挑坎掺气槽过流空腔区掺气特性的研究

本文探讨了挑坎掺气槽过游空腔区的掺气特性。对掺气机理、临界掺气所条件、所泡上浮特性、紊动扩散系数、断面含气液度和通气量进行了较详细的理论分析。主要结果得到实测资料的验证。     

紊流结构与掺气

在介绍溢洪道掺气模型上下游水流紊动量测结果的基础上，对水流紊动的各种影响因素作了分析，主要包括：试验水糟中不同挑坎角度和渠槽宽深比对水流紊动的影响；挑坎作为紊动源对水流紊动的影响，以及挑坎下游水舌在不同条件下紊动的衰减程度。本项研究旨在探索建立水流掺气预报的新途径。     

掺气坎射流出射角的修正方法

掺气坎后射流出射角受到来流水深和射流紊动扩散的影响,不等于挑坎的挑角,计算掺气空腔长度时,应该对出射角进行修正。而目前采用的考虑紊动扩散对出射角影响的修正方法存在不合理的假设。考虑到坎末水流流态为充分发展的紊流,射流边缘处于紊动能耗散区,提出了一种紊动扩散对出射角影响的修正方法。采用该方法计算的射流紊动扩散角与试验结果更吻合。对出射角修正后,结合简单的抛射体公式,就能较精确地估算掺气空腔长度。     

跌坎型掺气槽过流的掺气特性

本文在分析实测资料的基础上，探讨了无挑角跌坎型掺气槽空腔区水舌的掺气特性，并重点研究了射流水舌的掺气超始流速，掺气层厚度，断面浓度分布以及通气量等参数的理论预测。     

低Fr数流动跌坎掺气槽的水力及掺气特性

通过模型试验和理论分析，研究了低Fr数(Fr<7)流动情况下空腔积水对跌坎掺气设施水力及掺气特性的影响。建立了计算跌坎掺气设施水力及掺气特性的预测数学模型。给出了射流出射角的修正式；积水尺寸的计算式；掺气设施实际运行工况(空腔长度、空腔负压、掺气量等)的预估方法。研究表明，低Fr数流动情况下，由于重力作用显著，积水对水力及掺气特性均有显著影响。     

泄槽底坡对掺气坎射流空腔积水的影响

通过作者建立的掺气坎射流曲线方程和掺气空腔积水方程,分析计算了泄槽底坡对跌坎型、挑坎型和挑跌坎型3种掺气坎掺气空腔积水的影响.计算结果表明,泄槽底坡对3种体型掺气坎掺气空腔积水的影响规律是一致的.随泄槽底坡增大,空腔积水减弱,最终消失;掺气坎后挑射水流与底板的冲击角随泄槽底坡增大而减小;不同体型掺气坎的临界冲击角是不一样的.研究成果可为掺气坎的设计提供参考.     

缓坡条件下掺气减蚀设施的体型研究

结合小湾泄洪洞掺气减蚀设施优化研究，提出了“当量坎高”的概念与凹型掺气坎的布置构想，在相同“当量坎高”的前提下，通过1：60水工模型试验，对平面凹型、平面凸型、平面梯形、U型坎，以及直线型挑坎等掺气坎体型进行了对比试验研究，从掺气浓度、空腔特性及通气量等指标看，凹型掺气坎是一种较优的布置形式．从物理机制上看，平面凹型掺气坎因空腔内水气交界面积大，对提高空腔内的总通气量、改善掺气条件有利；另外，相对于其他异型掺气坎而言，凹形掺气坎在两侧边墙处空腔更为完整一些，这对提高边壁角隅区域水流的掺气能力，增进边墙的抗空蚀效果也有一定的助益．     

设掺气挑坎渥奇面流场数值模拟计算研究

采用了引入VOF法的κ～ε紊流模型方程对设掺气挑坎的渥奇面流场进行了数值模拟研究,共模拟了两种挑坎布设位置的方案.本模型采用有限体积法对控制方程进行离散,计算了挑流流场和掺气空腔,并通过与模型试验数据对比验证,证实该模型可较精确地模拟实际流场.分析表明:相同体型和水力条件下挑坎布于渥奇段下游优于上游,且流态稳定,下游掺气较佳,可较成功地解决渥奇段下接高速水流区的掺气减蚀问题,该数值模型结果对掺气挑坎设计选型及位置优化有指导意义.     

侧掺气空腔长度计算方法研究

掺气空腔长度是衡量掺气减蚀效果的核心水力指标。针对关于侧掺气空腔长度计算方法的研究成果偏少的现状,通过模型试验和量纲分析,对陡槽上不同坎高和坡度侧掺气坎的空腔特性和射流扩散特性开展了研究,分析侧掺气坎体型参数及来流水力学参数对侧空腔长度的影响,推导出侧空腔长度计算公式,并采用多组实验数据进行了验证。结果表明该公式能较准确地估算侧掺气空腔长度。     

明流泄洪洞掺气减蚀设施优化试验研究

通过水工常压模型试验，对高水头、大单宽流量、小底坡龙抬头式明流泄洪洞掺气坎进行了系统的试验研究及优化试验，提出了一种新型的V形掺气挑坎。该掺气坎的空腔长度沿水流的横断面方向是连续变化的，射流挑距两边长、中间短，尽管最小空腔的长度可能已小于临界值，但由于最大空腔长度仍远大于临界值，在其作用下，便可使回流退去，空腔恢复，保证一定的通气量。这对类似工程掺气设施的合理设计有十分重要的参考意义。     

