Olivier Chazot

Olivier Chazot
von Karman Institute for Fluid Dynamics · Department of Aeronautics and Aerospace

Professor

About

217
Publications
51,277
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2,298
Citations

Publications

Publications (217)
Conference Paper
The present study investigates the aerodynamic separation of compact fragment clusters composed of spheres and cubes. This experimental analysis was conducted in the VKI Longshot hypersonic wind tunnel at Mach 12 flow conditions, using a dual camera free-flight testing methodology. The test articles are initially confined in a sabot, which separate...
Article
Full-text available
In the domain of re-entry and hypersonic vehicles, advancing material development requires comprehensive material testing to thoroughly understand the aero-thermo-chemistry at the surface. This paper overviews hypersonic, high-temperature activities conducted at the von Karman Institute for Fluid Dynamics (VKI) Plasmatron facility, employing three...
Conference Paper
The operational map of the H3 Mach 6 blowdown wind tunnel, at the von Karman Institute for Fluid Dynamics (VKI), is extended towards lower Mach numbers with a new axisymmetric contoured nozzle to achieve Mach 5 testing conditions. Following the design, manufacturing, instrumentation and integration of the Mach 5 nozzle, an extensive commissioning c...
Article
This work deals with the stochastic inference of gas-phase chemical reaction rates in high temperature air flows from plasma wind tunnel experimental data. First, a Bayesian approach is developed to include not only measurements but also additional information related to how the experiment is performed. To cope with the resulting computationally de...
Article
Full-text available
The accumulation of space debris objects on Earth’s orbit is raising environmental and safety concerns yielding an urgent need to develop Design for Demise methodologies. Free-flight testing in hypersonic wind tunnels has shown superior capabilities to conventional sting-supported model experiments using aerodynamic balances for analyzing debris ob...
Conference Paper
Full-text available
Free-flight testing in hypersonic wind tunnels has shown good capabilities for analyzing the flight of debris objects and scenarios for their separation. The free-flight methodology implemented in the VKI Longshot facility was recently updated to facilitate the aerodynamic analysis of trajectories with six degrees of freedom. The image processing a...
Conference Paper
Free-flight testing methodologies have shown superior capabilities to aerodynamic balances for testing space debris and analyzing proximal body separation scenarios in short-duration hypersonic wind tunnels. A free-flight testing methodology has been established for the VKI Longshot wind tunnel previously, and the present paper discusses the advanc...
Preprint
Full-text available
This work deals with the stochastic inference of gas-phase chemical reaction rates in high temperature air flows from plasma wind tunnel experimental data. First, a Bayesian approach is developed to include not only measurements but also all additional information related to how the experiment is performed. To cope with the resulting computationall...
Article
Full-text available
Accurate surface temperature and recession measurements are crucial experimental data for plasma wind tunnel testing of ablative thermal protection materials. In this work we propose a novel methodology to reconstruct infrared temperature maps on 3D geometries undergoing surface recession. An optical calibration technique is used to extract 3D metr...
Conference Paper
This paper presents a renewed characterization of a Mach 6 hypersonic wind tunnel. The H3 hypersonic facility, located at the von Karman Institute, is a blowdown-type wind tunnel with a useful test duration of the order of one second to one minute, currently equipped with a fixed-Mach, axisymmetric contoured nozzle. The H3 is a "cold" hypersonic wi...
Conference Paper
Full-text available
Spacecraft entering a planetary atmosphere are surrounded by a plasma layer containing high levels of ionization. The high electron number densities cause attenuation and rotation of the polarization of the emitted signal, leading to communication blackout. This work presents experimental measurements of radio signal attenuation and Faraday rotatio...
Article
This paper outlines the initial development of a novel magnetohydrodynamic (MHD) plasma control system which aims at mitigating shock-induced heating and the radio-frequency communication blackout typically encountered during (re-)entry into planetary atmospheres. An international consortium comprising universities, SMEs, research institutions, and...
