Numerical simulation of evaporation model in a weno-z based eulerian-lagrangian code

En este TFM se discute la implementación de un modelo de evaporación en un código WENO-Z de alto orden basado en el modelo Euleriano-Lagrangiano (EL) para un flujo de partículas a alta velocidad en cámaras de combustión supersónicas. El método EL aproxima la ecuaciones de Euler que gobiernan el movimiento del gas con el esquema mejorado “high order weighted essentially non-oscillatory” (WENO-Z), mientras que las partículas individuales son trazadas en el marco Lagrangiano utilizando esquemas de integración de alto orden. Tanto el gas portador como las partículas derivadas en función el tiempo mediante el método Runge-Kutta TVD de tercer orden. Una interpolación de alto orden (ENO) determina las propiedades del gas portador en la posición de las partículas. La evaporación de una partícula es verificada con la ley D² de evaporación y se estudia el problema unidimensional de la interacción de una onda de choque con una nube de partículas.Departamento de Ingeniería Energética y FluidomecánicaMáster en Ingeniería Industria

Study of the growth and development of a particle-laden richtmyer-meshkov instability using high order methods

La inestabilidad de Richtmyer-Meshkov (RM) ocurre cuando dos fluidos de distintas densidades son sometidos a una gran aceleración en una dirección opuesta al gradiente de densidades. Para resolver las ecuaciones de Navier-Stokes suponemos un flujo compresible en un dominio cerrado en dos dimensiones. Por un lado, iniciamos el código con una nube de partículas simulando un 4% en volumen y con velocidad inicial nula. Por otro lado, inicializamos la fase gaseosa de acuerdo con una onda de choque con un valor de Mach de 2.8. En el flujo acelerado tras el paso de la onda de choque, parecen dos tipos de inestabilidades de RM: una de ellas es gobernada por los fenómenos de baroclinidad, relacionada con los gradientes de presión y densidad; la otra se encuentra en la fase de partículas, en la cual, al no tener un gradiente de presión, no debería seguir la baroclinidad. En este trabajo mostramos los efectos y similitudes tanto cuantitativas como cualitativas del desarrollo de la fase no baroclínica de la inestabilidad de RM en la fase gaseosa. Palabras clave: Richtmyer-Meshkov, Inestabilidad, partículas, CFD, baroclinidad.Departamento de Ingeniería Energética y FluidomecánicaMáster en Ingeniería Industria

Numerische Modellierung und Simulation von Kavitationsblasenwolken mit einer Lagrange-Euler-Methode

In this thesis, the Lagrangian-Eulerian coupling model is proposed to investigate dynamically the cavitation bubble cloud. Based on the Lagrangian-Eulerian one-way coupling model, the homogeneous cavitation nucleation inside microchannel is studied. Furthermore, we develop the Lagrangian-Eulerian two-way coupling for the numerical simulation of the bubble cluster with pressure wave interaction and the bubble cloud Rayleigh collapse.In dieser Doktorarbeit wird das Lagrange-Euler-Kopplungsmodell vorgeschlagen, um die Kavitationsblasenwolke dynamisch zu untersuchen. Basierend auf dem Lagrange-Euler-Einweg-Kopplungsmodell wird die homogene Kavitationskeimbildung im Mikrokanal untersucht. Darüber hinaus entwickeln wir die Lagrange-Euler-Zweiwege-Kopplung zur numerischen Simulation des Blasenclusters mit Druckwellenwechselwirkung und dem Rayleigh-Kollaps der Bubble Cloud

