Numerical study of the heat and mass transfer processes with the Lattice Boltzmann method: Laminar Mixed Convection in a Square Open C
- Autores: Javier Burgos Vergara
- Directores de la Tesis: Clara Salueña Pérez (dir. tes.), Ildefonso Cuesta Romeo (codir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2016
- Idioma: inglés
- Tribunal Calificador de la Tesis: Francesc Xavier Grau Vidal (presid.), Ingrid Martorell (secret.), César Huete Ruiz de Lira (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The Lattice Boltzmann LBM method has become in tool for studying hydrodynamically and thermally developing, and also chemical reaction and fluid structure interaction among other. Several researchers have aroused great interest of the LBM in all fields of computational fluid dynamic CFD. Due to his easy implementation, variety of the numerical methods could be found in many literature to solver the Navier-Stoker equation. The topic of this thesis is the study of the LBM and implementation in a fluid flow, temperature and concentrations fields, we focus on boundary conditions and accuracy of the method. In order to apply the method, a developed code of Lattice Boltzmann was built. The code was developed using an open-source LBM code and modified for the purpose to simulate the heat and mass transfer phenomena. This thesis is divided in two sections. (I) Various simulations were carried out using LBM for the different approaches of the method, for two-dimensional numerical simulation case, using the D2Q9-model Multiple Relaxation Time model (MRT), this model was implemented for the fluid flow, and temperature concentration field.
Three different case for laminar flow were studied in order to validate the method, first stage a Hagen-Poiseuille flow in a channel and a pipe were simulate, the results were compared with the exact solution of the Poiseuille-flow equations. As well as, the Lid-driven cavity for a incompressible laminar flow was executed for a set of Reynolds number, Re= 100, 1000 and 7500, obtained good result by comparing with other numerical method, such as U.Ghia et al, at 1982 presented a benchmark of the Lid-driven cavity for High Reynolds number using a multi-grid method.
Moreover, convection-diffusion problem of a Gaussian pulse, Natural convection in a closed cavity and mass flux rate in a flat plate were performed with the objective to analyze the boundary condition of LBM implement for passive scalar concentration (Dirichlet boundary condition), these results were compared with previous research. (II) Second stage, the main objective of this thesis was the study of the steady and unsteady laminar flow in a channel with open cavity and heated bottom wall. A two-dimensional simulation has been carried out for the mixed convective flow, using a D2Q9 model for the flow and temperaturefields.
MRT-model with a Boussinesq approximation equation were applied, and it obtained a good accuracy and stability. LBM is compared against results obtained by ANSY-Fluent software for validation. Temperature, velocity and Nusselt number, calculated with TLBM presented very well agreement in the range of Reynolds and Richardson numbers studied, i.e. 50 Re1000 and 0.01 Ri 10. The observations indicate that the effect of the buoyancy force is negligible for Ri0.1, for all values of the Reynolds number considered. For Ri 4 and Re 200, buoyancy effects are important causing the development of the upstream secondary vortex and the stratification of the flow into two main recirculating cells.
For high enough Ri, the recirculation is no longer encapsulated, therefore the flow becomes unsteady, and an oscillatory instability develops. According to the simulation results, observed from Re = 500, Ri = 10. The analysis of the unsteady regime reveals a very rich phenomenology where the geometry of the problem couples with the oscillatory thermal instability. This regime is characterized by the periodic emission of pairs of vortices generated from the upper downstream vertex of the square cavity, and pseudo-periodic variations of the Nusselt number which persist at least up to Re = 1500, while the two main vortices remain in the cavity.
The observations extend previous studies and shed a new light on the characteristics of the oscillatory instability and the role of the Reynolds and Richardson numbers.
