Printing the axial induction factor in FAST

Discuss the theory and modeling of rotor aerodynamics.

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Mostafa.Haggag
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Printing the axial induction factor in FAST

Postby Mostafa.Haggag » Thu Jun 28, 2018 12:11 pm

Hello
I wanted to ask if it possible to output the axial induction factor for the turbine in my output files to see what is happening
I am not sure where exactly could i pick the output of the turbines. I mean I read the manual and I knew how things work but what I do not know how to pick which output to be printed to my text file or is it forced to print all of the output related to turbines.
The main question is how to print the axial induction for my turbine.
The axial induction factor should be the Uinf-Urotor/Uinf for the actual disk model but I am not sure if it is like that in the model I am using or not. I am using a 5MW NREL turbine with fast 8.


thank you so much

Jason.Jonkman
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Re: Printing the axial induction factor in FAST

Postby Jason.Jonkman » Thu Jun 28, 2018 1:10 pm

Dear Mostafa,

Are you using AeroDyn v15 within FAST v8? Within the AeroDyn v15 module, the axial induction factor is available as output BαNβAxInd, for node β of blade α. See Appendix E of the draft AeroDyn v15 User's Guide and Theory Manual for more information: https://nwtc.nrel.gov/system/files/Aero ... 15.04a.pdf.

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

Mostafa.Haggag
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Re: Printing the axial induction factor in FAST

Postby Mostafa.Haggag » Fri Jun 29, 2018 8:19 am

Dear Dr Jason,
I am using open fast and I am reading the manual you gave me. it seems that there is a way to output the axial induction factor as I can see in the appendix. I am still wondering how to print it out in the output folder. I mean I am using the AeroDyn v15 and i am getting many variables in the <>.out file but it does not have the aif. is there something in the input fast of fast I need to change so that I can print the aif ?
thank you so much for your help
yours
Mostafa

Mostafa.Haggag
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Re: Printing the axial induction factor in FAST

Postby Mostafa.Haggag » Fri Jun 29, 2018 8:29 am

Hey Dr Jason
if I understood correctly, Fast is connecting different modules together.I have more than one input file. so to change in the output for the AeroDyn v15 module, I have to change in the NRELOffshrBsline5MW_Onshore_AeroDyn15.dat output parameters. I am testing it right now but I thought to ask while investigating more in the topic.
thanks

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Re: Printing the axial induction factor in FAST

Postby Jason.Jonkman » Fri Jun 29, 2018 9:02 am

Dear Mostafa,

Yes, your understanding is correct.

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

Mostafa.Haggag
Posts: 34
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Re: Printing the axial induction factor in FAST

Postby Mostafa.Haggag » Sun Jul 01, 2018 10:59 am

Dear Dr Jason
there is an axial induction factor for each blade for each node and I have 17 nodes. what i need is the axial factor for the rotor averaged value. Is there a way for fast to output this value only? IF not, how can i post process my axial induction factor then to get the rotor averaged axial induction factor?
I was thinking about outputting the axial induction factor for each node for each blade and then calculating the average but that seems to be really stupid as 17 nodes * 3 blades is so many outputs to be post-processed in matlab. I am saying that I will have so many reading of axial induction factor
i would like to ask if this method i am suggesting is proper to get the average axial induction factor.
should i add the aif for the 17 nodes then divided by 17 as if i am getting the average ai for each blade then I get the average aif for each blade and divide by 3 to get the average aif for the rotor.
thank you in advance
mostafa

Mostafa.Haggag
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Re: Printing the axial induction factor in FAST

Postby Mostafa.Haggag » Sun Jul 01, 2018 11:08 am

IS there a way i could edit the adero dyn v15 files so that it could output for me right a way the averaged value . I mean is it possible that i use fast to do the post processing. where exactly should i head to if i want to do something like this ?

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Re: Printing the axial induction factor in FAST

Postby Jason.Jonkman » Mon Jul 02, 2018 6:40 am

Dear Mostafa,

The rotor-disk averaged axial induction factor is not a standard output of AeroDyn v15. You could, of course, output the axial induction factors for every node, but as you said, this would be a lot of outputs. For this calculation, it may be preferred if you modify the source code directly to calculate and output what you want.

Please note that if you are averaging axial induction across the rotor, it may be preferred to weight the local axial induction factor by the local radius/circumference because the outer nodes sweep more distance than the inner nodes when the rotor is rotating.

