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How to Predict Rotor Rotational Speed
Dear all,
I would like to inquire about using Q-Blade software for simulation purposes. During the simulation, I am prompted to input RPM values to obtain predicted aerodynamic performance, including aerodynamic power, torque, and others. However, for wind turbine configurations under the same wind speed conditions, but with different blade inertias, hub, etc, different power outputs and torques will be produced. My question is: how can I adjust Q-Blade to incorporate blade inertia effects and obtain predicted rotor speed (omega) and power output? Thank you. I am new to Q-Blade software and would appreciate any guidance on this matter. Thank you.
Regards
Setiawan
Hi Setiawan,
from a purely aerodynamic analysis you can find out at which windspeed/rpm combination your blade design will perform best (Cp vs TSR curves).
To add mass, inertia and other structural properties you need to assign a complete structural model. Check out the examples in the download section, most contain a complete structural model definition. Turbines with a structural definition can then also be simulated with a controller which tries to operate the rotor at the optimum rpm for each windspeed. How the rotor rpm is following a change in windspeed is then also affected by the rotor inertia.
So the real life operation of a wind turbine has to modeled as a combination of aerodynamics, structural dynamics and control (causing opposing generator torque and blade pitch actions). Each simulation that does not take all of these aspects into account is a simplification or idealization. For example you could also run an aero-elastic simulation without a controller but with a prescribed constant rpm. Or you could run a simulation with a “free” rpm where the rotor is only affected by aerodynamic forces but opposing generator torque is missing. In such a case the rpm would simply increase until the simulation starts to diverge.
Best,
David
Dear David
Thanks for your explanation. I really appreciate it. Based on your guidance, now I can predict the rotational speed of my rotor by including the structural properties (mass, inertia, etc). I have run several simulations by varying the windspeed velocity and I got the results as shown in figure 1 and 2 attached below. The green, red, and blue lines describe the constant/uniform windspeed at 5 m/s, 7 m/s and 9 m/s respectively. I think the result is quite good and make sense, however when I try to vary the windspeed profile (figure 3) then I got the other results (figure 4 and 5). Let me ask you, would you please explain to me why do I get a negative aerodynamic power value when the rotor rotational speed value is dropping? Note: The windspeed profile that I created comes from by modifying the Hub height file on the Qblade documentation.
Regards
Setiawan
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Hi Setiawan,
whan the turbine is operating at a high TSR it’s power coefficient (CP) will be negative. As you know TSR is the ratio of rotational speed vs windspeed, so a high TSR can either be cause through and increase in rpm or through a decrease in windspeed. I guess thats the reason why you are seeing negative power.
If you dont include a generator which is applying its torque to the rotor, the turbine will simply accelerate until it reaches the TSR at which the power coefficient has reached zero and the rotor rpm is in equilibrium aerodynamic torque is zero.
BR,
David
