Javier Urzay’s research while affiliated with United States Air Force Research Laboratory and other places

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Publications (57)


General Velocity-Altitude Flight-Regime Diagram for Aeronautics and Astronautics
  • Article

November 2024

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79 Reads

Journal of Spacecraft and Rockets

Javier Urzay




An integrated heterogeneous computing framework for ensemble simulations of laser-induced ignition
  • Preprint
  • File available

February 2022

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167 Reads

An integrated computational framework is introduced to study complex engineering systems through physics-based ensemble simulations on heterogeneous supercomputers. The framework is primarily designed for the quantitative assessment of laser-induced ignition in rocket engines. We develop and combine an implicit programming system, a compressible reacting flow solver, and a data generation/management strategy on a robust and portable platform. We systematically present this framework using test problems on a hybrid CPU/GPU machine. Efficiency, scalability, and accuracy of the solver are comprehensively assessed with canonical unit problems. Ensemble data management and autoencoding are demonstrated using a canonical diffusion flame case. Sensitivity analysis of the ignition of a turbulent, gaseous fuel jet is performed using a simplified, three-dimensional model combustor. Our approach unifies computer science, physics and engineering, and data science to realize a cross-disciplinary workflow. The framework is exascale-oriented and can be considered a benchmark for future computational science studies of real-world systems.

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The turbulent bubble break-up cascade. Part 2. Numerical simulations of breaking waves

April 2021

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153 Reads

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58 Citations

Journal of Fluid Mechanics

Breaking waves generate a distribution of bubble sizes that evolves over time. Knowledge of how this distribution evolves is of practical importance for maritime and climate studies. The analytical framework developed in Part 1 (Chan, Johnson & Moin, J. Fluid Mech., vol. 912, 2021, A42) examined how this evolution is governed by the bubble-mass flux from large- to small-bubble sizes which depends on the rate of break-up events and the distribution of child bubble sizes. These statistics are measured in Part 2 as ensemble-averaged functions of time by simulating ensembles of breaking waves, and identifying and tracking individual bubbles and their break-up events. The large-scale break-up dynamics is seen to be statistically unsteady, and two intervals with distinct characteristics were identified. In the first interval, the dissipation rate and bubble-mass flux are quasi-steady, and the theoretical analysis of Part 1 is supported by all observed statistics, including the expected −10/3 power-law exponent for the super-Hinze-scale size distribution. Strong locality is observed in the corresponding bubble-mass flux, supporting the presence of a super-Hinze-scale break-up cascade. In the second interval, the dissipation rate decays, and the bubble-mass flux increases as small- and intermediate-sized bubbles become more populous. This flux remains strongly local with cascade-like behaviour, but the dominant power-law exponent for the size distribution increases to −8/3 as small bubbles are also depleted more quickly. This suggests the emergence of different physical mechanisms during different phases of the breaking-wave evolution, although size-local break-up remains a dominant theme. Parts 1 and 2 present an analytical toolkit for population balance analysis in two-phase flows.


Figure 6. Wall-normal profiles of Favre-averaged molar fractions of (a) molecular nitrogen, (b) molecular oxygen, (c) nitric oxide, (d) atomic oxygen and (e) atomic nitrogen.
Figure 9. Wall-normal profiles of the r.m.s. of the Favre fluctuations of the molar fractions of (a) molecular nitrogen, (b) molecular oxygen, (c) nitric oxide, (d) atomic oxygen and (e) atomic nitrogen.
Direct numerical simulation of a hypersonic transitional boundary layer at suborbital enthalpies

February 2021

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361 Reads

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76 Citations

Journal of Fluid Mechanics

A Mach-10 hypersonic boundary layer of air overriding a cold, isothermal, non-catalytic flat wall, and with a stagnation enthalpy of 21.6 MJ kg −1 , is analysed using direct numerical simulations. The calculations include multicomponent transport, equilibrium vibrational excitation and chemical kinetics for air dissociation. The initially laminar boundary layer undergoes transition to turbulence by the resonance of a two-dimensional mode injected by a suction-and-blowing boundary condition imposed over a narrow spanwise porous strip. The ensuing turbulent boundary layer has a momentum Reynolds number of 3826 near the outflow of the computational domain. The relatively low temperature of the free stream renders the air chemically frozen there. However, the high temperatures generated within the boundary layer by viscous aerodynamic heating, peaking at a wall-normal distance y 10-20 in semi-local viscous units, lead to air dissociation in under-equilibrium amounts equivalent to 4 %-7 % on a molar basis of atomic oxygen, along with smaller concentrations of nitric oxide, which is mainly produced by the Zel'dovich mechanism, and of atomic nitrogen, the latter being mostly in steady state. A statistical analysis of the results is provided, including the streamwise evolution of (a) the skin friction coefficient and dimensionless wall heat flux; (b) the mean profiles of temperature, velocity, density, molar fractions, chemical production rates and chemical heat-release rate; (c) the Reynolds stresses and root-mean-squares of the fluctuations of temperature, density, pressure, molar fractions and chemical heat-release rate; and (d) the temperature/velocity and mass-fraction/velocity correlations.


