Mechanical & Fluid Systems

Reverse-Tangent Injection in a Centrifugal Compressor

The compressor flow can be stabilized against stall and surge. Injection of working fluid into a centrifugal compressor in the reverse tangent direction has been invented as a way of preventing flow instabilities (stall and surge) or restoring stability when stall or surge has already commenced. If not suppressed, such instabilities interrupt the smooth flow of the working fluid and, in severe cases of surge, give rise to pressure and flow oscillations that can be strong enough to damage the compressor and adjacent equipment.

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Magnetostrictive Inertial-Reaction Linear Motors

Fine positioning could be achieved at temperatures from near absolute zero to ambient. Linear-translation motors containing inertial-reaction masses driven by magnetostrictive actuator elements are undergoing development. These motors could be used to make fine position adjustments in diverse scientific and industrial instruments that operate at temperatures ranging from near absolute zero to room temperature; for example, they could be used to drive translation stages in scanning tunneling microscopes that operate at liquid-helium temperature (4 K), or to move cryogenic-temperature optical elements that must be located at long but precise distances from each other (as in interferometers). [These motors should not be confused with proposed magnetostrictive motors that would move in "inchworm" fashion and would be used for similar purposes, described in "Magnetostrictive Actuators for Cryogenic Applications," NASA Tech Briefs, Vol. 20, No. 3 (March 1996), page 84.]

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Hybrisol Rocket Engines

These engines offer potential safety and cost advantages over solid-fuel engines. "Hybrisol" denotes a proposed rocket engine that would contain hybrid and solid-propellant parts within a single combustion chamber. ["Hybrid" as used here denotes a type of rocket engine in which a solid fuel is burned by use of a liquid or gaseous oxidizer and the flow of the oxidizer can be throttled to control the engine. Unlike conventional solid rocket propellants, a solid fuel for a hybrid rocket engine can be made relatively inert in the absence of the oxidizer and therefore presents little hazard of explosion or inadvertent ignition.] Inside a hybrisol rocket engine, there would be two concentric tubular energy-storage layers: an outer layer of conventional solid rocket propellant and an inner layer of solid hybrid fuel (see figure).

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Cobra Probes Containing Replaceable Thermocouples

A modification of the basic design of cobra probes provides for relatively easy replacement of broken thermocouples. [Cobra probes are standard tube-type pressure probes that may also contain thermocouples and that are routinely used in wind tunnels and aeronautical hardware. They are so named because in side views, they resemble a cobra poised to attack.] Heretofore, there has been no easy way to replace a broken thermocouple in a cobra probe: instead, it has been necessary to break the probe apart and then rebuild it, typically at a cost between $2,000 and $4,000 (2004 prices). The modified design makes it possible to replace the thermocouple, in minimal time and at relatively low cost, by inserting new thermocouple wire in a tube.

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Automated Aerial Refueling Hitches a Ride On AFF

Data from flight tests will be used in designing an automated refueling system. The recent introduction of uninhabited aerial vehicles [UAVs (basically, remotely piloted or autonomous aircraft)] has spawned new developments in autonomous operation and posed new challenges. Automated aerial refueling (AAR) is a capability that will enable UAVs to travel greater distances and loiter longer over targets. NASA Dryden Flight Research Center, in cooperation with the Defense Advanced Research Projects Agency (DARPA), the Naval Air Systems Command (NAVAIR), the Naval Air Force Pacific Fleet, and the Air Force Research Laboratory, rapidly conceived and accomplished an AAR flight research project focused on collecting a unique, high-quality database on the dynamics of the hose and drogue of an aerial refueling system. This flight-derived database would be used to validate mathematical models of the dynamics in support of design and analysis of AAR systems for future UAVs. The project involved the use of two Dryden F/A-18 airplanes and an S-3 hose-drogue refueling store on loan from the Navy (see Figure 1). In this year-long project, which was started on October 1, 2002, 583 research maneuvers were completed during 23 flights.

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Rover Wheel-Actuated Tool

A report describes an interface for utilizing some of the mobility features of a mobile robot for general-purpose manipulation of tools and other objects. The robot in question, now undergoing conceptual development for use on the Moon, is the All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) rover, which is designed to roll over gentle terrain or walk over rough or steep terrain. Each leg of the robot is a six-degree-of-freedom generalpurpose manipulator tipped by a wheel with a motor drive. The tool interface includes a square cross-section peg, equivalent to a conventional socket-wrench drive, that rotates with the wheel. The tool interface also includes a clamp that holds a tool on the peg, and a pair of fold-out cameras that provides close-up stereoscopic images of the tool and its vicinity. The field of view of the imagers is actuated by the clamp mechanism and is specific to each tool. The motor drive can power any of a variety of tools, including rotating tools for helical fasteners, drills, and such clamping tools as pliers. With the addition of a flexible coupling, it could also power another tool or remote manipulator at a short distance. The socket drive can provide very high torque and power because it is driven by the wheel motor.

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A New Approach to Railgun Operation Requires Analysis of Electromagnetic Fields

To find the best materials and design for effective railguns, analysis must be performed to determine how electromagnetic fields are generated and distributed. Railguns, which propel a projectile using electromagnetic forces instead of chemical explosions, promise to revolutionize projectile launchers. Such guns have been built and operated successfully on a test basis, but several problems are holding them back from usage in the field. To solve these problems, researchers must understand the inner workings of these weapons. Several groups are conducting research taking different approaches to how the electromagnetic fields within these guns operate. One group, whose proposals differ from traditional thought, is using COMSOL Multiphysics software to illustrate the validity of their views.

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