垂直锐孔自由出流的孔前流动影响区机械能损失模型

Model of mechanical energy loss of fluid in contributing flow region in front of vertical sharp-edged orifice

对流体通过具有相同孔径的流线型收缩孔和垂直锐孔的自由出流进行了实验,用收缩孔的机械能损失模拟垂直锐孔的孔前流动机械能损失,并将孔前流动的机械能损失与垂直锐孔整个孔流过程的机械能损失进行了对比。实验结果定量说明了不同流动状态下典型大孔和典型小孔的孔前流动机械能损失占孔流总机械能损失的比例,该比例还反映出了大孔、小孔入孔以后流动的机械能损失差异及其随板厚变化的规律,从而验证了前期对孔流机理的分析。此外,根据前期提出的孔前流动影响区的物理模型,结合计算流体力学软件Fluent6.2模拟得到的孔前区流场数据,得出了孔前流动影响区内阻力系数模型基本方程,在此基础上,对孔前流动的机械能损失实验数据进行拟合,建立了稳定湍流状态下孔前流动影响区的机械能损失模型。

The experiments on the characteristics of the fluid discharging through the streamlined contractive orifice and the vertical sharp-edged orifice with same diameter were carried out.The mechanical energy loss of the fluid flowing in front of vertical sharp-edged orifice was imitated by that of the fluid through the streamlined contractive orifice,which was compared with the mechanical energy consumed in the whole orifice discharge process through vertical sharp-edged orifice.Thus,the proportion of the upstream mechanical energy loss to total mechanical energy loss can be obtained quantitatively with respect to typical ＂large orifice＂ and ＂small one＂ at different operating conditions.The proportion reflects the difference of the mechanical energy consumed inside orifice between large orifice and small orifice,as well as the effects of the plate thickness.Moreover,the flow mechanism of orifice discharge proposed in the study before this work was verified.Afterwards,according to the physical model of the contributing flow region in front of orifice and the data of the flow field simulated with computational fluid dynamics（CFD）software Fluent 6.2 before this work,the basic mode of equation on the resistance coefficient of the contributing flow region in front of orifice was obtained.Therefore,the model of mechanical energy consumed upstream at fully developmental turbulent regime was founded by simulated the experimental data.