Engineering aspects of hypersonic turbulent flows at suborbital enthalpies

January 2021

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2,477 Reads

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24 Citations


Transcritical diffuse-interface hydrodynamics of propellants in high-pressure combustors of chemical propulsion systems

January 2021

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126 Reads

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98 Citations

Progress in Energy and Combustion Science

Rocket engines and high-power new generations of gas-turbine jet engines and diesel engines oftentimes involve the injection of one or more reactants at subcritical temperatures into combustor environments at high pressures, and more particularly at pressures higher than those corresponding to the critical points of the individual components of the mixture, which typically range from 13 to 50 bars for most propellants. This class of trajectories in the thermodynamic space has been traditionally referred to as transcritical. However, the fundamental understanding of fuel atomization, vaporization, mixing, and combustion processes at such high pressures remains elusive. In particular, whereas fuel sprays are relatively well characterized at normal pressures, analyses of dispersion of fuel in high-pressure combustors are hindered by the limited experimental diagnostics and theoretical formulations available. The description of the thermodynamics of hydrocarbon-fueled mixtures employed in chemical propulsion systems is complex and involves mixing-induced phenomena, including an elevation of the critical point whereby the coexistence region of the mixture extends up to pressures much larger than the critical pressures of the individual components. As a result, interfaces subject to surface-tension forces may persist in multicomponent systems despite the high pressures, and may give rise to unexpected spray-like atomization dynamics that are otherwise absent in monocomponent systems above their critical point. In this article, the current understanding of this phenomenon is reviewed within the context of propulsion systems fueled by heavy hydrocarbons. Emphasis is made on analytical descriptions at mesoscopic scales of interest for computational fluid dynamics. In particular, a set of modifications of the constitutive laws in the Navier–Stokes equations for multicomponent flows, supplemented with a high-pressure equation of state and appropriate redefinitions of the thermodynamic potentials, are introduced in this work based on an extended version of the diffuse-interface theory of van der Waals. The resulting formulation involves revisited forms of the stress tensor and transport fluxes of heat and species, and enables a description of the mesoscopic volumetric effects induced by transcritical interfaces consistently with the thermodynamic phase diagram of the mixture at high pressures. Applications of the theory are illustrated in canonical problems, including dodecane/nitrogen transcritical interfaces in non-isothermal systems. The results indicate that a transcritical interface is formed between the propellant streams that persists downstream of the injection orifice over distances of the same order as the characteristic thermal-entrance length of the fuel stream. The transcritical interface vanishes at an edge that gives rise to a fully supercritical mixing layer.


Citations (38)


... One of the key points is that the strength and direction of the hydrodynamic ejection is determined by the laser energy deposition profile [12]. In their DNSs of indirect ignition of non-premixed shear layers, Wang et al. [13] further found that the kernel distance from the shear layer affects the ignition outcome. Therefore, with indirect ignition, the hydrodynamic jet ejection of hot gases generated from the plasma plays a critical role on ignition probability [10]. ...

Reference:

Large-Eddy Simulations of a Laser-Ignited Subscale Rocket Combustor: Modeling Strategies and Experimental Comparison
Laser-induced indirect ignition of non-premixed turbulent shear layers
  • Citing Article
  • June 2024

Combustion and Flame

... Energy exchange between these non-equilibrium internal degrees of freedom and the rotational-translational modes proves crucial not only for predicting heat fluxes but also for the evaluation of chemical production rates, with the effective vibrational excitation modulating the reaction rates through vibration-dissociation coupling. 59 For finite-rate thermochemical relaxation that proceeds on the advective timescale, namely Da ≃ 1, direct numerical solution of the relevant non-linear conservation laws generally proves necessary for characterizing the non-equilibrium flow physics [60][61][62] . ...

Navier-Stokes characteristic boundary conditions for high-enthalpy compressible flows in thermochemical non-equilibrium
  • Citing Article
  • April 2024

Journal of Computational Physics

... In case of the latter, the highfidelity solver (HiPSTAR, see section 2.1) can use multiple CPU cores via multi-core and multi-threading (hybrid OpenMP/MPI) to optimally utilize the otherwise-idle CPU cores. Such a copacking strategy has been reported previously in [5], where different fidelities were considered in terms of performing LESs via grid refinement and grid coarsening using the same source code compiled with the Legion runtime environment which handles the concurrent CPU/GPU execution internally [6]. The novelty of the present study is the employment of two fundamentally different source codes, respectively optimized for different fidelities, i.e. ...

