Computational Fluid Dynamic

What Is Computational Fluid Dynamics?

Computational fluid dynamics (CFD) is the computer simulation of air or fluid in a defined situation. CFD uses sophisticated mathematical calculations to simulate fluid dynamic effects on real-world objects to aid in the creation of new products. CFD reduces the need and expense of physical prototyping in certain engineering applications.

CFD simulations run multiple calculations simultaneously to predict the forces and flow of fluids around a three-dimensional object, taking into account environmental conditions including velocity, pressure, fluid viscosity, density, and temperature. These calculations are iterated through time to create a full simulation that can be stored and replayed. CFD is used in the design of many products including cars, planes, boats, and turbine generators. CFD helps engineers increase the efficiency and safety of these machines, and test them under rigorous conditions without risk.

History of Computational Fluid Dynamics

For several centuries, scientists and mathematicians like Davinci, Isaac Newton, and Bernoulli have worked on equations and theories to explain and predict fluid mechanics. Modern CFD is based on the Navier-Stokes equations which were created by Marie Henry Navier and completed in the mid-19th century by George Stokes. These new equations were built upon previous research and included new variables such as viscosity. These equations are complicated and couldn’t be reasonably applied to fluid dynamic models until the invention of digital computing in the late 20th century. Today, advanced CFD models are still built upon these equations.

Computational Fluid Dynamics Applications

Simulating Turbulent Flow

Turbulent flow is the sudden or irregular movement of air, water, or other fluids. Due to the complexity of real-world applications, most CFD models deal with turbulent flow. A common use case for simulating turbulent flow is accounting for turbulence in aircraft design, which can pose a serious threat to unprepared aircraft and pilots. CFD can be used to simulate the effects of turbulence on an aircraft design, allowing engineers to ensure it can handle even the most serious turbulence.

Machinery Design

Machines like compressors, pumps, and gas turbines utilize fluid dynamics to accomplish their intended task. The fluid pressure and fast-moving parts of these machines can create instability that strains machine parts. CFD simulations can be used to understand this stress and improve designs without the need for repeated physical prototyping and real-life stress testing. 

HVAC Optimization

CFD can simulate not only airflow but also temperature flow within a space or between components. Architects and engineers can use CFD to simulate the effectiveness of heating and air conditioning system designs for new buildings. The simulation can help them design systems that are more efficient and effective.

Aerodynamics

Aerodynamics is the study of how air flows around objects in motion. Automobile designers, aerospace engineers, and even sports equipment manufacturers use CFD to make products that are faster, more efficient, and more precise. CFD simulations save time and money by reducing physical prototyping, allowing engineers to quickly iterate designs to achieve optimal performance.

Pressure Simulation

Many industries rely on high-pressure pipes, valves, and machinery to transport air, water, fuel, and other materials. CFD can be used to simulate the forces exerted by this pressure and ensure that these systems are safe and effective. CFD can also be used to predict the longevity of aging infrastructure and identify places where repairs or replacements may be necessary to maintain functionality.

The Computational Fluid Dynamics Process

Create a CAD Model

The first step to running a CFD simulation is to create a digital 3D representation of the part, machine, or environment being optimized. Engineers use computer aided design (CAD) programs to create these virtual models. This three-dimensional model will be subdivided by the computer into small cells and the simulation will run calculations based on the geometry of each cell. This model can be changed and updated over time.

Establish Fluid Domain

The fluid domain is the area where fluid will interact with the model. This can be internal, like water through a pipe or valve, or external, like air across an airplane wing. The fluid domain may include the entire model or a small part of it. Defining the fluid domain also includes establishing the fluid’s properties such as density, viscosity, and thermal characteristics.

Specify Boundary Conditions

Boundary conditions are the conditions at the start of the simulation. They include data such as fluid velocity, inlet and outlet pressure, and mass flow. They also include the temperature of the fluid or model, gravity, and the motion of any parts within the model.

Run the Simulation

After fully preparing the model and flow conditions, the simulation can begin. The output of the simulation can be data across time or data from a steady state in which the model has reached equilibrium.

Evaluate Results

The CFD simulation will yield data including velocity, temperature, and pressure at various points across the model. This data can be used to optimize the original CAD design until the output is satisfactory.