Help about BEM and NREL's Phase VI
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Re: Help about BEM and NREL's Phase VI
Sir, thanks for the file that you provided. I checked it and observed that the data concerning structural properties covers the radius until 5m only.
I'm using the r= 5.029m.
any idea about this one sir? should I extrapolate for instance to get the data @ 5.029m?
I'm using the r= 5.029m.
any idea about this one sir? should I extrapolate for instance to get the data @ 5.029m?
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Re: Help about BEM and NREL's Phase VI
Dear Wesley,
You could extrapolate, or perhaps use the data from r=5 at the tip.
Please keep in mind that these are "estimates" and their accuracy is not guaranteed. You may need to do "tuning" anway to get the desired response.
Also keep in mind that the UAE Phase VI rotor was very rigid for conventional blade standards. It may not matter how accurate the properties are because the aeroelastic effects of this rotor are mostly negligible.
Best regards,
You could extrapolate, or perhaps use the data from r=5 at the tip.
Please keep in mind that these are "estimates" and their accuracy is not guaranteed. You may need to do "tuning" anway to get the desired response.
Also keep in mind that the UAE Phase VI rotor was very rigid for conventional blade standards. It may not matter how accurate the properties are because the aeroelastic effects of this rotor are mostly negligible.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 21
 Joined: Sun Apr 17, 2016 12:18 am
 Organization: self
 Location: Philippines
Re: Help about BEM and NREL's Phase VI
Sir,
Good day!
Sir, if I'll use NREL Phase VI for aerodynamic validation, could I use cn, ct as the parameters of comparison for my BEM code? I've seen a tabulated data about this (i.e. Jonkman, 2003), though I have some reservation upon reading that these data (cl, cd, wind speed, aoa, cn, ct) reflects the operational environment of the wind turbine. Should I use the experimental data concerning power, torque (as functions of wind speed) instead?
Kind regards,
Wesley
Good day!
Sir, if I'll use NREL Phase VI for aerodynamic validation, could I use cn, ct as the parameters of comparison for my BEM code? I've seen a tabulated data about this (i.e. Jonkman, 2003), though I have some reservation upon reading that these data (cl, cd, wind speed, aoa, cn, ct) reflects the operational environment of the wind turbine. Should I use the experimental data concerning power, torque (as functions of wind speed) instead?
Kind regards,
Wesley

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Re: Help about BEM and NREL's Phase VI
Dear Wesley,
I guess it all depends on what you intend to validate. All channels recording during the NREL Phase VI Unsteady Aerodynamics Experiment (UAE) will well tested/calibrated.
Best regards,
I guess it all depends on what you intend to validate. All channels recording during the NREL Phase VI Unsteady Aerodynamics Experiment (UAE) will well tested/calibrated.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 21
 Joined: Sun Apr 17, 2016 12:18 am
 Organization: self
 Location: Philippines
Re: Help about BEM and NREL's Phase VI
I see, thanks sir.
My data got closer to the computed power, however variation exists in cn, ct.
Sir, concerning the formula for cn, ct= are they in terms of inflow angle or angle of attack?
btw, sir, regarding structural modelling,any idea how's proportional modelling approached?
Kind regards,
Wesley
My data got closer to the computed power, however variation exists in cn, ct.
Sir, concerning the formula for cn, ct= are they in terms of inflow angle or angle of attack?
btw, sir, regarding structural modelling,any idea how's proportional modelling approached?
Kind regards,
Wesley

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Re: Help about BEM and NREL's Phase VI
Dear Wesley,
I'm sorry, but I don't understand your questions. Please clarify.
Best regards,
I'm sorry, but I don't understand your questions. Please clarify.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 21
 Joined: Sun Apr 17, 2016 12:18 am
 Organization: self
 Location: Philippines
Re: Help about BEM and NREL's Phase VI
Sir,
I'm doing BEM using Excel for initial testing.
I notice for the blade element at the tip (i.e. r=R), the axial and tangential induction factor becomes 1 and 1 after the first run. This becomes a problem when the second run starts as the Relative Velocity at that element is zero. Any idea about this one sir?
Kind regards,
Wesley
I'm doing BEM using Excel for initial testing.
I notice for the blade element at the tip (i.e. r=R), the axial and tangential induction factor becomes 1 and 1 after the first run. This becomes a problem when the second run starts as the Relative Velocity at that element is zero. Any idea about this one sir?
Kind regards,
Wesley

