Flow Simulations, Inc.
Computational Fluid Dynamics (CFD) Models
Provided on a Consulting Basis for Industry
954-843-1400
info@flowsimulations.com
 
Contours of liquid volume
fraction inside of a crude
vacuum distillation tower
 
Eulerian multi-phase model

CFD Consulting Services



Flow Simulations has been offering CFD Consulting since 1994. CFD Consulting is the practice of making CFD models for companies (and people) on a contract basis. Over the past 22 years we’ve developed some guidelines which we believe are useful for companies that require CFD consulting. There are undoubtedly additional technical issues but this is intended as more of a business guide.

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Recommended CFD Consulting Best Practices

Item 1: Is CFD a core part of the vendor’s (or consultancy’s) business?

For example you may be buying a heat exchanger and the equipment vendor may boast of their capability and experience in just doing CFD models of heat exchangers. Also they may offer a very good price on the CFD consutling, simulation, or model,.

However, the CFD model cost: a few thousand dollars, may be insignificant compared to the value of the equipment sale. Thus an innate bias exists, however well-intentioned the vendor. Thus if a more time consuming meshing method (for example discretizing the mesh down to the laminar sublayer) would show deficiencies in their equipment, they may not put the extensive additional work into the CFD model to show performance problems with their equipment.

CFD consulting example: heat exchanger X-section mesh

Item 2: Does the CFD vendor do CFD as a core part of their business?

Flow Simulations had an experience where a very large and prestigious engineering consulting firm, based in Houston, TX, was engaged to do CFD consulting and modeling of part of a distillation column. They had a very prestigious background in structural mechanics modeling: FEM (finite element method) and made a very strong case for doing the CFD modeling as well.

However they requested 50% of the CFD modeling fee up front.

Long story short, they had no in-house CFD capability. They used the 50%, paid in advance, to hire a CFD consultant: who as it turned out was a specialist in FEM. Thus their meshes were constructed for FEM and were unable to resolve complexities in critical flow areas. Also because of the FEM basis, they were unable to converge: hence the CFD consultancy presented unconverged results to the client, without telling them that the results were not converged. Fluent, now Ansys, published the following warning: “Unconvergeed Results can be very misleading and should not be used for engineering judgements”.

Item 3: Always request convergence plots as part of your results set

There should be no additional charge for this. Also always mention that you wish to have a copy of the model files themselves. Our model files come in three parts (Gallia est omnis divisa in partes tres). The mesh files, the case / data file set, and Excel spreadsheets carrying the setup calculations and boundary condition calculations.

There should be a minimal charge for these items: we typically charge for 1-2 hours for a DVD set. If a charge is much higher, one has to wonder if they’re making it unduly hard to be able to check their work.

Item 4: Communications

When I worked for Bechtel I found that most client/ vendor problem interactions were due to miscommunications. Either some line item was missed or an assumption was made about wording. Thus it is imperative that CFD proposals and expectations of the items to be delivered should be clearly delineated. Thus if written and spoken communications are not clear then consider looking elsewhere for CFD consulting.