Closed petebachant closed 9 years ago
Plot angle of attack and relative velocity squared for the upwind half of the rotation to show what the ideal Cl/Cd curve would look like. Maybe the integral weighted based on the PDF of AoA and relative velocity squared.
Really we should be looking at tangential force coefficients. I did a simulation with XFOIL for a NACA 0020 and 4520 foil--the 4 percent camber at half-chord added to try to mimic the flow curvature.
Calculated max 2-D turbine torque coefficient from geometric considerations only (no induction) and XFOIL static data. I think this is a good way to predict Reynolds number dependence.
Note how the camber does push the Reynolds number dependence down as you had mentioned before, @wosnik, which explains why the Re-dependence is weaker for the RVAT compared to the RM2--a little preview for the next paper on that.
These results also suggest the use of an outward (opposite blade path) camber foil to improve performance, similar to the UGE design.
This also explains the differences we are seeing between the UNH-RVAT and the RM2.
Basically L/D ratio for a blade. Make an updated version of the old diagram I used during my MS for turbine loading with high and low L/D.