# Positive vs Negative yaw Error Effect **URL:** \ **Category:** Computer-Aided Engineering Software Tools\ **Created:** [November 14, 2012, 3:14pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608 "2012-11-14T15:14:41Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Neelabh.Gupta](https://avatars.discourse-cdn.com/v4/letter/n/df788c/32.png) [@Neelabh.Gupta](https://forums.nlr.gov/u/Neelabh.Gupta)\ **Post date:** [November 14, 2012, 3:14pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/1 "2012-11-14T15:14:41Z")
Hello all, I wanted to check the effect of yaw error on NREL 5MW reference turbine for a steady wind speed (no vertical shear) of 9 m/s when I came across this strange plot: ![Yaw_error.PNG](https://europe1.discourse-cdn.com/nrel/original/1X/641e3a208b4ce318659524971cfcc88319943017.png) - Why there are variations in generator speed for negative yaw error and not for positive yaw error (as yaw error creates 1P excitation in rotating frame) - Moreover, these excitations repeat after every 2 s or so it not 1P in any ways? - Why is generator power fluctuating in all the three scenarios? I have removed the initial computational transients from the run Hope to get more understanding on this! Thanks a lot, Neelabh ---
**Author:** ![Neelabh.Gupta](https://avatars.discourse-cdn.com/v4/letter/n/df788c/32.png) [@Neelabh.Gupta](https://forums.nlr.gov/u/Neelabh.Gupta)\ **Post date:** [November 14, 2012, 3:55pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/2 "2012-11-14T15:55:14Z")
I am sorry, I ‘took vertical shear (0.2) into account’. ---
**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\ **Post date:** [November 16, 2012, 1:52pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/3 "2012-11-16T13:52:41Z")
Dear Neelabh, The frequency of osciallation seen in the generator power and generator speed plots seems to be around 0.52 Hz, which is the 3P frequency for a rotor speed of around 10.4 RPM that is consistent with the generator speed of around 1010 RPM (= ( 10.4 RPM rotor speed ) \* ( 97:1 gearbox ratio ) ) and makes sense for the NREL 5-MW turbine at a wind speed of 9 m/s. The 3P oscillation results from the asymmetry of the flow due to wind shear and yaw error. (Even without shear in the wind, the NREL 5-MW has a shaft tilt that will induce shear.) (Asymmetry in the flow will cause a 1P oscillation in the rotating frame, which leads to a 3P oscillation in the fixed frame; a 1P oscillation in the fixed frame would only result from an imbalance in the rotor.) The “odd” square shape of the generator speed time series is likely due to the small round-off error that results from the fact that FAST is only outputting 4-digits of precision based on the setting of OutFmt = “ES10.3E2” in FAST’s primary input file. My guess is that the shape would look more rounded if you added at least one more digit of precision in the output format. This roundoff is also likely the reason why you only see generator speed oscillation in one of the three time series. See the following forum topic for more information on OutFmt: [FAST Integrator, step size & precision](http://forums.nlr.gov/t/fast-integrator-step-size-precision/247/1). I hope that helps. Best regards, ---
**Author:** ![Neelabh.Gupta](https://avatars.discourse-cdn.com/v4/letter/n/df788c/32.png) [@Neelabh.Gupta](https://forums.nlr.gov/u/Neelabh.Gupta)\ **Post date:** [November 18, 2012, 12:40pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/4 "2012-11-18T12:40:42Z")
Thanks a lot Jason for this insight. It does help in understanding it. Meanwhile, you are correct about the round off error in FAST, - why does negative yaw error gives less power (mean value) than positive error. Is it due to the effect of positive and negative torque acting due to cross wind component in respective scenarios? - also when I plotted root moment (flapwise) at blade 1, I came across this plot which shows 1P fluctuatuion. Is this because of difference in reference frame used for Generator speed and root moments? Thanks again for your help, Neelabh ---
**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\ **Post date:** [November 19, 2012, 2:30pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/5 "2012-11-19T14:30:44Z")
Dear Neelabh, I would expect negative and positive yaw error to give the same power in the absence of wind shear. It is the combination of yaw error and wind shear that causes the differences in power output. Yes, in the rotating frame (e.g., the blade root), you will see loads that are harmonics of the rotor speed, 1P, 2P, 3P, etc. But in the fixed frame (e.g., rotor speed, rotor torque, or tower), these loads are translated into harmonics of 3-times the rotor speed, 0P, 3P, 6P, etc., unless the rotor loads are imbalanced. Best regards, ---
