突扩断面流道压力损失分析

突扩断面流道是各类液压元件的基本结构形式,流体流经突扩断面流道时将产生压力损失,现有设计资料往往将这类压力损失视为与雷诺数(Re)无关的常值。采用理论分析方法,将流体流经突扩断面的总压力损失系数分解为近似理论值、与突扩断面对上游流速扰动对应的压力损失系数、与上游流道实际壁面摩擦对应的压力损失系数、与下游流道实际壁面摩擦对应的压力损失系数以及与突扩断面两侧压差对应的压力损失系数等5个组成部分;采用CFD模拟方法,研究了Re对总压力损失系数的影响规律。结果表明,存在临界雷诺数Re_(cr),当实际Re低于Re_(cr)时,总压力损失系数不再是一常值而随Re反比变化;在低Re时,与突扩断面两侧压差对应的压力损失系数是总压力损失系数的主要成分;而在高Re时,近似理论值及与下游流道实际壁面摩擦对应的压力损失系数是总压力损失系数的主要成分。提出的理论分析方法及数值模拟结果可为各类液压元件中过液孔道的结构优化奠定有益基础。

Pressure Loss Analysis of Sudden Expansion Channel

Sudden expansion channel is the basic geometric structure of hydraulic components, the local pressure loss in this kind of geometric structure has always been treated as a constant value among standard textbooks. Based on overall balance of energy and momentum, the local pressure loss has been decomposed into 5 parts, namely the approximate theoretical value, the pressure loss caused by distortion of velocity in the upstream channel, the pressure loss caused by actual wall friction in the upstream channel, the pressure loss caused by actual wall friction in the downstream channel and the pressure loss caused by the nonuniformity of pressure at the expansion plane. By means of the CFD simulation approach, the local pressure loss in sudden expansion has been calculated among a range of Reynolds numbers. The research results show that, there is a critical Reynolds number Recr, when the actual Reynolds number Re is smaller than the Recr, the local pressure loss coefficient is inversely proportional to the Re; for low-Re cases, the pressure loss caused by the nonuniformity of pressure at the expansion plane is the major part of the local pressure loss; however, for high-Re cases, the approximate theoretical value and the pressure loss caused by actual wall friction in the downstream channel are the majors part.The theoretical analysis method proposed by this paper can be used for reference to the structural optimization of the sudden expansion channel among the hydraulic components.