CFD Course Ep. 2: What is CFD? & CFD Introduction

Computational Fluid Dynamics (CFD) is essentially the use of computers to solve fluid mechanics problems. As the name suggests, CFD employs computational methods to address challenges in fluid dynamics. With CFD becoming increasingly user-friendly, many people now utilize it without fully understanding its fundamentals. This article will cover the basics of CFD and its underlying principles.

Fluid dynamics is the study of fluid flow and behavior. A fluid can be either a liquid or a gas. From my perspective, fluid dynamics is everywhere. Whether you’re brushing your teeth, sipping your morning coffee, experiencing a windy commute, watching rain fall, observing rivers flow, or seeing rockets launch—fluid dynamics is an inescapable part of life.

CFD Introduction and Analysis

Discussing analytical fluid mechanics can be challenging. However, as computers have advanced, solving fluid problems has become more feasible and affordable. This evolution is why CFD software is now widely used. Let’s delve into some of the technical aspects.

Differential Equations in Fluid Dynamics

Fluid mechanics is governed by fundamental principles: conservation of mass, momentum, and energy.

• Conservation of Mass: Mass cannot be created or destroyed. For example, in a pipe, the mass of fluid entering must equal the mass exiting. This principle is expressed mathematically as an integral equation.
• Conservation of Momentum: This principle, derived from Newton’s second law of motion, states that the rate of change of momentum equals the applied force. The momentum equation can be presented both as an integral and a differential form, with the latter being more intuitive.
• Conservation of Energy: Similar to momentum, but includes temperature as a variable. This principle is crucial when dealing with fluids where temperature and density change.

These principles form the Navier-Stokes (NS) equations which describe any fluid flow. They are partial differential equations and are often highly coupled. Solving these equations analytically is nearly impossible due to their complexity. Instead, we simplify the problem using boundary conditions and initial conditions.

The Role of CFD

CFD involves three main steps:

1. Discretization: Dividing a large fluid volume into smaller, manageable elements. This step is critical—if not done correctly, the results may be inaccurate or non-existent. In computing terms, this is known as “garbage in, garbage out.”
2. Solution: Solving the discretized equations.
3. Post-processing: Analyzing the results.

Understanding these steps will provide a clearer picture of CFD and its capabilities. In the next part of this series, we will explore the concept of discretization in more detail.

References

1. Introduction to Computational Fluid Dynamics
   • Description: Provides a comprehensive overview of CFD principles, including transient and steady-state simulations.
   • Source: Introduction to Computational Fluid Dynamics: A Practical Approach by Atul Sharma
   • Link: SpringerLink – Introduction to Computational Fluid Dynamics
2. Fundamentals of Fluid Mechanics
   • Description: Detailed explanation of fundamental concepts in fluid mechanics, including time-dependent and steady-state analyses.
   • Source: Fundamentals of Fluid Mechanics by Bruce A. Finlayson
   • Link: Wiley – Fundamentals of Fluid Mechanics
3. CFD for Engineers
   • Description: Discusses practical applications of CFD, including transient and steady-state simulations in engineering contexts.
   • Source: CFD for Engineers by David C. Wilcox
   • Link: Wiley – CFD for Engineers