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-   -   CFD code for very low Re Flow (http://www.cfd-online.com/Forums/main/866-cfd-code-very-low-re-flow.html)

Raj May 31, 1999 04:10

CFD code for very low Re Flow
 
Hi everyone, I am working on Aerodynamic Design of a MAV (Micro Air Vehicle) The size of my MAV is 6" weighing about 100 gms. and the reynolds number range is 5000 t0 20,000. I didnt come across any litrature published on tests on aerofoils for such low reynolds number range. My problem is to find a aerofoil which will give me the best performance for such low reynolds number application. 1. Is it possible to assist the performance of aerofoils in such low

Re range using CFD codes where span of the aerofoil is limited to few inches

& the aspect ratio is very less and so the 3D and the viscous effects are predominant.At such low Re range flow seperation and

the transition are the main problems which effects the aerofoils

performance. 2. please do let me know if you know of some experimental study done

on aerofoils at these low reynolds numbers. Regards Raj -------------------------------------------------------------------

Johan Schulten May 31, 1999 05:18

Re: CFD code for very low Re Flow
 
Hello Raj, In the Reynolds number range you are interested in (5-20K), experimental data are sparse indeed. Two references that may be helpful are: Hacklinger, Max, "Theoretical and Experimental Investigation of Indoor Flying Models", Journal of the Royal Aeronautical Society, Vol.68, Nov.1964, pp.728-734.[Re = 5K) Muesmann, G., "Measurements and Boundary Layer Observations on Fan Blade Sections (in German)", Zeitschrift fuer Flugwissenschaften, Vol.7, No.9, Sept. 1959, pp.253-264 [Re >= 17K] Even if you do not read German, the second reference is still valuable since it contains many self-explaining data. There may be well more recent publications in this area. I would advise to look also for papers on (small) animal flight analysis. Regards, Johan Schulten

John C. Chien May 31, 1999 22:06

Re: CFD code for very low Re Flow
 
(1). There are two ways to obtain data needed from a airfoil or a wing. (2). The first one is the wind tunnel testing. And this approach is practical. All you need to do is to find a wind tunnel, and put the wing in the test section. If you are working on wing, then it is likely that you are in the Aero-department. Some kind of low speed wind tunnel normally is available in the Aero-department. If you don't have access to a wind tunnel, then you can build one. I am sure that there are books on low speed wind tunnel testing. A one-foot test section should be adequate in this case. An electric fan or a blower should be enough for this purpose. (3). The other approach is to use a CFD code. You can try the laminar flow solution first. Then, you can run a turbulent flow case. In the process, you should be able to know whether there is a flow separation, or flow transition in your problem. From there, you can move into the research domain of transitional flow. (4). The approaches are rather straight forward. It all depends on how much data you are look for. Actually, you can scale down the published NACA airfoils and try to use lift-drag coefficient data first. In this way, you will have an opportunity to find out whether it is going to work or not. (5). You could contact NASA research labs to see whether you can talk to some one there.


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