With the advent of rotating machinery, high-speed rotors have been of interest to engineers. Rotating machinery has been employed in a wide range of applications in the past century, ranging from steam turbines for electric power generation to the turbo pumps used in the Space Shuttle Main Engines. As these machines have become more commonplace, there has been an increased demand for lightweight, compact designs. The required power output of these units has also increased, leading to higher power-to-weight ratios. These leaner designs are the hallmark of the aerospace industry.
Vibration problems, which occur more frequently in high-power-to-weight machines, often lead to costly downtime, subsequent redesign, and in some instances, catastrophic failure. A disproportionate number of vibration problems in rotating machinery can be attributed to highly pre-swirled fluid entering tight clearance locations such as seals and fluid bearings. The relationship between high fluid pre-swirl and undesirable vibration issues is clear. Machines with high levels of fluid pre-swirl are more susceptible to instabilities and vibration problems.
A top priority in rotor dynamic design, therefore, is to develop devices to minimize the level of fluid pre-swirl entering tight clearance locations. Researchers have developed the Reverse Vortex Ring (RVR), a mechanism for improving rotordynamic stability and response in turbomachinery.
The RVR was designed to condition the flow prior to entering the seal (or axial flow fluid-film bearing) so that the flow through the annular clearance is, at a minimum, purely axial. While conventional swirl brakes have only been shown to reduce pre-swirl by up to 30 percent, the RVR can reverse the direction of the swirl, so that circumferential fluid velocity flows in a direction counter to shaft rotation. Thus, a classic detriment to rotating machinery becomes an asset to ameliorate vibration issues through the RVR. The RVR is axially efficient, typically increasing the axial length of a smooth annular seal on the order of 10 to 12 percent. It allows turbopumps and similar devices to be made smaller, lighter, faster, and safer.