🚀 Your first CFD Simulation? A Step-by-Step Guide for CFD beginner 🚀

Welcome to my beginner’s 4-step guide to successfully conducting Computational Fluid Dynamics (CFD) simulation projects. Looking back after working on several CFD projects alongside professionals, I find myself wishing I had access to this guide during my graduate school days. It would have made my life so much easier. Hence, my aim in writing this is to help guide beginners who are just getting started in CFD. To CFD experts, kindly share your thoughts and experiences in the comments.

Step One: Have a clear understanding of what you want to do.

Every successful CFD simulation begins with a clear understanding of your objectives and how to justify your results.

Let me illustrate this by using a project I worked on involving the design of a supersonic nozzle for testing the thermal property for newly developed materials using our plasma technology at Plasnix. The concise CFD objective then becomes:

Investigate the hydrodynamics of proposed nozzle designs and recommend an optimized design that meets specific client criteria, including:

1. Achieving a minimum diverging diameter that covers the intended specimen area.
2. Maintaining a minimum Mach number of 3.
3. Ensuring the back pressure is within the client's pump capacity.

Understanding these objectives led to a crucial question: What parameter should be used to judge a good design? In this context, the absence of shock within the diverging section emerged as a critical component.

If multiple designs met the client's criteria, a Figure of Merit which measure the absence of shock becomes the guide for justifying a design. However, in cases where the criteria couldn't be met, proposing adjustments to the client becomes very crucial.

This well-defined objective not only clarified the project's goal but also provided a roadmap for the entire CFD simulation, from model setup to result interpretation.

Step Two: Understand the physics that will be involved and what models will be required to account for it.

Having established the objectives for the nozzle design, the next crucial step involves understanding the underlying physics and the suitable models/solver for the anticipated flow phenomena. Using the provided example, the physics involved include:

1. Compressible Flow (density based solver): Compressible flow analysis deals with fluids where density significantly changes due to pressure alterations. Significant compressibility effects typically manifest at Mach numbers exceeding 0.3.
2. Heat Transfer: Due to the necessity of cooling the nozzle wall to prevent melting, heat transfer becomes crucial.
3. Turbulence: Anticipating turbulence requires an appropriate turbulence model.

At this juncture, proficiency in utilizing these models/solvers becomes evident. It highlights whether further learning or reference materials are necessary to effectively employ these tools for simulating the desired nozzle behavior.

Step Three: Understand your geometry and boundary conditions.

Based on the complexity of the geometry and the physics involved, and timeline for delivering results, determine whether a 2D or 3D simulation is appropriate. Consider the trade-offs between computational resources, accuracy, and the complexity of the flow phenomena to be captured. Begin by comprehending the nozzle's geometry, recognizing that not all 3D models are convertible to 2D. This understanding forms the basis for defining boundary conditions and simplifying the geometry without compromising the physics under study. What I like to do especially when working with 2D simulations, is to first utilize a tool like AutoCAD to draft a preliminary geometry sketch. This can be done on paper too. Label the boundary conditions (inlet, outlet, walls, etc.) to be employed in the simulation setup. This step is really important for precise simulation setup, ensuring an accurate representation of the physical system. And it aids your understanding of the problem and helps clarify what you are doing. Below is an example of what I mean.

Step Four: Plan your Mesh Layout

Print out the AutoCAD sketch and with a pencil sketch what you want the mesh to look like. This preparatory step is essential because it gives you insight into how to properly draw your geometry.

Based on the meshing technique (method, sizing, etc.), you will know where and how best to slice the geometry to ensure a mapped mesh or to ensure a continuous inflation layer).

The thought process here makes you appreciate the meshing techniques and will further provide more understanding of how to use them well. Also, this is to ensure that your simulation accurately captures the physics.

By diligently following these steps, I believe you'll become well-prepared to tackle that CFD project because these steps not only highlight your weaknesses but also provide valuable feedback on concepts you might not have fully grasped.

In conclusion, these steps ensure a comprehensive understanding of every aspect of your simulation. Stay tuned for my upcoming videos, where I'll demonstrate the process and offer guidance on maintaining an organized project file.