Preface

Nature has four phases: solid, liquid, gas, and plasma. All phases except solid are in flowing states without having fixed molecular structures. In physics, matter and energy are known as exchangeable quantities, and water is a vital resource for human life as it makes up more than 70 percent of the human body. In engineering practices, humans create an artificial non-equilibrium state and induce nature to seek a local equilibrium within a reasonable time scale. Gradients of some physical quantities such as mass, heat, and momentum generate their fluxes that are amounts passed through a unit surface area per unit time. Engineering can be understood as a set of processes that convert these spontaneous fluxes into available resources. Fluid dynamics stems from Newton's second law for many individual particles interacting in viscous motion, which is represented using Navier–Stokes equations. Water is one of the representative fluids in engineering and sciences, having a pseudo-constant density, indifferent from temperature. A water molecule consists of one oxygen and two hydrogen molecules, of which molecular interactions determine the macroscopic properties. The hydraulic pressure can be explained, instead of force per unit area, as energy per unit volume that is equivalent to an energy density providing better understanding due to its scalar nature. Fluid mechanics is linked to statistical mechanics through pressure. The pressure is proportional to the negative gradient of the enthalpy per mass in an adiabatic system or Helmholtz energy per mass in an isothermal-isovolumetric system. Fluid dynamics is, by definition, a problem of solving the Navier–Stokes equation within a reasonable time frame. Computational fluid dynamics (CFD) is often used to analyze, optimize, and predict engineering phenomena and processes of practical interest. Transport of molecular matter such as salts, contaminants, reactants, and even macro-organics is often described using continuum equations that include convection, diffusion, reaction, and sourcing processes. When particles and solutes move relative to a moving fluid, (simultaneous) translation and rotation of multiple particles provide the intrinsically coupled feedback to the local fluid motion. Coupled simulations of fluid and particles are possible in principle but computationally challenging due to the mathematical complexity and computation demand. CFD simulation results can be, therefore, much more efficiently used if simulation runtime is significantly reduced so that more candidates of probable engineering scenarios are thoroughly investigated. On the other hand, highly accurate results are also of great necessity in fluid dynamics fundamentals. Open problems in CFD research literature include seamlessly merging fluid and particle dynamics while their relative motion is coupled due to the viscous characteristics of the solvent and rigorous analytic solutions for flow fields in geometrically less complex channels. In this vein, this book covers a wide range of state-of-the-art

CFD topics, providing future perspectives of advanced CFD methods as general tools of multi-physics simulations for sciences and engineering disciplines.

> **Albert S. Kim**  Department of Civil and Environmental Engineering, University of Hawaii at Manoa, Honolulu, Hawaii

> > Section 1

Computational Particle

Hydrodynamics

1

Section 1
