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Introduction
Former researcher at Univ. Castilla-La Mancha (pre-doc) and Univ. of California-San Diego (post-doc), César is an associate tenured professor at Univ. Carlos III de Madrid that typically works on topics related to compressible fluid dynamics. From mostly theoretical frameworks, the research carried out is applicable to high-Mach-number Aerodynamics and Combustion, where shock/detonation-related physics is dominant, and to other problems associated to High-Energy-Density Physics.
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Position
- Professor (Associate)
Description
- Lecturer in: Engineering Fluid Mechanics, Compressible Fluid Dynamics, Hydraulic Turbomachinery, Combustion, Explosion Dynamics, Industrial Facilities I.
August 2013 - July 2015
May 2012 - June 2013
Publications
Publications (73)
The interaction between a weakly turbulent free stream and a hypersonic shock wave is investigated theoretically by using linear interaction analysis (LIA). The formulation is developed in the limit in which the thickness of the thermochemical nonequilibrium region downstream of the shock, where relaxation toward vibrational and chemical equilibriu...
We present a theoretical stability analysis for an expanding accretion shock that does not involve a rarefaction wave behind it. The dispersion equation that determines the eigenvalues of the problem and the explicit formulae for the corresponding eigenfunction profiles are presented for an arbitrary equation of state and finite-strength shocks. Fo...
Magnetized target fusion approach to inertial confinement fusion involves the formation of strong shocks that travel along a magnetized plasma. Shocks, which play a dominant role in thermalizing the upstream kinetic energy generated in the implosion stage, are seldom free from perturbations, and they wrinkle in response to upstream or downstream di...
We present a linear stability analysis of the Richtmyer-Meshkov instability that develops when a shock wave reaches a sinusoidally perturbed premixed flame from behind. In the hydrodynamic regime, when acoustic contributions dominate the flame growth rate, the problem is analytically addressed by the direct integration of the sound wave equations a...
Hypersonic flight involves a variety of complex flow phenomena that directly impact the aerothermodynamic loading of high-speed vehicles. The turbulence encountered during a typical flight trajectory influences and interacts with the shock waves on and around the surface of a vehicle and its propulsion system, affecting both aerodynamic and power p...
An asymptotic analysis of a planar combustion front in a condensed phase with an arbitrary temperature dependence of thermal conductivity has been carried out by the method of matched asymptotic expansions. The Zel'dovich number is used as a large parameter, and three expansion terms are obtained for the flame velocity. The asymptotic results are c...
First predicted by Richtmyer in 1960 and experimentally confirmed by Meshkov in 1969, the Richtmyer–Meshkov instability (RMI) is crucial in fields such as physics, astrophysics, inertial confinement fusion and high-energy-density physics. These disciplines often deal with strong shocks moving through condensed materials or high-pressure plasmas tha...
We use a two-dimensional particle-in-cell (PIC) simulation to study the propagation of subcritical fast magnetosonic shocks in electron-nitrogen plasma and their stability against an initial deformation. A slab of dense plasma launches two planar blast waves into a surrounding ambient plasma, which is permeated by a magnetic field that points out o...
The interaction of turbulence with shock waves significantly modulates the frequency and amplitude of hydrodynamic fluctuations encountered by aerospace vehicles in low-altitude hypersonic flight. In these high-speed flows, intrinsic compressibility effects emerge together with high-enthalpy phenomena in the form of internal-energy excitation. The...
We study with particle-in-cell (PIC) simulations the stability of fast magnetosonic shocks. They expand across a collisionless plasma and an orthogonal magnetic field that is aligned with one of the directions resolved by the 2D simulations. The shock speed is 1.6 times the fast magnetosonic speed when it enters a layer with a reduced density of mo...
We study with particle-in-cell (PIC) simulations the stability of fast magnetosonic shocks. They expand across a collisionless plasma and an orthogonal magnetic field that is aligned with one of the directions resolved by the 2D simulations. The shock speed is 1.6 times the fast magnetosonic speed when it enters a layer with a reduced density of mo...
The Combustion Toolbox (CT) is a newly developed open-source thermochemical code designed to solve problems involving chemical equilibrium for both gas- and condensed-phase species. The kernel of the code is based on the theoretical framework set forth by NASA’s computer program CEA (Chemical Equilibrium with Applications) while incorporating new a...
We present a theoretical and numerical stability analysis for a piston-driven planar shock against two-dimensional perturbations. The results agree with the well-established theory for isolated planar shocks: in the range of h c < h < 1 + 2M 2 , where h is the D'yakov-Kontorovich (DK) parameter related to the slope of the Rankine-Hugoniot curve, h...
