Development of a two-temperature open source CFD model for hypersonic reacting flows

The highly complex flow physics that characterise re-entry conditions have to be reproduced by means of numerical simulations with both an acceptable level of accuracy and within reasonable timescales. In this respect, a new CFD solver, hyFoam, has been developed within the framework of the open-source CFD platform OpenFOAM for modelling hypersonic reacting flows. hyFoam has been successfully validated for two 0-degree adiabatic heat bath test cases and the limitations of a one-temperature CFD model have been highlighted. To cope with high-temperature gas chemistry, the internal energy has been decomposed into its elementary energy modes, thus introducing the translational-rotational and the vibrational temperatures. A two-temperature CFD model is being implemented in order to attain a better agreement between CFD and DSMC results. Validation of the code for a single species has been executed while mixture-related libraries are currently being developed. The vibrational-translational relaxation time formulation has also been presented and discussed

An open-source hybrid CFD-DSMC solver for high speed flows

During re-entry, a spacecraft will experience flow conditions ranging from highly rarefied to continuum. To simulate regions in between, a hydrodynamic-molecular gas hybrid solver should be used to provide accuracy and effciency. Currently available hybrid codes are in-house codes or do not provide the capabilities to simulate all of the phenomena a spacecraft will experience during re-entry. An open-source CFD-DSMC hybrid code is being developed within the OpenFOAM framework, coupling the solvers dsmcFoam and hy2Foam. In this paper, comparison between the CFD, DSMC and hybrid codes have been performed for simple cases. The dsmcFoam and the hybrid code have shown to compare satisfactorily

A two-temperature open-source CFD model for hypersonic reacting flows, part two : multi-dimensional analysis

hy2Foam is a newly-coded open-source two-temperature computational fluid dynamics (CFD) solver that has previously been validated for zero-dimensional test cases. It aims at (1) giving open-source access to a state-of-the-art hypersonic CFD solver to students and researchers; and (2) providing a foundation for a future hybrid CFD-DSMC (direct simulation Monte Carlo) code within the OpenFOAM framework. This paper focuses on the multi-dimensional verification of hy2Foam and firstly describes the different models implemented. In conjunction with employing the coupled vibration-dissociation-vibration (CVDV) chemistry–vibration model, novel use is made of the quantum-kinetic (QK) rates in a CFD solver. hy2Foam has been shown to produce results in good agreement with previously published data for a Mach 11 nitrogen flow over a blunted cone and with the dsmcFoam code for a Mach 20 cylinder flow for a binary reacting mixture. This latter case scenario provides a useful basis for other codes to compare against

A separated vortex ring underlies the flight of the dandelion

Wind-dispersed plants have evolved ingenious ways to lift their seeds1,2. The common dandelion uses a bundle of drag-enhancing bristles (the pappus) that helps to keep their seeds aloft. This passive flight mechanism is highly effective, enabling seed dispersal over formidable distances3,4; however, the physics underpinning pappus-mediated flight remains unresolved. Here we visualized the flow around dandelion seeds, uncovering an extraordinary type of vortex. This vortex is a ring of recirculating fluid, which is detached owing to the flow passing through the pappus. We hypothesized that the circular disk-like geometry and the porosity of the pappus are the key design features that enable the formation of the separated vortex ring. The porosity gradient was surveyed using microfabricated disks, and a disk with a similar porosity was found to be able to recapitulate the flow behaviour of the pappus. The porosity of the dandelion pappus appears to be tuned precisely to stabilize the vortex, while maximizing aerodynamic loading and minimizing material requirements. The discovery of the separated vortex ring provides evidence of the existence of a new class of fluid behaviour around fluid-immersed bodies that may underlie locomotion, weight reduction and particle retention in biological and manmade structures

An open-source CFD solver for planetary entry

hy2Foam is a newly-coded open-source two-temperature computational fluid dynamics(CFD) solver that aims at (1) giving open-source access to a state-of-the-art hypersonic CFD solver to students and researchers; and (2) providing a foundation for a future hybrid CFD-DSMC (direct simulation Monte Carlo) code within the OpenFOAM framework. Benchmarking has firstly been performed for zero-dimensional test cases and hy2Foam has then been shown to produce results in good agreement with previously published data for a 2D-axisymmetric Mach 11 nitrogen flow over a blunted cone and with the dsmcFoam code for a series of Fourier cases and a 2D Mach 20 cylinder flow for a binary reacting mixture. This latter case scenario provides a useful basis for other codes to compare against. hy2Foam and dsmcFoam capabilities have eventually been utilised to derive and to test a new set of chemical rates based on quantum-kinetic theory and that could be employed for Earth atmospheric re-entry computations.hy2Foam is a newly-coded open-source two-temperature computational fluid dynamics(CFD) solver that aims at (1) giving open-source access to a state-of-the-art hypersonic CFD solver to students and researchers; and (2) providing a foundation for a future hybrid CFD-DSMC (direct simulation Monte Carlo) code within the OpenFOAM framework. Benchmarking has firstly been performed for zero-dimensional test cases and hy2Foam has then been shown to produce results in good agreement with previously published data for a 2D-axisymmetric Mach 11 nitrogen flow over a blunted cone and with the dsmcFoam code for a series of Fourier cases and a 2D Mach 20 cylinder flow for a binary reacting mixture. This latter case scenario provides a useful basis for other codes to compare against. hy2Foam and dsmcFoam capabilities have eventually been utilised to derive and to test a new set of chemical rates based on quantum-kinetic theory and that could be employed for Earth atmospheric re-entry computations

