Aerodynamic Characteristics of Underexpanded Coaxial Impinging Jets

Abstract

Flow behavior of underexpanded coaxial impinging jets is investigated experimentally and simulated numerically by solving compressible Navier-Stokes equations. Two converging coaxial nozzles, one with outer annular jet parallel to an inner circular one, and the other with inclined annular jet, are fabricated and tested. The flow visualization using the shadowgraph method, the pressure measurements at the impinged surface and the numerical simulation show that the presence of the outer annular jet has favorable effects for reducing the diameter of the Mach shock disk which is formed in the inner jet. However, the maximum pressure on the impinged flat plate obtained in the present study is lower than that produced previously by a simple annular jet, showing that the simple annular jet can be more favorable for laser cutting.