A convergent nozzle for the standardisation of thrust-rig measurements

Abstract

Summary. It is shown that an increase of Mach number from approximately 0.2 to 0.4 at entry to a convergent nozzle of specified shape does not appreciably change its performance. Such a nozzle is thus recommended as a standard device for calibrating the air meter on any thrust rig. For more general application as a means of mass-flow measurement, a value of discharge coefficient can be taken from this work, provided the flow conditions at entry are reasonably uniform, and excluding high temperatures. Use of that value may be subject to certain corrections, and its absolute accuracy when applied to any nozzle of the same nominal specification may not be better than ±0.3 per cent.