**Author:** ![Neelabh.Gupta](https://avatars.discourse-cdn.com/v4/letter/n/df788c/32.png) [@Neelabh.Gupta](https://forums.nlr.gov/u/Neelabh.Gupta)\ **Post date:** [November 21, 2012, 2:57pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/6 "2012-11-21T14:57:46Z")
Dear Jason, I understand your 2nd point but to your 1st reasoning, I switched off wind shear (no vertical shear and shaft tilt= 0 degree) and still observed some fluctuations in generator power for 0° yaw error. Though, for positive and negative yaw errors the mean generator power became significantly closer. ![No_Wind_Shear.PNG](https://europe1.discourse-cdn.com/nrel/original/1X/5433a1e31d2369a3b456831e2a77cfefc646ab42.png) Thanks, Neelabh ---
**Author:** ![Neelabh.Gupta](https://avatars.discourse-cdn.com/v4/letter/n/df788c/32.png) [@Neelabh.Gupta](https://forums.nlr.gov/u/Neelabh.Gupta)\ **Post date:** [November 21, 2012, 3:26pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/7 "2012-11-21T15:26:31Z")
Does tower influence has to do something with this oscillation? But this being an Upwind turbine, this effect must be minimal? ---
**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\ **Post date:** [November 21, 2012, 4:27pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/8 "2012-11-21T16:27:32Z")
Dear Neelabh, If you’ve enabled the upwind tower-influence model in AeroDyn, “yes” this would influence the torque, power, etc. of the response. The upwind tower influence would have a 1P effect in the rotating frame a 3P effect in the fixed frame. Best regards, ---
**Author:** ![Neelabh.Gupta](https://avatars.discourse-cdn.com/v4/letter/n/df788c/32.png) [@Neelabh.Gupta](https://forums.nlr.gov/u/Neelabh.Gupta)\ **Post date:** [November 21, 2012, 9:30pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/9 "2012-11-21T21:30:35Z")
Dear Jason, I use the ‘NEW TOWER’ feature in Aerodyn (with potential flow around the tower) and the ‘tower shadow’ option in set to False. So am not sure how does Aerodyn account for this tower influence? Thanks, Neelabh ---
**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\ **Post date:** [November 21, 2012, 9:46pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/10 "2012-11-21T21:46:24Z")
Dear Neelabh, Please see the following post form information about how to enable the upwind tower-influence model: [Tower shadow effect in FAST (1.5MW, test13)](http://forums.nlr.gov/t/tower-shadow-effect-in-fast-1-5mw-test13/364/1). Best regards, ---
**Author:** ![Neelabh.Gupta](https://avatars.discourse-cdn.com/v4/letter/n/df788c/32.png) [@Neelabh.Gupta](https://forums.nlr.gov/u/Neelabh.Gupta)\ **Post date:** [November 22, 2012, 8:29pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/11 "2012-11-22T20:29:30Z")
Thanks a lot Jason for all your inputs. I really appreciate your responses. This gave me a good insight on harmonics seen in fixed and rotating frames. Hope to learn from from you in future 🙂 Neelabh ---
**Author:** ![Sangwon.Lee](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/sangwon.lee/32/4526_2.png) [@Sangwon.Lee](https://forums.nlr.gov/u/Sangwon.Lee)\ **Post date:** [May 2, 2023, 3:38pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/12 "2023-05-02T15:38:47Z")
Dear @Jason.Jonkman I ran simulations using the IEA 15MW UMaine Semi type to check the change in power generation under yaw error and wind-wave misalignment conditions. - Wind-wave misalignment angle: 0°, 20°, 40°, 60°, 80°, 90° - Yaw error angle: -15°, -8°, 0°, +8°, +15° But there is a difference between positive yaw error and negative yaw error. For example, power generation when the yaw error is +15° and -15° is different. According to my limited knowledge, it should have the same power generation. I checked and found that the wind-wave misalignment doesn’t affect much power generation. Is it because of the rotor’s rotation orientation? You described it well above, but I am still confused. 🙂 Here are my results. * * * - ‘β’ means wind-wave misalignment angle. ![image](https://europe1.discourse-cdn.com/nrel/original/2X/7/70efd3c640437f0b07c2597894d5d96f6334acd8.png) ![image](https://europe1.discourse-cdn.com/nrel/original/2X/5/53e48e22a2045b9fd120ec360ac58444343d70f7.png) ![image](https://europe1.discourse-cdn.com/nrel/original/2X/c/cf39b97997813b845f3ad3ce58f7a11496e4986a.png) * * * ---
