What is the characterisitc length of the flow in this case?

Question

We can compute Reynolds number to determine if the flow is laminar or turbulent, therfore we need a characteristic length; for example, In the case of external flow around an airfoil, we can consider $ L =c$ the chord of the airfoil. For internal flows, the characteristic length is the hydraulic diameter
My question is: in the case of a cigarette smoke, what is the characteristic length? How can we evaluate the nature of the flow in this case?
EDIT: Can we evaluate the nature of a flow without relating it to an object?

DilithiumMatrix · Answer

The only thing that provides scale to the problem: The size (edit: diameter) of the cigarette.

Always keep in mind that 'characteristic lengths' are generally poorly defined (e.g. why the cord of the airfoil instead of the height?  the maximum cord or ... ?).  The type of answer you get will generally be an order of magnitude one.

Floris · Answer

The smoke emanates from a certain area of the cigarette - namely the tip. The column of smoke is roughly the size of the top initially but as the hot air picks up speed the column quickly becomes narrower.

Note that is you spewed (cigarette) smoke from a large chimney, the aperture of the chimney would set the characteristic length. For the cigarette it is the size of the tip.

In all cases, these things only set an approximate scale of the problem.

What is the characterisitc length of the flow in this case?

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