准定常流法测定瞬时流量的判据研究

Study on the Criterion for Measuring the Instantaneous Flowrate with the Quasi-steady Flow Method

准定常流法是测定瞬时流量常用的方法 ,但其应用受相似准则Strouhal数的限制 ,Strouhal数应甚小。除了从流体运动偏微分方程组导出Strouhal数以外 ,本文从物质导数的表达式出发 ,也给出了上述的结论 ,但它具有简单明了的优点。当采用层流流量计测定内燃机瞬时流量时 ,因其流道直径甚小 ,使得Strouhal数约为 0 0 0 1左右。在S110 0A柴油机上所做的实验证实了采用层流流量计按准定常流法测定瞬时流量时 ,因Strouhal数甚小 。

The quasi steady flow method is applied widely for measuring the instantaneous flowrate, but its application is restricted by the similarity criterion Strouhal number which should be very small. Besides it's derivation from the partial differential equations of flow dynamics based on the similarity theory, the Strouhal number is derived from the substantive derivative in this paper. The advantage of this derivation is simple and clear. When the intake instantaneous flowrate of ICE is measured by the laminar flowmeter, because of its very small diameter of flow passage, the Strouhal number is about 0.001. It is verified that the quasi steady flow method is effective for measuring the instantaneous flowrate, as long as the Strouhal number is very small.