Numerical modeling of airflow in ultrasonic nozzles

To achieve ultrasonic airflow in the wind tunnel test section, the airflow must pass through the initial stagnation conditions in a series of convergent-divergent nozzles to reach the appropriate speed and pressure. The ratio of the area of the nozzle throat and the test chamber, as well as the pressure ratio between the wind tunnel stall and the outlet of the test site, determines the Mach number of the test area and its static properties, respectively. The geometry of the nozzles directly affects the flow quality, in particular the Mach number distribution and the angle of movement of the airflow in the test area. The more uniform the velocity of the air fluid flow and the Mach number distribution within the test area, the more realistic the test results. Therefore, uniform distribution of Mach number in the wind tunnel test area is a requirement. In order for the Mach number distribution to be uniform, a unique geometry is required for the divergent section of the nozzle, which depends on the test area and the Mach number to be created. Investigations have shown that the designed nozzle contour can provide a current of Mach ۳ at its output without causing any shock, which means that the developed numerical code is accurate. In the next step, the uniformity of the output current from the nozzle is investigated. For this purpose, the uniformity of current at the nozzle output from the nozzle center line to the edge of the boundary layer was investigated. It was found that according to the available aerodynamic criteria, the flow at the nozzle output is quite uniform.

Keywords:

Ultrasonic wind tunnel , Supersonic nozzle , Computational fluid dynamics , Shock , Prantel Meyer method