Experimental and numerical study of twin underexpanded impinging jets

In this paper, the dual underexpanded impinging jets are experimentally and numerically studied. The experiments were performed by measuring the unsteady and averaged wall static pressures and by visualizing density fields using schlieren method. Numerical calculations were also conducted by solving unsteady three dimensional compressible Navier-Stokes equations with Baldwin-Lomax turbulence model. The main parameters for the dual jets are the non-dimensional distance between the two nozzle centers H/D covering 1.5, 2.0, the nozzle to plate separation L/D 2.0, 3.0,4.0 and 5.0 and the pressure ratio defined by po/pb 1.0–6.0, where D is the diameter of each nozzle exit, po the stagnation pressure and po the back pressure. It is found that the agreement between the experiments and the calculations is good. The fountain flow at the middle of the two jets is observed both in the experiments and the calculation. According to FFT analysis of the experiments for the twin jets, relatively low frequency (up to 5 kHz) is dominant for H/D=1.5, L/D=2.0 and pressure ratio po/pb=3.0 and 5.0, which is confirmed by the experiments.