High performance conjugate heat transfer with the openpalm coupler

Optimizing gas turbines is a complex multi-physical and multi-component problem that has long been based on expensive experiments. Today, computer simulations can reduce design process costs and are acknowledged as a promising path for optimization. Although the simulations of specific components of gas turbines become accessible, these stand-alone simulations face a new challenge: to improve the quality of the results, new physics must be introduced. Based on the simulation of conjugate heat transfer within an industrial combustor to predict the temperature of its walls, the current work aims at studying the scalability of code coupling on HPC architectures. Coupling accurately solvers on massively parallel architectures while maintaining their scalability is challenging. The strategy investigated relies on recent developments made in a generic parallel coupler. Performance tests have been carried out until 12,288 cores on the CURIE supercomputer (TGCC / CEA). Results show a good behavior and advanced analyzes are carried out in order to draw new paths for future developments in coupled simulations

Interplanetary Lyman α\alpha line profiles: variations with solar activity cycle

Interplanetary Lyman alpha line profiles are derived from the SWAN H cell data measurements. The measurements cover a 6-year period from solar minimum (1996) to after the solar maximum of 2001. This allows us to study the variations of the line profiles with solar activity. These line profiles were used to derive line shifts and line widths in the interplanetary medium for various angles of the LOS with the interstellar flow direction. The SWAN data results were then compared to an interplanetary background upwind spectrum obtained by STIS/HST in March 2001. We find that the LOS upwind velocity associated with the mean line shift of the IP \lya line varies from 25.7 km/s to 21.4 km/s from solar minimum to solar maximum. Most of this change is linked with variations in the radiation pressure. LOS kinetic temperatures derived from IP line widths do not vary monotonically with the upwind angle of the LOS. This is not compatible with calculations of IP line profiles based on hot model distributions of interplanetary hydrogen. We also find that the line profiles get narrower during solar maximum. The results obtained on the line widths (LOS temperature) show that the IP line is composed of two components scattered by two hydrogen populations with different bulk velocities and temperature. This is a clear signature of the heliospheric interface on the line profiles seen at 1 AU from the sun.Comment: 9 pages, 9 figure

Reflectivity of Venus’s Dayside Disk During the 2020 Observation Campaign: Outcomes and Future Perspectives

We performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52–1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283–800 nm wavelengths. Considerable absorption is present in the 350–450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns

14-day forecast of solar indices using interplanetary Lyman α background data

International audienceWe present a new method which can be used to forecast the variations of solar indices on the time scale of a half solar rotation. This method uses the Lya interplanetary glow data obtained by the SWAN instrument on SOHO. We show how the maps of solar Lya flux distributions derived from the SWAN data can be linked to the variation of activity on the solar disk. Active regions which are known to be brighter in Lya radiation than the quiet sun illuminate more interplanetary H atoms through resonance scattering. This excess of illumination related to active regions is clearly seen in full-sky Lya maps recorded by the SWAN instrument on SOHO. These maps include also those excesses resulting from active regions which are on the far side of the Sun, i.e. not visible to solar disk imagers near Earth. From these data, we can derive a farside to nearside flux ratio. This ratio is then used to predict the evolution of solar indices like the solar Lya flux seen at Earth, the 10.7cm radio flux or the MgII solar index. This technique could be used in the future to improve the quality of space weather forecast, in particular to predict atmospheric heating and increased orbital drag of sensitive spacecraft

UV studies and the solar wind

International audienceThe solar wind carves a cavity in the flow of interstellar H atoms through the solar system by charge-exchange ionization. The resulting Ly-α sky pattern depends on the latitude distribution of the solar wind flux and velocity. We review how the solar wind characteristics (mass flux latitude distribution) can be retrieved from Ly-α observations, yielding a new remote sensing method of solar wind studies, through UV optical measurements

Introduction

In this book we discuss the problems encountered for calibrating space-borne instruments in the spectral range 50-300 nm. We also discuss the level of accuracy that can be achieved, and review the different sources of emissions that can be used in that range, i.e. the interplanetary background, stars, and solar system bodies such as planets, moons, and comets. As most of the work presented here is based on comparisons with older datasets obtained by experiments that have been calibrated independently, we also analyse the consistency between existing datasets. Whenever possible, we suggest a correction factor if an older dataset is in disagreement with a more recent one. For example, a comparison of the interplanetary background data acquired by the two ultraviolet (UV) spectrometers on Voyager 1 and Voyager 2 with models and other more recent datasets shows that it is indeed necessary to derive new calibration factors for these two instruments

