352 research outputs found
Wall-Modeled Lattice Boltzmann and Navier-Stokes Approaches for Separated Flows
Lattice Boltzmann (LB) and hybrid Reynolds-averaged Navier-Stokes/large eddy simulation (RANS/LES) methods within the Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework are applied to NASA's Revolutionary Computational Aerosciences (RCA) standard test cases for separated flows. A detailed comparison between the performance and accuracy of the two emerging numerical methodologies for turbulence resolving simulations, i.e. the LB and hybrid RANS/LES methods will be presented. This contribution addresses the RCA technical challenge to identify and down-select critical turbulence, transition, and numerical method technologies for 40% reduction in predictive error for standard turbulence separated flow test cases. Results for the 2D NASA wall-mounted hump and the axisymmetric transonic bump including time-averaged pressure coefficient, skin friction, and velocity pro les, as well as resolved and modeled Reynolds stresses for both numerical approaches will be presented and differences between LB and hybrid RANS/LES will be discussed
Wall Modeled Lattice Boltzmann and Navier-Stokes Approaches for Selected RCA Cases
No abstract availabl
Recent Advancements in LAVA for Jet, Rotor-Blade and Fan Noise Prediction
No abstract availabl
Monitoring the large-scale magnetic field of AD~Leo with SPIRou, ESPaDOnS and Narval. Toward a magnetic polarity reversal?
One manifestation of dynamo action on the Sun is the 22-yr magnetic cycle,
exhibiting a polarity reversal and a periodic conversion between poloidal and
toroidal fields. For M dwarfs, several authors claim evidence of activity
cycles from photometry and analyses of spectroscopic indices, but no clear
polarity reversal has been identified from spectropolarimetric observations.
Our aim is to monitor the evolution of the large-scale field of AD Leo, which
has shown hints of a secular evolution from past dedicated spectropolarimetric
campaigns. We analysed near-infrared spectropolarimetric observations of the
active M dwarf AD Leo taken with SPIRou between 2019 and 2020 and archival
optical data collected with ESPaDOnS and Narval between 2006 and 2019. We
searched for long-term variability in the longitudinal field, the width of
unpolarised Stokes profiles, the unsigned magnetic flux derived from Zeeman
broadening, and the geometry of the large-scale magnetic field using both
Zeeman-Doppler Imaging and Principal Component Analysis. We found evidence of a
long-term evolution of the magnetic field, featuring a decrease in axisymmetry
(from 99% to 60%). This is accompanied by a weakening of the longitudinal field
(-300 to -50 G) and a correlated increase in the unsigned magnetic flux (2.8 to
3.6 kG). Likewise, the width of the mean profile computed with selected
near-infrared lines manifests a long-term evolution corresponding to field
strength changes over the full time series, but does not exhibit modulation
with the stellar rotation of AD Leo in individual epochs. The large-scale
magnetic field of AD Leo manifested first hints of a polarity reversal in late
2020 in the form of a substantially increased dipole obliquity, while the
topology remained predominantly poloidal and dipolar. This suggests that
low-mass M dwarfs with a dipole-dominated magnetic field can undergo magnetic
cycles.Comment: 26 pages, 18 figures, 8 table
Magnetic fields & rotation periods of M dwarfs from SPIRou spectra
We present near-infrared spectropolarimetric observations of a sample of 43
weakly- to moderately-active M dwarfs, carried with SPIRou at the
Canada-France-Hawaii Telescope in the framework of the SPIRou Legacy Survey
from early 2019 to mid 2022. We use the 6700 circularly polarised spectra
collected for this sample to investigate the longitudinal magnetic field and
its temporal variations for all sample stars, from which we diagnose, through
quasi-periodic Gaussian process regression, the periodic modulation and
longer-term fluctuations of the longitudinal field. We detect the large-scale
field for 40 of our 43 sample stars, and infer a reliable or tentative rotation
period for 38 of them, using a Bayesian framework to diagnose the confidence
level at which each rotation period is detected. We find rotation periods
ranging from 14 to over 60d for the early-M dwarfs, and from 70 to 200d for
most mid- and late-M dwarfs (potentially up to 430d for one of them). We also
find that the strength of the detected large-scale fields does not decrease
with increasing period or Rossby number for the slowly rotating dwarfs of our
sample as it does for higher-mass, more active stars, suggesting that these
magnetic fields may be generated through a different dynamo regime than those
of more rapidly rotating stars. We also show that the large-scale fields of
most sample stars evolve on long timescales, with some of them globally
switching sign as stars progress on their putative magnetic cycles.Comment: MNRAS, in press (25 pages, 15 figures, 3 tables
- …