几何比尺对正态模型沙波相似性的影响

中文摘要: 不同几何比尺对模型水流结构及泥沙运动特性的比尺效应不同，模型沙波相似性也存在差异。首先基于对泥沙沉速的理论分析，计算了当原型沙粒径、 λ (γs-γ)/γ和 η等参数一定时，满足起动相似所选模型沙沉降速度偏离程度随不同几何比尺的变化规律。计算结果显示： λ l<1时，模型沙沉降速度偏离程度随着几何比尺的进一步减小而迅速增大；当 λ l≥1时，模型沙沉降速度偏离程度随着几何比尺的增大表现为先增大后减小，且在几何比尺为2的附近达到极大值。为研究沉降速度偏离幅度较大时模型沙波的相似性及几何比尺改变时沙波波高、波长与原型的偏离特性，设计进行了 λ l=0.84、1.59和2.06的正态水槽试验，发现3组模型中的沙波波高、波长偏差幅度均不大于6 %，其中 λ l=0.84的模型沙波偏小，而 λ l=1.59和2.06的沙波偏大。结合理论分析结果和水槽试验数据，得到以下结论：1）对于几何正态模型，当 λ l<1、原型沙与模型沙重率相同时，满足起动相似的模型沙沉降速度偏小，相同水流条件下泥沙落淤速度慢，模型中的沙波波高、波长均较原型偏小；当 λ l≥1时，满足起动相似的模型沙沉降速度偏大，泥沙落淤较快，相应模型中沙波波高波长都较原型偏大。2）若 λ l≥1，模型沙波波高、波长偏差幅度均不大于6 %，即模型沙波波高、波长的相似性较好。
Abstract:Different geometric scales have different effects on model flow and sediment motion characteristics,so does with model sand wave similarities.Firstly,for model sand that is satisfied with incipient motion similarity,the variation laws of settling velocity deviations with different geometric scales are numerically analyzed when prototype sand diameter, λ (γs-γ)/γ and η are the same.The results showed that for the case of λ l<1,the settling velocity deviations of model sand increase rapidly with the decreasing geometry scales.While for the case λ l≥1,the settling velocity deviations of model sand rise firstly and then fall with the increasing geometry scales,reaching its peak when the geometry scale is 2.Besides,to better understand model sand similarities at a large settling velocity deviation and deviation characteristics of model sand wave height and length from those of the prototype at different geometry scales,the normal flume experiments are designed with λ l=0.84,1.59 and 2.06,respectively.The results represented that both sand wave height deviation and sand wave length deviation were less than 6 % in these three experiments.The sand wave with λ l=0.84 was relatively smaller while the sand waves with λ l=1.59 and λ l=2.06 were relatively larger.Finally,the following conclusions were reached by integrating theoretical analysis with flume experiment methods:1） for geometric normal model,when λ l<1 and model sand and prototype sand had the same weight ratio,the settling velocity of model sand was relatively smaller,resulting in slower sediment deposition rate.Furthermore,both sand wave height and sand wave length were smaller than those of the prototype.When λ l≥1,the settling velocity of model sand was relatively larger,resulting in a greater sediment deposition rate.Moreover,both sand wave height length were larger than those of the prototype.2）When λ l≥1 and both sand wave height deviation and sand wave length deviation were less than 6 %,the model sand