模拟降雨条件下坡面流水动力学特性研究

为探明降雨条件下沙黄土坡面水流水动力学特性,以流体力学和泥沙运动力学理论为依据,通过5个坡度和5个雨强组合条件下室内模拟降雨试验,系统研究了坡面水流水力参数的变化规律。结果表明,降雨条件下坡面薄层水流雷诺数均小于580,处于层流失稳区;水流流型随雨强和坡度的变化而发生转捩,当坡度较缓、雨强较小时,床面形态处于低能态区和过渡区,床面出现沙纹现象,水流宏观上呈缓流,反之,坡度较陡、雨强较大时,床面由沙纹和沙垄向动平床过渡,宏观上多呈急流;并根据薄层水流阻力组成特点,推导出沙黄土坡面薄层水流阻力计算公式。验证结果表明,该式误差较小,可为坡面侵蚀预报模型的构建提供参考。

Experimental study of shallow flow hydraulics on a hillslope under artificial rainfall conditions

In order to understand the hydrodynamic characteristics of overland flow on hillslopes,based on the theories in fluid mechanics and sediment transport mechanics,variations in hydraulic parameters of overland flow are studied experimentally for 5 artificial rainfall intensities and 5 slope gradients.The results show that the Reynolds numbers of shallow flow are found to be less than 580 under all 5 artificial rainfall conditions,and the corresponding flow regimes are all unstable laminar flow.The flow type varies with the rainfall intensities and the slope gradients.For gentle slopes and low rainfall intensities,the bed forms are at the low-energy condition and in the transition state.Sand ripples appear on the bed surface and the flow is sub-critical in general.In contrast,for steep slopes and high rainfall intensities,the transition from sand ripples to sand dunes occurs on the bed surface and the flow is supercritical in general.A formula is derived to estimate the shallow flow resistance and tested using the experimental data.The result shows that the formula gives negligible error in resistance calculations.The formula can thus be used as a reference to the establishment of prediction models for the soil erosion simulation on hillslopes.