When you are sitting in a room where there is a source of bad smell, such as som

Question

When you are sitting in a room where there is a source of bad smell, such as somebody smoking or some other source of bad smell, it is often a solution to simply move to another spot where bad smell is not present. Assuming you are not actually the source of the smell, this will work for a while until you notice the smell has somehow migrated to exactly the spot where you are now sitting. Frustrating.

This got me thinking about the fluid mechanics of this problem. Treat bad smell as a gas that is (perhaps continuously) emitted at a certain fixed source. One explanation could be that human breathes and perhaps creates a pressure differential that causes the smell to move around. Is there any truth to this? Please provide a reasoned argument with reference to the relevant thermodynamic and/or fluid quantities in answering the question. Theoretical explanation is desired, but extra kudos if you know of an experiment.

Explanation / Answer

From a fluid dynamics standpoint, as a body moves through a fluid, a small region of fluid is dragged along with it. This is what forms the boundary layer. In the near-body region, odor will be dragged along with the body.

Likewise, behind a moving person is a turbulent wake and a low pressure region. The low pressure reason will "suck" the odor along with the body, and the turbulence will mix the odor into the air which will also help distribute it.

Turns out there is an experiment, in this paper, that looks at the effect of a stationary body and a moving body (as in human body) in a room with stratified contaminants. The principles discussed therein are along the lines of your question.

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