水工减压模型试验理论的探讨

Discussion on theory of hydraulic model for pressure relief test

分析了传统减压试验理论中存在的矛盾,认为以饱和蒸汽压强定义的空化系数及其原、模型空化系数相等的要求,实际上是在重力流动的相似模拟系统中,又按压强相似定律定义了一个相对压强相似的附加条件。阐明了若按空化系数相等规则控制,而忽视模型水温的影响,除导致原型与模型之间在空化程度、气水流综合密度、全局流动等的不相似结果外,还会给空化模型试验的相似效果和可比性带来较大影响。这是在同一模拟系统中重力相似定律与压强相似定律之间的矛盾体现,不能全部归结为模型缩尺效应。

Based on the analysis of the conflict in the traditional theory of the hydraulic model for pressure relief test, it is considered that an additional condition of a relative pressure similarity defined by the pressure similarity （Euler） is actually put into the similarity simulation system of the gravity flow under the condition of the cavitation coefficient defined with the saturated vapor pressure and requirement that the cavitation coefficients of both the prototype and the model must be equal. It is illustrated that if it is controlled with the rule of equal cavitation coefficients and neglects the effect from the water temperature of the model, not only the dissimilarities between the cavitation degree, comprehensive density of air-water flow and integrated flow movement will result, but the similar result and comparability of the cavitation model test concerned also will be largely affected. This is a conflict between the gravity similarity law （Froude） and pressure similarity law （Euler） in a same simulation system, which is not fully caused by the effect of scale.