Hello everyone!
I was designing a turbine blade for wind speeds in the region of 6.75 meters per second in Qblade. When creating the 2D Polaris in Qblade I have to input Reynold's number, (which is 1mil by default). After that, I can move onto the next portions. I understand that to Find Reynold's number you need the chord length of the airfoil.
Do, I have to assume a chord length(Like a constant 0.2m whole spanwise chord length)? or is there any other way for it?
Or is there any standard Reynolds number range for different turbines?
My rotor diameter is 40 meters and it generates around 120kW of power.
Please help in this regard.
QBlade's simplification is to assume that airfoil polars depend only slightly on Reynolds number, Re, (which is true as long as there are no large variations in Re, and Re is not too low). There is an optional correction to the drag coefficients when the actual Re in a simulation deviates from the one used to define the polars (at that point the whole blade, chord included, must be already defined).
In summary, it is ok to define the polars using the default 1e6 Reynolds number.
You can find more details in the "QBlade Guidelines" document found in their webpage.
For rotating wing it is common to use the 0.75R section as the reference section which represents the entire blade.
Thus, you can just use a single set of polars, matching the 0.75R section.
This brings some inaccuracies, which are minor.
For more meticulous estimation, one should use a Re dependent polar with interpolation capabilities.
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