 Posts: 4862
 Joined: Thu Nov 03, 2005 4:38 pm
 Location: Boulder, CO
 Contact:
Re: Help about BEM and NREL's Phase VI
Dear Wesley,
I'm assuming this Excel file you are referring to has your own implementation of BEM?
When looking at the limit of the BEM solution with the Prandtl tiploss model as r > R at the tip, I would expect that a > 1 and a' > 0, which is what we have implemented in AeroDyn v15. (AeroDyn v14 and earlier never allowed nodes to lie right at the tip.)
In our AeroDyn v15 implementation, we simply set a = 1 and a' = 0 for any nodes lying right at the tip when Prandtl tip loss is enabled. You can do the same in your Excel implementation of BEM, or you can probably get around any problems right at the tip by ensuring that nodes are not placed within some tolerance of the tip location.
Best regards,
I'm assuming this Excel file you are referring to has your own implementation of BEM?
When looking at the limit of the BEM solution with the Prandtl tiploss model as r > R at the tip, I would expect that a > 1 and a' > 0, which is what we have implemented in AeroDyn v15. (AeroDyn v14 and earlier never allowed nodes to lie right at the tip.)
In our AeroDyn v15 implementation, we simply set a = 1 and a' = 0 for any nodes lying right at the tip when Prandtl tip loss is enabled. You can do the same in your Excel implementation of BEM, or you can probably get around any problems right at the tip by ensuring that nodes are not placed within some tolerance of the tip location.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 21
 Joined: Sun Apr 17, 2016 12:18 am
 Organization: self
 Location: Philippines
Re: Help about BEM and NREL's Phase VI
Jason.Jonkman wrote:Dear Wesley,
I'm assuming this Excel file you are referring to has your own implementation of BEM?
When looking at the limit of the BEM solution with the Prandtl tiploss model as r > R at the tip, I would expect that a > 1 and a' > 0, which is what we have implemented in AeroDyn v15. (AeroDyn v14 and earlier never allowed nodes to lie right at the tip.)
In our AeroDyn v15 implementation, we simply set a = 1 and a' = 0 for any nodes lying right at the tip when Prandtl tip loss is enabled. You can do the same in your Excel implementation of BEM, or you can probably get around any problems right at the tip by ensuring that nodes are not placed within some tolerance of the tip location.
Best regards,
Sir, thanks for this!
Yes sir, the Excel file has my own implementation (i.e. following the usual procedure of BEM as explained in several texts).
The value of a, a' you provided sir are irrespective of the empirical correction used concerning turbulent wake state (e.g. Glauert, Buhl)?
As for the matlab implementation, the path to follow sir is using newton raphson?
Kind regards,
Wesley

 Posts: 4862
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 Location: Boulder, CO
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Re: Help about BEM and NREL's Phase VI
Dear Wesley,
Regarding the limiting values at the tip, "yes," that is correct.
There are different methods to solve the BEM equations. Newton iterations are one method. In AeroDyn v15, we use Brent's method.
Best regards,
Regarding the limiting values at the tip, "yes," that is correct.
There are different methods to solve the BEM equations. Newton iterations are one method. In AeroDyn v15, we use Brent's method.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 21
 Joined: Sun Apr 17, 2016 12:18 am
 Organization: self
 Location: Philippines
Re: Help about BEM and NREL's Phase VI
Jason.Jonkman wrote:Dear Wesley,
Regarding the limiting values at the tip, "yes," that is correct.
There are different methods to solve the BEM equations. Newton iterations are one method. In AeroDyn v15, we use Brent's method.
Best regards,
I see,
thanks sir!
Kind regards,
Wesley

