低雷诺数音速喷嘴临界背压比的实验研究

音速喷嘴是气体流量标准装置中最常用的标准流量计,喷嘴临界背压比直接关系到装置的准确度,喉部雷诺数低于2×105的喷嘴需要进行临界背压比测试。建立了一套基于喷嘴串联方法的临界背压比测试系统,将不易准确测量的质量流量转换为较易准确测量的压力,实现了临界背压比的准确高效测量。研究表明,低喉部雷诺数喷嘴临界背压比小于其设计值,且喉部雷诺数越小,临界背压比越低;另外可能出现一种"非临界状态提前"现象,引起临界背压比的进一步降低,且降低程度与喷嘴加工水平有关,更加说明了临界背压比测试的必要性。

Experimental study on critical back-pressure ratio of sonic nozzle at low Reynold number

Sonic nozzle is the most common standard flow meter in gas flow calibration facilities,and it is necessary to test the critical back-pressure ratio(CBPR) for nozzles whose throat Reynold numbers are smaller than 2×105,because CBPR is directly related to the accuracy of the facilities.A test system based on nozzle-in-series method has been built,which uses pressure measurement instead of mass flow rate measurement to determine CBPR accurately and efficiently.Experimental results show that the CBPR is smaller than the designed value for nozzles with low throat Reynold number,and that the smaller the throat Reynold number,the lower the CBPR.Probable premature unchoking phenomena can cause further decrease of CBPR,and the decrease degree of CBPR is related to the manufacturing level of the nozzles,which also explains the necessity of testing CBPR.