Conference Paper
Full-text available
Three methods of determining the enthalpy of the flow in an Inductively Coupled Plasma (ICP) wind tunnel that is, the semi-empirical ASTM E-637 formulation, the deterministic procedure employed at the von Karman Institute (VKI) Plasmatron facility and a stochastic inverse method based on a Bayesian framework, are compared. The comparison consists o...
Conference Paper
Hypersonic facilities are essential for the investigation of aerothermodynamic phenomena which have a direct impact on high-speed vehicles' design. The flow quality and characterization is of utmost importance for the ground testing experiment. The paper is looking at the expansion flow in a hypersonic nozzle and presents a methodology to determine...
Conference Paper
Full-text available
A design methodology for supersonic and hypersonic contoured axisymmetric nozzles in presence of real gas effects is presented. The design approach relies on the method of characteristics and includes both dense gas effects and high-temperature effects. The implementation of the methodology relies on tabulated flow properties issuing from appropria...
Conference Paper
Full-text available
Aerodynamic predictions in the hypersonic regime may be obtained to a good degree of accuracy using the Newtonian theory. The present paper describes the ANTARES code (short for Application of New-tonian Theory for ARbitrary Entry Shapes) which has been developed at the von Karman Institute for Fluid Dynamics for such predictions on 3-dimensional a...
Conference Paper
Full-text available
In the present work, we aim at implementing a temperature-sensitive-paint measurement technique (TSP) for the determination of heat fluxes during experiments in the hypersonic facilities operated at the von Karman Institute for Fluid Dynamics (VKI). To do so, an evaluation method for TSP mixtures is established, including spectrometry, calibrations...
Conference Paper
The aerodynamics of a free-flying ring model interfering with a steady crossflow cylinder in Mach 14 cold hypersonic flow has been investigated experimentally in the VKI Longshot facility. A ring model was initially suspended at a 90-degree incidence upstream to a transversely mounted cylinder. Upon the arrival of the flow, the ring's thin support...
Conference Paper
This paper aims to document the design and preliminary characterization of three new supersonic nozzles developed at the von Karman Institute for Fluid Dynamics. They intend to extend the operating capabilities of the VKI-Plasmatron for future high heat flux and high shear experiments in the scope of a better understanding of the space debris demis...
Conference Paper
The ReChar project aims at establishing guidelines for standardized material characterization techniques focusing on carbon-phenolic ablative materials through the execution of several test phases in different, independent laboratories using ZURAM as test case material. This shall define standard measurement methods and procedures, which allow reli...
Article
Since March 2014, all ESA satellites and launcher upper stages which will be disposed of by atmospheric re-entry at the end of their operational life must demonstrate that the risk from fragments surviving the re-entry and causing casualties on ground is less than 1 in 10,000. This casualty risk is calculated by re-entry tools simulating the uncont...
Article
This work presents a dedicated plasma wind tunnel experimental methodology that significantly improves the stochastic characterization of TPS catalytic efficiencies when dealing with uncertain measurements and model parameters. We first use synthetic data to test whether the proposed experimental methodology brings any advantages in terms of uncert...
Article
The catalytic properties of materials used in re-usable thermal protection systems (TPSs) of re-entry vehicles are mainly characterized in plasma wind tunnels. These facilities are adequate to reproduce the thermo-chemical environment found in hypersonic flights. Catalytic recombination coefficients (W) determined empirically for the TPS design pro...
Article
This paper analyzes the nozzle start-up of the von Kármán Institute Longshot, an impulse hypersonic gun tunnel, using a combination of the Lagrangian L1D code (used to model the initial compression process of the test gas into a reservoir by an inertial piston) and unsteady Reynolds-averaged Navier–Stokes simulations to model the flow expansion thr...
