Dissipative Particle Dynamics Study On Multi-drive Heat Convection Problem

In recent years, with the rapid development of emerging technology, fluid dynamics presents two major challenges, complex fluids and complex flow. In the context of the application of emerging technology, complex flow results from the interaction of multi-physics field. Physical effect or chemical effect even biological effect can be major driving force of fluid flow in special environment. Multiple driving forces and their none-linear coupling make fluid flow problem and accompanying heat transfer problem complicated, diversified and none-linearized. Therefore, a great deal of exploration and study is devoted to dealing with these problems. As a Lagrangian particle-based numerical method, energy-conserving dissipative particle dynamics(short for e DPD) has great potential for solving complex problem. However, it is only decades after e DPD is developed to simulate hydrodynamic phenomenon of thermal fluid and only a few successful cases are reported. Mountains of work is needed to promote the development of this method. For these reasons, the aim of this thesis is to develop e DPD and utilize e DPD to tackle the flow and heat transfer problem involving multi-physical field.As a starting point, a brief introduction of e DPD is presented and theoretical foundation for e DPD simulation is systematically discussed. Applying kinetic theory, macroscopic conservation and balance equations for mass density, momentum density and energy density are obtained. Next, some details for e DPD simulation such as boundary treatment, integration algorithm, interrelated parameter setup and so on, are mentioned. A feasible novel approach to the matchup the mesoscopic parameter in e DPD model with macroscopic transport coefficient is first proposed. Then two simple simulations for Couette flow driven by shear force and natural convection in square induced by buoyance force are conducted. Simulation results show good agreement with analytical results or those by finite volume method(FVM), respectively.Shear force is an important measure for enhancing the heat transfer and plays a significant role in engineering application. So the mixed convection induced by shear force and buoyance force arouses great interest. Considerable research of mixed convection in simple square has been reported. However, most engineering problems have complex geometries. Therefore, a detail study of mixed convection in an isothermal square within a elliptic heat source is conducted in this thesis by applying the e DPD method. To validate the e DPD code, a comparative research of natural convection and mixed convection in lid-driven square is carried out and the simulation results by e DPD is in correspondence with those by other numerical method such as finite volume method(FVM), lattice Boltzmann method(LBM), differential quadrature method(DQM),etc. Then on this basis, convection phenomenon caused by the transverse and tractive shear force respectively is investigated and the effect of the strength of shear force on fluid flow and heat transfer is discussed in detail. The results show that the basic characteristics of fluid flow and heat transfer induced by the transverse force are different with those induced by the tractive force.Biomagnetic fluid, as one of the most popular complex fluid, attracts people’s widespread attention. The hydrodynamic behavior of non-isothermal biomagnetic fluid in inhomogeneous magnetic field is both different from ferrohydrodynamics and magnetohydrodynamics, under the influence of buoyance force, Kelvin force and Lorentz force. A DPD simulation for convection in a semi-annular cavity filled with biomagnetic fluid are conducted carefully. The effects of Magnetic number, Hartmann number, Rayleigh number and Prandtl number on the ?ow and heat transfer characteristics have been examined. As Magnetic number increases, primary vortex in each side turns in to two smaller vortexes and three thermal plume appears over the hot wall, which is different form natural convection.It is concluded that for a fluid system driven by many factors, different metastable structure will appear when the major driving factor changes under certain conditions. DPD is powerful tool to solve the complex convection problem in an irregular cavity and DPD can help researchers find new and interesting physical phenomenon. DPD will play an important role in the research on fluid flow and heat transfer problem.