Pressure coeficient

Mohammad

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Jul 23, 2011
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Hi guys;
I have a question . I'm working on a CFD model of a wind turbine. I have got some results and now I want to plot the Cp.
be cause the blades has a twist angle and so different AOA at different radial positions , I want to know that which coordinate system should i choose for plotting the pressure coefficient. Global x direction or I MUST choose local one with the "X" axis along the chord length.????
Please pay attention that if I use Global coordinate system when I have AOA, two point at the same Global X position don't have the same local X positions??? and the Cp always is plotted according to "x/C"....but which "x"?:help:
 
DF = Mohammad Al Farris...! Dude are you serious...? F'nn Unbelievable!!!!! Again how many times can you get away with it??????????????
 
That’s funny; I smelled a rat but didn’t put it all together.

No one attempted to answer Mr. Mohammad’s questions because they didn’t make a lick of sense.
 
Just speculation.

Just speculation.

For the basic turbine calculations two coordinates of a cylindrical coordinate system should do. X [the rotors axis of rotation] will represent air velocity. R will represent the positions [elements] along the span of the twisted blades.

Perhaps, a cylindrical coordinate system might be required if the air flow is not aligned with the rotor's axis of rotation, due to a slope of the land or vertical airflow anomalies.

If you are using the isobars to determine the wind's force and direction then maybe you do need to use a global or spherical coordinate system; and then map between systems.


Dave
 
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Hello Mohammad, Chuck, Dave,

I have been "lurking" on this forum for a number of years ... thought I could help out on this topic.

The 2010 Edition of Germanischer Lloyd Guideline for the Certification of Wind Turbines, Appendix 4a contains Coordinate System definitions for: Blade CSYS, Chord CSYS, Hub CSYS, Rotor CSYS, Yaw CSYS and finally Tower CSYS. I find these definitions much more complete/clear that other Rotorcraft CSYS definitions. The Guide is downloadable free of cost, after registration.

In general CSYS usage is dependant on ones design space, or what one is currently defining (ie a Blade profile, Blade Planform, Hub configuration or Rotor configuration).

Cp contours are a very useful design trade, so I use the CSYS appropriate for my current design space, keeping in mind the Design Point (Flight Case and appropriate Blade/Rotor deformation from nominal state)

robert
 
CSYS images

CSYS images

Here are the six CSYS diagrams for a Wind Energy Conversion (WEC) system
 

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What is your reading of angle of attack varying as a result of twist, Dave?

Hi Chuck. I figured that, like Blade Element Theory, the data on the airfoil plus airflow angle and velocity etc. would then be calculated in 2D or 3D at each element.


Robert, Your answer to Mohammad is probably exactly what he is looking for. It is interesting to consider that the research and development that is currently going into wind turbines probably far exceeds the R&D that is going into rotorcraft.

Dave
 
Dave,
Hello from an ex-Vancouverite (Alert Bay/Richmond),
In my experience (EC135 Flexbeam @ OTN/DON), I have always been impressed with HAWT-WEC Blades, especially considering the low specification materials and mfg processes available in the their cost spectra. The suboptimal (heavy) but robust design was always much more durable (>6month inspection intervals) any than rotorcraft would be required to be AND was much more sensitive to flexural degradation (no CF) This meant a suboptimal (robust) design that did not fail (flexurally speaking).

Aerospace has a LOT to learn from both the automotive and industrial use of non-metallics.

In my opinion ... :)

robert
 
robert,

What do you mean by "ex-Vancouverite"? I was under the impression that nobody left Vancouver once they had lived here. :)

IMHO, the rotorblade is the essence of rotorcraft. The industry would be significantly more advanced today if the primary manufactures had directed their conceptual and engineering talents toward deriving lift from the Reverse Velocity Region.

The X2 and the X3 are both recreations of older ideas, and they both are restrained by not having previously addressed the RVR problem.


Dave
 
Yea well ... I really do not miss the cloudy, damp, wet weather .... the 2 weeks of sunshine and a snow line on the North Shore did not quite make up for the rest ... :)

I unfortunately am not a rotor designer ... give me a planform, and Flexural Distribution curves and I can do something.

I do agree that diminishing rotor performance returns are not attributable to materials but rather the initial functional design.

A missed opportunity that still bugs me, is a variable speed (Vc=Slowed Rotor) reaction drive (cold/warm air) rotor based on work (MBB and NASA) by Heidelberg and Dorand.

I agree with you on the X2 but do not forget that the X3 is expanding the slowed rotor envelope. This I believe is new for a Flight Test Vehicle. If successful they (EC) will have "overcome" the vibration transition into a partial load rotor state.

Robert
 
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