A Two-Temperature Open-Source CFD Model for Hypersonic Reacting Flows, Part Two: Multi-Dimensional Analysis

hy2Foam is a newly-coded open-source two-temperature computational fluid dynamics (CFD) solver that has previously been validated for zero-dimensional test cases. It aims at (1) giving open-source access to a state-of-the-art hypersonic CFD solver to students and researchers; and (2) providing a foundation for a future hybrid CFD-DSMC (direct simulation Monte Carlo) code within the OpenFOAM framework. This paper focuses on the multi-dimensional verification of hy2Foam and firstly describes the different models implemented. In conjunction with employing the coupled vibration-dissociation-vibration (CVDV) chemistry–vibration model, novel use is made of the quantum-kinetic (QK) rates in a CFD solver. hy2Foam has been shown to produce results in good agreement with previously published data for a Mach 11 nitrogen flow over a blunted cone and with the dsmcFoam code for a Mach 20 cylinder flow for a binary reacting mixture. This latter case scenario provides a useful basis for other codes to compare against

Simulations of rarefied and continuum hypersonic flow over re-entry objects

Numerical simulations of high-speed, high-altitude flow over re-entry objects have been carried out for a variety of flow conditions corresponding to test cases proposed for the 1st Spacecraft Demise Workshop. In the continuum regime, conventional computational fluid dynamics (CFD) has been employed to characterise the aerothermodynamic loads acting on the bodies and to predict the shock structures in the surrounding flow fields. In the upper atmosphere, transition-continuum regime the direct simulation Monte Carlo (DSMC) approach has been applied using the quantum-kinetic (Q-K) chemistry model to account for the dissociation of nitrogen. Both CFD and DSMC approaches have been applied within the framework of the open-source CFD toolbox OpenFOAM

Surround the Nonlinearity: Inserting Foldable Convolutional Autoencoders to Reduce Activation Footprint

International audienceModern deep learning architectures, while highly successful, are characterized by substantial computational and memory demands due to their large number of parameters or the storing of activations. That is why it is hard to adapt a neural network to the constraints of hardware, especially at the edge. This paper presents an investigation into a novel approach for activation compression, which we term 'Projection-based compression on channels' or 'ProChan'. Our method involves interposing projection layers into a pretrained network around the nonlinearity, reducing the channel dimensionality through compression operations and then expanding it back. Our module is made to be then totally fused with the convolutions around it, guaranteeing no overhead, and maximum FLOPs reduction. We studied its absorption of the cost of quantization, to combine the two approaches for footprint reduction. Our findings indicate that the projections likely perform an 'adaptive stretching' operation on the feature space, enabling the preservation of essential information when constrained by dimensional limitations. We also perform an ablation study on the different possible strategies for a stable and quick training, and analyse the interactions with different quantization paradigms, namely PACT for activations and posttraining quantization (PTQ) methods for weights

Tragopogon dubius, considerations on a possible biomimetic transfer

peer reviewedTragopogon dubious is a small herbaceous plant that uses the wind as dispersal vector for its seeds. The seeds are attached to stalked parachutes which increase the aerodynamic drag force on the seeds. This decreases their rate of descent, and hence increases the total distance traveled. The relatively large natural parachute of Tragopogon dubious is an ideal model in a biomimetic structure owing to its relative large size, sturdy and robust structure, and the hierarchical distribution of its fibers. The present contribution describes some preliminary results on the structural properties and aerodynamical behavior of this seed, with the goal of developing new stream of designs of lighter or more robust parachute for possible extra-terrestrial purposes. © 2012 Springer-Verlag

A Two-Temperature Open-Source CFD Model for Hypersonic Reacting Flows, Part One: Zero-Dimensional Analysis

A two-temperature CFD (computational fluid dynamics) solver is a prerequisite to any spacecraft re-entry numerical study that aims at producing results with a satisfactory level of accuracy within realistic timescales. In this respect, a new two-temperature CFD solver, hy2Foam, has been developed within the framework of the open-source CFD platform OpenFOAM for the prediction of hypersonic reacting flows. This solver makes the distinct juncture between the trans-rotational and multiple vibrational-electronic temperatures. hy2Foam has the capability to model vibrational-translational and vibrational-vibrational energy exchanges in an eleven-species air mixture. It makes use of either the Park TTv model or the coupled vibration-dissociation-vibration (CVDV) model to handle chemistry-vibration coupling and it can simulate flows with or without electronic energy. Verification of the code for various zero-dimensional adiabatic heat baths of progressive complexity has been carried out. hy2Foam has been shown to produce results in good agreement with those given by the CFD code LeMANS (The Michigan Aerothermodynamic Navier-Stokes solver) and previously published data. A comparison is also performed with the open-source DSMC (direct simulation Monte Carlo) code dsmcFoam. It has been demonstrated that the use of the CVDV model and rates derived from Quantum-Kinetic theory promote a satisfactory consistency between the CFD and DSMC chemistry modules