Spallation is the mostly undesirable phenomenon where solid particles are ejected from ablative materials leaving less mass to be decomposed at the ablator surface. The exact mechanisms and conditions that promote spallation as well as the extent of it are unclear to this date. This paper presents the results of an extensive test campaign targeted at measuring spallation of carbonaceous ablator materials in an arc heated air flow of [Formula: see text]. The employed diagnostic methods are photogrammetric surface measurements, high-speed imaging, thermography, and two-color-ratio pyrometry using the raw digital single-lens reflex camera images from the photogrammetry setup. Data from the high-speed camera show a much higher spallation rate for the carbon preform Calcarb than for carbon-phenolic ablators. Temperature measurements show a difference of up to 300 K between carbon fibers and surrounding matrix. The pyrolysis gas from the phenolic resin is found to decrease the spallation rate of the carbon-phenolic ablator ZURAM compared to Calcarb, and the pyrolysis gas pressure slightly increases the distance that particles travel upstream after ejection from the front surface.

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 couplingis 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.

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Atmospheric entry of spacecraft is an interesting and challenging problem in aerospace engineering as it involves a highly non-equilibrium aerothermodynamic shock layer environment. Re-entry of spacecraft into Earth's atmosphere occurs at very high entry speeds ranging from 8-12 km · s −1 , giving rise to a bow shock wave in front of the blunt body vehicle. The associated shock layer is characterised by a very rapid increase in pressure and temperature. The kinetic energy of the hypervelocity flow is converted into thermal and chemical energy, which is partially dissipated in the form of convective and radiative heat transfer. The gases traversing the shock layer undergo thermochemical changes such as dissociation, ionisation and recombination. To safeguard the re-entry vehicle from such a harsh thermal environment, a thermal protection system (TPS) is employed on the surface of the vehicle. The TPS material, when exposed to the re-entry heating, may undergo ablation due to the combined effect of heat flux and shear from the shock layer flow. The excited gas species in the shock and boundary layer react with the atomic/molecular species ablated from the solid TPS material. However, due to the uncertainties associated with the total heat flux estimation, large safety factors are currently being used in the TPS design, particularly for the afterbody region, compromising the payload mass and vehicle safety.The main objectives of this thesis were to experimentally simulate ablation product interactions with an expanding re-entry flowfield, to characterise the radiation of the entrained ablation products using ultra-violet emission spectroscopy targeting CN radicals, and to compare the ablating flowfields with non-ablating ones. The experiments were performed in the X2 expansion tube by using a stainless steel wedge model designed with a provision to mount a graphite ablation source on its compression face. The test flow condition, representative of a point in the Hayabusa capsule re-entry trajectory, was generated in X2 with a freestream velocity of 8.6 km · s −1 and a temperature of 2500 K, corresponding to an enthalpy of 38 MJ · kg −1 . As the test times available in X2 are limited, the ablating material cannot reach such wall temperatures by aero heating alone, and hence ablation in these experiments was created by electrically preheating the graphite strip to high wall temperatures representative of re-entry conditions. The wall temperatures realised in this work ranges from 1000-3000 K, which were measured by nonintrusive filtered image thermography using a dual-wavelength signal ratio technique. The hot graphite strip, upon exposure to the re-entry flow, ablates and mixes with the flow, and passes through the expansion fan and further into the afterbody region.The flowfield and interaction processes were optically diagnosed using a high frame rate video camera, two-dimensional filtered imaging and UV emission spectroscopy. CN emission measurements were made at various locations in the flowfield such as the fore...

Accumulation of senescent cells contributes to age related diseases including idiopathic pulmonary fibrosis (IPF). Insulin-like growth factor binding proteins (IGFBPs) are evolutionarily conserved proteins that play a vital role in many biological processes. Overall, little is known about the functions of IGFBP2 in the epigenetic regulation of cellular senescence and pulmonary fibrosis. Here, we show that Igfbp2 expression was significantly downregulated at both mRNA and protein levels in a low-dose bleomycin-induced pulmonary fibrosis model of aged mice. Using the reduced representation of bisulfite sequencing technique, we demonstrated Igfbp2 downregulation is attributed to DNA methylation of CpG islands in fibrotic lungs of aged mice. Furthermore, Igfbp2 siRNA knockdown increased both P53 and P21 protein levels in mouse lung epithelial cells exposed to hypoxia treatment. Lentiviral mediated expression of Igfb2 decreased P21 protein levels and significantly reduced beta galactosidase activity in mouse lung epithelial cells challenged with a senescent drug (atazanavir) and hypoxia treatments. Using the RT2 Profiler PCR Array, we found that P21, PAI-1, IRF-5 and IRF-7, important regulators of senescence pathway, were significantly downregulated specifically in type-II alveolar epithelial cells (AECs) of aged human-Igfbp2 transgenic mice after bleomycin challenge. Finally, transgenic expression of human-Igfbp2 in type-II AECs from aged bleomycin challenged mice significantly decreased senescent associated secretory phenotype factors and also reduced extracellular matrix markers compared to aged wild-type mice challenged with bleomycin injury. Collectively, these findings reveal that epigenetic repression of Igfbp2 promotes pulmonary fibrosis and that restoring IGFBP2 in fibrotic lungs could prove effective in IPF treatment.