| Mechanical & Fluid Systems

Novel Design of an Orifice Control Element

An instability mitigation device can replace traditional orifice elements in pipelines.

An orifice element is commonly used in liquid rocket engine test facilities either as a flow metering device, a damper for acoustic resonance, or to provide a large reduction in pressure over a very small distance in the piping system. The orifice as a device is largely effective in stepping down pressure; however, it is also susceptible to a wake-vortex instability that generates pressure fluctuations that propagate downstream and interact with other elements of the test facility, resulting in structural vibrations. Exacerbating the situation in cryogenic test facilities is the possibility of the formation of vapor clouds when the pressure in the wake falls below the vapor pressure, leading to cavitation. Cavitation has the potential for highamplitude fluctuations that can cause catastrophic damage to a facility.

Vortex shedding and cavitation create instabilities when facility pressure is stepped down with an orifice element.

Researchers at CRAFT Tech have developed a flow conditioning device that can be used as a replacement for traditional orifice elements in the pipeline. The new device is an axial element that provides resistance to the flow in a piping system, thereby stepping down the pressure in a pipeline much like an orifice. However, unlike an orifice element, the device suppresses the generation of instabilities and does not generate or shed vortex structures that could create feedline instabilities downstream.

Rigorous sub-scale testing has demonstrated that the device does not generate hydrodynamic or cavitation instabilities, and the resultant flow was quiet when compared with a single-hole orifice that generated sizeable tones in the pipeline. Full-scale testing has also shown that the device generated significantly fewer pressure fluctuations than a traditional orifice under high-pressure testing.

Sub-scale tests of a traditional orifice and the new device showing mitigation of hydrodynamic and cavitation instability through the system.

The device is relatively inexpensive to manufacture, easy to fabricate and install, and can be tailored to meet the performance requirements of a given facility. Additionally, water testing has demonstrated that the device can also effectively be used in water cooling systems and plume suppression environments. The device will be used to replace traditional orifice elements in experimental systems/test facilities, and could ultimately lead to safe and reliable operation of test facilities for aerospace applications, cooling systems in pressurized nuclear reactor water facilities, and full-scale cryogenic facilities.

This work was done by Vineet Ahuja, Roger Birkbeck, Jeremy Shipman, and Ashvin Hosgandi of Combustion Research and Flow Technology Inc. (CRAFT Tech) for Stennis Space Center. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact This email address is being protected from spambots. You need JavaScript enabled to view it.. SSC-00460