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Results for “rotating spoke”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Two-component phase-averaged turbulence statistics downstream of a rotating spoked-wheel wake generator

Flow-field measurements of unsteady turbulent flow downstream of a rotating spoked-wheel wake generator were performed in a short-duration light-piston tunnel, and the instantaneous-velocity data were phase averaged based on a signal synchronized with the bar-passing frequency. Mean axial velocities were found to agree well with those obtained from measurements behind a stationary cylinder and to be independent of both Reynolds and bar-passing Strouhal numbers. Reynolds stresses were found to be consistent with related cylinder-wake measurements, but were significantly higher than corresponding measurements obtained in large-scale research turbomachines. Phase-averaged triple velocity correlations were calculated from the digital velocity records, revealing the sign and the magnitude of skewness in the velocity probability density distributions for the two components.

O'Brien, J. E.↗
NASA NTRS1973

Hot ion production in a modified Penning discharge

Roth (1973) has shown in a preliminary experiment with a 15-cm diameter anode ring that the ion thermal velocity is directly proportional to the velocity of an ion spoke in the anode sheath. The earlier investigations are extended to four anode rings with diameters in the range from 5.08 to 20.32 cm. A theoretical and experimental study of the rotating spoke dynamics is also discussed, giving attention also to theoretical expressions for electron and ion spoke rotation frequencies.

Roth, J. R.↗
NASA NTRS2023

Hubble Detects the Start of a New Saturn Ring Spoke Season

Saturn's ring spokes typically appear over an 8-year duration centered on equinox. Hubble Space Telescope observations in 2021 indicate the beginning of a new spoke season as Saturn approaches equinox in 2025. The spokes show increased contrast and longevity in 2022, persisting for up to 11 hours. The spokes are visible from UV to near-IR and are slightly bluer (i.e., less red) than the rings, but we find no significant wavelength dependence in the spectral contrast, which approximates their optical depth). Spoke rotation rates are between 606 and 626 min, consistent with either Keplerian rotation or possibly the variable rotation rate of Saturn's kilometric radiation. Spoke activity is expected to increase over the next several years.

Amy A. Simon↗
NASA NTRS1971

Origin of hot ions observed in a modified Penning discharge.

Ions with a Maxwellian energy distribution and kinetic temperatures ranging from below 100 eV to several keV have been observed in a steady-state modified Penning discharge. Observations in the plasma, with capacitive probes at several azimuthal locations, are consistent with the existence of two distinct spokes rotating with different velocities in the sheath between the plasma and the anode ring. The faster (0.5-10 MHz) spoke consists of electrons rotating with the E/B drift velocity. The slow (0.1-1.0 MHz) spoke consists of ions, the measured thermal velocity of which is directly proportional to the spoke velocity. The interaction of the two spokes is apparently responsible for the observed electrostatic ?turbulence' and ion thermalization. The anode sheath thickness is smaller than the ion gyrodiameter in this plasma. Thus the ions are in the electric field of the sheath for only a fraction of their orbit, and their E/B drift (spoke) velocity is smaller than that of the electrons.

Roth, J. R.↗
NASA NTRS1973

Origin of hot ions observed in a modified Penning discharge.

Ions with a Maxwellian energy distribution and kinetic temperatures ranging from below 100 eV to several keV have been observed in a steady-state modified Penning discharge. Observations in the plasma, with capacitive probes at several azimuthal locations, are consistent with the existence of two distinct spokes rotating with different velocities in the sheath between the plasma and the anode ring. The faster (0.3-10 MHz) spoke consists of electrons rotating with the E/B drift velocity. The slow (0.06-0.8 MHz) spoke consists of ions, the measured thermal velocity of which is directly proportional to the spoke velocity. The interaction of the two spokes is apparently responsible for the observed electrostatic turbulence and ion thermalization.

Roth, J. R.↗
NASA NTRS1971

Origin of hot ions observed in a modified Penning discharge

Ions with a Maxwellian energy distriubtion and kinetic temperatures ranging from below 100 eV to several keV are observed in a steady state modified Penning discharge. Observations in the plasma, with capacitive probes at several azimuthal locations, are consistent with the existence of two distinct spokes rotating with different velocities in the sheath between the plasma and the anode ring. The faster (0.5 to 10 MHz) spoke consists of electrons rotating with the E/B drift velocity. The slow (0.1 to 1.0 MHz) spoke consists of ions whose measured thermal velocity is directly proportional to the spoke velocity. The interaction of the two spokes is apparently responsible for the observed electrostatic turbulence and ion thermalization. The anode sheath thickness is smaller than the ion gyrodiameter in this plasma. Thus the ions are in the electric field of the sheath for only a fraction of their orbit, and their E/B drift (spoke) velocity is smaller than that of the electrons.