 Posts: 21
 Joined: Sun Apr 17, 2016 12:18 am
 Organization: self
 Location: Philippines
Re: Help about BEM and NREL's Phase VI
Sir,
Good day!
Sir, I'm using trapezoidal rule in the computation of Tangential Force/Torque/Power.
The formula requires indicating segments (i.e. distance between two radial positions, r(n+1)r(n)).
My computation started with r=1.257m (since this is the section where s809 is utilized).
Sir, if I will get the Tangential force for the first blade element (n=1), any idea what would the segment be?
Will the segment of the first blade element covers be r=1.257 and r=1.343?
Kind regards,
Wesley
Good day!
Sir, I'm using trapezoidal rule in the computation of Tangential Force/Torque/Power.
The formula requires indicating segments (i.e. distance between two radial positions, r(n+1)r(n)).
My computation started with r=1.257m (since this is the section where s809 is utilized).
Sir, if I will get the Tangential force for the first blade element (n=1), any idea what would the segment be?
Will the segment of the first blade element covers be r=1.257 and r=1.343?
Kind regards,
Wesley

 Posts: 4862
 Joined: Thu Nov 03, 2005 4:38 pm
 Location: Boulder, CO
 Contact:
Re: Help about BEM and NREL's Phase VI
Dear Wesley,
I'm sorry, but I don't understand your question. Are you using AeroDyn v15, an older version of AeroDyn, or something else? What does your nodal distribution look like?
Best regards,
I'm sorry, but I don't understand your question. Are you using AeroDyn v15, an older version of AeroDyn, or something else? What does your nodal distribution look like?
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

 Posts: 45
 Joined: Mon Sep 12, 2016 8:34 pm
 Organization: IIT Bombay
 Location: Mumbai
Re: Help about BEM and NREL's Phase VI
Dear Jason,
I have implemented axial induction factor calculation in MATLAB as given in the paper "Ning, Andrew, et al. "Development and validation of a new blade element momentum skewedwake model within AeroDyn." 33rd Wind Energy Symposium. 2015".
I get good match for AxInd and TanInd between MATLAB code and FAST at the middle section of the blade, but at the tip , FAST reports, AxInd =1 and TanInd =1; (I chose Wakemod=1, included tip, hub loss, drag is taken in the induction factor calculation)
But my matlab implementation gives values different from 1 and 1. From reading this post, I realized that AxInd and TanInd are hardcoded to be 1 and 1 respectively near tip. Is it incorrect to proceed with the values given by the algorithm given in the paper? I understand the problem with the implementation in paper right at the tip. Could you please elaborate on the implications of this on the further calculations.
Also, I don't see hard coded values for AxInd and TanInd in the source code (given below). Where is this implemented in the code?
Regards,
Kumara
I have implemented axial induction factor calculation in MATLAB as given in the paper "Ning, Andrew, et al. "Development and validation of a new blade element momentum skewedwake model within AeroDyn." 33rd Wind Energy Symposium. 2015".
I get good match for AxInd and TanInd between MATLAB code and FAST at the middle section of the blade, but at the tip , FAST reports, AxInd =1 and TanInd =1; (I chose Wakemod=1, included tip, hub loss, drag is taken in the induction factor calculation)
But my matlab implementation gives values different from 1 and 1. From reading this post, I realized that AxInd and TanInd are hardcoded to be 1 and 1 respectively near tip. Is it incorrect to proceed with the values given by the algorithm given in the paper? I understand the problem with the implementation in paper right at the tip. Could you please elaborate on the implications of this on the further calculations.
Also, I don't see hard coded values for AxInd and TanInd in the source code (given below). Where is this implemented in the code?
Code: Select all
! compute axial induction factor
if (phi > 0.0_ReKi) then ! momentum/empirical
! update axial induction factor
if (k <= 2.0_ReKi/3.0_ReKi) then ! momentum state
if ( EqualRealNos( k, 1.0_ReKi) ) then
k = k  0.1_ReKi ! Need to bump k to avoid singularities
end if
a = k/(1.0_ReKi+k)
else ! Glauert(Buhl) correction
g1 = 2.0_ReKi*F*k  (10.0_ReKi/9F)
g2 = 2.0_ReKi*F*k  (4.0_ReKi/3F)*F
g3 = 2.0_ReKi*F*k  (25.0_ReKi/92*F)
if (abs(g3) < 1e6_ReKi) then ! avoid singularity
a = 1.0_ReKi  1.0_ReKi/2.0/sqrt(g2)
else
a = (g1  sqrt(g2)) / g3
end if
end if
else ! propeller brake region (a and ap not directly used but update anyway) !bjj: huh? when k is slightly larger than 1, a is definitely getting used (and causing issues)...
if (k > 1.0_ReKi .and. .not. EqualRealNos(k, 1.0_ReKi) ) then
!if (sigma_pcn > Fsphi) then
a = k/(k1.0_ReKi) !sigma_pcn / (sigma_pcn  Fsphi ) !
! axial induction is blowing up, so I'm putting a bandaid here. BJJ 25Feb2016
a = min(a, 10.0_ReKi )
else
a = 0.0_ReKi ! dummy value
end if
end if
! compute tangential induction factor
if ( cphi==0.0_ReKi ) then ! We don't want NaN here
kp = HUGE(kp)
else
kp = sigma_p*ct/4.0_ReKi/F/sphi/cphi
end if
! Per conversation with Rick, we should only trigger this if phi = 0 , so we will return predefined values as if phi=0.0
if (EqualRealNos(kp, 1.0_ReKi)) then
fzero = 0.0_ReKi
a = 0.0_ReKi
ap = 0.0_ReKi
return
end if
ap = kp/(1.0_ReKikp)
! tangential induction is blowing up, so we're putting a bandaid here. GJH, JMJ, BJJ 1Sep2015
if ( abs(ap) > 10.0_ReKi ) then
ap = sign( 10.0_ReKi, ap )
end if
!bjj: 3jun2015: TODO: was able to trigger dividebyzero here using ccBlade_UAE.dvr without tiploss or hubloss
if (.not. wakerotation) then
ap = 0.0_ReKi
kp = 0.0_ReKi
end if
Regards,
Kumara

