Hypersonic shock tunnel studies of Edney Type III and IV shock interactions

Of all the possible outcomes of the shock interaction problem, Edney Type-III and Type-IV are considered to be of great importance as they lead to high heat transfer rates on the surface in the vicinity of the interaction. The enhancement in heat transfer occurs because of shear layer attachment in Type III interaction and impingement of supersonic jet in Type-IV interaction. In this study, unsteady nature of these interactions is studied in conventional shock tunnel at moderate enthalpy condition of 1.07 Mj/kg at flow Mach number of 5.62. A hemispherical model, 50 mm in diameter, mounted with thin film Platinum gauges is used along with a 25 wedge to serve as a shock generator. The schlieren images are captured along with the surface convective heat transfer rate measurements for the analysis of flowfield over the model during the test time. The pixel intensity scan is performed along several lines running horizontally to estimate the steadiness of the flowfield. These are correlated with the heat transfer rate measurements to understand the non-steady nature of the interaction during the small test times offered by the shock tunnel. (C) 2017 Elsevier Masson SAS. All rights reserved

Spatially resolved solid-phase temperature characterization in a sillimanite tube furnace using a broadband two-color ratio pyrometry

Tube furnaces are heating devices used for the synthesis of inorganic and organic compounds. It is essential to predict the spatially resolved temperature of solid substances placed inside tube furnaces in contact with its walls for a fixed steady temperature of the furnace walls. This enables efficient study of transport phenomena and control of the fabrication process in the furnace. In this work, the two-color ratio pyrometry (TCRP) using a digital single lens reflex camera has been used for the temperature characterization of a stainless steel metal sheet placed at the center of a 1000 mm long tube furnace. Temperature was measured for furnace walls set between 1000 K and 1426 K. The TCRP technique accounted for intensity from the heated target over the broadband visible region. The camera was calibrated and tested for signal linearity in its color channels for a fixed source illumination. The technique yields a mean sheet temperature of 979.5 K +/- similar to 24% (attributed to camera noise and uncertainties in gray level intensity, calibration lamp output, and monochromator and photodetector efficiency) and 1391 K +/- 6.7% for a furnace wall temperature of 1000 K and 1426 K, respectively. Experiments showed that the effect of distance between the target and the camera on temperature measurement was negligible. Emission spectroscopy in the vis-near-infrared region (650-1100 nm) was also performed to predict sheet temperature. It yields results within 4.5% of TCRP at low furnace temperature but deviates by about 8.6% for temperatures above 1150 K, most likely due to experimental errors in spectroscopy. Analytical heat balance on the sheet, IR imaging, and numerical simulations yield temperatures within 5% of TCRP. This work shows that the TCRP technique can be used for spatially resolved temperature measurements of metals in tube furnaces and can readily be extended to ceramics or other class of solid materials whose emissivity can be shown to be invariant with wavelength in the visible region

Response of shock wave deformation in AA5086 aluminum alloy

The AA5086 aluminum alloy sheets with different starting textures were subjected to shock wave deformation with an input impulse of similar to 0.2 Ns. Microstructural examination indicate no significant change in grain size; however, the evolution of substructure manifesting intra-granular misorientation was evident. The improvement in hardness indicates the absence of recovery and strain hardening during shock deformation. Shock deformed samples show characteristic texture evolution with high Brass {110}< 112 > component. The study demonstrates the viability of high velocity forming of AA5086 aluminum alloy sheet using shock wave. (C) 2014 Elsevier B.V. All rights reserved

Temperature characterization of a radiating gas layer using digital-single-lens-reflex-camera-based two-color ratio pyrometry

The two-color ratio pyrometry technique using a digital single-lens reflex camera has been used to measure the time-averaged and path-integrated temperature distribution in the radiating shock layer in a high-enthalpy flow. A 70 mm diameter cylindrical body with a 70 mm long spike was placed in a hypersonic shock tunnel, and the region behind the shock layer was investigated. The systematic error due to contributions from line emissions was corrected by monitoring the emission spectrum from this region using a spectrometer. The relative contributions due to line emissions on R, G, and B channels of the camera were 7.4%, 2.2%, and 0.4%, respectively. The temperature contours obtained clearly distinguished regions of highest temperature. The maximum absolute temperature obtained in the experiment was similar to 2920 K +/- 55 K, which was 20% lower than the stagnation temperature. This lower value is expected due to line-of-sight integration, time averaging, and losses in the flow. Strategies to overcome these limitations are also suggested in the paper. (C) 2017 Optical Society of Americ

Time-resolved temperature characterization of a hypersonic shock layer using a single high-speed color camera for aerospace design applications

