AERODYNAMIC CHARACTERISTICS OF UNDEREXPANDED COAXIAL IMPINGING JETS

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