The interaction between a weakly turbulent free stream of air and a hypersonic shock wave is investigated theoretically by using linear interaction analysis (LIA). The perturbation-free jump conditions across the shock are computed using Combustion Toolbox, an in-house thermochemical code capable of capturing high-temperature phenomena such as diss...
El interés por el desarrollo de armas hipersónicas está aumentando en los últimos años de forma notable. Las principales potencias mundiales han ensayado con éxito misiles hipersónicos de crucero, que, a diferencia de sus competidores directos (misiles balísticos o de crucero subsónico), ofrecen maniobrabilidad a velocidades que superan en un facto...
Se presenta un código termoquímico (en adelante Combustion Toolbox, CT) para el cálculo de problemas de combustión gaseosa con especies condensadas, choques reactivos y no reactivos, descomposición exotérmica de materiales energéticos y rendimiento teórico de cohetes. En particular, se exponen dos de los cuatro módulos que lo componen: CT-EXPLO y C...
The dynamic response of structural elements subjected to blast loading is a problem of growing interest in the field of defense and security. In this work, a novel computational tool for the rapid evaluation of the effects of explosions, hereafter referred to as SimEx, is presented and discussed. The classical correlations for the reference chemica...
The dynamic response of structural elements subjected to blast loading is a problem of growing interest in the field of defense and security. In this work, a novel computational tool for the rapid evaluation of the effects of explosions, hereafter referred as SimEx, is presented and discussed. The classical correlations for the reference chemical (...
Poster to be presented at The 1st Spanish Fluid Mechanics Conference (SFMC)
Despite the extensive literature accumulated since the pioneering works of D'yakov and Kontorovich in the 1950s, the stability of steady shocks is still an open question when realistic boundary conditions are accounted. The consideration of a supporting mechanism, which is indeed a necessary condition for shock steadiness, modifies the perturbation...
Slides of the talk "Development of an open-source thermochemical code. Fundamentals and application to shock turbulence interaction problems in the hypersonic regime", presented as part of the activities of the PhD Programme in Mechatronics Engineering of Universidad de Málaga (RD 99/2011).
In the range of $h_c<h<1+2 M_2$, where $h$ is the D'yakov-Kontorovich parameter, $h_c$ is its critical value corresponding to the onset of the spontaneous acoustic emission, and $M_2$ is the downstream Mach number, the classic analysis predicts a special form of the instability of isolated steady planar shock waves: non-decaying oscillations of sho...
Compressible mixtures in supersonic flows are subject to significant temperature changes via shock-waves and expansions, which affect several properties of the flow. Besides the widely-studied variable transport effects such as temperature-dependent viscosity and conductivity, vibrational and rotational molecular energy storage is also modified thr...
We propose a linear asymptotic theory to describe the propagation of planar detonation fronts through heterogeneous mixtures of reactive gases consisting of random fluctuations in the fuel mass fraction. The analysis starts with the derivation of the transfer functions that relate the upstream fuel-mass-fraction inhomogeneities with the burnt-gas p...
Un aspecto clave en el diseño de infraestructuras críticas es el análisis de su integridad estructural, así como la seguridad de las personas que las ocupan, frente a ataques terroristas con explosivos. La detonación de una carga explosiva origina una onda expansiva que se transmite por el aire y es la principal responsable de los daños estructural...
As firstly predicted by D'yakov and Kontorovich (DK), an initially disturbed shock front may exhibit different asymptotic behaviours depending on the slope of the Rankine-Hugoniot curve. Adiabatic and isolated planar shocks traveling steadily through ideal gases are stable, in the sense that any perturbation on the shock front decays in time with t...
D’Yakov–Kontorovich instability in planar reactive shocks – ERRATUM - Volume 884 - César Huete, Marcos Vera
The standard D’Yakov and Kontorovich (DK) instability occurs when a planar shock wave is perturbed and then oscillates with constant amplitude in the long-time regime. As a direct result, pressure perturbations generated directly behind the shock propagate downstream as non-evanescent sound waves, an effect known as spontaneous acoustic emission (S...
A simplified formulation, based on treating the ratio of the heat release to the postshock thermal enthalpy as a small parameter, accommodating arbitrary chemistry descriptions, is shown to reproduce computationally the same variety of phenomena as more complex formulations for oblique detonations with supersonic postshock flow. The resulting small...
