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[en] This paper presents a new idea to produce matter in the high energy density physics (HEDP) regime in the laboratory using an intense ion beam. A gas bubble created inside a solid metal may collapse by driving it with an intense ion beam. The melted metal will compress the gas bubble and supply extra energy to it. Simulations show that the spherical implosion ratio can be about 5 and at the stagnation point, the maximum density, temperature and pressure inside the gas bubble can go up to nearly 2 times solid density, 10 eV and a few megabar (Mbar) respectively. The proposed experiment is the first to permit access into the Mbar regime with existing or near-term ion facilities, and opens up possibilities for new physics gained through careful comparisons of simulations with measurements of quantities like stagnation radius, peak temperature and peak pressure at the metal wall.
[en] Heat transfer in the stagnation point area of a heated cylinder is investigated using Direct Numerical Simulation (DNS). The heated cylinder is subjected to the turbulent wake of a smaller cylinder placed upstream. Two Reynolds numbers based on the diameter of the heated cylinder of 13,200 and 48,000 are chosen. In accordance with correlations in the literature, an increase in heat transfer compared to fully laminar flow is found for all angles along the front circumferential area of the heated cylinder. However, due to the presence of the wake, the maximum increase is shifted away from the centerline. The characteristic turbulence level and Nusselt number in the present study are an order of magnitude higher than those reported in previous simulations. The DNS results obtained, are in good agreement with an existing experimental correlation. Finally, relevant flow structures and instantaneous temperature fields are visualized.
[en] The characteristics of the flow field around a square prism containing a small triangular prism upstream were investigated by measuring lift and drag and visualizing the flow field through particle image velocimetry. Experimental parameters included triangular prism-to square prism width ratio (H/B, H and B are side lengths of the triangular and square prisms, respectively) and triangular prism-to-square prism gap ratio (G/B, G is the gap distance between the triangular and square prisms). The drag reduction rate of the square prism increased and then decreased with increasing G/B at a constant H/B but increased with increasing H/B at a constant G/B. The maximum drag reduction rate was 78.5% at H/B = 0.6 and G/B = 1.5. The width and gap ratios also minimally affected the lift reduction rate of the square prism, with an average value of 52.4%. Stagnation regions were further observed upstream and downstream of the square prism.
[en] Starting from an exact solution of the dissipative MHD equations for a magnetic neutral layer with intrinsic stagnation point flow a normal magnetic field component is introduced as a perturbation. The resulting set of coupled ordinary differential equations is solved numerically and the behaviour of the perturbed quantities with distance from the neutral layer is presented and discussed. (author). 3 refs.; 5 figs
[en] The stagnation dynamics of a cathode-directed streamer discharge in two-dimensional geometry has been studied for the first time. It has been shown that as the streamer decelerates the radius of the streamer head decreases more rapidly than its potential, which, in turn, leads to an increase in the maximum electric field as well as an increase in the charged particle densities in the streamer head. (brief communication)
[en] Interaction between two parallel propagating plasma plumes have been investigated in two different ablation schemes e.g. laser-blow-off (LBO) of thin film and conventional laser ablation (LPP). Fast imagine technique is used to study the dynamical and geometrical aspect of seed plasmas and induced stagnation layer in between the two expanding seed plasmas. Interaction between the energetic particles, coming from the seed plasmas are responsible for formation of stagnation layer. It has been found that geometrical shape, size, kinetic energy and divergence of plasma plumes are highly dependent on the ablation geometry. These variations in seed plasmas initiate the significant differences in the stagnation layer formed by LBO and LPP geometry. In this presentation, characteristic feature of stagnation layer which includes density, initiation time, emissive life time and geometry in both LBO and LPP geometry are briefly discussed. A comparative study of present results suggests that the plume composition and directionality of seed plasma play crucial role in mechanistic aspect of stagnation layer. (author)
[en] Impinging jets have been used in a number of applications to enhance heat and mass transfer; this includes cooling steel plates, the tempering of glass, drying papers and films, cooling turbine blades, cooling electronic components, etc. Studies have included the effects of Reynolds number, nozzle-to-plate distance, nozzle geometry, jet temperature, orientation, multiple jets, crossflow, and impinging surface shape on the resulting flow and heat transfer. Critical reviews of impinging jet heat transfer studies have been published. Martin, Jambunathan et al., and Viskanta reviewed the heat transfer data for single jets and for arrays of axisymmetric and planar jets. Heat transfer measurements for various nozzle geometries and flow conditions have been made and studied the heat transfer characteristics for a turbulent air jet issuing from an elliptical nozzle
[en] Highlights: • An extended Henry–Fauske model was evaluated for developing critical flow maps. • Suggestion of critical flow maps for critical flow rate and pressure. • Critical flow maps useful for instructive guidelines in engineering and experiments. - Abstract: Critical flow maps were suggested for a critical mass flux and pressure of steam–water flow with respect to upstream stagnation conditions using an extended Henry–Fauske model. Most of selected test data were compared to the model and found that the model showed nearly conservative predictions with reasonable ranges. The suggested critical flow maps showed quite different trends in the vicinities of saturated liquid region compared to Moody’s homogeneous model. The critical flow maps can be used as instructive guides, especially for an understanding of the critical flow phenomena in steam–water flow and the application of engineering design and experiments
[en] In this paper, the problem of a steady laminar boundary layer flow of a an electrically conducting fluid in the presence of a magnetic field near the stagnation point with slip on a moving plate is studied. The transformed boundary layer equations are solved numerically using the shooting method. Numerical results are obtained for various values of the magnetic parameter M and the slip factor λ. The skin friction coefficients and the velocity profiles f'(η), g(η) and h(η) for various values of M and λ are obtained and discussed.
[en] We measured velocity distribution in cross sections of a fully developed turbulent pipe flow upstream and downstream of a 90 degree sign bend by synchronizing two sets of a particle image velocimetry (PIV) system. Unsteady undulation of Dean vortices formed downstream from the bend was characterized by the azimuthal position of the stagnation point found on the inner and outer sides of the bend. Linear stochastic estimation was applied to capture the upstream flow field conditioned by the azimuthal location of the stagnation point downstream from the bend. When the inner-side stagnation point stayed below (above) the symmetry plane, the conditional streamwise velocity upstream from the bend exhibited high-speed streaks extended in a quasi-streamwise direction on the outer side of the curvature above (below) the symmetry plane.