In this study, the construction of supersonic wind tunnel and counterflow jet experiments are conducted. The supersonic wind tunnel has been improved to Mach 3.79, with a cross-sectional area of 200 X 250 mm for counterflow jets experiments by expanding the test section of the Mach 2.5 small supersonic wind tunnel.
Counterflow jets experiments conducted using improved supersonic wind tunnel, the effects of counterflow jets are analyzed depending on the nose shape of the supersonic vehicles in the supersonic environment.

1. Free-jet supersonic wind tunnel
The expansion study of the small supersonic wind tunnel was carried out in three stages. In the first step, one-dimensional modeling using the AMEsim software was performed to select the appropriate nozzle throat diameter. In the second step, the characteristics of Free-jet supersonic wind tunnel were analyzed using MATLAB coding under different supersonic diffuser conditions. In the third stage CFD analysis was performed. Through the above three processes, the supersonic wind tunnel was designed and manufactured.
As a results, the cross-sectional area of the supersonic wind tunnel was expanded from 30 X 40 mm to 200 X 250 mm, and the test Mach number of the supersonic wind tunnel was increased from 2.5 to 3.79.

2. Characteristics analysis of counterflow jets
A study on the characteristics of counterflow jets was carried out using improved supersonic wind tunnel. Counterflow jets experiment was performed with various supersonic nose shapes, which are cone, blunt, and Highly blunted shape. The experimental variable was the nozzle thrust coefficient, which divided the force of the counterflow jets into dynamic pressure and the cross-sectional area of the model. The experimental results showed that the effect of drag reduction by counterflow jets disappeared from the point where the nozzle thrust coefficient was equal to the drag coefficient of the model. As a result, the aerodynamically disadvantageous shape was found to maximize the effect of the counterflow jets.