In the context of core-collapse supernova explosions (CCSNe), the interaction of standing accretion shocks with upstream vorticity perturbations is investigated by linear theory analysis. The endothermic effect associated to the nuclear dissociation, which takes place right behind the shock wave, affects the amplitude of the perturbations amplified...
An oblique shock impinging on a shear layer that separates two uniform supersonic streams, of Mach numbers $M_{1}$ and $M_{2}$ , at an incident angle $\unicode[STIX]{x1D70E}_{i}$ can produce regular and irregular interactions with the interface. The region of existence of regular shock refractions with stable flow structures is delineated in the pa...
The standard D'yakov and Kontorovich (DK) instability refers to planar shock waves that, once perturbed, oscillate with constant amplitude in the long-time regime. For the DK-regime to be achieved, the slope of the Rankine-Hugoniot curve in the post-shock state must meet certain conditions, which have been usually related to non-ideal equations of...
In the context of core-collapse supernova explosions (CCSNe), the interaction of standing accretion shocks with upstream vorticity perturbations is investigated by linear theory analysis. The endothermic effect associated to the nuclear dissociation, which takes place right behind the shock wave, affects the amplitude of the perturbations amplified...
La respuesta dinámica de una estructura sometida a cargas explosivas es un problema de gran importancia en el ámbito de la Defensa y Seguridad. Entre las medidas de protección pasiva más utilizadas en la actualidad destacan las barreras mitigadoras (T-Wall o HESCO® Bastion) cuyo objetivo es minimizar el impacto de la onda expansiva sobre el element...
This work examines the interaction of a shear layer separating two uniform supersonic streams of Mach numbers M1 and M2 with an oblique shock approaching at an incident angle σi. The development considers the outer problem of oblique–shock impingement on a supersonic vortex sheet of infinitesimal thickness, for which the region of existence of regu...
El objeto del presente trabajo es la elaboración de un modelo teórico-numérico de combustión aplicable a la nueva generación de motores supersónicos: shcramjet. En particular, se pretende estudiar la viabilidad conceptual del uso de hidrógeno en este tipo de motores, los cuales se presentan como firmes candidatos para ser utilizados en combustión a...
Convective instabilities in the advanced stages of nuclear shell burning can play an important role in neutrino-driven supernova explosions. In our previous work, we studied the interaction of vorticity and entropy waves with the supernova shock using a linear perturbations theory. In this paper, we extend our work by studying the effect of acousti...
Convective instabilities in the advanced stages of nuclear shell burning can play an important role in neutrino-driven supernova explosions. In our previous work, we studied the interaction of vorticity and entropy waves with the supernova shock using a linear perturbations theory. In this paper, we extend our work by studying the effect of acousti...
This paper examines the steady interaction of a shear layer separating two uniform supersonic streams of Mach numbers M1 and M2 with an oblique shock approaching from the faster stream at an incident angle σi sufficiently small for the postshock flow to remain supersonic everywhere. The development begins by considering the related problem of obliq...
Una de las herramientas más populares para el estudio de las ondas expansivas es la simulación numérica. Los códigos numéricos permiten simular la evolución temporal de la onda de choque que lidera el proceso, así como el movimiento del fluido arrastrado por ella en todo el dominio de interés. La oferta de códigos numéricos capaces de simular el ef...
Linear interaction analysis (LIA) is employed to investigate the interaction of reactive and nonreactive shock waves with isotropic vortical turbulence. The analysis is carried out, through Laplace-transform technique, accounting for long-time effects of vortical disturbances on the burnt-gas flow in the fast-reaction limit, where the reaction-regi...
Convective perturbations arising from nuclear shell burning can play an important role in propelling neutrino-driven core-collapse supernova explosions. In this work, we analyze the impact of vorticity waves on the shock dynamics and the post-shock flow using the solution of the linear hydrodynamics equations. We show that the entropy perturbations...
Convective perturbations arising from nuclear shell burning can play an important role in propelling neutrino-driven core-collapse supernova explosions. In this work, we analyze the impact of vorticity waves on the shock dynamics and the post-shock flow using the solution of the linear hydrodynamics equations. We show that the entropy perturbations...
Ignition in a supersonic hydrogen–air mixing layer interacting with an oblique shock wave is investigated analytically under conditions such that the postshock flow is supersonic and the peak postshock temperature before ignition remains below the crossover temperature. The study requires consideration of the flow structure in the postshock ignitio...
This paper extends to transonic mixing layers an analysis of Lighthill ("Reflection at a Laminar Boundary Layer of a Weak Steady Disturbance to a Supersonic Stream, Neglecting Viscosity and Heat Conduction," Quarterly Journal of Mechanics and Applied Mathematics, Vol. 54, No. 1, 1950, pp. 303-325.) on the interaction between weak shocks and laminar...
