How to Convince Your Approval Engineer of CFD Analyses for Wind Load Determination

Introduction

With the increasing complexity of building geometries and the growing demand for precise wind load data, computational fluid dynamics (CFD) has emerged as a powerful tool for wind load determination. However, many engineers and structural designers still face a common challenge: how to gain the approval of the Prüfingenieur (approval engineer) for CFD-based wind simulations. In this article, we address the typical concerns approval engineers may have and offer strategies, arguments, and references to help justify the use of CFD for structural design according to accepted standards. One key advantage of using CFD is its ability to provide a complete picture of wind-induced loads, including both compressive and suction forces. Users often inquire whether the program delivers the corresponding suction loads on the leeward side in addition to the windward compressive loads. CFD simulations make this transparent, allowing for a detailed assessment of load distribution over the entire structure an insight that is not always as readily accessible through traditional methods.

1. Understand the Concerns of the Approval Engineer

Before presenting your CFD results, it’s crucial to understand why some approval engineers remain cautious:

• CFD is sensitive to input assumptions (e.g., turbulence model, inflow profile, mesh quality, etc.).

• Verification and validation are not always transparent.

• Unlike wind tunnel testing, CFD does not always have an established chain of trust for every scenario.

• Many national regulations still emphasize physical testing or code-based load models as the default.

By understanding their concerns, you can give explanations that solve real issues, rather than simply discussing the technology itself.

2. Reference the Standards: CFD Is Permitted

CFD is not just a futuristic idea, it’s explicitly allowed in several standards. For example:

• EN 1991-1-4: According to Section 1.5 of EN 1991-1-4, numerical simulations may be used in supplements to calculations and physical wind tunnel tests, as long as they are proven and/or properly validated.

• ASCE 7-22: ASCE 7-22, through reference to ASCE 49, recognizes that while CFD is increasingly applied in wind engineering, its use must be carefully controlled. Since there is currently no dedicated standard detailing the full procedures for CFD in this context, ASCE emphasizes that any application of CFD to determine wind loads on the Main Wind Force Resisting System (MWFRS), Components and Cladding (C&C), or other structures must undergo peer review and a Verification and Validation (V&V) study to ensure the accuracy and reliability of the results.

✅ Key Message: If your CFD analysis is based on validated models and reflects the actual wind environment, it is code-compliant.

• Building Trust in CFD: Validation, Verification, and Calibration for Wind Simulation Acceptance

• How to Conduct Validation Example in RWIND

3. Show Evidence of Validation

The credibility of a CFD model hinges on validation.

• Compare your CFD results with experimental wind tunnel data (e.g., from Tokyo Polytechnic University (TPU) ).

• Show agreement in output results such as pressure coefficients, force coefficients, or support reactions.

• Document your turbulence model, boundary conditions, and mesh sensitivity analysis.

• If you have papers published in peer-reviewed and validated journals, presenting them could greatly enhance the credibility of your work:

• One-Way FSI Coupling with Steady-State and Transient CFD Analysis for the Umbrella Form of Tensile Membrane Structure

• Analyzing Progressive Damage of the Millennium Dome’s Tensile Membrane under Storm Eunice

📌 Tip: Use examples where CFD results have already been accepted by approval engineers or used in completed projects. If available, share formal acceptance letters or project references.

4. Emphasize the Practical Advantages

Make it clear why CFD was the best choice in your specific case:

• CFD clearly shows both compressive and suction loads, giving users a complete understanding of wind effects across the entire structure.

• More accurate for complex geometries where Eurocode simplifications don’t apply.

• Better spatial resolution of pressure distribution (especially for facade and cladding design).

• Ability to simulate local effects such as corner vortices, separation zones, or shielding effects.

• Cost- and time-efficient compared to wind tunnel testing, especially during early design stages.

• CFD-FEM integration enabled accurate wind load application, supported Eurocode and LRFD design standards, and reduced the need for wind tunnel tests, resulting in safer, more efficient structural designs.

5. Provide a Clear Documentation Package

Approval engineers appreciate transparency and traceability. Prepare a report that includes:

1. Objectives of the CFD study
2. Description of the numerical domain and boundary conditions
3. Justification of selected turbulence model
4. Mesh convergence study
5. Validation against experiments or standards
6. Interpretation of results in structural design context (e.g., load combinations in RFEM)

📁 Include appendix materials such as screenshots, coefficient graphs, and summary tables for pressure and force results.

6. Offer a Collaborative Discussion

If needed, propose a meeting with the approval engineer to discuss:

• The simulation approach and assumptions

• Previously accepted use cases

• Areas where conventional methods fall short

Engineers are more likely to accept CFD when it’s presented transparently and dialogically, not dogmatically.

7. Use Accepted Software and Reference Projects

Use reputable CFD tools that are already known in the industry (e.g., RWIND, OpenFOAM, etc.) and emphasize that they are used in parallel with FEM tools for load transfer and design verification. If the software has been used in public infrastructure, towers, or antenna projects, mention them.

• References Projects

Conclusion

Convincing your approval engineer of CFD’s value in wind load determination is not about replacing traditional methods, but augmenting them responsibly. By referencing the standards, demonstrating validation, and providing clear documentation, you can show that CFD is not only accurate but also a reliable and accepted tool in modern structural wind engineering.