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Hypersonic laminar flow past a compression corner has been numerically investigated using time-accurate computational fluid dynamics (CFD) approach. Two flow conditions were considered relevant to high and low enthalpy conditions with a total specific enthalpy of 19MJ/kg and 2·8MJ/kg. The Mach number and unit Reynolds number per metre were 7·5, 9·1 and 3·10 × 105 and 32·2 × 105 respectively. These free stream conditions provided attached, incipiently separated and fully separated flows for ramp angles between θw = 5° to 24°. A grid independence study has been carried out to estimate the sensitivity of heat flux and skin friction in the strong interaction regions of the flow. The investigation was carried out assuming the flow to be laminar throughout and high temperature effects such as thermal and chemical nonequilibrium are studied using Park’s two temperature model with finite rate chemistry. A critical comparison has been made with existing steady state computational and experimental data and the study has highlighted the importance of high temperature effects on the flow separation and reattachment.
Hypersonic, high-enthalpy flow over a rearward-facing step has been numerically investigated using computational fluid dynamics (CFD). Two conditions relevant to suborbital and superorbital flow with total specific enthalpies of and , are considered. The Mach number and unit Reynolds number per metre were 7.6, 11.0 and , respectively. The Reynolds number based on the step height was correspondingly and . The computations were carried out assuming the flow to be laminar throughout and the real gas effects such as thermal and chemical non-equilibrium are studied using Park’s two-temperature model with finite-rate chemistry and Gupta’s finite-rate chemistry models. In the close vicinity of the step, detailed quantification of flow features is emphasised. In particular, the presence of the Goldstein singularity at the lip and separation on the face of the step have been elucidated. Within the separated region and downstream of reattachment, the influence of real gas effects has been identified and shown to be negligible. The numerical results are compared with the available experimental data of surface heat flux downstream of the step and reasonable agreement is shown up to 30 step heights downstream.
Burn rates of various nano-energetic composites were measured by two techniques; on-chip method and conventional optical method. A comparison is presented to confirm the validity of on-chip method. On-chip initiators were prepared using platinum heater films and nanoenergetic composites. Thin film Pt heaters were fabricated with different dimensions and ignition delay was studied using a nano-energetic composite of CuO nano-rods and Al-nano-particles. The ignition delay as a function of electrical power is presented for the same energetic composite. Heater with smaller surface area is found to be more efficient, which may be due to the lower heat losses.
Current approaches of mixing fuel and oxidizer nanoparticles or adding fuel nanoparticles to oxidizer gel lead to an overall reduced interfacial area of contact between them and thus, limit their burn rates severely. We have developed an approach of self-assembling fuel nanoparticles around an oxidizer matrix using a monofunctional polymer, poly(4)-vinyl pyridine (P4VP). The polymer has been used to accomplish binding of fuel and oxidizer in a molecularly engineered manner. We use composite of Al-nanoparticles and CuO nanorods for executing this self-assembly. TEM images of this composite confirms the self-assembly of Al-nanoparticles around the oxidizer nanorods. The burn rate of self-assembled composite has been found significantly higher than that of the composite prepared by simple mixing.
The optical degradation of polysilane copolymer has been studied in spin cast thin films and solutions using light source of 325 nm wavelength. The room temperature photoluminescence (PL) spectrum of these films show a sharp emission at 368 nm when excited with a source of 325 nm. However, the PL intensity deteriorates with time upon light exposure. Further the causes of this degradation have been examined by characterizing the material for its transmission behaviour and changes occurring in molecular weight as analysed by GPC data.
Tungsten silicide (WSix) films, deposited by chemical vapour deposition are normally amorphous in nature, and need to be annealed at high temperature to obtain low resistivity required for interconnections and metallization layers in VLSI circuits. In this paper, we focus on this annealing process for films deposited on Si and SiO2 substrate, and having Si/W ratio of 2.4. The characterization methods used were time-resolved X-ray diffraction, Resistivity measurement, and Rutherford backscattering spectroscopy analysis. We observe that 30 minutes is not sufficient for complete transformation of the WSi2.4 films on Si substrate. We also report on the dependence of annealing behaviour of nonstoichiometric WSixfilm on the substrate type.
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