Concept of variable mach number flexible nozzle and controls for NAL 0.6m blowdown wind tunnel

In a supersonic wind tunnel, the contour of the nozzle, the second throat setting and the stagnation pressure controlled by the Pressure Regulating Valve (PRV) are fundamental parameters without which the required Mach number in the test section cannot be achieved. For operating the Variable Mach number Flexible Nozzle (VMFN) at supersonic Mach numbers in the NAL 0.6m wind tunnel, it is proposed to keep the second throat in a fixed position (corresponding to starting condition at low Mach numbers. Thus, the PRV control and the VMFN throat control are the important parameters. Since these two are totally independent dynamical systems with their own time contrants, proper matching of the two is necessary for efficient handling and operation of the complete wind tunnel. Mach number in the VMFN is controlled by a single hydraulic jack, which outputs a voltage proportional to its displacement (Temposonic sensor). For every Mach number, there exists a certain minimum (safe) stagnation pressure that must be delivered and maintained by the PRV. The stagnation pressure must always be kept between the safe value and a certain maximum value. The command input to the PRV is a voltage signal. A correlation function between the two signals has been established and the performance analyzed through simulation.