New paper about Leading Edge Vortices in a moth

The first study of the flow above the wings of a freely flying insect, showing the structure of the lift boosting leading edge vortex, is published today by the Animal Flight Lab in Scientific Reports. The leading edge vortex is generally seen as a stable vortex, attached to the top surface of the wing, but this new study finds it to have a complex structure. At the inner wing the vortex has a single core, but mid wing and outwards the vortex is highly variable with multiple simultaneous cores. The highly variable flow may affect the aerodynamic control of the moth. In addition to the high complexity, the circulation of the vortex on the outer part of the wing is higher than the circulation measured in the wake behind the animal. This implies that the vortex accounts for the entire lift production at the outer wing and is in fact stronger than is necessary to generate the required lift force, which suggests a high aerodynamic cost of flight in the moths. These new findings will serve as a baseline comparison for past and future studies of the aerodynamics of insect flight based on tethered animals and mechanical flappers.

Composite image of a representative vector field, color coded by vorticity, showing the complex leading edge vortex above the wing on top of a photo of a Hummingbird hawkmoth (Macroglossum stellatarum)

Money money money

A great day for Animal Flight Lab as both Christoffer Johansson and Per Henningsson bagged research council grants for their research! This means excellent opportunities to carry out research of highest quality the coming 3-4 years. Per has just returned from a 3 year postdoc in Oxford, where he studied insect flight with Richard Bomphrey, will now get the opportunity to become established as a researcher. He will develop comparative studies of maneuvering flight between insects birds and bats, while Christoffer will aim at understanding more about the aerodynamic control of flight.

Congratulaitons!

Update from Brown about bat flight

Last Friday AFL alumni Rhea von Busse visited and gave a talk about her postdoc work at Brown University. Rye Waldman, also at Brown, also presented his work on flow visualization using dual plane light sheets and his work on the aerodynamics of compliant membranes. Rhea showed some really nice X-ray films of flying bats. These experiments nicely showed the movements of the wing skeleton during flight. Rhea also showed that bats can swim, but if they really liked it was not apparent from the footage.

Rye Waldman and Rhea von Busse.

Rye Waldman explains a wake.

New blue thing

As we are waiting to get the laser fixed a new shiny blue storing cabinet arrived. This will help us keep track of all the auxiliary equipment, such as lenses and manuals that now populate all other spaces in the control room to the wind tunnel. Here we can se it be assembled and put into place.

An intelligence test: the locking mechanism is put into function
Up to the right a female common scooter can be seen.

New paper on flight speeds of birds

When we wish to calculate how far a bird can migrate given a certain fuel load, or how fast a bird is expected to fly in a specific context (such as display, foraging or migratory flight), we often make use of flight mechanical theory. The backbone of this theory is the U-shaped relationship between power required to fly and the flight speed through the air (airspeed). The theory was developed/adapted for bird flight more than 40 years ago by the English scientist Colin Pennycuick. Over the years Colin has amended the theory by various experiments and measurements, often involving wind tunnels. Accurate predictions from this theory rely on a number of parameters that describe the aerodynamic properties of the avian body and the wings. Some of these parameters, the induced drag factor and the body drag coefficient, have now been explored in the light of new measurements of flight speeds using an ornithodolite. It turns out that birds are probably more efficient in generating the lift than previously assumed, and also that the body drag coefficient (describing how much drag the body is generating) may vary among species. The fieldwork for this study was carried out last autumn by CAnMove scientists together with Colin Pennycuick, who is at Bristol University, using a new ornithodolite consisting of a Vector range finder (a pairs of binoculars with a laser range finder), an anemometer for wind measurements and a computer for data recording. The fieldwork was carried out on the south east coast of Öland during the autumn migration period in 2012, where large numbers of a variety of species migrated. The paper is published in the Journal of Royal Society Interface, and is open access.

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.

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.

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.