臨界ノズルの形状と音速維持範囲の関係

抄録

The critical nozzle is used as standard in gas flow rate measurement. In this usage, the discharge coefficient of the nozzle must be calibrated before hand. To determine the discharge coefficient and to calibrate a flow meter, it is necessary that the nozzle has a large unchoking back-pressure ratio.
This paper describes the effect of the nozzle profile on the unchoking back-pressure ratio by a qualitative analysis based on the Laval nozzle theory. The following results are obtained.
1) The unchoking back-pressure ratio is increased with the decrement of the divergent included angle at a fixed divergent to throat diameter ratio and also with the increment of that ratio at a fixed angle.
2) A relation between the Reynolds number and the unchoking back-pressure ratio is obtained for geometrically similar nozzle.