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Re: Help about BEM and NREL's Phase VI
Dear Kumara,
The BEM solution of AeroDyn generally follows Ning et al's paper from AIAA SciTech 2015, but some of the details have been changed to ensure AeroDyn is robust for all cases, e.g., aeroelastic interaction under turbulent wind inflow.
Which version of FAST / AeroDyn are you using? In the current version of OpenFAST / AeroDyn v15, I would expect the axial induction to be 1.0 and the tangential induction to be 0.0 at the root and tip, when hub and tip losses are enabled. This is calculated in routine BEMTUncoupled/BEMTU_InductionWithResidual(). I would recommend upgrading if you are not at least using OpenFAST 0.1 or newer because AeroDyn v15 was upgraded and made more robust between FAST v8.16 and OpenFAST v0.1.
We need to develop documentation with the most uptodate implementation of BEM, based on updates to Ning et al's paper, but we do not currently have the resources to do so. Until then, the source code is probably your best resource as to the details of the implementation.
Best regards,
The BEM solution of AeroDyn generally follows Ning et al's paper from AIAA SciTech 2015, but some of the details have been changed to ensure AeroDyn is robust for all cases, e.g., aeroelastic interaction under turbulent wind inflow.
Which version of FAST / AeroDyn are you using? In the current version of OpenFAST / AeroDyn v15, I would expect the axial induction to be 1.0 and the tangential induction to be 0.0 at the root and tip, when hub and tip losses are enabled. This is calculated in routine BEMTUncoupled/BEMTU_InductionWithResidual(). I would recommend upgrading if you are not at least using OpenFAST 0.1 or newer because AeroDyn v15 was upgraded and made more robust between FAST v8.16 and OpenFAST v0.1.
We need to develop documentation with the most uptodate implementation of BEM, based on updates to Ning et al's paper, but we do not currently have the resources to do so. Until then, the source code is probably your best resource as to the details of the implementation.
Best regards,
Jason Jonkman, Ph.D.
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
Senior Engineer  National Wind Technology Center (NWTC)
National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway  Golden, CO 80401
+1 (303) 384 – 7026  Fax: +1 (303) 384 – 6901
nwtc.nrel.gov
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