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

Mostafa.Haggag
Posts: 34
Joined: Tue Jun 26, 2018 7:50 am
Organization: self
Location: Egypt

Re: Printing the axial induction factor in FAST

Postby Mostafa.Haggag » Tue Jul 03, 2018 7:59 am

Jason.Jonkman wrote:Dear Mostafa,

The rotor-disk averaged axial induction factor is not a standard output of AeroDyn v15. You could, of course, output the axial induction factors for every node, but as you said, this would be a lot of outputs. For this calculation, it may be preferred if you modify the source code directly to calculate and output what you want.

Please note that if you are averaging axial induction across the rotor, it may be preferred to weight the local axial induction factor by the local radius/circumference because the outer nodes sweep more distance than the inner nodes when the rotor is rotating.

Best regards,

is it possible to explain more how to weight the loca axial induction factor by the local radius ?the method of implementing it .i understand my axial induciton factor changes with the radius.
thank you so much

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Re: Printing the axial induction factor in FAST

Postby Jason.Jonkman » Tue Jul 03, 2018 8:29 am

Dear Mostafa,

Here is a simple implementation if r(b,n) is the local radius to node n of blade b and a(b,n) is the local axial induction:

Code: Select all

WeightedAvgInd = 0
rSum=0
FOR b = 1,NumBlades
   FOR n = 1,NumNodes
      WeightedAvgInd = WeightedAvgInd + r(b,n)*a(b,n)
      rSum = rSum + r(b,n)
   END
END
WeightedAvgInd = WeightedAvgInd/rSum

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

Mostafa.Haggag
Posts: 34
Joined: Tue Jun 26, 2018 7:50 am
Organization: self
Location: Egypt

Re: Printing the axial induction factor in FAST

Postby Mostafa.Haggag » Tue Jul 03, 2018 11:26 am

how can i know the node postion ?is there an Output paramater to know to node radial postion ? how do i know the Maximum number of nodes ?is the node equal to Number of blade input stations?I found that Parameter called station_total saying that i have 49 Input Station for the blade .is that the number of nodes ?
i found a Parameter in elasto dyn Folder called BldNodes (with a Deskription of ''Number of blade nodes '')is that it ?
my Problem is that when i opened the AeroDyn v15 source Output files i found out the following

Code: Select all

   
   INTEGER(IntKi), PARAMETER      :: B1N1AxInd =  520
   INTEGER(IntKi), PARAMETER      :: B1N2AxInd =  521
   INTEGER(IntKi), PARAMETER      :: B1N3AxInd =  522
   INTEGER(IntKi), PARAMETER      :: B1N4AxInd =  523
   INTEGER(IntKi), PARAMETER      :: B1N5AxInd =  524
   INTEGER(IntKi), PARAMETER      :: B1N6AxInd =  525
   INTEGER(IntKi), PARAMETER      :: B1N7AxInd =  526
   INTEGER(IntKi), PARAMETER      :: B1N8AxInd =  527
   INTEGER(IntKi), PARAMETER      :: B1N9AxInd =  528

there is only 9 Output Parameters per blade which mean there is only 9 nodes !!! however that is totally a different number compared to the parameters mentioned above .so how many nodes do i have ?is it possible that i do not get outputed the axial induction factor for all of the nodes ?also how do i know the postion of the node the radial postion to be exact ?

thank you so much
msotafa

Mostafa.Haggag
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Re: Printing the axial induction factor in FAST

Postby Mostafa.Haggag » Tue Jul 03, 2018 4:27 pm

I have another question
in the aerodyn 15 file
i outputed "B1N1AxInd" and set NBlOuts to 1 and BlOutNd to 1 and i get in my Output file the variable but all of my axial induction factor is Zero
i do not know why
secondly
according to the 5mw turbine , the pitch angle can be changed with a Maximum Absolute Blade Pitch Rate of 8 degree per second. What i am doing is using open Loop function in simulink and sending the commands with pitch angles. The idea is i am doing a sinsoidal Motion with my blade .TO explain it more , i want my blade to follow this equation, pitch angle of blade 1 =Amp*sin(Omega*simulationtime)
my amp is the Amplitude (1 degree or 2 degree ) and the Omega is 2*pi/period the period is the period of my sin function.my question is what frequency or period should i be using that i can get realistic results and to be able to implement it with the turbine?

