Some Characteristics of Compressible Air Impingement Jet Applied in Pneumatic Dimensional Control

Abstract

The present paper studies the impingement of compressible air jet on a flat plate primarily from the aspect of its application in the domain of pneumatic metrology, i.e. in cases of small distance between the jet nozzle exit and the flat plate. Besides this direct application in the area of pneumatic metrology, the distance between the nozzle exit and the flat plate has been considerably increased and the case of a free jet was analysed with a view to compare the results applicable in various domains. This experimental study demonstrates that the structures of a free jet and this special case of an impingement jet are totally different. In the pressure distribution of the impingement jet, pressure discontinuity above the flat plate may occur, which is shown to be the result of low intensity shock waves and transonic flow. The experimental results show that the pneumatic sensitivity of a pneumatic comparator is a function of the supply pressure and the internal orifice diameter, as well as that the impingement air jet is a typical case of non-isentropic flow.