Novel Design of Orifice Type Control Element for Mitigating Instabilities

An orifice element is commonly used in liquid rocket engine test facilities either as a flow metering device, or to provide a large reduction in pressure over a very small distance in the piping system. While the orifice as a device is largely effective in stepping down pressure, it is also susceptible to a wake-vortex type instability that generates pressure fluctuations that propagate downstream and interact with other elements of the test facility resulting in structural vibrations. Furthermore in piping systems an unstable feedback loop can exist between the vortex shedding and acoustic perturbations from upstream components resulting in an amplification of the modes convecting downstream. Such was the case in the Arianne 5 strap-on P230 engine in a static firing test where pressure oscillations of 0.5% resulted in 5% thrust oscillations. The innovation described in this proposal directly relates to a proprietary design of a step down orifice that inhibits the instability modes generally associated with the operation of a traditional orifice while meeting performance guidelines. In the Phase I effort we will demonstrate the effectiveness of the new device through a combination of analysis and sub-scale testing in a cryogenic environment.