Conference Paper
Full-text available
This paper presents the experimental characterization of the recently commissioned Mach 14 hypersonic nozzle of the Longshot gun tunnel. The Longshot facility of the von Karman Institute for Fluid Dynamics is a short-duration hypersonic wind tunnel, which is capable of reproducing the high Mach and Reynolds numbers experienced during most atmospher...
Chapter
Full-text available
Validation processes for aerospace flight modeling require to articulate uncertainty quantification methods with the experimental approach. On this note, the specific strategies for the reproduction of re-entry flow conditions in ground-based facilities are reviewed. It shows how it combines high-speed flow physics with the hypersonic wind tunnel c...
Conference Paper
Full-text available
Spacecraft entering a planetary atmosphere are surrounded by a plasma layer containing high levels of ionization. The high electron number densities cause attenuation of the electromagnetic waves emitted by the on-board antennas, leading to communication blackout for several minutes. This work presents experimental measurements of signal propagatio...
Conference Paper
The present work aims at assessing how to measure physical quantities that relate to Electron Transpiration Cooling (ETC) phenomena. This is carried out through a test campaign in the Plasmatron facility at the Von Karman Institute, which allows reaching high surface temperatures under flows stagnating on candidate samples. Graphite samples (work f...
Preprint
Full-text available
This work focuses on the development of a dedicated experimental methodology that allows for a better stochastic characterization of catalytic recombination parameters for reusable ceramic matrix composite materials when dealing with uncertain measurements and model parameters. As one of the critical factors affecting the performance of such materi...
Article
Full-text available
Testing thermal protection system materials in ground-based facilities, such as plasma wind tunnels, is a key step in the development of entry vehicles. The Local Heat Transfer Simulation methodology offers a systematic approach to identify, from a set of flight conditions such as altitude, velocity and vehicle size, the proper aerothermochemical t...
Article
Full-text available
The in-gas-jet laser spectroscopy method relies on the production of uniform and low-temperature gas jets to fully resolve the atomic hyperfine structure and efficiently determine fundamental nuclear properties of short-lived isotopes from, e.g., the hardly accessible actinide and transactinide elements. In this article we present the studies devot...
Article
Full-text available
Cork P50 thermal protection material was characterized under the Earth atmospheric entry conditions in the framework of the in-flight experiment QARMAN. A total of 25 P50 samples were exposed to air plasma ranging the chamber static pressure values of 1500, 4100, 6180, and 20,000 Pa and heat fluxes between 280 and 3250 kW/m2. The sample radius was...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2021-3137.vid We study the ablation and transient thermal response of a quartz sample in air plasma.The experiment is carried out in the Plasmatron facility of the von Karman Institute for Fluid Dynamics. The aero-thermodynamic environment reproducing the atmospheric entry in the boundary layer of...
Article
Full-text available
This work deals with the inference of catalytic recombination parameters from plasma wind tunnel experiments for reusable thermal protection materials. One of the critical factors affecting the performance of such materials is the contribution to the heat flux of the exothermic recombination reactions at the vehicle surface. The main objective of t...
Chapter
Full-text available
In this work, we review selected experiments and inference methods for the determination of atmospheric entry gas-surface interaction models for air catalysis and nitrogen ablation. Accurate prediction of the gas-surface interaction during spacecraft reentry remains a challenging problem for thermal protection system design. Attempts to model the s...
Conference Paper
Full-text available
Plasma jets naturally develop hydrodynamic instabilities originating from thermal and momentum exchanges with the cold and quiescent surrounding fluid. This work investigates the hydrodynamic instabilities of a simulated plasma jet using multiscale data-driven modal analysis. The investigated conditions are representative of the flow produced in th...
Conference Paper
A comprehensive numerical study has been carried out to simulate the Mach 15 contoured nozzle flow in the VKI intermittent Longshot facility. The study has considered thermal nonequilibrium and real gas effects on the nozzle flow. The simulations were performed using a compressible flow Navier-Stokes solver, US3D, well suited for hypersonic flow si...
