Computational Investigation of Lightning Strike Effects on Aircraft Components

A lightning strike to the aircraft seriously affects the aircraft and its components in various ways. As one of the most critical threats to the flight safety of an aircraft, fuel vapour ignition by lightning can occur through various means, notably through hot spot formation on the fuel tank skins. In this study, a coupled thermal-electrical approach using the commercial software ABAQUS is used to study the effects of a lightning strike on aircraft fuel tanks. This approach assumes that the electrical conductivity of a material depends on temperature, and that a temperature rise in a material due to Joule heat generation depends on electrical current. The inter-dependence of thermal and electrical properties-the thermal-electrical coupling-is analyzed by a coupled thermal-electrical analysis module. The analysis elucidates the effects of different material properties and thicknesses of tank skins and identifies the worst case of lightning zones

4-(4-Chlorophenyl)-1,2,3-selenadiazole

In the title compound, C8H5ClN2Se, the dihedral angle between the planes of the selenadiazole and chlorophenyl rings is 16.6 (2)°. In the crystal, the packing of the molecules is consolidated by weak C—H...N hydrogen bonds, which generate [001] chains, and π–π stacking interactions are observed between the phenyl and selenadiazole rings, with a centroid–centroid distance of 3.884 (2) Å. There is also a short Se...Cl contact of 3.468 (1) 

Carbon ablation in hypervelocity air and nitrogen shock layers

Experiments studying carbon ablation were performed with electrically heated graphite strips embedded into a steel base structure. The test articles were exposed to hypervelocity air and nitrogen flows to investigate a previously proposed coupling effect of surface carbon monoxide production on the levels of cyanogen via gas phase reactions. Based on the relative levels of cyanogen emissions between the two conditions, it was concluded that, although carbon monoxide interactions were a nonnegligible contributor to cyanogen production, the majority was due to direct surface nitridation. In terms of overall trends, the nitrogen condition results showed continually increasing cyanogen emissions with surface temperature. For air, cyanogen emissions reduced with the temperature above 2500 K, which was consistent with the previous experiments in air. The combination of these observations suggested that the oxidationrate decreased above 2500K.This phenomenoniswell known, butithas not previously been observed for an ablating body with the additional influence of a realistic hypervelocity shock layer. High-speed video recordings for these experiments allowed observationofspallation phenomenain much greater detail than for previous work.Itwas clearly seen that spallation can significantly alter the flowfield, and it is a phenomenon that must be given greater consideration in future studies

High frame rate emission spectroscopy for ablation tests in plasma wind tunnel

This article describes a novel high frame rate emission spectroscopy setup developed for measurements in high enthalpy flow fields. The optical setup and the associated hardware arrangements are described in detail followed by test case data to demonstrate the capability of recording spectral images at 1 kHz frame rate. The new system is based on a classical Czerny-Turner spectrograph but with a particular setup for high frame rate detection using a Generation II intensifier coupled with a high-speed camera. The high frame rate spectral images acquired enable, for the first time, investigation of the spatial distribution and temporal tracking and evolution of molten droplets of an ablating sample. In this paper, an example is shown from ablating meteorite samples tested in a high enthalpy plasma flow field corresponding to a flight scenario at an altitude of 80 km. This new instrumental configuration allows emission spectroscopic analysis of transient phenomena simulated in the high enthalpy ground test facilities with kHz resolution. The particular feature of this system is the ability to measure very faint spectral lines at high temporal and spatial resolution

Filtered image thermography for high temperatures in hypersonic preheated ablation experiments

Thermography for measuring high temperatures, ranging from 1000 to 2900 K, in hypersonic preheated ablation experiments is demonstrated in this work. Filtered images at different wavelengths were acquired to obtain temperature maps by two methods: dual-wavelength signal ratio and multiwavelength Planck fit. This technique was applied for temperature measurements of resistively heated graphite ablators used in ablation experiments performed in the X2 super-orbital expansion tube at The University of Queensland, Australia. Six different narrow band pass filters with center wavelengths of 450, 500, 600, 700, 800, and 900 nm housed in a motorized filter wheel, coupled to a camera, were used in this work. The dual-wavelength method involves acquiring optical images of the target with two different optical filters, and the signal ratio between those two images was used to calculate the temperature map. The multiwavelength method uses more than two filtered images, from the signals of which a temperature map was directly obtained. This technique, being a noncontact, nonintrusive method without any instrumentation on the models, has proven to be very useful for hypersonic ablation experiments

