水利水电工程施工导截流模型试验中的阻力相似问题

施工导截流模型阻力不相似会导致试验成果与实际存在较大偏差。采用理论分析及水力计算方法,剖析了长导流隧洞壁面沿程阻力相似的影响因素,揭示了截流模型试验中阻力危机现象,提出了解决阻力不相似问题的途径。研究表明:对于隧洞导流模型受模型比尺制约,模型水流往往处于紊流过渡区,洞壁阻力系数是模型雷诺数的函数,如忽视模型阻力相似问题,会导致模型泄流能力试验值和洞内流态与原型存在较大偏差,可采取加大流量法或通过系统试验拟合阻力系数与模型雷诺数的关系,再对模型试验泄流能力成果予以修正。对于截流模型,块体抗冲稳定相似需满足推阻力系数相似,模型雷诺数Re_m只有在3×10⁴~2×10⁵时,绕流阻力系数C_d才为常数,可通过合理选择模型比尺使模型水流进入自模拟区,避免阻力危机。

Similarity of Resistance in Model Test of River Diversion and Closure in Construction of Water Conservancy and Hydropower Projects

The dissimilar resistance of river diversion and closure models will lead to a large deviation between test results and actual situation. Factors affecting the similar resistance along the wall of long diversion tunnel are analyzed by using theoretical analysis and hydraulic calculation methods. The resistance crisis in the closure model test is revealed,and the approaches of solving the problem of resistance dissimilarity is proposed. In the case of tunnel diversion model,the modeling discharge capacity can be corrected by increasing the flow rate or fitting the relationship between the resistance coefficient and the model Reynolds number through system test because the water flow in tunnel diversion model is often in turbulence transition zone as restricted by the model scale,and the resistance coefficient of tunnel wall is a function of the model Reynolds number. In the case of closure model,the model water flow can be adjusted entering the self-simulation area by reasonably selecting the model scale to avoid resistance crisis because the similarity of thrust resistance coefficient must be satisfied when the blocks are similar in anti-shock stability,and the surrounding flow resistance coefficient is constant only when the model Reynolds number is 3×10⁴～2×10⁵.