Two-color ratio pyrometry (TCRP) using a high-speed color camera has been used for temperature characterization of a hypersonic shock layer. The camera, used as a pyrometer, was calibrated in-house using a monochromator to determine its spectral responsivity and was used to acquire time-resolved images of the flow field over test models at a frame rate of 20 000 fps to understand the evolution of temperature inside the shock region. The optical efficiency of the monochromator and other optical equipment were determined separately and corrected for. Two test models, a flat-faced cylinder of diameter 70 mm and a hemisphere of diameter 80 mm, were used for the experiments to study the effect of geometry on the results. Experiments were performed in a free-piston-driven shock tunnel at a stagnation enthalpy of 5.2 MJ kg(-1). The average steady-state temperature in the stagnation region in the cylinder was about 3650 K +/- 3% (uncertainty in the shock layer due to camera noise), and for the hemisphere it was 3300 K +/- 6%. The resolved temperature was 14% higher than that obtained from a similar, but time-integrated, measurement obtained using a digital single lens reflex (DSLR) camera. Steady 2D numerical simulations were performed to reconstruct the 3D flow assuming azimuthal symmetry, and an algorithm was developed to use the shape of the temperature profile along the line-of-sight (LOS) derived from simulations to predict the actual stagnation-plane temperature from the experimental LOS-integrated TCRP-derived temperature. The actual temperature in the stagnation region on the vertical plane of symmetry (stagnation plane) for the cylinder and the hemisphere were higher by 2.76% and 1.77%, respectively, than the corresponding TCRP-derived LOS-integrated temperature. The results are promising for future use in determining intense temperature gradients and heat flux in the vicinity of space vehicles and for the design of efficient thermal protection systems

L'Auto-vélo : automobilisme, cyclisme, athlétisme, yachting, aérostation, escrime, hippisme / dir. Henri Desgranges

18 octobre 19091909/10/18 (A10,N3289)

Mahogany seed - a step forward in deciphering autorotation

This article presents an experimental approach for evaluating the various flight characteristics of a mahogany seed in its autorotative descent. Analytical formulae proposed by Yasuda and Azuma are used to interpret the results. The findings are used in the development of a sophisticated blade element computational model, primarily to analyse planar autorotating systems. This approximate computational approach is then used to predict the flight performance of mahogany seeds and the results are compared with experimental data. The potential use of the computational model in the design of autorotating systems is then brought to light

Mechanism of transformation in Mycobacteria using a novel shockwave assisted technique driven by in-situ generated oxyhydrogen

We present a novel method for shockwave-assisted bacterial transformation using a miniature oxyhydrogen detonation-driven shock tube. We have obtained transformation efficiencies of about 1.28 x 10(6), 1.7 x 10(6), 5 x 10(6), 1 x 10(5), 1 x 10(5) and 2 x 10(5) transformants/mu g of DNA for Escherichia coli, Salmonella Typhimurum, Pseudomonas aeruginosa, Mycobacterium smegmatis, Mycobacterium tuberculosis (Mtb) and Helicobacter pylori respectively using this method which are significantly higher than those obtained using conventional methods. Mtb is the most difficult bacteria to be transformed and hence their genetic modification is hampered due to their poor transformation efficiency. Experimental results show that longer steady time duration of the shockwave results in higher transformation efficiencies. Measurements of Young's modulus and rigidity of cell wall give a good understanding of the transformation mechanism and these results have been validated computationally. We describe the development of a novel shockwave device for efficient bacterial transformation in complex bacteria along with experimental evidence for understanding the transformation mechanism

Microstructural and crystallographic response of shock-loaded pure copper

Microstructural and crystallographic aspects of high-velocity forming or ``rapid'' forming of rolled sheets of pure copper have been investigated in this work. Significant changes in crystallographic orientation and microstructure were observed when thin (0.5 mm) metal sheets of annealed copper were subjected to high strain rate deformation in a conventional shock tube at a very low impulse magnitude (similar to 0.2 N s), which is inconceivable in conventional metal forming. Shock-loaded samples show characteristic texture evolution with a high brass {110} < 112 > component. A significant change in grain orientation spread was observed with increasing amount of effective strain without any drastic change in grain size. The texture after deformation was found to be strain-dependent. The path of texture evolution is dependent on the initial texture. Misorientation was limited to less than 5 degrees. Deformation bands and deformation twins were observed. There was a decrease in twin Sigma 3 coincidence site lattice (CSL)] boundary number fraction with increasing strain due to the change in twin boundary character to high-angle random boundary (HARB) as a result of dislocation pile up. The study shows the probability of a high-velocity shock wave forming pure Cu