Cross-calibration of far UV spectra of solar system objects and the heliosphere

This book is the result of a working group sponsored by ISSI in Bern, which was initially created to study possible ways to calibrate a Far Ultraviolet (FUV) instrument after launch. In most cases, ultraviolet instruments are well calibrated on the ground, but unfortunately, optics and detectors in the FUV are very sensitive to contaminants and it is very challenging to prevent contamination before and during the test and launch sequences of a space mission. Therefore, ground calibrations need to be confirmed after launch and it is necessary to keep track of the temporal evolution of the sensitivity of the instrument during the mission. The studies presented here cover various fields of FUV spectroscopy with the exclusion of direct solar UV spectroscopy, including a catalog of stellar spectra, data-sets of lunar Irradiance, observations of comets and measurements of the interplanetary background. Detailed modeling of the interplanetary background is presented as well. This work also includes comparisons of older data-sets with current ones. This raises the question of the consistency of the existing data-sets. Previous experiments have been calibrated independently and comparison of the data-sets may lead to inconsistencies. The authors have tried to check that possibility in the data-sets and when relevant, suggest a correction factor for the corresponding data

Lyman α observations as a possible means for the detection of the heliospheric interface

International audienceWe first summarize our current knowledge of the flow of interstellar H and He gas through the solar system. Both come from the same direction, but the H velocity is 20 km/s, whereas the He velocity is 26 km/s as recently determined by Ulysses, identical to the velocity found for the local interstellar cloud (LIC) as recently determined from absorption lines detected in the spectrum of nearby stars. This velocity difference may be assigned to the deceleration of H atoms at the heliospheric interface through coupling with the partially ionized interstellar plasma. Seen from the inner solar system, the Lyman α emission pattern of H atoms (resonance scattering of solar photons) is quite compatible with a standard model including no interaction for H at the heliopause and therefore cannot be used to characterize such an interaction. We investigate three other types of Lyman α observations which could bear the signature of the heliopause. First, it is shown from Monte Carlo modeling of the interface perturbation that the Lyman α line profile (accessible through high resolution spectroscopy from Earth orbit) varies in a different way from upwind to downwind direction, whether there is a perturbation or not at the heliopause. Indeed, some Prognoz data show such a behaviour, and the potential of planned future observations is discussed (HST and SOHO). Second, since some interaction models predict a decrease of H density at heliopause crossing along the wind (or H increase when cruising upwind), the slope of the radial antisolar Lyman α intensity between 15 and 50 AU, characterized by γ, such as I ≈ k rγ, is computed for various models of H density. It is shown that (1) the value of γ recorded along downwind trajectories depends too much on solar parameters (radiation pressure and ionization) to be very useful to detect a departure from a standard model; (2) the value of γ along upwind trajectories is much less sensitive to solar parameters but radiative transfer of Lyman α in the interplanetary medium must absolutely be taken into account for a correct interpretation; (3) if taken at face value, the value γ = − 0.78 reported for Voyager data between 15 and 50 astronomical units cannot be explained with any standard model, and calls for an increase of density somewhere further upwind. A good fit is obtained with a doubling of the density at 54 astronomical units (hydrogen wall), but this is not a unique solution. Finally, the use of Lyman α intensity maps recorded at large distances (30 ‐ 50 AU) is considered. The shape of the map is different when a hydrogen wall is present, and this method is less prone to instrumental drift and solar Lyman α changes than the preceding one. The first method works whatever is the distance of the heliopause, whereas the two others require observations from upwind region, not too far from the heliopause (a few tens of astronomical units at most)

Cross-Calibration of Far UV Spectra of Solar System Objects and the Heliosphere. ISSI Scientific Report Series, Vol. 13

This book is the result of a working group sponsored by ISSI in Bern, which was initially created to study possible ways to calibrate a Far Ultraviolet (FUV) instrument after launch. In most cases, ultraviolet instruments are well calibrated on the ground, but unfortunately, optics and detectors in the FUV are very sensitive to contaminants and it is very challenging to prevent contamination before and during the test and launch sequences of a space mission. Therefore, ground calibrations need to be confirmed after launch and it is necessary to keep track of the temporal evolution of the sensitivity of the instrument during the mission. The studies presented here cover various fields of FUV spectroscopy with the exclusion of direct solar UV spectroscopy, including a catalog of stellar spectra, data-sets of lunar Irradiance, observations of comets and measurements of the interplanetary background. Detailed modeling of the interplanetary background is presented as well. This work also includes comparisons of older data-sets with current ones. This raises the question of the consistency of the existing data-sets. Previous experiments have been calibrated independently and comparison of the data-sets may lead to inconsistencies. The authors have tried to check that possibility in the data-sets and when relevant, suggest a correction factor for the corresponding data