The inception cavitating flows over an axisymmetric body with a blunt head-form

The inception cavitating flows around a blunt body are studied based on flow visualizations and velocity field measurements. The main purpose of the present work is to study the incipient cavity evolution and the interplay between the inception cavitation and the local turbulent flows. A high-speed video camera is used to visualize the cavitating flow structures, and the particle image velocimetry(PIV) technique is used to measure the velocity field, the vorticity, and the Reynolds stresses under non-cavitating and inception cavitating flow conditions. It is found that the appearance of visible cavities is preceded by the formation of a cluster of micro-bubbles not attached to the body surface and in a hairpin-shaped vortex structure. During its evolution, the cavity moves downstream with a lower speed. The effect of the incipient cavity is significant on the local vortical structures but slight on the timeaveraged velocity distribution. The mean Reynolds stress distributions in the turbulent shear flow can be substantially altered by the incipient cavities. The presence of the incipient cavities can lead to the production of turbulent fluctuations.     

WALL PRESSURE FLUCTUATIONS OF TURBULENT FLOW OVER BACKWARD-FACING STEP WITH AND WITHOUT ENTRAINMENT： MICROPHONE ARRAY MEASUREMENT

1. INTRODUCTION Turbulent boundary layer flows over surface irregularity are of significant importance from both fundamental and practical essences. Among others, turbulent flows over backward-facing step (hereinafter referred to BFS) received widespread …     

MODELLING AND COMPUTATION OF UNSTEADY TURBULENT CAVITATION FLOWS

1. INTRODUCTION Cavitatating flows are important phenomena happened in industry setups and many under-water vehicles. It leads to performance losses and modifications of blade load when happened in machines, especially turbo-machinery. Nevertheless, cavit…     

HYDRAULIC RESEARCH OF AERATORS ON TUNNEL SPILLWAYS

The selection of the configuration and size of an aerator was of importance for a tunnel spillway under the conditions of high speed flows. Experimental investigations were conducted on the effects of entrained air on the tunnel spillway in the Goupitan Project, based on the criterion of gravity similarity and the condition of aerated flow velocity of over 6 m/s, with physical models. The configurations of the aerators were presented of a larger bottom air concentration, to protect the tunnel spillway from cavitation as well as to see no water fills in the grooves.     

矩形明渠三维紊流的数值模拟

在明渠三维流动中，紊流产生的二次流起关键作用，它对主流流场分布，壁面应力及污染物的扩散有很大影响，有时还影响床面的稳定，Ｋ－ε紊流模型及类似的双方程模型不能计算这种二次流动。本文将非线性Ｋ－ε紊流模型用于明渠三维紊流的计算，模型用张量形式推出，比代数应力模型更易推广到复杂边界流动，应用这一模型及另两种代数应力模型对矩形明渠流动进行计算，所得结果，尤其是表述紊流特征的量，与实测资料进行了详细比较，并     

基于POD方法的圆型喷口射流速度场结构分析

大空间建筑中分层空调系统喷口送风射流运动卷吸会造成热量自上部非空调区向下部空调区转移,这是导致空调系统负荷增加的原因之一。本文搭建圆型喷口射流运动盐水模型实验台,利用粒子速度测量系统(PIV)提取喷口卷吸剪切层附近流场速度矢量场信息,借助特征正交分解方法(POD)剖析剪切层内的相干结构及其能量分布、竖向与横向速度特征值比例,为后期研究喷口卷吸运动引起的大空间对流转移热量提供实验与理论参考。     

淹没紊动射流三维流场特性的数值模拟

采用RNGk-ε紊流模型对有限空间的单孔、双孔紊动射流的流场进行了三维数值模拟研究。研究结果表明:无论入流条件如何变化,经无量纲处理后的轴线流速分布曲线几乎都落在同一条无量纲速度分布曲线上,说明流动存在相似性。双孔射流时,流场存在分区结构,在不同的喷嘴间距下,射流的卷吸程度不同,S/D越大,射流之间的卷吸掺混作用越弱。     

PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows

PIV is one of the most popular measurement techniques in hydraulic engineering as well as in fluid sciences. It has been applied to study various turbulent phenomena in laboratory experiments related to natural rivers, e.g., bursting phenomena near the bed, mixing layers observed at confluences, wake turbulence around dikes and piers, and so on. In these studies, PIV plays important roles in revealing the space-time structure of velocity fluctuations and coherent vortices. This review article focuses particularly on the applications of PIV to turbulent open-channel flows, which have been conducted for the past decade in Hydraulics Laboratory of Kyoto University. In Section 2, we introduce our experimental setup and PIV/PTV algorithm. In Section 3, we apply the PIV measurements to reveal turbulence characteristics and coherent structures in open-channel flows as well as in vegetated canopy flows. For complex flow situations, various applications of PIV to compound open-channel flows and wind-induced water waves are considered to reveal coherent vortices. In Section 4, we discuss some advanced PIV measurements in open-channel flows. The free-surface-elevation fluctuations and velocity components were measured simultaneously with two sets of cameras to examine phase-averaged parameters of turbulence. A multi-layer scanning PIV was developed to reveal 3D turbulence structure in compound open-channel flows. Our discriminator PIV/PTV was applied successfully to sediment-laden open-channel flows and revealed the fluid/particle interaction and the relationship between coherent structures and sediment concentration. Finally, we conducted simultaneous measurements of velocity and dye concentration with a combination of PIV and LIF in vegetated open-channel flow, which enables us to examine turbulent scalar flux of a passive contaminant.