Friction has long been a thorny problem for sealing-device designers. Traditional sealing devices rely on a contacting relationship between surfaces and sealing elements to prevent fluid leakage, but in the case of moving elements, this contact produces friction that causes wearing and eventual failure of the sealing system. Friction also consumes energy and produces harmful debris. In a new breakthrough, however, researchers at NASA’s Glenn Research Center have patented an acoustic seal that generates a pressure barrier to prevent fluid leakage from a high-pressure area. Instead of using contacting components as a seal, the patented seal employs acoustic technology to generate pressure waves that control, mitigate, or prevent fluid leakage. The result is a very low-leakage, non-contact seal that eliminates problems associated with friction. In addition, when traditional seals are needed in extremely high-temperature environments, Glenn innovators have developed new processes to enable the fabrication of single-crystal superalloys that can increase the upper limit of thermal seals to greater than 2000 °F.
The first of Glenn’s innovative sealing technologies features an acoustic resonator, which creates acoustic waveforms that generate a sealing pressure barrier blocking fluid flow from an area of high pressure to an area of low pressure. Through the use of resonant macrosonic synthesis (RMS), the device permits non-contacting sealing operation. To increase the effect, Glenn researchers discovered that an oscillating driver can be coupled with the resonator to achieve an RMS pressure- multiplying effect. In this way, the combination of the oscillating driver and the resonator cavity can create four to ten times greater pressure at the seal, thereby enabling optimal sealing.
These sealing devices are also very versatile for practical applications. The resonators can be selected from several different shapes to produce the desired RMS effect. Moreover, the high- and low-pressure areas in the application can be in contact with a structure while the resonator is not in contact, allowing a wide array of design strategies to integrate the sealing device.
For extremely-high-temperature sealing applications, Glenn researchers have devised novel methods for using nickel-based, single-crystal superalloys. One process involves fabricating a rapid prototype spring “pattern” to create the required cavity in a ceramic mold, and then casting a coiled spring to form at least one coil spring configuration based on the ceramic mold. The second process comprises determining the orientation of the single crystal in a single crystal slab to “harvest” a single crystal spring with optimal properties. In this way, the single crystal preloader can be manufactured in a variety of configurations to meet the requirements of particular applications.
This technology can be used in aerospace systems, gas turbine engines, compressors, computer disk drives (preventing particles from reaching components), microelectromechanical systems (MEMS), and medical materials (preventing contamination).