Ignition in a supersonic mixing layer interacting with an oblique shock wave is investigated analytically and numerically under conditions such that the post-shock flow remains supersonic. The study requires consideration of the structure of the post-shock ignition kernel that is found to exist around the point of maximum temperature, which may be...
To complement our previous analysis of interactions of large-scale turbulence with strong detonations, the corresponding theory of interactions of small-scale turbulence is presented here. Focusing most directly on the results of greatest interest, the ultimate long-time effects of high-frequency vortical and entropic disturbances on the burnt-gas...
We present the asymptotic linear theory describing the propagation of a planar detonation front through a gaseous mixture with small-scale nonuniform perturbations. The interaction of the planar detonation wave with a monochromatic pattern of small-size entropic-vortical perturbations is resolved by normal modes, which result in the asymptotic ampl...
We present the exact small-amplitude linear Laplace-transform theory describing the propagation of an initially planar detonation front through a gaseous mixture with nonuniform density perturbations, complementing earlier normal-mode results for nonuniform velocity perturbations. The investigation considers the fast-reaction limit in which the det...
We present an analytical model that describes the linear interaction of two successive shocks launched into a non-uniform density field. The re-shock problem is important in different fields, inertial confinement fusion among them, where several shocks are needed to compress the non-uniform target. At first, we present a linear theory model that st...
We present an analytical model that describes the linear interaction of a planar shock wave with an isotropic random sonic field. First, we study the interaction with a single-mode acoustic field. We present the exact evolution for the pressure, velocity, vorticity, and density field generated behind the shock wave, and we also calculate exact and...
Interaction of a shock wave with preshock random density nonuniformities is known to generate turbulence in the postshock flow. The turbulent motion, in turn, modifies the shock jump conditions. As first detected in the simulations by Hazak et al. [Phys. Plasmas 5, 4357 (1998)], shock compression of a deuterium-filled foam is less than that predict...
We present here an anaytical model that describes the linear interaction
of a planar shock front with a field of randomly oriented acoustic
waves. The dynamics of the interaction with a single mode is studied in
detail at first. The mode averaging is performed as usual, by
integrating over the angle that the pre-shock mode wavenumber vector
forms w...
We present an analytical linear model describing the interaction of a planar shock wave with an isotropic random pattern of density nonuniformities. This kind of interaction is important in inertial confinement fusion where shocks travel into weakly inhomogeneous cryogenic deuterium-wicked foams, and also in astrophysics, where shocks interact with...
When a planar shock wave interacts with a random pattern of pre-shock density non-uniformities, it generates an anisotropic turbulent velocity/vorticity field. This turbulence plays an important role at the early stages of the mixing process in the compressed fluid. This situation emerges naturally in shock interaction with weakly inhomogeneous deu...
Direct-drive laser targets are often designed with DT-filled CH foam ablator. Accurate modeling of these targets requires understanding of shock propagation in such non-uniform media. The interaction of the shock front with the preshock random density non-uniformities generates a random motion (turbulence) in the postshock flow. The energy coupled...
Interaction of shock waves with vortical, entropic and acoustic preshock fluid perturbations must be well understood to study and model shock interaction with more general turbulent flows, which is important for ICF and many other areas. We focus here on the interaction of a shock front with a random isotropic field of acoustic waves. The dynamics...
The response of a shock front to different kinds of perturbations in the
fluid upstream is of paramount importance to several fields, in
particular to ICF. We present here an analytical linear model that
describes the interaction of a shock front with a random pre-shock
density perturbation field. Exact expressions for the velocity, density,
vortic...
An exact analytical model for the interaction between an isolated shock wave and an isotropic turbulent vorticity field is presented. The interaction with a single-mode two-dimensional (2D) divergence-free vorticity field is analyzed in detail, giving the time and space evolutions of the perturbed quantities downstream. The results are generalized...
An analytical model is presented to describe the interaction of a planar incident shock wave with a 3D field of vorticity perturbations, a problem of fundamental importance which attracts the attention of the scientific community for more than fifty years [1]. Assuming isotropy of the perturbations in the fluid ahead of the shock front, the mode av...
The response of a shock front to small preshock nonuniformities of density, pressure, and velocity is studied theoretically and numerically. These preshock nonuniformities emulate imperfections of a laser target, due either to its manufacturing, like joints or feeding tubes, or to preshock perturbation seeding/growth, as well as density fluctuation...
