The flow parameters control in wind tunnels is an area of intense research in recent years, with the aim of improving quality and efficiency of the wind tunnel operation. In this paper, an attempt is made to contribute to a better understanding of the stagnation pressure control in supersonic blowdown-type facilities. The stagnation pressure control strategy in the VTI Belgrade T-38 wind tunnel is discussed. An improved mathematical model for a supersonic wind tunnel is suggested and applied to the T-38 facility. Comparisons of simulation and experimental data are made to demonstrate accurate prediction of the facility response in supersonic flow conditions by the mathematical model. The model is used to incorporate a modified feedforward control in the original T-38 wind tunnel control system. The actual wind tunnel tests confirm model-predicted decrease of flow stabilization time and increase of available measurement time, bringing significant improvement in the wind tunnel operation efficiency.

Over the last few decades, the accuracy requirements for wind tunnel testing have become much more stringent as aircraft industry strives to achieve the best performance of their products. Investments in advanced capabilities are necessary to obtain more accurate test results more efficiently, ensuring that the wind tunnels stay productive well into the future. The VTI Belgrade T-38 wind tunnel responded to these challenges by applying a hierarchical approach to design a distributed multilevel control system, a part of which is the variable-geometry nozzle positioning system, presented in this paper. It follows the hierarchy of the entire wind tunnel control system, with critical positioning loops at the field-programmable gate array (FPGA), and the user interface with real-time data analysis capability implemented on a central wind tunnel computer. In addition to more accurate positioning, the FPGA-based control system significantly improved overall operation efficiency, speed and reliability. Since the nozzle geometry uniquely determines supersonic Mach number, the improved positioning accuracy is verified in wind tunnel tests

No abstract