Flow inclination definition

[windmueller]

Hi,
I could not find an answer about the definition of the flow inclination algebraic sign:

I assume that a positive flow inclination means that the flow has an upward component and a negative flow inclination has a downward component. Could you confirm that?

Thanks!

[Morten]

Your assumption is correct.

[ebazus]

Hello,
I am not sure if the tilt angle (or flow inclination) value for each sector is the maximum value of all values inside each sector (30º), or maybe it is weighted somehow inside each sector?
Thank you in advance!

[Morten]

Hi Ebazus,


Normally WAsP Engineering calculates for specific wind conditions, not sectors. However, the tool called 'prepare data for WAT' produces a result table for the same number of sectors as defined in the supplied wind atlas file, which is a result from WAsP. These calculations are made with one reference wind for each sector with a wind direction equal to the center angle of each sector. The reference winds are generalized winds, i.e. for flat terrain with surface roughness z0=0.05m, and they may deflect over real terrain. Thus the flow inclination angle (or tilt) are calculated for a case where the local wind direction is a bit off the sector center angle, especially in complex terrain.


Cheers, Morten

[bepi]

Dear WAsP Team,

sorry to reopen an old topic but have a question regarding flow inclination: I read in another topic (below) that flow angle (tilt..etc) is calculated using simple trigonometry involving the three components of wind speed, these three components are calculated with the WAsP model similar to the old LINCOM but more advanced. Two questions: is there a way to visualize these three velocity (x,y,z) components?

I thought that WAsP was using somehow IEC61400-1 Paragraph 11.2 to simulate flow inclination using the fitted plane theory, but maybe I got wrong info..right?

 

Thanks a lot.

Bepi

 

 

 

 

[Morten]

Dear Bepi,

The previous question by HPJ concerned flow inclination angles by the WAsP Engineering program. To see a map for a specific wind direction you click Insert> New wind from the WAsP Engineering main menu, select Maps and sites> Wind Grid maps, right-click Flow inclination grid and select Open in new spatial view from the popup menu. WAsP Engineering will display maps of individual velocity components in a similar way.   

Flow inclination angles are included as fields in the WAsP resource grids. These results are only valid when using the WAsP CFD flow model, not the standard WAsP flow model called IBZ. I think the result for all directions still are calculated as the worst local inclination angle for any wind direction, as defined in previous editions of the IEC 61400-1 standard. To see the inclination angles defined in the current IEC 61400-1 Edition 4 - which is an energy-weighted average over all wind directions - you can either use tools> WAsP CFD results viewer from the WAsP main menu or the Windfarm Assessment Tool.

Chapter 11.2 of the IEC 61400-1 standard presents a method involving planes fitted to the terrain elevation surface. The purpose of this is just to assess the terrain complexity, not flow inclination angles. This assessment is implemented in the WAsP CFD results viewer and the Windfarm Assessment Tool, not directly in WAsP or WAsP Engineering.

Cheers,
Morten

[Hardik Naik]

Hello,

I have a question on this topic. Why do my sectoral values of inflow angles have equal number of negative and positive values in WEng ? For Sites which are on top of the steep hill also show 6/12 sectors with positive values while the other 6/12 shows negative values.

Regards,

Hardik

[Morten]

Hi Hardik, 

A linear flow model, as the one used by WEng, will predict nearly mirrored inflow angles for opposite directions. The directional average will be close to zero even for high inflow angles in individual sectors, which sounds like a bad compliance check. I therefore decided to let WAT calculate the energy-weighted average inflow angle by absolute values of sector-wise inflow angles. The design-load case for IEC 61400-1 wind-turbine classifications specifies positive inflow angles for load simulations. Thus, for site assessment, it could make sense to ignore all negative inflow angles or maybe calculate averages of positive and negative inflow angles as two independent measures. Let us hope that future versions of the IEC 61400-1 standard will be more specific about this site-compliance check.

[Hardik Naik]

Hi Morten,

Thanks for your response. As a follow up, how are these sign conventions decided? Is it based on the energy weightage? Meaning, for a combination of sectors that are 180 degrees apart from each other, does the sector having the highest energy take a positive sign while the other takes a negative?