Twin underexpanded impinging jets are experimentally and numerically studied in this paper. The experiments were performed by two dimensional wall static pressure measurements and by the schlieren method. Numerical calculations were also conducted by solving three dimensional compressible Navier-Storkes equations in generalization curvilinear coordinate. The main parameters for the twin jets are the nondimensional distance between the two nozzle centers H/D covering 1.5 and 2.0, the nozzle to plate separation L/D 2.0 and 3.0 and the pressure ratio defined by p0/p 2.5–5.0, where D is the diameter of each nozzle exit, p0 the stagnation pressure and p the back pressure. It is found that, so called, a fountain flow which occurs at the middle position between the two jets breaks jets boundaries due to its unsteadiness. Comparison between the experiments and the calculations shows that in case of shorter distancce between two nozzle and higher pressure ratio, two jets interact before they reach the impinging wall causing clear pressure peak at the middle position between the jets.
