Is CFD an Exact Science? #Design_Eng
Deriving value from simulation requires scrutiny but not hyper-accuracy.
As a CFD analysis consultant I have been subjected to the question “Is CFD exact?” many times. How exact is exact, exactly? Confusing isn’t it? The answer really depends on CFD analysis objectives.
I’ve been asked to carry out results data to 3 or 4 decimal places! Really? Do results showing 4.015 psi drive product development in a different direction than 4 psi? If so, you don’t need CFD simulation; you need a professor and enough capital to embark on a six-month research project. Don’t get me wrong, CFD analysis can be exact. However, it requires a high degree of scrutiny and more time to capture every minuscule detail. I come across many engineers who feel the need to include every detail to derive any value from simulation. This cannot be further from the truth. CFD can be exact, but CFD does not have to be exact to drive product development decisions.
CFD results should always be verified with hand calculations and various sanity checks to ensure their validity; however, CFD being a mathematical model constrained by user inputs is inherently different than the physical world so differences in results should be expected. If an initial baseline analysis shows a 10% discrepancy with physical testing, does that mean there is no value in the analysis results? What about the power in visualizing the flow fields, temperatures gradients, and other trends not accessible through physical testing or hand calculations? This insight, and its interpretation, will provide the information required to make informed design modifications. As long as analysis assumptions are maintained across design configurations and sound engineering judgment is used, the result yielded will be a qualitative comparison of which design is better. Given enough time and resources CFD can be spot on; but it does not have to be if developing a better product (performance, cost, weight, etc.) with less time and testing is your goal!
This article originally appeared on the IMAGINiT CFD Analysis Consulting blog.
Ryan Stamm is the Director Business Development, CFD Consulting at ImaginIT Technologies. Before starting IDP he was VP, North America Sales for Blue Ridge Numerics where he spent 8 years growing the CFdesign software and services business. Ryan can be reached at firstname.lastname@example.org.