峡谷河道综合糙率变化规律的预报

Prediction of synthetic resistance in gorge channel

本文揭示了峡谷与宽谷河道水流结构特性与阻力损失的机理和同异，指出前者的综合糙率常比后者大１～３倍，其原因除了通常认识的周界粗糙度不同有影响外，主要因素是河型和断面形态不同，紊流涡体的产生、规模、强度和分布不同，集中表现在水流内部结构不同所引起的能损不同的结果．论证了阻力系数公式（５）仍可用于三维水流。但卡门常数Ｋ值不再是０．４；峡谷河道水流的Ｋ值可用式（８）或式（９）求解。宽阔河道水流的Ｋ值可用文献［４］的公式计算．在动床水流中，Ｋ值不仅是表征流速分布变化的一个参数，也是衡量水流阻力系数变化和床面形态定性变化的一个指标，是阻力系数的重要组成部份．引入紊流能损理论（即Ｋ值的变化）之后，水流阻力变化规律便与水流结构变化和床面形态变化建立起有机的联系，取得了与实测值基本一致的结果，解决了现有的糙度阻力系数公式无法求解超高（低）阻力的难题．

The relation of the characteristics of flow structure to the mechanism of the resistance lossin gorge and broad channel with movable bed is showed in the paper.It is found that the synthetic roughness coefficient in gorge channel is usually two to four times of that in the broadchannel. This phenomenon is mainly caused by the difference of channel patterns, cross sectionshapes,intensity and distribution of turbulence and large scale vortices,etc. It is also found thatthe theoretical resistance eq.(5)is approximately suitable for 3-D flow,but the correspondingKarman coefficient K is no longer equal to 0. 4. It is suggested that eq.(8)or eq.(9)in this paper can be used to calculate the average K of flow in gorge channel,and equations presented inreference[4]to calculate the average K of flow in broad channel.In fact,the Karman coefficient K of flow with movable bed is not only a parameter showingthe variations of velocity distribution,but also a index measuring the variation of flow resistanceand bed forms. Therefore,the variation of flow resistance is directly related to the variations offlow structure and bed forms.Eqs.(7)～(14)presented in this paper are used to solve the extra higher(or lower)resistance, and the computed values are in agreement with the measured,which cann't be solved by the existing equations of roughness coefficient for the condition of Kto be 0.4.