An integrated heterogeneous computing framework for ensemble simulations of laser-induced ignition
  • Citing Conference Paper
  • June 2023

... We analyse various statistics related to entrained gas bubbles and liquid droplets formed through bubble collapse, such as their total counts, positions and size distributions. Nevertheless, computing these quantities is not trivial since the liquid-gas interface is captured implicitly with the help of the volume fraction field C. To detect bubbles and droplets, existing algorithms in the literature (Herrmann 2010;Chan et al. 2021;Gao et al. 2021) scan through the domain and first identify a grid point with C = 0 (for bubble detection) or 1 (for droplet detection). They then successively search for neighbouring grid points with the same value of C until the boundary of the bubble or droplet is detected. ...

The turbulent bubble break-up cascade. Part 2. Numerical simulations of breaking waves
  • Citing Article
  • April 2021

Journal of Fluid Mechanics

... This has led to an increased interest in scale-resolving studies of turbulent shock wave/boundary layer interactions [14][15][16][17] as well as hypersonic boundary layers with thermochemical effects. 10,15,18 In these studies, it is crucial to isolate the various thermo-physical flow phenomena involved in order to draw meaningful conclusions, as exemplified by Larsson et al. 19 Thus, while boundary layers play a key role in the aero-thermomechanical design of hypersonic vehicles and associated heat management, 20 the fundamental interaction between shock waves and turbulence also warrants analysis through isolated studies. ...

Direct numerical simulation of a hypersonic transitional boundary layer at suborbital enthalpies

Journal of Fluid Mechanics

... More sophisticated, nonlinear representations have been attempted with some success 33,34 . Conducting experiments in these conditions is generally impractical or impossible, because of the extreme thermodynamic conditions and huge amounts of electric power needed to operate highenthalpy wind tunnels 35 . On the other hand, numerical simulations are also very challenging, depending on the complexity of the thermochemical models in use, and on the range of physical space and time scales to be simulated. ...

Engineering aspects of hypersonic turbulent flows at suborbital enthalpies

... Considering VLE in real-fluid thermodynamics effectively eliminates the drawbacks of DG-based approaches for describing the two-phase region [6,9,10]. For example, as shown in Fig. 1, problems such as negative pressure values with non-physical compression during volume expansion as reported by Ma et al. [11], or non-physical anti-diffusion due to the negative derivative of fugacity of species relative to its mole fraction as reported by Jofre et al. [12], disappear via the phase-splitting calculations with the MT method. ...

Transcritical diffuse-interface hydrodynamics of propellants in high-pressure combustors of chemical propulsion systems
  • Citing Article
  • January 2021

Progress in Energy and Combustion Science

... In modern aerospace engineering, thin-walled structures often serve in a harsh temperature field because of the aerodynamic heating of high-speed aircraft [1][2][3][4]. The combination of the thermal stress and compressive load leads to a complex thermoelastic response for the lightweight panels, which are prone to buckling accompanied by obviously geometrical nonlinearities. ...

Shock-induced heating and transition to turbulence in a hypersonic boundary layer

Journal of Fluid Mechanics

... The implementation of the proposed models and numerical schemes was completed in the highly parallel Hypersonic Task-based Regent (HTR) solver [92,93,94]. HTR is a task-based solver built on the Legion runtime which provides portability to run distributed simulations on both CPUs and GPUs [95]. ...

HTR solver: An open-source exascale-oriented task-based multi-GPU high-order code for hypersonic aerothermodynamics
  • Citing Article
  • March 2020

Computer Physics Communications

... The electrostaticenhanced deposition of small-inertia particles is also confirmed by later direct numerical simulations, where a comprehensive numerical framework is proposed to calculate both PP and PW interactions acting on each particle (Yao & Capecelatro 2021). Meanwhile, when studying the wall-normal accumulation of identically charged particles, Di Renzo et al. (2019) suggest that it is the collective self-induced electric force (i.e. the PP repulsion) that drives particles towards the wall. And in the later work by Zhang et al. (2023a) that studies the behaviour of bidispersed oppositely charged particles, the PP attraction between different particle groups was found to be essential in determining the wall-normal particle distribution compared with the monodispersed case. ...

Mitigation of turbophoresis in particle-laden turbulent channel flows by using incident electric fields

Physical Review Fluids