claude-andrew (asker) Apr 23, 2012:

@Kwiland Bear Your suggestion would be fine except that, like Tony's "contrary to", it requires an object after "to", which would be awkward to fit in to the sentence. Thanks anyway for your contribution.

claude-andrew (asker) Apr 18, 2012:

@Chris I like it, Chris - bring back "contrariwise"! (129 000 google hits actually ...)
I note that, according to wikipedia, Horace Lamb said ""I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.""

chris collister Apr 18, 2012:

shift of emphasis? ...EVEN THOUGH the path is more or less rectilinear; hence the flow is not turbulent, but IS rotational. Personally, I don't have a problem with "on the other hand", or even the archaic "contrariwise" as the great Horace Lamb might have said (and probably did).

claude-andrew (asker) Apr 18, 2012:

Don't apologise Tony, if one is arse about face it's best to know!
"In contrast to this, fluid particles turn about themselves in a flat-plate boundary layer while their path is quasi-rectilinear, and so this is rotational, not turbulent flow".
Views very welcome!

Tony M Apr 18, 2012:

Er... sorry Claude... ...but that's really rather arse-about-face, if you'll pardon the expression!

I think it's both awkward and unclear, and as I have said already, I feel that in EN the flow of ideas needs to start with your end part, with the 'unlike....' clause parenthetically within it. There is no logic to your semicolon or 'this, then...' — in fact, it could even be read as implying that 'this' refers to what immediately precedes (i.e. laminar flow), whereas in fact it needs to refer back to the preceding sentence.

claude-andrew (asker) Apr 18, 2012:

What I came up with In contrast to this, in a laminar boundary layer, the fluid particles themselves rotate while their trajectory is virtually rectilinear; this, then, is not turbulent but rotational flow.

Tony M Apr 18, 2012:

In contrast... Claude, I think it could work too, but look first at the logic of the sentence and the 'donc', I feel you may well do best to start with that and then take it from there.

claude-andrew (asker) Apr 18, 2012:

@ Chris I know, Chris - the semi-colon is a neglected species in French. I've always been a great fan of this puncruation mark, and (by the way) have always recommended it to my English students as our way of writing "En effet".

chris collister Apr 18, 2012:

Punctuation As in English, French seems to be abandoning the semi colon or full stop in favour of the comma. A semicolon after "even though their paths may be quasi-rectilinear" makes more sense, as would a comma after "A l'opposé".

claude-andrew (asker) Apr 18, 2012:

@ Tony What about "In contrast to this"?

Tony M Apr 18, 2012:

'on the other hand' Although informally we understand the sense of this, in actual fact, it wouldn't really work very well starting your sentence with it here. The contrast is between two types of particle behaviour, but 'on the other hand' doesn't quite fit here, IMHO.

claude-andrew (asker) Apr 18, 2012:

@Chris As you say, Chris, "On the other hand". Thanks.

chris collister Apr 18, 2012:

My early days of fluid dynamics made my head ache, but the concept of "rotatation" is essentially this: imagine a compass rotating around a circle; the needle always points north, regardless of what the compass is doing, so the fluid is not rotational. By definition, laminar flow is never turbulent.
In answer to the question, I think he just means "on the other hand" or "by contrast", are rotating about themselves in a plane laminar boundar layer.

claude-andrew (asker) Apr 18, 2012:

Thnaks to all for quick replies, and yes kiwiland, it is straightforward now, on re-reading; I simply need to start the sentence with "On the other hand,". This happens from time to time: I get stuck on a sentence which might be a bit clearer if the order were changed.

Ronald van Riet Apr 18, 2012:

different types of turbulence In the first case, it is layers of air, internally quite stable, that have a rotating motion and form the turbulence. This is the typical wing tip vortex that in moist air can be clearly seen as the air condenses into white plumes streaming off the wing tip.
In the second case, the layer itself is quite stable, but the molecules inside the layer are moving about. Although I must say that laminar flow is not normally regarded as very turbulent internally. Laminar flow over the wings gives the least drag and that can only happen if there are few collisions between the individual molecules and the wing surface. But who knows, perhaps the writer has discovered a new phenomenon ;-)