Mechanical & Fluid Systems

Laser Anemometer Measures Flow in a Centrifugal Compressor

High-resolution data are representative of flows in practical centrifugal compressors. Detailed measurements of complex flow fields within the NASA Low Speed Centrifugal Compressor (LSCC) have been acquired. The measurement data provide insight into the fundamental physics of flow in centrifugal compressors, and can be used to assess computational fluid dynamics codes and to develop flow-physics models. The resultant benefit is better predictive computational tools and shorter design cycle times.

Posted in: Briefs, TSP

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High-Altitude Flight Test of the Perseus B Airplane

Flawless aerodynamic, propulsion, and control performance was observed. The Perseus B remotely piloted vehicle (RPV) has achieved a record altitude for a single-engine, propeller-driven airplane of 60,260 ft (18,367 m) on June 27, 1998. The Perseus B is one of the test-bed aircraft developed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program for use in conducting high-altitude, long-duration missions carrying atmospheric sampling and sensing payloads for the scientific community within NASA and other agencies.

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Pneumatic Accelerator for Launching a Spacecraft

A report proposes the development of a ground-based launch-assist apparatus that would accelerate a spacecraft to a speed of about 270 m/s. The apparatus would include a track along which the spacecraft would ride on a sled coupled to a large piston driven by compressed air along a tube (more precisely, a concrete tunnel lined with stainless-steel sheet) below the track. The connection between the sled and the piston would be made via a coupling plate that would slide along a slot on top of the tube. The slot would seal after passage of the coupling plate. As described thus far, the apparatus could be characterized as a modern, high-acceleration, high-speed version of pneumatic drives with slot connections to rail cars that were used in Europe during the 1840s.

Posted in: Mechanics, Briefs, TSP

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High-Temperature Switched-Reluctance Electric Motor

Motors like this one would be incorporated into gas turbines as starter/generators. An eight-pole radial magnetic bearing has been modified into a switched-reluctance electric motor capable of operating at a speed as high as 8,000 rpm at a temperature as high as 1,000 °F (Å540 °C). The motor (see figure) is an experimental prototype of starter-motor/ generator units that have been proposed to be incorporated into advanced gas turbine engines and that could operate without need for lubrication or active cooling.

Posted in: Mechanics, Briefs

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Ice-Melting Probe Using Steam and Jets of Hot Water

This probe would overcome some of the deficiencies of prior ice-melting probes. An improved probe has been proposed for burrowing vertically into ice for scientific exploration of polar icecaps, glaciers, and the like. The predecessor of the improved probe is a Philbert probe, which contains an electric heater to melt the ice in contact with it and thereby make it descend through the ice under its own weight. A Philbert probe also contains a mechanism from which the wires for the electric heater and any sensors in the probe are paid out behind the probe; these wires become sealed into the overlying ice as the probe descends. The two major drawbacks of a Philbert probe are that (1) it tends not to go straight down and (2) a plug of dust, sand, rock, and/or other debris tends to build up in the meltwater ahead of the probe, eventually becoming large enough to halt the descent by interrupting the heat-transfer interface between the vehicle nose and the ice. The improved probe is designed to eliminate these drawbacks.

Posted in: Mechanics, Briefs, TSP

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Lightweight, Low-Backlash Robot Wrist With Epicyclic Drive

Several design features contribute synergistically to versatility and efficiency. A unique lightweight wrist with three degrees of rotational freedom has been developed as a prototype of wrists for future anthropomorphic robots that would perform a variety of tasks on Earth and in outer space. The three degrees of freedom (two rolling, one bending) intersect at the center of the wrist. Included in the wrist is a power transmission with an epicyclic ring-gear configuration that enables efficient packaging and provides a wide internal passage through the center of rotation for routing of wires and drive cables. The power transmission combines lowbacklash planetary gearing and a tripleinput differential with a triple-loadpath, cable-driven output stage that generates minimal radial bearing loads and no thrust (that is, axial) bearing loads.

Posted in: Mechanics, Briefs

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Program Computes Pointing Corrections for a Radiotelescope

TLC is a computer program that determines corrections for radiotelescopepointing errors associated with tilts and elastic deformations. These errors occur because for rotation in azimuth, a radiotelescope is mounted on wheels that move on a circular track that deviates from perfect flatness. TLC processes radiotelescope field data through smoothing, filtering, segment-fitting, trend-removal, Fourier-transform, and high-passfiltering algorithms to generate a lookup table that contains the pointing corrections. The field data in question are readouts from four inclinometers, the relative positions of the inclinometers, and readouts from an azimuth-angle encoder. Written in the Matlab software system, TLC is a user-friendly program that provides a graphical user interface that enables even an unfamiliar user to proceed, step by step, to the final result.

Posted in: Mechanics, Briefs, TSP

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