Javier Urzay's research while affiliated with Stanford University and other places

... Thermochemistry is firmly rooted in the study of combustion problems, high-speed flows, reactive and non-reactive shocks, rocket engine performance, and high explosives [41,42]. For instance, strong hypersonic shocks involve changes in the molecular structure of the gas, including vibrational excitation leading to dissociation [43,44], and later electronic excitation leading to ionization [45], which eventually transform the gas into a plasma. Turbulent combustion and gaseous detonations have also been the topic of intense research due to their high thermodynamic efficiency in propulsion applications [46,47]. ...

... Some studies using Direct Numerical Simulations (DNS) were able to model every turbulent scale and each bubble individually for small domains and low Reynolds numbers [29][30][31][32], but this type of approach is unfeasible for most practical applications [21]. A technique that has been gaining popularity in the last few years consists in using the interface-capturing/tracking algorithm to track only the largest pockets of air. ...

... Turbulent combustion and gaseous detonations have also been the topic of intense research due to their high thermodynamic efficiency in propulsion applications [46,47]. But they often exhibit strong deviations from equilibrium due to the wide range of length and time scales involved, making it necessary to rely on complex fluid dynamical analyses and numerical simulations with a high computational cost [48,49]. Despite the deep understanding provided by the latter approach, there are still cases in which a proper physical explanation can not be found based only on numerical results. ...

... being = 1/3 the recovery factor [Zhang et al., 2018], where is the Prandtl number. However, in hypersonic boundary layers, the recovery temperatures are so high that the wall temperature is usually lower [Urzay and Di Renzo, 2021], generating large heat fluxes to the wall. This affects the flow dynamics in concurrency with the Mach number, enriching the physical effects that have to be accounted for when developing theoretical relations and reduced order models. ...

... In so-called transcritical conditions, flows operate in virtually multi-phase conditions, i.e., there is coexistence of both gas-like and liquid-like states. However, unlike subcritical two-phase flow, single-component transcritical flows are always in the continuous regime, as a consequence of the small Knudsen numbers (Kn ≪ 1) resulting from small mean free paths at high pressures [2,3]. Trans-and supercritical fluids are relevant in many engineering applications, including internal-combustion and rocket engines, among others. ...

... The shock-induced separated flow can support various local and global flow instabilities (Robinet 2007;Egorov, Neiland & Shvedchenko 2011;Guiho, Alizard & Robinet 2016;Sansica, Sandham & Hu 2016;Bugeat et al. 2022) that may lead to unsteadiness and a laminar-turbulent transition. Experiments and direct numerical simulations (DNSs) with many canonical configurations (Chapman, Kuehn & Larson 1958;Ginoux 1960;Simeonides & Haase 1995;Benay et al. 2006;Willems, Gülhan & Steelant 2015;Roghelia et al. 2017;Currao et al. 2020;Fu et al. 2021) have shown that strong interactions can promote the laminar-turbulent transition near flow reattachment, which is frequently accompanied by streamwise streaks in the reattached boundary layer. These instabilities can also be understood by examining the spectrum of the linearised Navier-Stokes operator. ...

... The resulting system of ordinary differential equations is integrated in time using a third order strong stability preserving Runge-Kutta scheme [55]. The calculations presented in this work are carried out with the described numerical procedure in the Hypersonic Task-based Research (HTR) solver [56][57][58]. The HTR solver leverages the runtime Legion [59][60][61] and the programming language Regent [62] to execute the described calculations on high-performance supercomputers with heterogeneous architectures. ...

... Despite significant advances in the last 30 years from experiments and simulations, numerical and theoretical models of multiphase flows are still not suitable for predictive capabilities in many realistic applications. Current state-of-the-art point-particle Lagrangian models coupled with an Eulerian flow description can be used to simulate thousands to millions of particles at the expense of computational power [15], [16], [17], but these numbers are still far from practical real-life situations involving billions or trillions of particles [18], [19]. In addition, the fidelity of those simulations depends on the range of particle-fluid nondimensional parameters that dominate the two-way coupled interactions being modeled. ...

... Similar to the work described by Chan et al. (2018Chan et al. ( , 2019Chan et al. ( , 2021c, an ensemble of numerical simulations of breaking waves was generated to obtain the desired statistics. Details of the simulation parameters may be found in the aforementioned references. ...

... Improved particle statistics are observed with models that apply a deconvolution op-erator on the LES velocity field [24][25][26], but these models merely modify the velocity field on the LES grid and do not augment the range of modeled scales. Bassenne et al. [27] combine the dynamical deconvolution of Park et al. [26] with the subgrid extrapolation of Domaradzki and Loh [9] and obtain realistic particle clustering with LES of homogeneous isotropic turbulence (HIT) and for a wide range of Stokes numbers. The high computational cost, originating from a divergence-free projection on a very fine grid make, this model unsuitable for LES. ...