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Blade station airfoil optimization
I have been mulling on how to optimize the foil design at each station. It seems like being able to see what the Cp per section is would be very helpful (vs. just for the whole rotor)? In the blade optimization section of the program, you can optimize for chord and angle of attack. That doesn’t necessarily mean that you are running the right foil in the first place. It may be optimized for that foil, but there may be a much better one out there. In the rotor BEM section of the software you can examine axial induction vs. radius or L/D vs. radius, but not Cp. Any tips from the QBlade community on what the best way to understand/optimize the specific performance of each section foil would be greatly appreciated.
Thanks!
Oran
Hi Oran,
you could obtain the local Cp value from the other variables that are plotted, such as:
CP_local = 4a(1−a) * tsr_local * sin^2(ϕ),
where ϕ is the inflow angle, a the axial indiction factor and tsr_local the local tip speed ratio.
In practice, having an axial induction factor of 1/3 along the span of the blade is optimal. When a is around 1/3, the product 4a(1−a) reaches its maximum – the maximum achievable power extraction for a given streamtube of wind.
However, note that in wind turbine design its not just about maximising power, but about finding a good balance between power and loads (rotor thrust), and the suitability, rigidity, manufacturability and roughness sensitivity of the airfoil sections chosen for a blade design.
BR,
David
