85 research outputs found
Numerical computation of viscous flows on the lee side of blunt shapes flying at supersonic speeds
Get PDFA numerical method for solving the parabolic approximation to the steady-state compressible Navier-Stokes equations is examined. The approximation neglects only the streamwise gradients of shear stress. An implicit finite difference method is used which advances the solution downstream from an initial data surface and determines the complete viscous-inviscid flow between the body and bow shock wave. It is necessary that the inviscid portion of the flow field be supersonic. Crossflow separation is determined as part of the solution. The method is applied to a 15 deg sphere-cone at 15 deg angle of attack, and the results are compared with an inviscid method-of-characteristics calculation
Catalytic surface effects on space thermal protection system during Earth entry of flights STS-2 through STS-5
Get PDFAn on going orbiter experiment catalytic surface effects experiment being conducted on the Space Shuttle is discussed. The catalytic surface effects experiment was peformed on four of the five flights of Columbia. Temperature time histories and distributions along the midfuselage and wing of the orbiter were used to determine the surface catalytic efficiency of the baseline high temperature reusable surface insulation. Correlation parameters are shown that allow the comparison of all flight data with predictions from the design and surface emittance decreased as a result of contaminants during the five flights of the Space Shuttle
Calculation of supersonic viscous flow over delta wings with sharp subsonic leading edges
Get PDFTwo complementary procedures were developed to calculate the viscous supersonic flow over conical shapes at large angles of attack, with application to cones and delta wings. In the first approach the flow is assumed to be conical and the governing equations are solved at a given Reynolds number with a time-marching explicit finite-difference algorithm. In the second method the parabolized Navier-Stokes equations are solved with a space-marching implicit noniterative finite-difference algorithm. This latter approach is not restricted to conical shapes and provides a large improvement in computational efficiency over published methods. Results from the two procedures agree very well with each other and with available experimental data
Simulation of large turbulent structures with the parabolic Navier-Stokes equations
Get PDFThe theoretical basis for well posed marching of a Parabolic Navier-Stokes (PNS) computational technique for supersonic flow is discussed and examples given to verify the analysis. It is demonstrated that stable computations can be made even with very small steps in the marching direction. The method is applied to cones at large angle of attack in high Reynolds number, supersonic flow. Streamline trajectories generated from the numerical solutions demonstrate the development of vortex structures on the lee side of the cone
High contrast at short separation with VLTI/GRAVITY: Bringing Gaia companions to light
Full text linkSince 2019, GRAVITY has provided direct observations of giant planets and
brown dwarfs at separations of down to 95 mas from the host star. Some of these
observations have provided the first direct confirmation of companions
previously detected by indirect techniques (astrometry and radial velocities).
We want to improve the observing strategy and data reduction in order to lower
the inner working angle of GRAVITY in dual-field on-axis mode. We also want to
determine the current limitations of the instrument when observing faint
companions with separations in the 30-150 mas range. To improve the inner
working angle, we propose a fiber off-pointing strategy during the observations
to maximize the ratio of companion-light-to-star-light coupling in the science
fiber. We also tested a lower-order model for speckles to decouple the
companion light from the star light. We then evaluated the detection limits of
GRAVITY using planet injection and retrieval in representative archival data.
We compare our results to theoretical expectations. We validate our observing
and data-reduction strategy with on-sky observations; first in the context of
brown dwarf follow-up on the auxiliary telescopes with HD 984 B, and second
with the first confirmation of a substellar candidate around the star Gaia DR3
2728129004119806464. With synthetic companion injection, we demonstrate that
the instrument can detect companions down to a contrast of
( mag) at a separation of 35 mas, and a contrast of
( mag) at 100 mas from a bright
primary (K<6.5), for 30 min exposure time. With its inner working angle and
astrometric precision, GRAVITY has a unique reach in direct observation
parameter space. This study demonstrates the promising synergies between
GRAVITY and Gaia for the confirmation and characterization of substellar
companions.Comment: 16 pages, 14 figures. Submitted to A&
Thermographic Investigations of Temperatures and Heat Fluxes in Hypersonic Large-Scale Plasma Flow
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Simulation of large turbulent vortex structures with the parabolic Navier-Stokes equations
No full textComputation of nonequilibrium, supersonic three-dimensional inviscidflow over blunt-nosed bodies
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