# How To Get An In-depth CFD Analysis Done

Computational Fluid Dynamics (CFD) is a design and engineering tool used to simulate the flow of fluids such as air, water or any fluid in the system and understand the effect of the fluid flow on the surroundings. CFD is best used in case studies, where the system behavior cannot be calculated using conventional calculation methods and needs complex mathematical modelling to capture the behavior. Traditionally, engineers used to rely on experimental and wind tunnel studies to capture the aerodynamics and the dynamics of the system. However, with the advent of CFD, it has become possible to go through a less expensive and time-consuming process to capture the same.

Despite the advent and advantages of CFD, there has always been a question about how do you get the CFD analysis done for any design or product given under particular conditions. There is a particular methodology which needs to be followed for performing the CFD analysis which will not only ensure accuracy, but also verification and validation of the CFD results obtained. Various CFD companies formulate a particular strategy right from defining the objective of the CFD analysis to postprocessing the results and providing a report to the client with analysis results and design recommendations.

Various CFD analysis services provide results for various studies such as laminar and turbulent flow, steady and unsteady analysis, thermal and multi-phase flow analysis. Based on the requirement, the basic approach of performing analysis remains the same. The CFD engineering and analysis need to begin with a simplified geometry, a detailed mesh, use of proper boundary conditions to simulate the real conditions and proper solver and schemes to capture the physics behind the fluid simulations. To understand the process of performing proper in-depth CFD analysis, there are particular steps that one needs to understand which will make sure the results obtained in the end are agreeable. Let us look at each one of them one by them

## Mesh Detail

One of the main criteria of getting in-depth CFD analysis correcting is creating the correct mesh. A correct mesh consists of using proper number of cells in region where high fidelity of results is required. The mesh has to be fine enough that the results at the location do not change with mesh size i.e., mesh convergence has occurred at the place in respect to various quantities such as velocity, pressure, etc. To identify the quality of the mesh, various parameters are used aspect ratio, Jacobian ratio, Skewness angle, warping factor and various others to determine whether the mesh created for the problem is sufficient for capturing the physics required.

## Choosing the proper solver and scheme

Every commercial software comes with many solvers and schemes which makes it difficult to decide on which solver or scheme to use. Depending on whether the flow considered is compressible or incompressible, either a pressure based or density-based solver are used for performing the CFD analysis. This is important to decide since according to the solver, the physics for the simulation are captured and accordingly the equations used for capturing the quantities change. Furthermore, based on the type of physics to capture, either laminar solver or turbulent solver are used for the simulation. Turbulent solvers such as k-epsilon or Spalart Almaras are selected based on the stability of the model in capturing the CFD analysis to be done in the CFD domain.

The selection of schemes for various quantities such as pressure, momentum, turbulence viscosity is next in line to capture these quantities accurately over the CFD domain. Depending on the accuracy and stability of the analysis required, either a first order, second order or third order scheme is selected for performing the CFD analysis. The higher the order of the scheme, the more accurate the value of the results. However, the disadvantage of using higher order schemes is that the solution becomes unstable and needs more time for performing the complete simulation. Hence a good grid and timestep is required to ensure that higher order schemes are stable and provide accurate results for the simulation.