Adjoint-based Particle Forcing Reconstruction and Uncertainty Quantification

The forcing of particles in turbulent environments influences dynamical properties pertinent to many fundamental applications involving particle-flow interactions. Current study explores the determination of forcing for one-way coupled passive particles, under the assumption that the ambient velocity fields are known. When measurements regarding particle locations are available but sparse, direct evaluation of the forcing is intractable. Nevertheless, the forcing for finite-size particles can be determined using adjoint-based data assimilation. This inverse problem is formulated with the framework of optimization, where the cost function is defined as the difference between the measured and predicted particle locations. The gradient of the cost function, with respect to the forcing can be calculated from the adjoint dynamics. When measurements are subject to Gaussian noise, samples within the probability distribution of the forcing can be drawn using Hamiltonian Monte Carlo. The algorithm is tested in the Arnold-Beltrami-Childress flow as well as the homogeneous isotropic turbulence. Results demonstrate that the forcing can only be determined accurately for particle Reynolds number between 1 and 5, where the majority of Reynolds number history along the particle trajectory falls in

numerical approaches to complex fluids

We are surrounded by a variety of fluids in our everyday life. Besides water and air, it is common to deal with fluids with a peculiar behaviour such as gel, mayonnaise, ketchup and toothpaste. While simple fluids made by identical molecules show a linear response to the applied forces, complex fluids with a microstructure, such as suspensions, may show a very complex response. In this chapter, we introduce numerical approaches for complex fluids focusing on the way the additional stress, due to the presence of a microstructure, is modelled and how rigid and deformable intrusions can be simulated

LES of Jets and Sprays Injected into Crossflow

The objective of this thesis is to numerically simulate a fluid jet injected into a crossflow of the same or another fluid, respectively. Such flows are encountered in many engineering applications in which cooling or mixing plays an important role, e.g. gas turbine combustors. The jet in crossflow (JICF) is used both for cooling and for injecting liquid fuel into the air stream prior to combustion. The numerical simulations regard three space dimensions and track also the flow dynamics by integrating the governing equations in time. The spatial and the temporal resolution are such that the large-scale flow structures are resolved. Such an approach is referred to as large eddy simulations (LES). The motion of the fuel droplets is treated by Lagrangian particle tracking (LPT) with the stochastic parcel method, along with submodels for evaporation, collision, breakup, and a novel submodel for aerodynamic four-way coupling: The particle drag is corrected depending on relative positions of the particles. Mixture fraction and temperature transport equations are solved to enable the modeling of droplet evaporation and the mixing of the gaseous fuel with ambient air. In the simulations of multiphase JICF, several computed results are shown to be inconsistent with the underlying assumptions of the LPT approach: The magnitude of the Weber numbers indicates that droplets are not spherical in large portions of the flow field in wide ranges of parameters which are relevant for gas turbine operation. The magnitude of the droplet spacing suggests that aerodynamic interaction (indirect four-way coupling) among droplets may be important. The LES with aerodynamic four-way coupling reveals significant effects compared to two-way coupling for monodisperse particles in a dense multiphase flow. For single-phase JICF, the impact of nozzle shape on the large-scale coherent structures and the mixing is studied. Effects of circular, square, and elliptic nozzles and their orientation are considered. It is demonstrated that square and elliptic nozzles with blunt orientation raise turbulence levels significantly. The scalar distribution in a cross-sectional plane is found to be single-peaked for these nozzles whereas circular and the nozzles with pointed orientation show double-peaked scalar distribution. It is the nozzles with a single-peaked distribution which are the better mixers. The differences and similarities of single- and multiphase JICF are compared, and it is demonstrated that the flow field solution for multiphase flow approaches the flow field solution of single-phase flow in the limit of small Stokes numbers

Gas-Particle Dynamics in High-Speed Flows

High-speed disperse multiphase flows are present in numerous environmental and engineering applications with complex interactions between turbulence, shock waves, and particles. Compared to its incompressible counterpart, compressible two-phase flows introduce new scales of motion that challenge simulations and experiments. This review focuses on gas-particle interactions spanning subsonic to supersonic flow conditions. An overview of existing Mach number-dependent drag laws is presented, with origins from 18th-century cannon firings, and new insights from particle-resolved numerical simulations. The equations of motion and phenomenology for a single particle are first reviewed. Multi-particle systems spanning dusty gases to dense suspensions are then discussed from numerical and experimental perspectives