动力平衡方程及泄洪洞需气量理论计算方法。研究成果可望为泄洪洞通气系统设计提供理论依据。

锦屏一级、糯扎渡、二滩等工程泄洪洞泄流期间，出现了高分贝啸叫声、泄洪洞出口间歇性喷水、爆震等现象。上述问题是由于泄洪洞补气不足、通气设施设计不当造成的，其根本原因是对高流速泄洪洞气流场特性研究不够系统深入，未建立精确的通风洞通气量计算方法。本项目采用原型观测、理论分析及物理模型试验相结合的方法对高速明流泄洪洞气流场特性及通气量问题进行了深入研究。主要研究内容包括：基于原型观测资料下泄洪洞气流场特性及通气量的变化规律；基于系统试验及原型观测成果，建立泄洪洞通气系统气体动力平衡方程及泄洪洞需气量理论计算方法；对泄洪洞气流通道内的流场和压场进行测量，研究泄洪洞洞顶余幅内水体与气体相互作用情况，明确结构因素变化对通风洞供气系统通气量及气相流场特性的影响。主要成果包括：研究了闸门开度及洞顶余幅对原型通气量的影响，建立了基于能量损失系数的闸后最大允许负压与通风洞平均风速之间的定量关系；构建了单通风洞及多通风洞供气系统较为完整的通气量理论计算方法，提出了基于理论分析及原型观测的通气量半理论半经验公式，并通过显影试验对泄洪洞气相流场特点进行分析；提出了物理模型试验中减小通气量缩尺效应影响的方法，揭示了水流拖曳力系数变系数项与水流表面法向脉动流速均方根之间的定量关系；构建了较为完善的多通风洞通气量理论公式。研究成果可为泄洪洞通气系统设计提供理论依据。.