Pre-conditioned flash lamps in place

As for the replacement from old to new flash lamps in the PIV laser, we now had a third batch of lamps to install. Replacing these lamps is a risky business for various reasons, not only the need of climbing the tunnel but also the actual replacing these delicate (easy to break) filaments. And when the fourth (final) lamp was to be inserted - i broke! A word signaling a problem was heard from the tunnel top and it was immediately clear that something had gone wrong. Immediately checking with Litron people, however gave some hope in that it might work with one of the non-conditioned lamps in tandem with a pre-conditioned one. Some more work and then a final test - it worked. So, now we have a laser with a complete set of flash lamps. We now only have to align the thing to optimize the set-up for maximum power output.

PIV laser gets new flash lamps

As the laser has lately given only about 25 mJ per pulse when set to maximum power, we figured it is perhaps time to change the flash lamps. In our Litron laser there are 4 lamps to replace, and on Friday afternoon we had everything in place, i.e. the lamps, new o-rings, appropriate laser manual and isopropyl alcohol to clean the new lamps. It took some time, and even if the manual explicitly said "do not lose" about 4 particular 3M bolts that was exactly what happened to one of them. It fell to the floor, two bounces was heard and then it was gone, probably it fell to the basement. The lost bolt must have moved a horizontal distance of at least 1 m, while subsequent experiments with a similar bolt showed an average horizontal displacement from the position of first floor contact of about 15 cm! However, we found new stainless steel 3M bolts and could proceed as planned. Also cooling water was renewed and before that we had changed to new filters. So, no we will hopefully get back the strong and clear light sheet that make stereo PIV such a nice method.

New Lab meeting procedures

As we have agreed we will try a new strategy regarding our lab meetings, by having one meeting every week, starting at 09:00 Monday. The place will be the seminar room "Argumentet". In this way we can keep ourselves more informed and it should facilitate co-ordination of wind tunnel activities during the rest of the week. So, this new system will begin next Monday, 19 October, and I have also selected a paper for us to read until then. The paper is "Flapping wing flight can save aerodynamic power compared to steady flight" by Umberto Pesavento and Jane Wang. It appears in Physical Review Letters, which is the tabloid equal for physical sciences.

New Lab Publication in J Exp Biol

In a new paper, published in J Exp Biol 212: 3365-3376 (2009), Christoffer Johansson and Anders Hedenström report on wake properties of blackcaps (Sylvia atricapilla) studied on the Lund University wind tunnel. They use a high speed stereo-3D PIV system to get information from the entire wake behind the flying bird. It was found that the wake geometry was slightly more complicated that previously thought about passerine birds. This is mainly due to that the PIV system used is capable of detecting more subtle features of the wake, than with previous 2D visualization. Another twist is that one bird accidentally molted its tail, but flying without a tail did not cause any dramatic changes as to the bird's wake. The function of the tail, whether it is a lift generating surface or if it works as a splitter plate that reduces the drag, remains unclear. New experiments will hopefully teach us more about what birds have tails for.

New Publication from Oxford Group

In a new paper published in Science last week the Oxford group of animal flight, headed by Adrian Thomas, shows how important it is for a locust to have appropriate camber and wing twist to maintain the high performance achieved by insect wings. The way they do it is by using a CFD (computational Fluid Dynamics) model, and in a stepwise manner remove the camber and twist exhibited by the real locust. Before trusting the model output, the CFD model was validated against real data using smoke flow visualization and PIV measurements obtained from locusts tethered in the wind tunnel. In accompanying podcast Adrian explain certain problems they had in modeling the upstroke of the hind wings, so go an listen also for that.

Final symposium tally

Abstract submission has closed for SICB's 2010 meeting, where we (Isabelle Bisson, Martin Wikelski, and I) will be holding our Integrative Migration Biology symposium. The way SICB organizes the meetings, the 13 symposium speakers (including Anders, Susanne and myself) are set, but people can apply to give a presentation in a coordinated session. The official numbers are in, and our symposium attracted more coordinated session speakers (24) than any other symposium this year! I can't wait to meet and talk with everyone who's coming; it sounds like there will be some great presentations.

You can still register for the meeting if you haven't already; it should be a lot of fun--and there are plenty of biomechanics talks for those of you who are less interested in migration than I am!

New Lab intern: Roel Vleugels

During the autumn 2009 Roel Vleugels, a student of aeronautical engineering at Delft University, is visiting our lab as part of his master program. Roel is going to adapt our aerodynamic balance for precise measurements of aerodynamic forces on different wings, such as flat plates and the Eppler 387. He will also make measurements on the drag of a swift look-alike model bird body. We welcome Roel to the group and hopes he gets a great time while here!