Inflow Model comparison

[Majjari.Chaitanya]

Hello All,

I have a question about the Equil and DynIn inflow models, we use in Aerodyn input file.

I have a loadcase, where my input wind velocity is 10m/s, rigid model and used Equil model. I have also simulated the same loadcase using DynIn model. The results with both load cases are not as expected. For example, My rotor speed began to drop after certain time period. I'm doing a compariosion with other simulation software like Bladed and the results are completly different from it. I have read a earlier post that Aerodyn has differnt behaviour for wind speed is 8m/s. However, In my case it is greater than 8m/s.
I have attached a file, which shows the results of my loadcase with "DynIn" model, in which the Red plot is FAST, Green plot(box) is Bladed.

Regards,
Chaitanya

[Jason.Jonkman]

Dear Majjari,

Is the green curve with "X" symbols the FAST EQUIL result?

My guess is you are seeing odd behavior because the rotor speed starts at zero. The dynamic-inflow model of AeroDyn (DYNIN) is formulated using nondimensional terms based a nominal tip-speed ratio (TSR) and while the model should be able to handle small variations in TSR, in your case, the TSR variation is very large, which I would guess would cause problems.

The DYNIN model functions best for cases involving a turbine operating in turbulence above rated wind speed. I would suggest being cautious applying DYNIN in other cases, where the EQUIL model is likely more appropriate.

Best regards,

[Majjari.Chaitanya]

Hello Jason,

Thanks for the reply. The green curve with "X" symbol is the results from another software called "OneWind". However, My FAST results with Equilibrium Inflow model look alike as BLADED.
I would like to elaborate about my loadcase:
>>Tip lossses -- ON
>>Rotor DOF -- ON
>>Pitch -- ZERO, fixed
>>Yaw -- ZERO, fixed
>> Rotot Inital Speed -- ZERO
>> My generator is OFF and my rotor is free to rotate
>> Wind speed --- Fixed 10m/s
>> Using FASTV8 with AerodynV14
I have also simulated the laod case with higher wind speeds (Rated wind speed of my turbine is 10.8 m/s), but the result is same. I have tried to look how my TSR varies. However, I could not find a sensor for TSR. I have found that we have a sensor for TSR in Aerodyn V15. Is it possible to control our TSR?

Regards,
Chaitanya

[Jason.Jonkman]

Dear Chaitanya,

I'm not sure I understand your question, but while you can output TSR with AeroDyn v15, it is not possible to output TSR with AeroDyn v14 without modifying the source code. However, you can compute TSR manually by outputting the rotor speed and wind speed.

Best regards,

[Majjari.Chaitanya]

Dear Jason,

I agree to your point that I can calculate the TSR manually. As TSR is dependent on the variables "Wind Speed" and "Rotor Speed", my "Wind Speed" is constant and I would like to know why my rotor speed began to drop after some time when I use Dynamic inflow model. I could even share my input files if you need to have a look at them.

Thanks,
Chaitanya

[Jason.Jonkman]

Dear Chaitanya,

I don't think DYNIN will give you good results if you start the rotor speed at zero because the TSR range is then guaranteed to be large and beyond the limits of the model. My guess is you'd get better behavior if you initialize your rotor speed closer to nominal speed (say between 20-25 rpm).

Best regards,