Numerical Simulations of Heat Fluxes for Atmospheric Re-Entries

2011 ◽  
Author(s):  
Romain Savajano ◽  
Daniel F. Potter ◽  
Pe´ne´lope Leyland
Keyword(s):  
Numerical Simulations ◽  
Transport Model ◽  
Reaction Scheme ◽  
Heat Fluxes ◽  
Data Comparison ◽  
Diffusion Phenomena ◽  
Speed Up ◽  
Radiative Model ◽  
Main Components ◽  
And Diffusion

During atmospheric (re-)entries, planetary probes encounter huge heat fluxes due to their significant speed (up to 13 km/s for an Earth re-entry). The total heat flux received by the probe can be divided into two main components: a convective one (coming from the conduction and diffusion phenomena occuring in the shock layer) and a radiative one (due to the radiation of certain species). Numerical simulations have been performed for both Titan (Huygens mission) and Earth (Fire II mission) entries. The main parameters influencing the results are the atmosphere composition, the chemical reaction scheme, the transport model and the radiative model. The results obtained gave us information on the flowfield (temperature, pressure, species densities...) and values for the heat fluxes on the wall that are useful for experimental or flight data comparison.

scholarly journals On Dynamic Parallelization of Multilevel Monte Carlo Algorithm

2020 ◽  
Vol 20 (6) ◽  
pp. 116-125
Author(s):  
Nikolay Shegunov ◽  
Oleg Iliev
Keyword(s):  
Monte Carlo ◽  
Numerical Simulations ◽  
Random Fields ◽  
Stochastic Partial Differential Equations ◽  
Computational Cost ◽  
Monte Carlo Algorithm ◽  
Multilevel Monte Carlo ◽  
Deterministic Problem ◽  
Speed Up ◽  
Main Components

AbstractMultiLevel Monte Carlo (MLMC) attracts great interest for numerical simulations of Stochastic Partial Differential Equations (SPDEs), due to its superiority over the standard Monte Carlo (MC) approach. MLMC combines in a proper manner many cheap fast simulations with few slow and expensive ones, the variance is reduced, and a significant speed up is achieved. Simulations with MC/MLMC consist of three main components: generating random fields, solving deterministic problem and reduction of the variance. Each part is subject to a different degree of parallelism. Compared to the classical MC, MLMC introduces “levels” on which the sampling is done. These levels have different computational cost, thus, efficiently utilizing the parallel resources becomes a non-trivial problem. The main focus of this paper is the parallelization of the MLMC Algorithm.

scholarly journals Accelerating simulations using REDCHEM_v0.0 for atmospheric chemistry mechanism reduction

2018 ◽  
Vol 11 (8) ◽  
pp. 3391-3407 ◽  
Author(s):  
Zacharias Marinou Nikolaou ◽  
Jyh-Yuan Chen ◽  
Yiannis Proestos ◽  
Jos Lelieveld ◽  
Rolf Sander
Keyword(s):  
Atmospheric Chemistry ◽  
Transport Model ◽  
A Priori ◽  
Chemical Mechanism ◽  
Climate Modelling ◽  
Mechanism Reduction ◽  
Computational Speed ◽  
Speed Up ◽  
Spatio Temporal ◽  
Skeletal Mechanism

Abstract. Chemical mechanism reduction is common practice in combustion research for accelerating numerical simulations; however, there have been limited applications of this practice in atmospheric chemistry. In this study, we employ a powerful reduction method in order to produce a skeletal mechanism of an atmospheric chemistry code that is commonly used in air quality and climate modelling. The skeletal mechanism is developed using input data from a model scenario. Its performance is then evaluated both a priori against the model scenario results and a posteriori by implementing the skeletal mechanism in a chemistry transport model, namely the Weather Research and Forecasting code with Chemistry. Preliminary results, indicate a substantial increase in computational speed-up for both cases, with a minimal loss of accuracy with regards to the simulated spatio-temporal mixing ratio of the target species, which was selected to be ozone.

The geometry and motion of sharp fronts within geochemical transport problems

1995 ◽  
Vol 449 (1935) ◽  
pp. 123-138
Keyword(s):  
Front Propagation ◽  
Singular Perturbation Theory ◽  
Advective Transport ◽  
Natural Systems ◽  
Diffusion Phenomena ◽  
Sharp Fronts ◽  
Geochemical Transport ◽  
Transport Problems ◽  
Groundwater Flow Field ◽  
And Diffusion

We consider some reactive geochemical transport problems in groundwater sys­tems. When incoming fluid is in disequilibrium with the mineralogy, sharp tran­sition fronts may develop. We show that this is a generic property for a class of systems where the time scales associated with reaction and diffusion phenomena are much shorter than those associated with advective transport. Such multi­ple timescale problems are relevant to a variety of processes in natural systems: mathematically, methods of singular perturbation theory reduce the dimension of the problems to be solved locally. Furthermore, we consider how spatial heteroge­neous mineralogy can make an impact upon the propagation of sharp geochemical fronts. We develop an asymptotic approach in which we solve equations for the evolv­ing geometry of the front and indicate how the non-smooth perturbations, due to natural heterogeneity of the mineralogy on underlying groundwater flow field, are balanced against the smoothing effect of diffusion-dispersive processes. Fronts are curvature damped, and the results here indicate the generic nature of sepa­rate front propagation within both model (idealized) and natural (heterogeneous) geochemical systems.

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