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Wake field simulation and output
Hi David
I noticed that you provided A calculation case of “POLIMI DTU 10MW 1:75”, and I guess you may have verified something with it. Have you verified the aerodynamic or wake of this reduction model? Is there any relevant literature you can provide?
In addition, I would like to ask, did you verify his velocity profile with experiments when you were doing wake calculation? For example, what method do you use to verify the velocity field from 1D to 10D calculated by free vortex wake?
BR，
Roby
Hi Roby,
you can checout this publication for a wake validation study with experimental data:
- S. Cioni, F. Papi, L. Pagamonci, A. Bianchini, N. Ramos-Garcia, G. Pirrung, D. Marten, C. Molins, R. Bergua, E. Branlard, J. Jonkman, A. Robertson et al., 2023, “On the characteristics of the wake of a wind turbine undergoing large motions caused by a floating structure: an insight based on experiments and multi-fidelity simulations from the OC6 Phase III Project“, Wind Energy Science Discussions, Preprint
Wake velocity profiles are usually extracted as time averaged data using the velocity-cut-plane functionality in QBlade. To get reliable far wake data it is important that the simulations are converged and that the wake length and -discretization is sufficient.
BR,
David
Hi David
I have a question for you. Turbulence is characterized by turbulence vortex viscosity value (0~800) in free vortex wake, which can make wake recovery faster. In addition, I saw that you adopted 2% turbulence when verifying the wind tunnel test of 1:75DTU10MW wind turbine, I wonder if this turbulence concept refers to the inflow wind speed with 2% turbulence generated by Turbsim. Or can the 2% turbulence be represented in a vortex model? How did you set up the 1:75 model? (inflowwind and turbulence vortex viscosity value)
BR,
Roby
Hi Roby,
for the vortex viscosity I use the default value suggested by QBlade for this rotor size. This value also doesnt have a large influence in the near wake region which was subjcet to the validation.
Regarding the turbulence I did not model any turbulence in this validation study, laminar inflow was used for all simulkated cases.
BR,
David
Hi David
I also want to ask you, I simulated the wind speed 4.19m/s and 6.03m/s two cases of paper, I would like to ask about their Settings:
Did you use 240 and 265 rpm for these two cases?
How do you set their total simulation time or number of revolutions?
Vortex roll up, vortex stretch, shedding vortex, trailing vortex Have you turned them all on? Why did you choose the two-point lift theorem?
BR,
Roby
Hi Roby,
I used the exact RPM as specified in the publication.
The simulation needs to be long enough to converge. I simulated for 100 revolutions with a wake length of 20 revolutions to be sure it has converged. The time step was chosen so that the rotor increment is 5° azimuth per timestep.
All wake features (with the exception of vortex stretching) were activated.
The two point lift-drag method should improve accuracy for VAWT’s or highly coned rotors, in this study it didnt have any effect – so whether its active or not doesnt change the result.
BR,
David
Quote from David on 13. April 2023, 13:52Hi Roby,
the velocity at the wake center is so large because there is no “rotor” causing induction at the wake center and the nacelle influence is not modeled.
In fact, at the wake center the velocity is even slightly larger than the freestream velocity, caused by the induction of the wake vortices. This is also true due to the continuity equation. In the attached image red regions have higher velocity than the freestream and blue regions have lower velocity.
BR,
David
Hi David
The velocity deficit at the center of the hub obtained through CFD calculation (modeling of the hub) is still relatively large, in addition, my own method mainly considers tip vortices and root vortices, so it also restores the actual situation, if I want to make the velocity deficit at the hub in Qblade, should I choose to open the structural module? How to implement the wheel hub modeling you are referring to?
BR,
Roby
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Hi Roby,
the velocity deficit in the hub region cannot be modled with the LLFVW formulation in QBlade. The LLFVW only account for the rotor induction but cannot model nacelle surface flows´, separation etc.
There is a nacelle drag model in QBlade but this model only accounts for the drag forces acting on the nacelle, but but not for the effect of the nacelle on the flow.
BR,
David
