Chemically reacting hypersonic flows over 3D cavities : flowfield structure characterisation

In this paper, a computational investigation of hypersonic rarefied gas flows in the transitional flow regime over 3D cavities is carried out by using the direct simulation Monte Carlo method. Such cavities give rise to geometric discontinuities that are often present at the surface of reentry vehicles. This work is focused on the flowfield structure characterisation under a rarefied environment and in the presence of chemical reactions. The cavities are investigated with different length-to-depth ratios, and the different flow structures are studied. In particular, for length-to-depth ratios of 1 and 2, a single recirculation is observed inside the cavities and the main flow is not able to enter the cavity due to the recirculation structure and high particle density. In the case of length-to-depth ratio 3, the flow is able to partially enter the cavity resulting in an elongated recirculation and the beginning of a secondary recirculation core is noticed. For the case of values 4 and 5, the main flow is able to penetrate deeper into the cavities and two recirculation zones are observed; however, for the length-to-depth ratio 5 the flow impinges directly on the bottom surface, which is a behaviour that is only observed in the continuum regime with a cavity length-to-depth ratio greater than 14

Aerothermodynamic comparison of two- and three-dimensional rarefied hypersonic cavity flows

The thermal protection system is a key element in atmospheric re-entry missions of aerospace vehicles. Usually, in the thermal load calculations, the analysis assumes that the vehicle has a smooth surface. However, discontinuities or imperfections are often present on the aerospace vehicle surfaces due to fabrication tolerances, sensor installations, spaces between the thermal protection plates, and differential expansion or ablation rates between non-similar materials. In the present work, rarefied hypersonic flows over two- and three-dimensional cavities at an altitude of 80km in the Earth’s atmosphere are studied numerically. To model flows in the transitional regime, where the validity of the Navier Stokes equations is questionable, the direct simulation Monte Carlo method has been used. The primary goal is to assess the sensitivity of heat transfer, pressure, and skin-friction coefficients for a family of two- and three-dimensional cavities defined by different length-to-depth ratios. The analysis shows that an assumption of two-dimensionality plays a key role in the over prediction of the aerodynamic properties. Previous work using a continuum approach shows that two recirculation regions and flow attachment occurs when the length-to-depth ratio is equal to 14; however, the same phenomena are observed in the transitional regime when the cavity length-to-depth ratio is equal to 4. A study of the influence of the cavity width has also been conducted. It is shown that increasing the cavity width results in an augmentation of the surface aerothermodynamic quantitie

Open source Direct Simulation Monte Carlo (DSMC) chemistry modelling for hypersonic flows

An open source implementation of chemistry modelling for the direct simulation Monte Carlo (DSMC) method is presented. Following the recent work of Bird [1] an approach known as the quantum kinetic (Q-K) method has been adopted to describe chemical reactions in a 5-species air model using DSMC procedures based on microscopic gas information. The Q-K technique has been implemented within the framework of the dsmcFoam code, a derivative of the open source CFD code OpenFOAM. Results for vibrational relaxation, dissociation and exchange reaction rates for an adiabatic bath demonstrate the success of the Q-K model when compared with analytical solutions for both inert and reacting conditions. A comparison is also made between the Q-K and total collision energy (TCE) chemistry approaches for a hypersonic flow benchmark case

Benchmark numerical simulations of rarefied non-reacting gas flows using an open-source DSMC code

Validation and verification represent an important element in the development of a computational code. The aim is establish both confidence in the algorithm and its suitability for the intended purpose. In this paper, a direct simulation Monte Carlo solver, called dsmcFoam, is carefully investigated for its ability to solve low and high speed non-reacting gas flows in simple and complex geometries. The test cases are: flow over sharp and truncated flat plates, the Mars Pathfinder probe, a micro-channel with heated internal steps, and a simple micro-channel. For all the cases investigated, dsmcFoam demonstrates very good agreement with experimental and numerical data available in the literature

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

Hemoglobin as AS/alfa talassemia - Importância diagnóstica

Sickle Cell disease is a generic term for a group of genetic disorders characterized by the predominance of hemoglobin S. These disorders include Sickle Cell anemia, the Sickle Cell beta Thalassemia syndromes and Hemoglobinopathies in which hemoglobin S is in association with another abnormal hemoglobin, such as hemoglobin S/C. The Sickle Cell trait (hemoglobin AS) associated with Alpha Thalassemia presents alterations in the red blood cells morphology, usually absent in the heterozygous for this hemoglobin variant. The interaction between hemoglobin Sand alpha Thalassemia has been described as one of the factors responsible for the improvement in the clinical picture of homozygous of hemoglobin S (Sickle Cell Anemia), decreasing the number of episodes of pain. The genetic mechanisms of this influence are evaluated using molecular analyses of the human globin genes. With the objective of verifying the presence of alpha Thalassemia in heterozygous of hemoglobin S, with anemia, sent to the Laboratory of Hemoglobins, Department of Biology, UNESP, São José do Rio Preto, SP, we analyzed 1002 blood samples with Sickle Cell trait, in the period from 1990 to 1998. The samples were picked with EDTA 5% as anticoagulant, after previous authorization of the carriers. Appropriated counseling and management requires definitive diagnosis. For the laboratorial diagnosis the blood samples were submitted to electrophoretic procedures in alkaline and acid pH and cytological evaluation of hemoglobin H. The electrophoretic procedures confirmed the presence of hemoglobin AS. The cytological evaluation evidenced the presence of alpha Thalassemia. Of this total analyzed, 16(1,59%) blood samples presented the association between hemoglobin AS and alpha Thalassemia and two individuals belonged of the same family. Our results addressed us to suggest to the routine laboratories, that is important to accomplish the research of alpha Thalassemia among the Sickle Cell trait, with anemia, to verify the interaction with alpha Thalassemia, supplying to the carriers a important information on its hematological profile, genetic pattern of hemoglobinopathies and the appropriated counseling. Rev.bras.hematol.hemoter.,2000,22(3):388-394