Flowfield Uncertainty Analysis for Hypersonic CFD Simulations

Uncertainty quantification (UQ) in the hypersonic flow regime offers valuable information to determine physical models in need of improvement and to assist in design of vehicles and flight experiments. Here we present results of UQ analysis based on polynomial chaos method to determine flowfield and surface heat flux uncertainty under typical blunt-body re-entry conditions. The NASA Langley code, LAURA, was used for axisymmetric CFD calculations of chemically reacting hypersonic flow over FIRE-II configuration. A third order polynomial chaos (PC) method using the Gauss-Hermite quadrature was applied for determining probability density functions and moments of output quantities. Input parameters such as freestream density, velocity, and temperature were varied and the propagation of their corresponding uncertainties on output properties of interest through the flowfield were studied. An order of magnitude increase in surface heat flux uncertainties was observed for an input freestream velocity uncertainty of ±100 ft/s, or 0.29%. This parameter thus has the greatest sensitivity to variations, and conversely the freestream temperature has the least sensitivity

Evidence of the inhibitory effects of the vagal imput upon the gastric motility in conscious sheep

Chez le mouton éveillé, la suppression chirurgicale des afférences vagales entraîne une augmentation de 17 à 46 % de la fréquence des cycles primaires gastriques. La réduction marquée des afférences gastriques, obtenue en sup primant la motricité du réticulo-rumen, provoque une augmentation de la fré quence de l’activité cyclique des neurones préganglionnaires vagaux innervant les préestomacs et une augmentation de la durée de leur décharge. Ces résultats sont en faveur de l’existence d’un effet inhibiteur permanent des afférences vagales sur les centres gastriques.In conscious sheep, surgical vagal deafferentation led the frequency of primary gastric cycles to be increased in the range between 17 and 46 %. The effects of a marked reduction of the gastric vagal input due to inhibition of gastric motility upon gastric vagal efferent neurones can ben evaluated by i) a shortening of the interval between onsets of two successive bursts, ii) an increase in the duration of their discharges. Interest in the common result of both experiments suggests that under physiological circonstances the result ing afferent drive from gastric comportments is inhibitory in the « gastric centres » and consequently on reticulo-rumen motility

Contrôle nerveux de la motricité du réticulo-rumen

International audienc

The microspace launcher: first step to the fully air-breathing space launcher

A possible application for the high-speed air-breathing propulsion is the fully or partially reusable space launcher. Indeed, by combining the high-speed air-breathing propulsion with a conventional rocket engine (combined cycle or combined propulsion system), it should be possible to improve the average installed specific impulse along the ascent trajectory and then make possible more performing launchers and, hopefully, a fully reusable one. During the last 15 years, a lot of system studies have been performed in France on that subject within the framework of different and consecutive programs. Nevertheless, these studies never clearly demonstrated that a space launcher could take advantage of using a combined propulsion system. During last years, the interest to air-breathing propulsion for space application has been revisited. During this review and taking into account technologies development activities already in progress in Europe, clear priorities have been identified regarding a minimum complementary research and technology program addressing specific needs of space launcher application. It was also clearly identified that there is the need to restart system studies taking advantage of recent progress made regarding knowledge, tools, and technology and focusing on more innovative airframe/propulsion system concepts enabling better trade-off between structural efficiency and propulsion system performance. In that field, a fully axisymmetric configuration has been considered for a microspace launcher (10 kg payload). The vehicle is based on a main stage powered by air-breathing propulsion, combined or not with liquid rocket mode. A “kick stage,” powered by a solid rocket engine provides the final acceleration. A preliminary design has been performed for different variants: one using a separated booster and a purely air-breathing main stage, a second one using a booster and a main stage combining air-breathing and rocket mode, a third one without separated booster, the main stage ensuring the initial acceleration in liquid rocket mode and a complementary acceleration phase in rocket mode beyond the air-breathing propulsion system operation. Finally, the liquid rocket engine of this third variant can be replaced by a continuous detonation wave rocket engine. The paper describes the main guidelines for the design of these variants and provides their main characteristics. On this basis, the achievable performance, estimated by trajectory simulation, are detailed

Optimization of supersonic axisymmetric nozzles with a center body for aerospace propulsion

This study is aimed at optimization of axisymmetric nozzles with a center body, which are suitable for thrust engines having an annular duct. To determine the flow conditions and nozzle dimensions, the Vinci rocket engine is chosen as a prototype. The nozzle contours are described by 2nd and 3rd order analytical functions and specified by a set of geometrical parameters. A direct optimization method is used to design maximum thrust nozzle contours. During optimization, the flow of multispecies reactive gas is simulated by an Euler code. Several optimized contours have been obtained for the center body diameter ranging from 0.2 to 0.4 m. For these contours, Navier-Stokes (NS) simulations have been performed to take into account viscous effects assuming adiabatic and cooled wall conditions. The paper presents an analysis of factors influencing the nozzle thrust