29 January 2013

Hummingbird aerodynamics

Todays lab meeting was fully devoted to hummingbird aerodynamics. Firstly, Marta Wolf, who has just returned from a 2-year postdoc in the flight lab at Berkeley University presented her fascinating results from studies of Anna's hummingbird. We learned a lot about how it is to work with hummingbirds, which seems to be easy on one hand but also difficult as birds mass is only about 4.5 g (like a rather lean goldcrest) and they can rapidly loose weight and may have to be released. Marta showed PIV data on the hovering wake, as well as nice illustrations about hummingbird hovering in a box.
Second on todays agenda was the paper from the Altshuler lab about the hovering wake in hummingbirds, which was published i Experiments in Fluids during the last week. The authors claim their data show that the wake consists of bilateral vortex loops, one shed from each wing. In this sense the hummingbird wake show similarities to the typical wake of bats. However, we had some difficulties on seeing what the authors could see in their smoke visualization movies, while we will have reason to return to these data.

19 January 2013

Cleaning up and some nostalgia

An old TV monitor is removed

Organization is restored
The old optic rail
Laser optics from MG
Space under test section where the PIV
laser used to live
Yesterday, Friday,  all Lundian members of the lab spent most of the day cleaning and tidying up in the wind tunnel. The reason is that we will soon get new PIV equipment and we need to free space around the test section in order to accommodate the new laser and camera set-ups. We also took the opportunity to clean out and organize the "control room" (the wind tunnel lab office), where lots of computers and monitors have accumulated over the years, which are not used anymore. The biggest operation was the removal of our first PIV laser, a 10 Hz rep rate pulsed laser from Spectra Physics. This laser has served us well and was instrumental to our first custom-built PIV system  that resulted in the first DPIV study of a live animal in free flight (Spedding, Rosén and Hedenström 2003, J Exp Biol). The same laser stayed with us when we replaced the two-camera system with one camera, which we used for our first PIV study of bat flight (Science 2007). After that we have used a stereo-PIV system and Litron laser of 200 Hz. Now it is time to get the 3rd PIV laser to the Lund wind tunnel, and we are grateful to the old equipment that has worked so well over the years. Especially the Spectra Physics laser has been very reliable, but at 10 Hz it is time for retirement. We also removed the rail of mirrors and light sheet optics from Melles Griot, which has been replaced by modern optic arms attached directly to the laser.

15 January 2013

Flight Lab 2013 initial efforts

The transition into 2013 has involved a well deserved holiday for members of the Animal Flight Lab, and we have now gathered  gain to resume activities. The Tuesday lab meetings are now populated by two more people than has been the rule the last year. Marta Wolf has returned back from her postdoc at Berkeley, California, and will now join us again, initially on her repatriation funds. Anders attended the annual meeting of the KTH Linnaeus FLOW centre, where he gave a talk about the research we have carried out over the last decade or so. After the meeting he visited the low turbulence windtunnel at the Department of Mechanics (see picture), where research on flow transition is a current point in focus.

Today the entire group made a joint effort to move the boxes containing the laser for our new PIV system. As last time we encountered some problems in getting the large and heavy wooden boxes into the wind tunnel building, but we completed with success. The image shows when we rejected the first method of getting the power supply in through the side door, an attempt that was abandoned in favour of the more direct route through the basement floor after having unpacked the box.