Hot gas control system design and vortex valve tests

As part of a conceptual study and test program for fluidic hot gas chamber bleed control systems, analytical and experimental investigations were performed on a number of vortex valve design configurations. Subscale vortex valve models (0.63 cm nozzle diam) were tested with high pressure cold gas (GN
2
) input as supply and control fluid, with flow rates up to, typically, 0.45 kg/s (1 lb/s) at pressures to approximately 17.5 MN/m
²
(2500 psi) resulting in maximum turn-down ratios of, typically, 4:1. During a second part (follow on) program, the geometry, of this vortex valve was scaled up. The selected system concept is based on the use of four pairs of back-to-back vortex valves with two opposing hot gas supply inlets to minimize erosion problems. The four valve pairs are connected to the rocket motor chamber (pole piece) by way of eight ducts; warm gas generators are provided as a control fluid source. A test fixture was designed and fabricated that contained one back-to-back pair of vortex valves, and tests were conducted with cold gas (GN
2
), warm gas (TAL-8; 1460 K), and hot gas (FAE-7; 3600 K) as supply fluid, using cold gas (GN
2
or GHe), or liquid (freon or hexane) as control fluid. Test data confirmed that the same range of turn-down ratio values can be achieved for cold gas GN
2
control of GN
2
supply, and for Helium control of hot supply gas (TR=4:1) (FAE-7) with the larger size valves as that obtained earlier with subscale valve models. A maximum turn-down ratio of 9:1 was realized for He control of cold GN
2
. The selected vortex valve configuration had a chamber to nozzle radius ratio of 3:1 and was found to be effective in achieving rapid cutoff of the hot supply gas without significant erosion problems, with flow rates up to 135 kg/s (3 lb/s) and with supply pressures near 6.9 MN/m
²
(1000 psi). Over the range of mass flow and pressures tested with a variety of supply and control fluids, it was found that a momentum turn-down ratio (MTR)