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Fluid Dynamics and BBQs


A few years back I built a brick BBQ just beyond the end of my patio. The idea in positioning it was to be able to look down the garden when cooking, but also be able to talk to friends on the patio. Strictly speaking it’s an Australian style BBQ, so I guess I should call it a barbie ;)

It has a brick built base, so I spent some time thinking about where to site it as its not exactly moveable. I think I got it right, except there’s a snag. Whenever I use it I get a face full of smoke. I initially thought it was just the wind blowing the smoke in my direction, but I now realize that’s not the problem. If I stand at the side I also get a face full of smoke, or even at the back. If I step away the smoke swirls around if there’s any breeze, but otherwise it basically goes straight upwards.

The barbie, viewed from the patio

The barbie, viewed from the patio

I strongly suspect that the Coandã effect is causing the plume get deflected in my direction, and once it sticks to me that’s it. I guess the same problem applies to most BBQs that are not sited against a wall, or better still in a corner.

Well I’m not going to move it! I need to find another solution. I’m torn between making a metal back plate for it and see if that fixes the problem, and attempting to simulate it. Simulating it I can convince myself it IS the Coandã effect, find out if a back plate that will fix the problem or if the thing will need a chimney. If I try using a back plate it will either work or it won’t but if it doesn’t work I won’t be any closer to knowing why, or what to do about it, like use a bigger back plate.

I guess I’m going to have to simulate it at some point…

Barbie, CFD, Coandã Effect, Smoke Movement

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About John Parry

John ParryI started my career in the consultancy group at CHAM Ltd., using PHOENICS for a variety of CFD applications. From the consultancy group I moved into support, helping customers debug models, and figuring out how to model new applications. That broadened into delivering training courses and creating training material. I was invited to join Flomerics when it started in 1989 to head up Customer Services, and I jumped at the chance to work for a startup. After a few years supporting customers using FloTHERM I moved across into research, developing thermofluid models of common electronic parts, like fans and IC packages, later managing the DELPHI and SEED projects. More recently I worked with Flomerics’ Finance Director on the acquisition of MicReD, helping to integrate MicReD’s business into Flomerics Group which was great fun. Since Flomerics acquired Nika, I’ve been responsible for promoting the FloEFD suite in education, and moved into marketing. I now work as part of the Mechanical Analysis Division’s Corporate Marketing group, responsible for ElectronicsCooling Magazine and the division’s Higher Education Program. Expertise: I’m a chemical engineer by training and did a PhD in reactor design before getting involved with CFD more than 25 years ago. Visit John Parry’s Blog

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Comments 2

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This sounds like the sort of topic the UK CFD community needs to read about to cope with this summer's weather. How about writing up your methods and conclusions for Benchmark Magazine?

12:24 PM Jul 27, 2009

Agreed. I've made some progress on this, but don't want to let the cat out of the bag until I've got to the bottom of it. One of the great things about CFD (as you know) is its ability to open your eyes to what's going on, and as in this case, so often there's more to it than you expect!

John Parry
12:31 PM Jul 27, 2009

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