块石形状尺寸对水平拖曳力系数影响的数值模拟

水平拖曳力系数是研究黄河坝垛水下散抛根石受水流作用的重要力学参数，而水流流速、根石尺寸和根石在水中的仰角对水平拖曳力系数有着不同程度的影响。基于试验数据，应用FLOW-3D数值模拟软件，采用RNG k-ε紊流模型、VOF方法和FAVOR技术模拟水下块体在水流作用下的水平拖曳力。在数值模拟结果验证可靠的前提下，分析块体不同尺寸及其与水流不同夹角对水平拖曳力系数的影响。数值模拟结果表明:当长高比小于等于3.0，水平拖曳力系数随块体长高比增大，先处于波动状态，随后趋于稳定；当长高比大于3.0，水平拖曳力系数随长高比增大而增大；水平拖曳力系数随块体宽高比增大而先增后减，最后保持稳定；水平拖曳力系数随着水流夹角角度增大而先减后增，当夹角为3°时出现最小值。

Numerical simulation of influences of underwater riprap blocks' hape and size on horizontal drag force coefficients

The horizontal drag force coefficients are the important mechanical parameters to study the effects of water flow on the scattered underwater riprap stones of the Yellow River dam buttress. And the flow velocities, the root stone size and the elevation angle of the root stones in the water have different effects on the horizontal drag force coefficients. Based on experimental data and FLOW-3D numerical simulation software in this study, RNG k-ε turbulence model, VOF method and FAVOR technique are used to simulate the horizontal drag force coefficients of the underwater riprap blocks under the action of current. Compared with experimental results, the results of numerical simulation are coinciding with the experimental data. The simulated results show that the model is reliable and practical. On the premise of verifying the reliability of the numerical simulation results, the influences of distinct block sizes and different angles between the blocks and current on the horizontal drag force coefficients are analyzed. The numerical simulation results show that when the length-height ratio is not greater than 3, the horizontal drag force coefficients fluctuate and then tend to be stable with the increase of the block length-height ratio. When the length-height ratio is not greater than 3, the horizontal drag force coefficients increase with the increase of the length-height ratio. With the increase of the block width-height ratio, the horizontal drag force coefficients increase first, then decrease and finally remain stable. When the angle between the blocks and the current increases, the horizontal drag force coefficients decrease first and finally increase, and the minimum value appears at the angle of 3 degrees. The results of this numerical simulation can provide a reference for the study of the root stone erosion at the Yellow River dam buttress.