Chapter
In this chapter, the operating principles of two major types of high-enthalpy facilities are reviewed. Both groups of facilities are complementary to reproduce high-speed flows and high thermal loads. The description focuses on the main elements and basic functioning of these wind tunnels, as well as the measurement techniques involved, including a...
Preprint
Full-text available
This work deals with the inference of catalytic recombination parameters from plasma wind tunnel experiments for reusable thermal protection materials. One of the critical factors affecting the performance of such materials is the contribution to the heat flux of the exothermic recombination reactions at the vehicle surface. The main objective of t...
Article
Full-text available
Stability features of two-stream coaxial plasma jet simulations are investigated using numerical solutions to the spatio-temporal one-dimensional linear stability theory problem. The base states obtained from magneto-hydrodynamic simulations consider the flow as a mixture of gases in local thermodynamic equilibrium (LTE) while stability computation...
Article
Full-text available
Hypersonic experiments are performed in the VKI Longshot wind tunnel on hemispherical and annular geometries representative of space debris, aiming at determining their lift, drag and pitching moment coefficients. A free-flight technique is used for this purpose where the model is automatically released in the hypersonic flow and safely recovered b...
Article
Full-text available
To predict the debris survivability during an atmospheric re-entry and assess the prospective risk on ground, CNES develops an engineering tool named DEBRISK, based on an object-oriented approach. This approach is currently limited to primitive shapes and is therefore difficult to apply to more complex shapes. The objective of this work is to prese...
Conference Paper
To predict the debris survivability during an atmospheric re-entry and assess the prospective risk on ground, CNES develops an engineering tool named DEBRISK, based on an object-oriented approach. This approach is currently limited to primitive shapes and is therefore difficult to apply to more complex shapes. The objective of this work is to prese...
Conference Paper
Full-text available
Hypersonic experiments are performed in the VKI Longshot wind tunnel on geometries representative of space debris, aiming at determining their lift, drag and pitching moment coefficients. A free-flight technique is used for this purpose where the model is automatically released in the hypersonic flow and safely recovered by the end of the experimen...
Conference Paper
Full-text available
Evaluation, prediction and control of laminar-turbulent transition and aero-acoustics in high-speed flow is still hampered by the non-availability of low noise windtunnel facilities in Europe. However low noise facilities in the USA, Russia Federation, China and Japan have already demonstrated the importance of these facilities for not only basic r...
Conference Paper
Carbon/phenolic ablators are commonly used as thermal protection material for spacecraft. Nevertheless, their com- plex thermal degradation is not yet fully understood. One of the current limitations preventing significant advance- ments in the modeling of the decomposition process and its effects on the material thermal response is the scarcity of...
Article
Hypersonic boundary-layer transition experiments are performed at the von Karman Institute for Fluid Dynamics in the low-enthalpy Longshot wind tunnel. Freestream Mach numbers are within the range 9.5≤M∞≤12, and freestream unit Reynolds numbers vary within the range 3.3×106/m≤Reunit,∞≤12.5×106/m. The model is a 7 deg half-angle cone, which is 800 m...
Conference Paper
This work provides catalytic recombination coefficients (γ) on water-cooled copper calorimeters at 350 K. Measurements are obtained on probes of different sizes, tested in a plasma wind tunnel at stagnation point configuration. Despite pressure and surface temperature are the same among the probes, different catalytic activities are observed. This...
Article
Flow characterization in plasma wind tunnels often relies on known catalytic properties of metallic surfaces. Copper is generally considered as fully catalytic standard for those purposes. However, long exposures to atomic oxygen enable the development of a stable oxidized layer and lead to a material with lower catalytic activity, falsifying the d...
Article
An investigation of outgassing effects on boundary-layer transition was carried out. This joint computational–experimental work mimicked heat-shield pyrolysis outgassing in atmospheric reentry conditions. A slender 7 deg half-angle cone with air wall blowing through a porous section near the apex was tested in the VKI-H3 Mach 6 hypersonic blowdown...
