Front-loading CFD: Highlights from NAFEM Seminar

A recent NAFEMS seminar on front-loading CFD in the design process provided some fascinating insight into the role of CFD within industries such as Formula 1, aerospace, telecommunications and motion control. Increasingly, CFD is moving up the engineering supply chain, and for companies like Rolls Royce, running multistage simulations throughout the design cycle has become standard practice.

 
To encourage an upfront approach to simulation, software packages like CFdesign are aimed at design and development engineers, for use in early stage product design to test design fundamentals at a point when major changes are relatively inexpensive. CFD simulation early in the design cycle saves on the time and costs associated with building and testing multiple prototypes and these savings apply to any manufacturing company.
 
Competitive Advantage
In a multi-billion dollar industry like Formula 1, using upfront CFD is less about saving money and more about gaining competitive advantage from the insight into the flow field that CFD provides. The gap separating the top nine drivers in the 2008 Brazilian Grand Prix was just 0.2 seconds. That one of the most high profile F1 teams has made a serious investment in upfront CFD instead of building a second wind tunnel shows just how far these companies are willing to push simulation technology for real performance gains on the car.
 
Irrefutable ROI
But it’s not just the makers of jet engines and F1 cars who stand to benefit from front-loading CFD. A presentation by Bruno Fairy from motion control specialist Parker Hannifin centred on four compelling examples, which showed “measurables”, based on an ROI methodology that factors in known costs, for virtual product development (VDP) using upfront CFD and conventional design-build-test methods. In every case there was irrefutable evidence of dramatic time and cost savings gained by going down the VDP route.
 
Verification and Validation
A question that invariably gets asked of upfront CFD is how accurate are the results? Independent consultant Michael Clapp, a member of the NAFEMS CFD Working Group and founder of Upfront Engineering Simulation Ltd, addressed this question in his presentation on verification and validation for design focused CFD.  Clapp concluded that as upfront CFD packages are essentially design tools, predicting trends is more important than absolute values, and that well-chosen validation studies are a valuable learning exercise.
 
Badly chosen studies can lead to the wrong lessons being learned. A classic example is the misguided practice of validating CFD against pipe flow measurements when the software will ultimately be used to aide flow control and valve designs.
 
The tiny pressure drops in simple pipe flows means the calculation is dominated by wall friction and end effects. These problems are best solved with a structured mesh. Valves involve much more complex geometry and the wall friction is a small proportion of the overall pressure loss and as such will benefit from an unstructured mesh; therefore using a pipe model as your verification case may lead to a CFD choice that will be unsatisfactory for valve design.
 
Other highlights included a presentation from Richard Bell at Prospect, which highlighted the fact that analysis is still underutilised in the oil and gas sector; an Indy Car racing case study from Koen Beyers of Voxdale, an engineering firm based in Belgium; an electronics cooling design example from Lucius Akalanne from Alcatel Lucent; and finally a presentation from Dr Althea de Souza, chair of the NAFEMS CFD Working Group and senior design engineer from DezineForce about supporting design engineers to simulate hydraulic assemblies.
 
Overall the event did well to highlight the major benefits in introducing CFD tools early on in the engineering design process, when the biggest changes in the design are practical. Companies who have invested in such technology are reaping major benefits. The NAFEMS seminar succeeded in answering some important questions, such as how companies have successfully implemented design based CFD, how they avoided the pitfalls associated with the complex physics involved, and what skill sets and training are needed to front load CFD in the design process.