Improving the quality of the supersonic flow field of free-jet wind tunnels

The fixed-total-pressure-based air-blowing method in free-jet wind tunnels only produces uniformity in a limited area for supersonic jets. To address the issue, we investigated the effect of total pressure on static pressures at the nozzle exit and test chamber. We proposed an air-blowing method for pressure matching and established corresponding equations while suggesting ways to determine its parameters. The pressure-matching method was experimentally verified to analyze and compare the effects of different air-blowing methods and pressure-matching parameters on jet uniformity. The results of the study are as follows: (1) The pressure-matching-based air-blowing method improved the uniformity of the flow field at Mach numbers (Ma) of 1.5, 2.0, and 3.0 by 445.5%, 275%, and 215.8%, respectively, when compared to the air-blowing method that maintains the total pressure above the designed value. (2) The pressure-matching-based air-blowing method reduced the root-mean-square deviation in the Ma of the flow field at a Ma of 2.0 by 47.1% compared to the air-blowing method that maintains the total pressure at the designed value. The findings indicate that the proposed air-blowing technique based on pressure matching can enhance the uniformity of the supersonic jet and the area of the uniform region in the flow field. This method is highly significant in improving the capabilities of free-jet wind tunnel facilities.