Experimental and three-dimensional numerical study on under-expanded impinging jets

Abstract

In this paper, under-expanded impinging jets issued from converging circular and rectangular nozzles were investigated. The ratio of the distance between the nozzle exit and the plate L to the diameter D was set at 2, 3, 4 for the circular nozzle and 2, 3 for the rectangular nozzle. Two-dimensional temperature and static pressure distributions on the impinging plate were measured using an infrared camera and a semi-conductor pressure sensor and flow fields were visualized by means of schlieren method. Three-dimensional numerical calculations were also conducted by solving the three-dimensional compressible Euler equations and compared to the experimental results. As a result, it is found that the numerical calculations for the circular and the rectangular nozzles are in good agreement with the experiments. In the experiments, it is found that the stagnation temperature on the plate depends on the pressure in the settling chamber and the distance between the nozzle exit and the plate. The temperature and pressure distributions in the experiments illustrate that even in the case of the circular nozzle, the distributions on the impinging plate are non-axisymmetric, which is confirmed by the three dimensional calculations. The calculation for the rectangular nozzle indicates that two circulating regions occur immediately upstream of the plate.