A hydraulic jump is a region of rapidly-varied flow that is extremely turbulent. While the one-dimensional continuity and momentum principles have been successfully applied to express the relationships between upstream and downstream conditions, the three-dimensional equations cannot be resolved without some complicated turbulence closure, often involving two phases, i.e. air and water. Based upon a new dataset, the current investigation has the double objective of presenting a novel experimental investigation of the air-water flow characteristics in hydraulic jumps with a small Froude number (Fr₁ = 2.1) and discussing the potential scale effects involving several Reynolds numbers (0.078 × 10⁵ < Re < 3.05 × 10⁵). Four unique features are the low inflow Froude number Fr₁ = 2.1, the wide range of Reynolds numbers tested systematically, the broad amount of air-water flow properties investigated, and the relatively high Reynolds number (Re = 3.05 × 10⁵) achieved in the largest experiment. More than two dozen of parameters were tested systematically under Froude similar conditions. All the data demonstrated that the selection of relevant (air-water) flow property(ies) used to assess similarity and scale effects is most essential. Further the concept of similarity and scale effects must be linked to specific flow conditions. At low Froude number (Fr₁ = 2.1), the present results showed that many hydraulic jump properties could not be extrapolated from laboratory study to full scale hydraulic structures without substantial scale effects. These findings have profound implications for engineering design applications, often operating with Reynolds numbers in excess of 10⁵.

水跃是一个快速变化的流动区域，非常湍急。虽然一维连续性和动量原理已成功应用于表达上游和下游条件之间的关系，但如果没有一些复杂的湍流闭合（通常涉及空气和水两相），则无法求解三维方程。基于一个新的数据集，当前的研究具有双重目标，即对具有小弗劳德数 (Fr ₁  = 2.1) 的水跃迁中的空气-水流特性进行新的实验研究，并讨论涉及多个雷诺数的潜在尺度效应(0.078 × 10 ⁵  < Re < 3.05 × 10 ⁵）。四个独特的特征是低流入弗劳德数 Fr ₁  = 2.1、系统测试的雷诺数范围广泛、研究的大量空气-水流动特性以及相对较高的雷诺数（Re = 3.05 × 10 ⁵）在最大的实验。在弗劳德类似的条件下，系统地测试了二十多个参数。所有数据表明，用于评估相似性和尺度效应的相关（空气-水）流动特性的选择是最重要的。此外，相似性和规模效应的概念必须与特定的流动条件相关联。在低弗劳德数 (Fr ₁ = 2.1)，目前的结果表明，许多水跃特性无法从实验室研究外推到没有实质性规模效应的全尺寸水力结构。这些发现对工程设计应用具有深远的意义，通常在雷诺数超过 10 ^{5 的情况下运行}。