Article
Various methodologies used to derive free-stream conditions in hypersonic wind tunnels using different sets of experimental inputs are reviewed. The accuracy of a relevant but seldom used approach, involving free-stream static pressure measurements, is improved in the present work by solving numerically shock conservation equations and by accountin...
Article
The present work proposes an extrapolation methodology that allows the local duplication of a hypersonic boundary layer at off-stagnation locations around a generic flying body, to a flat plate model that could be introduced in a plasma wind tunnel. Such extrapolation is assessed using computational fluid dynamics computations of the Intermediate e...
Article
The detailed characterization of the thermal boundary layer under periodic fluctuations is vital to improve the performance of cooled turbine airfoils, as well as to assess noise thermal and structural fatigue. In the present contribution, we performed detailed unsteady Reynolds averaged Navier–Stokes (URANS) simulations to investigate wall heat fl...
Article
Heat shields used to protect space capsules during very high-speed atmospheric entry incorporate lightweight insulating refractories based on carbon-fiber preforms. These ablators, with up to 80% porosity, present exceptional thermal and chemical properties. A joint experimental and modeling approach to study such materials is presented, which cont...
Presentation
Aerothermodynamics ground testing in high-enthalpy flow facilities is essential for the development and design of aerospace vehicles. It is a convenient step regarding the intensive cost of flight experiments. Moreover, these facilities also have a very practical use to assess the performance of materials, to determine their surface and in-depth pr...
Conference Paper
Unsteady effects impact the aerothermal performance of the turbine blade rows, originating noise, mechanical and thermal fatigue. Blade row interactions are due to the relative motion between nearby rows of airfoils, the periodic occurrence of flow distortions generated by the airfoil rows or combustors. The detailed characterization of the thermal...
Article
Binary scaling is a similitude law used to study the aerothermodynamics of hypersonic vehicles in ground-based high-enthalpy facilities. It enables the duplication of shock layer flows in the vicinity of the stagnation point, including binary chemistry and nonequilibrium processes, over length scales that are practical for experimental testing. It...
Conference Paper
Full-text available
The operation of the VKI Longshot hypersonic gun tunnel strongly depends on its compression process by which high-pressure and high-temperature gases are generated in the nozzle reservoir. The main part of this process takes place in a driven tube where a light supersonic piston compresses the test gas nearly adiabatically. In order to provide an e...
Conference Paper
Full-text available
Study on the definition of test conditions, based on the LHTS methodology, for QARMAN full-scale test in CIRA’s SCIROCCO PWT.
Article
Full-text available
3D Carbon-fiber reinforced carbon composites (3D ) are widely used as thermostructural protections in various applications. Among them, thermal protection systems for atmospheric re-entry encounter one of the most aggressive environments, where 3D are exposed to strong ablation. Because flight tests are extremely expensive, Inductively Coupled Plas...
Article
Atomic recombination is an important process to consider when computing the heat flux transferred to the wall of a re-entry vehicle. Two chemical processes are influencing the species diffusion in the boundary layer surrounding a re-usable Thermal Protection System: gas phase reactions and catalytic recombination at the surface. The coupling betwee...
Article
The capability for CFD prediction of hypersonic shock wave laminar boundary layer interaction was assessed for a double wedge model at Mach 7.1 in air and nitrogen at 2.1. MJ/kg and 8. MJ/kg. Simulations were performed by seven research organizations encompassing both Navier-Stokes and Direct Simulation Monte Carlo (DSMC) methods as part of the NAT...
Conference Paper
In re-entry, spacecrafts require a Thermal Protection System (TPS) to withstand severe heat flux conditions on the surface. The most critical thermal load is located at the stagnation point, becoming the TPS design reference. Nevertheless, the design can be improved at off-stagnation through a new extrapolation methodology that duplicates in high e...