**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\ **Post date:** [May 2, 2023, 3:49pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/13 "2023-05-02T15:49:04Z")
Dear @Sangwon.Lee, I’m guessing the slight asymmetry between positive and negative yaw error is a result of wind shear. Even if you’ve set the wind shear to zero in the simulation, there is likely some shear across the rotor anyway as a result of shaft tilt, tower deflection, or floater heel. FYI: The following more recent forum topic is likely of interest to you: [Power loss with yaw misalignment](https://forums.nlr.gov/t/power-loss-with-yaw-misalignment/2619). Best regards, ---
**Author:** ![Sangwon.Lee](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/sangwon.lee/32/4526_2.png) [@Sangwon.Lee](https://forums.nlr.gov/u/Sangwon.Lee)\ **Post date:** [May 2, 2023, 4:00pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/14 "2023-05-02T16:00:22Z")
Dear @Jason.Jonkman Now that it makes sense to me, I thank you for your detailed response. Also, I appreciate your link for information. Have a nice day! Best regards, Sangwon ---
**Author:** ![Sangwon.Lee](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/sangwon.lee/32/4526_2.png) [@Sangwon.Lee](https://forums.nlr.gov/u/Sangwon.Lee)\ **Post date:** [May 9, 2023, 8:49am UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/15 "2023-05-09T08:49:23Z")
Dear @Jason.Jonkman I have another question about power generation under yaw error and wind-wave misalignment conditions. According to my power generation standard deviation (StDev) results, I found some doubts. I thought wind-wave misalignment conditions might affect each yaw error condition the same. But _ **there are certain points where StDev is higher than I expected** _. (marked by a black circle in the bar graph) They have in common that the wind direction is over 90 degrees. 1st mark: 98° (wind direction) = 90° (wind-wave misalignment angle) + 8° (yaw error angle) 2nd mark: 105° (wind direction) = 90° (wind-wave misalignment angle) + 15° (yaw error angle) (The wave direction is fixed at 0°.) I know Platform’s pitch and roll motion influence power generation’s StDev. But according to my results, I couldn’t find a correlation between platform 6-DOF and my question. I understood that the asymmetry of power generation might be caused by wind shear. Is this phenomenon also caused by the same reason? * * * I set the parameter as follows: - Wind-wave misalignment angle: 0°, 20°, 40°, 60°, 80°, 90° - Yaw error angle: -15°, -8°, 0°, +8°, +15° - Wind type: NTM (IEC Class 1B) - Wave type: Irregular wave - Wind speed: 10.59 m/s - Wave height(Hs): 1.641 m - Wave period(Tp): 7.544 s ![Yaw error and wind-wave misalignment set-up condition](https://europe1.discourse-cdn.com/nrel/original/2X/6/69a6e28f9795492ae4dc696b0350f3861a766aa9.png) * * * * * * Here are my simulation results: - ‘β’ means wind-wave misalignment angle. ![Correlation between yaw error and wind-wave misalignment for power generation StDev](https://europe1.discourse-cdn.com/nrel/original/2X/7/756959dc3635b7b3e0590bfdcf530783d1ecda6b.png) ![Correlation between yaw error and wind-wave misalignment for Platform 6-DOF](https://europe1.discourse-cdn.com/nrel/original/2X/f/f90781e087e74485af4a1d05d2d01e9b76a664f4.jpeg) * * * Best regards, Sangwon ---
**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\ **Post date:** [May 9, 2023, 12:43pm UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/16 "2023-05-09T12:43:15Z")
Dear @Sangwon.Lee, I’m not sure what platform motions (means or standard deviations?) in your lower figure, but I do see several asymmetries here with respect to yaw error, so, it is not surprising that you are seeing asymmetries in the power with respect to yaw error as well. Best regards, ---
**Author:** ![Sangwon.Lee](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/sangwon.lee/32/4526_2.png) [@Sangwon.Lee](https://forums.nlr.gov/u/Sangwon.Lee)\ **Post date:** [May 10, 2023, 1:26am UTC](https://forums.nlr.gov/t/positive-vs-negative-yaw-error-effect/608/17 "2023-05-10T01:26:20Z")
Dear @Jason.Jonkman Platform motion data are mean values. As you mentioned, these might result from a combination of asymmetries. Thank you for your response, and I will keep studying. Have a nice day! Best regards, Sangwon