Hi,
i am simulating flow past a rotaionally oscillating cylinder. i've read some papers related to this and found that some authors were taking Re based on the perimeter and some based on the sqrt(a.b) (a,b- half of major and minor axes).
Mean position of the cylinder is going to be the major axis which is perpendicular to the flow.
Thanks.
it depend on which length scale you want to measure as the characteristic length always use to describe Re and Re length definition change according to the range of scales you work with
but any way the first vortex length can be define by D/2 for your body
The general rule of thumb is that the largest length scale in the flow is associated with the geometry. For the case of a flow around a cylinder (static or rotating), the largest length scale should be equal to the diameter. There are also interesting topological reasons why the cylinder diameter is taken to be the length scale (A. Widmann, 2015).
Therefore if you are interested in the "global" Reynolds number, you may simply use the cylinder diameter. You may also use the sqrt(a*b), which is equal to the radius for a cylinder. Some people choose to use the radius rather than the diameter, which is fine. But I personally prefer to use the diameter due to its physical meaning in vortex shedding dynamics. (Refer to A. Widmann, 2015).
In an external flow or Internal flow problems
In General D (Diameter of cylinder) is proffered.
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