How about some photos? Does anyone have an example of such behavior so we can get a better idea of what we are talking about?
As a glider pilot, I've spent a great deal of time studying airflow over both wings and terrain features. I think it will be very difficult to make general statements about this type of wear because of many complex factors. There will be both large and small scale factors. Placement of the dials is an important large scale factor because most are probably NOT situated where they are exposed to wind that is consistent in direction or velocity. An example of a consistent site would be on a ridgeline or seashore where there are no obstructions. In just about any other location, trees, buildings etc. cause turbulent airflow that is difficult to model. On a small scale, with consistent airflow, there is no doubt that incised lettering will disrupt airflow and could cause modification of wear pattern. This will probably happen even with a turbulent, non-laminar airflow as a dial face but it is much more likely to be inconsistent. Tom >I'm sure there must be many list members conversant with fluid flow who might be able to comment on a possible alternative which occurred to me viz. is it at all likely that turbulence caused by the deeply-incised lettering would somehow cushion the lettering and its immediately surrounding areas and protect them from wind-borne sand etc. while flat areas took it full in the face?< Very interesting - it would be nice to know. We do see this effect quite a lot on very old UK dials and most such dials are South -ish facing - at least I have not recognised any trend to say that this effect is only present on dials with certain declinations. Aren't our winds predominately from the SW? I suspect that if it were caused by wind generated turbulence we should expect to see some bias in the weathering to one side of the letters. I don't recall that but will now try and have a look! (Anything to divert me from decorating...!!) Patrick -
