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This study explores the efficiency of employing a particle-spray cloud to mitigate shock wave propagation, which is essential in various industrial applications, especially in preventing potential hydrogen explosions within nuclear reactor containment buildings. Numerical simulations, primarily in one- and two-dimensional configurations, are utilized to examine the interaction between shock waves and a cloud of polydisperse particles, considering both air and hydrogen–air mixtures as carrier gases. A novel reduced-order theoretical model is developed to analyze the dispersion pattern of polydisperse particles, with validation conducted through direct numerical simulations. Results demonstrate that the polydispersion of cloud particles significantly reduces shock wave propagation compared to monodisperse particles. Notably, particles with smaller diameters and higher standard deviations (σ) show increased attenuation effects. Additionally, scenarios with higher particle volume fractions ( τ v , 0 ) contribute to enhanced shock wave attenuation. A critical incident Mach number is identified, indicating a significant change in shock wave transmission from supersonic to subsonic when M s < 2.8. [ABSTRACT FROM AUTHOR]

This work studies the development of a thermal boundary layer during the laminar-to-turbulent transition process over a concave surface. Direct numerical simulations are performed where the temperature variable is treated as a passive scalar. The laminar flow is perturbed with wall-roughness elements that are able to produce centrifugal instabilities in the form of Görtler vortices with a maximum growth rate. It is found that Görtler vortices are able to greatly modify the surface heat-transfer by generating a spanwise periodic distribution of temperature. Similar to the Görtler momentum boundary layer, elongated mushroom-like structures of low-temperature are generated in the upwash region, whereas in the downwash region, the thermal boundary layer is compressed. Consequently, temperature gradients are increased and decreased in the downwash and upwash regions, respectively, thereby generating an overall enhancement of the heat-transfer rate of ∼400% for the investigated Prandtl numbers (Pr = 0.72, Pr = 1, and Pr = 7.07). This enhancement surpasses the turbulent heat-transfer values during the transitional region, characterized by the development of secondary instabilities. However, downstream, the heat-transfer rate decays to the typical turbulent values. Streamwise evolution of several thermal quantities such as temperature wall-normal distribution, thermal boundary layer thickness, and Stanton number is reported in different regions encountered in the transition process, namely, linear, nonlinear, transition, and fully turbulent regions. These quantities are reported locally at upwash and downwash regions, where they present minima and maxima, as well as globally as spanwise-averaged quantities. Furthermore, it is found that the Reynolds analogy between streamwise-momentum and heat-transfer holds true throughout the whole transition process for the Pr = 1 case. Moreover, the turbulent thermal boundary layer over a concave surface is analyzed in detail for the first time. The viscous sub-layer and the log-law region are described for each investigated Pr. Besides, the root-mean-squared temperature fluctuations are computed, finding that its wall-normal distribution exhibits a higher peak when Pr is increased. [ABSTRACT FROM AUTHOR]

This work reports a numerical investigation of shock focusing phenomena over concave surfaces. The study focuses on the effects of Reynolds and Mach numbers on the detailed behavior of flow features related to shear-layer instabilities and jet formation in the post-shock region. Computations are done for four incident-shock Mach numbers covering subsonic and transonic flow regimes and a wide range of Reynolds numbers. The simulations reveal a number of interesting wave features starting from early stage of shock interaction and transition from inverse-Mach reflection to transitioned regular reflection followed by very complex flow patterns at focusing and post focusing stages. Different subsequent flow characteristics develop as a result of multiple shock/shear layer interactions. During the later stage of the flow interaction, a formation of two opposing jets is predicted by the simulation in accordance with the experiments. It is shown that the formation of primary opposing jets as well as the development of Kelvin-Helmholtz instabilities can be hindered for low Mach and Reynolds numbers. However, for high flow regimes a second pair of opposing jets appears and develops far from the wall, exhibiting similar features as the primary pair of opposing jets at moderate Mach numbers. Two new bifurcations in flow patterns are observed at this stage which promote further development of vortex structures and shear-layer rollup. [ABSTRACT FROM AUTHOR]