An open carbon–phenolic ablator for scientific exploration

Abstract Space exploration missions rely on ablative heat shields for the thermal protection of spacecraft during atmospheric entry flights. While dedicated research is needed for future missions, the scientific community has limited access to ablative materials typically used in aerospace. In this paper, we report the development of the HEFDiG Ablation-Research Laboratory Experiment Material (HARLEM), a carbon–phenolic ablator designed to supply the need for ablative materials in laboratory experiments. HARLEM is manufactured using polyacrylonitrile-based carbon fiber preforms and a simplified processing route for phenolic impregnation. We characterized the thermal protection performance of HARLEM in arcjet experiments conducted in the plasma wind tunnel PWK1 of the Institute of Space Systems at the University of Stuttgart. We assessed the performance of the new material by measuring surface recession rate and temperature using photogrammetry and thermography setups during the experiments, respectively. Our results show that HARLEM’s thermal protection performance is comparable to legacy carbon–phenolic ablators that have been validated in different arcjet facilities or in-flight, as demonstrated by calculations of the effective heat of ablation and scanning electron microscopy of as-produced samples. In-house manufacturing of carbon–phenolic ablators enables the addition of embedded diagnostics to ablators, allowing for the acquisition of data on internal pressure and more sophisticated pyrolysis analysis techniques

Aperçu du projet MetSpec - météores artificiels en test au sol

International audienceWe provide an overview of the MetSpec project, which aims to connect meteorite ablation laboratory experiments with meteor spectral observations in the atmosphere aiming at the development of a methodology to identify incoming planetary material distribution into the Earth’s atmosphere. We have selected 28 meteorites of different types to represent known planetary material compositions coming from asteroids, Vesta, Mars and the Moon. Some samples have been tested twice which resulted in overall 31 experiments. Three distinct test campaigns were realized in 2020, 2021 and 2022 with the High Enthalpy Flow Diagnostics Group in the Plasma Wind Tunnel PWK1 where they have developed a unique testing scenario. During the last and most elaborated campaign, 16 cameras observed the artificial meteors in the laboratory. Besides videos and online live streaming, instruments included several spectrometers, and optical and imaging instruments covering UV, visible and IR spectral range. This special collection in Icarus collects the resulting output from the different instruments and results. This overview article provides an introduction and summarizes the main findings of the experimental campaigns.Nous présentons une vue d'ensemble du projet MetSpec, qui vise à relier les expériences d'ablation de météorites en laboratoire aux observations spectrales de météorites dans l'atmosphère, dans le but de développer une méthodologie permettant d'identifier la distribution des matériaux planétaires entrants dans l'atmosphère terrestre. Nous avons sélectionné 28 météorites de différents types pour représenter les compositions connues de matériaux planétaires provenant d'astéroïdes, de Vesta, de Mars et de la Lune. Certains échantillons ont été testés deux fois, ce qui a donné lieu à 31 expériences au total. Trois campagnes d'essais distinctes ont été réalisées en 2020, 2021 et 2022 avec le High Enthalpy Flow Diagnostics Group dans la soufflerie à plasma PWK1, où ils ont développé un scénario d'essai unique. Au cours de la dernière campagne, la plus élaborée, 16 caméras ont observé les météores artificiels dans le laboratoire. Outre les vidéos et la diffusion en direct, les instruments comprenaient plusieurs spectromètres et des instruments optiques et d'imagerie couvrant les gammes spectrales de l'UV, du visible et de l'IR. Cette collection spéciale d'Icarus rassemble les résultats obtenus par les différents instruments. Cet article présente une introduction et résume les principaux résultats des campagnes expérimentales