Roth, J. R.↗
NASA NTRS2023

Hubble Detects the Start of a New Saturn Ring Spoke Season

Saturn’s ring spokes typically appear over an 8-year duration centered on equinox. Hubble Space Telescope observations in 2021 indicate the beginning of a new spoke season as Saturn approaches equinox in 2025. The spokes show increased contrast and longevity in 2022, persisting for up to eleven hours. The spokes are visible from UV to near-IR and are slightly bluer (i.e., less red) than the rings, but we find no significant wavelength dependence in the spectral contrast, which approximates their optical depth). Spoke rotation rates are between 606 and 626 minutes, consistent with either Keplerian rotation or possibly the variable rotation rate of Saturn’s kilometric radiation (SKR). Spoke activity is expected to increase over the next several years.

Amy A. Simon↗
NASA NTRS1976

Characteristics of the NASA Lewis bumpy torus plasma generated with high positive or negative applied potentials

The toroidal ring of plasma contained in the NASA Lewis bumpy-torus superconducting magnet facility may be biased to positive or negative potentials approaching 50 kilovolts by applying direct-current voltages of the respective polarity to 12 or fewer of the midplane electrode rings. The electric fields which are responsible for heating the ions by E/B drift then point radially outward or inward. The low-frequency fluctuations below the ion cyclotron frequency appeared to be dominated by rotating spokes.

Roth, J. R.↗
NASA NTRS1986

Unsteady heat transfer and direct comparison to steady-state measurements in a rotor-wake experiment

Circumferentially local and time-resolved heat transfer measurements were obtained for a circular cylinder in crossflow located downstream of a rotating spoked wheel wake generator in a steady flow tunnel. The unsteady heat transfer effects were obtained by developing an extension of a thin film gauge technique employed to date exclusively in short-duration facilities. The time-average thin film results and conventional steady-state heat transfer measurements were compared. Time-averaged wake-induced stagnation heat transfer enhancement levels above the nowake case were about 10% for the four cylinder Reynolds numbers. This enhancement level was nearly independent of bar passing frequency and was related directly to the time integral of the heat transfer spikes observed at the bar passing frequency. It is observed that the wake-induced heat transfer spikes have peak magnitudes averaging 30 to 40% above the interwake heat transfer level.

Obrien, J. E.↗
NASA NTRS1986

Unsteady heat transfer and direct comparison to steady-state measurements in a rotor-wake experiment

Circumferentially local and time-resolved heat transfer measurements were obtained for a circular cylinder in crossflow located downstream of a rotating spoked wheel wake generator in a steady flow tunnel. The unsteady heat transfer effects were obtained by developing an extension of a thin film gauge technique employed to date exclusively in short-duration facilities. The time-average thin film results and conventional steady-state heat transfer measurements were compared. Time-averaged wake-induced stagnation heat transfer enhancement levels above the nowake case were about 10 percent for the four cylinder Reynolds numbers. This enhancement level was nearly independent of bar passing frequency and was related directly to the time integral of the heat transfer spikes observed at the bar passing frequency. It is observed that the wake-induced heat transfer spikes have peak magnitudes averaging 30 to 40 percent above the interwake heat transfer level.

Obrien, J. E.↗
NASA NTRS1974

Spoke wavenumbers and mode transitions in NASA-Lewis bumpy torus

Waveforms of fluctuations of plasma potential, resulting from rotating electron and ion charge concentrations, have been observed in the Lewis bumpy torus. Since these fluctuations are thought to be spoke rotations in the direction of the E x B drift, measuring the direction of spoke rotation should determine the direction of the electric fields over much of the plasma surface. Since inward pointing electric fields should enhance confinement of the hot ions in this device, knowledge of the direction of the spoke rotation could give valuable information on the mechanism of plasma confinement and radial transport. A Langmuir probe was inserted into the plasma to measure the floating potential of the plasma; hence the direction of the electric field could be checked another way.

Gerdin, G. A.↗
NASA NTRS1981

On the braids and spokes in Saturn's ring system

Two of the features in the Saturnian ring system recently observed by the Voyager 1 spacecraft are (1) the braiding of the F-ring and (2) the radial spokes that rotate across the B-ring. Both of these phenomena are explained by recognizing that the grains that constitute both the F-ring and the spokes are charged to high electrostatic potentials and are sufficiently small to be strongly affected by the magnetic field of the planet. Processes for the charging of the grains are also suggested.

Hill, J. R.↗
NASA NTRSDate not supplied

Rotating Balance Design Methodology

Several upcoming wind tunnel turbofan tests at NASA Glenn Research Center (GRC) require new rotating balances to meet test needs. As the name implies, a rotating balance rotates with the fan providing direct thrust and torque measurements to estimate fan efficiency and performance. One main feature of the new rotating balances requested by GRC, is a more compact design compatible with high bypass fans that are of interest for gains in fuel efficiency. In support of this measurement need, NASA Langley Research Center (LaRC) developed an understanding and methodology for the design of two-component rotating balances. During the development of the methodology, a thorough FEA analysis was conducted, torque analysis of laboratory test specimens, and a study of analytical models were investigated. This presentation will summarize the developed rotating balance design methodology that is detailed in a NASA Technical Memorandum. This TM will detail the analysis required to design, and fabricate a two-component spoke-type rotating balance.

Kenneth Toro↗