Jason.Jonkman
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Re: Printing the axial induction factor in FAST

Postby Jason.Jonkman » Wed Jul 04, 2018 3:59 am

Dear Mostafa,

NREL does not have the resources to change the source code for you. You'll have to study the source code yourself if you wish to make the changes you want.

To answer some of your questions:
  • The number of aerodynamic blade analysis nodes is specified via input NumBlNds in the AeroDyn blade input file.
  • AeroDyn v15 is limited to outputting only 9 of the NumBlNds. Which nodes can be output is specified via AeroDyn inputs NBlOuts and BlOutNd in the AeroDyn primary input file.
  • When AeroDyn is coupled to FAST with blade flexibility enabled, the radial position of each aerodynamic analysis node will change every time step. The positions of the nodes are available within the source code, but are not standard outputs from AeroDyn.
  • The axial induction may in fact be zero at the blade root or tip due to the hub- and tip-loss induction factors, when enabled.
  • I'm not sure what you mean by "realistic results" because it sounds like the sinusoidal blade-pitch motion you are prescribing is quite idealistic. The maximum pitch rate of the NREL 5-MW turbine is set at 8 deg/s, but normal pitch rates would be much less than this.

I hope that helps.

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

Mostafa.Haggag
Posts: 34
Joined: Tue Jun 26, 2018 7:50 am
Organization: self
Location: Egypt

Re: Printing the axial induction factor in FAST

Postby Mostafa.Haggag » Wed Jul 04, 2018 4:45 am

Jason.Jonkman wrote:Dear Mostafa,

NREL does not have the resources to change the source code for you. You'll have to study the source code yourself if you wish to make the changes you want.

To answer some of your questions:
  • The number of aerodynamic blade analysis nodes is specified via input NumBlNds in the AeroDyn blade input file.
  • AeroDyn v15 is limited to outputting only 9 of the NumBlNds. Which nodes can be output is specified via AeroDyn inputs NBlOuts and BlOutNd in the AeroDyn primary input file.
  • When AeroDyn is coupled to FAST with blade flexibility enabled, the radial position of each aerodynamic analysis node will change every time step. The positions of the nodes are available within the source code, but are not standard outputs from AeroDyn.
  • The axial induction may in fact be zero at the blade root or tip due to the hub- and tip-loss induction factors, when enabled.
  • I'm not sure what you mean by "realistic results" because it sounds like the sinusoidal blade-pitch motion you are prescribing is quite idealistic. The maximum pitch rate of the NREL 5-MW turbine is set at 8 deg/s, but normal pitch rates would be much less than this.

I hope that helps.

Best regards,




thank you so much for your help Doctor
secondly i want ask few things.if i output the 9 of the numblnd to calculate the average rotor axial induction, does that mean my results does not count as an accurate as i am not using the whole nodes of the blade ? secondly i do not understand what you meant by blade flexibility is that an option(i am checking the manuals right now but i thought to ask you )? also if the nodes are changing their position at each time step ,does this mean the output coming out from aerodyn for the axial induction factor is for different positions ?like at each interval the axial induction factor is for a node at a different position ? am i understanding it correctly?
another general question
for a student who is not the best with fast and has no experience with openfoam and he wants to try using SOWFA do you think it is possible ? i have experience with another LES but not SOWFA.is such thing even possible?I am trying to learn fast really quickly

Jason.Jonkman
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Re: Printing the axial induction factor in FAST

Postby Jason.Jonkman » Thu Jul 05, 2018 2:16 am

Dear Mostafa,

I would think you could get an accurate representation of the induction if you distribute the 9 output nodes along the blade. Of course, outputting data at 9 nodes will be less accurate than outputting data at all blade nodes, but the induction should be fairly smoothly distributed along the blade.

By "flexibility", I mean structural deflection when running AeroDyn coupled to ElastoDyn or BeamDyn within FAST. Both ElastoDyn and BeamDyn can model blade deflection and these have an aero-elastic interaction with AeroDyn. "Yes," if the blade structural degrees of freedom are enabled, the local radius to each aerodynamic output node will change in time as a result of the blade deflection.

SOWFA is much more difficult to learn than FAST. You mention experience with LES; any experience with OpenFOAM would be useful to learn to SOWFA.

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


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