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-   -   Turbulence settings for external flow around a kite (http://www.cfd-online.com/Forums/main/90578-turbulence-settings-external-flow-around-kite.html)

RobinTU July 14, 2011 07:36

Turbulence settings for external flow around a kite
 
Recently i started to investigate on kite aerodynamics. I would like to know about turbulence settings when using the k-w SST Transitional model.

I am simulating the flow around a kite at about 100m-200m height. I noticed that setting turbulence intensity and length scale can have major impact on your results. When it is defined at for example the inlet, then intensity reduces depending on length scale and therefore lower intensity reaches the kite/wing. In this way one could find multiple combinations of turbulence intensity and length scale to arrive at a required value arriving at the wing. Still then length scale will influence the amount of turbulence originating on the wing.

How could one find the required settings for e.g. this case of a kite?

julien.decharentenay July 14, 2011 21:02

Hi,

The short answer is that it "depends" or in other words you will have to make an educated guess.

The turbulence parameters (turbulence intensity/kinetic energy and length scale) are a reflection of the turbulent wind environment. My guess is that it should not be too turbulent at 100m-200m height as long as you are surrounded in a low-height environment (away from mountains and high rise buildings).

To guess-estimate parameters, I would recommend looking at atmospheric boundary layer(ABL) profiles - more specifically at papers looking at simulation the ABL using CFD. There has been work done to develop inlet and free-stream boundary conditions to allow for the simulation of ABL. Some authors are hinting that the inlet profiles of velocity and turbulence are essential together with a free-stream boundary condition that maintain momentum.

Reference (since it is likely to be the next question): "Appropriate boundary conditions for computational wind engineering model revisited", by P.J Richards and S.E Norris, Journal of Wind Engineering and Industrial Aerodynamics 99(2011) 257-266.

Hope this help.
Julien

RobinTU July 15, 2011 06:26

Thanks Julien!:D:D

I will take a look at the reference. Will let you know if I'll still get stuck.


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