Profiles are not made cylindric when applied in circular context.
All blade profiles I use come from cylinder sections of real life turbine blades collected at design operating angle to cut close to the core profile they may originate from. Profiles are then flatened from cylinder elements and normalized to xfoil coordinates with chord length 1.
In QBlade it looks like the profiles are used in blades without making them cylindric by the radius they are applied. For wide blades the curvature becomes totally false and the blade exported in STL 3D format consists of straight profile elements and do no longer, even closely, reflect the blade they originated from.
Profiles on slim or wide blades should be located with an offset perpendicular to blade axis, rotated to desired angle and then wrapped onto the cylinder they belong.
1. Profiles collected from original blade outside QBlade
2. Profiles used in a QBlade blade
3. QBlade STL output
As a newbie - maybe missed some option?
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I dont exactly understand what you are explaining. Maybe try to explain the issue in other words?
One option you might find helpful though is the "Advanced blade design" tab in the HAWT blade designer. There you can assign an offset to each individual blade station and also change the point around which the airfoil is rotated due to the twist angle.
CHeers,
David
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
If you design a 3-blade rotor with short straight blades with six equal foils you see the foils packed side by side:
If this rotor would be put in use in real life conditions a thin air stream would not travel mainly along one single airfoil wich is the assumtion of airfoil analyzis made earlier. It is probably the asumption in QBlade calculation too. Who would analyze a foil for straight travel and then put it in a rotating motion without bending it to the probable path of the flow across the blade?
If a rotor is made of the STL file exported it would have profiles lined up for travel along a streaight line but rotated in circular motion.
New feature: Airfoils on bent blade axis and oriented with the wind
As this is corrected - a cool feature would be if Qblade could use calculated path across the blade and physically line up profiles upp that way when constructing the blade. Near rotor center it would be more cylindric/conic and furher out the blade cross sections have foils tilted inwards and even scewed to stay with the airstream and in all cases appear to the wind as in the straight airfoil analyzis.
That would make blades where you know air travels mostly along the airfoils of your design and you could predict the behaviour based on airfoil data and calculations made.
New feature: Spline to locate foils on blade axis
Tilted foils mean thinner blade cross section so the another thing to add is the blade axis being a spline to make curved blades easy to experiment with wing tip losses and blades bent against the wind direction. Wind interactive flow vectors by radius would give designer a sense of what the wind would do given the blade profiles and axis "curving".
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
One of the main assumptions of the BEM and LLFVW simulation methods in QBlade is that the flow is 2D over the airfoil sections of the blade(s) (and there is no crossflow). This is also the reason why we can use 2D airfoil polars for the simulation of a 3D rotor.
For most realistic wind turbine blades this assumption holds true as the chordlength of the airfoils is rather small compared to the circumference of the rotational blade path. This ratio between the circumference and the chord at a blade station is called the local solidity. At the root section of blades (as in your example) the solidity can be quite high at times - however, as the airfoils used here are cylindric and dont contribute to the performance significantly, this does not have a large impact on the results. All turbines that are in operation today have been designed with a BEM method, under the assumption of 2D flow at the airfoils - so this is common practice.
If you want to look at "wide" blades, as in the picture above - you might lose accuracy and need to switch to a different, higher order, method such as CFD to accurately represent blade crossflows and other 3D effects.
Regards,
David
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
My point is that the real world will automatically aproximate a circle to a straight line where needed.
I will argue below for the straight profiles being an aproximation that should not be performed at all.
In HAWT configuration the basic asumption is the foil is wraped to a rotating cylinder or even better aligned to the actual flow. Staying exactly on the same radius or something similar is a great starting point of observation and makes you stay close to what you know about the airfoil from data.
The "objection" is puting straight profiles on a square blade is just mathematically wrong and has no connection to the amazing calculation just peformed by QBlade. No matter how many decimals you need the transformation choosen is wrong given the model used by QBlade.
As profiles are twisted and chordlength varies throughout the blade, adding the real profile cylindric or else curved, would not add to final complexity to the product - just make it mor accurate.
Conclusion.
1. HAWT blades are circular by nature - they just look square when blades are long
2. Display wings with profiles following the same path as used in flow calculation.
3. If user desires a straight corner wing - terminate the blade with straight edges.
4. It is ok to chop the blade in straight elemts for convenince or practice, but blade curvature is allways defined from curved foils.
That would serve all users: ignorant, pragmatic, stubborn or picky. What do you think?
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
using 2D airfoils in a 3D simulation is of course a large approximation - but amazingly it gives very accurate results for slender blades, even when compared to real life measured wind tunnel data or CFD simulations that naturally take the curvature into account.
Changing the approach to curved foils would require a a completely overhaul of the used methodology - and simple 2D airfoil polars could not be used in the simulations anymore - so the whole common practice of how to design WT blades would need to change.
Also, this assumption is not the only simplification and assumption that the BEM or LLFVW models inherit. Again, to get the full picture use CFD - if you want to have quick results use the simplified methods and take results with a grain of salt.
Cheers,
David
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
The origin of flat 2D world
In my world the 2D world originates from the idea of a thin section of an infinite wing where the same mass volume enters and exits the profile. To produce a similar setup with a rotating wing we can normally relocate the foil to a cylinder concentric with the turbine shaft.
After the the foil is transformed we notice if rotor spins in zero wind the air travels along the foil in a similar way it does with a linearly moving wing in zero wind speed. In the new 2D world the foil travels at constant radius with the speed v = ωr. In the simplest model it is now a plane with curved profiles running in circles.
The exact location of the airfoil?
So what I try to get across is the profile from the flat airfoil has a mechanical representation in the physical world of the rotor. It is located along the flow because that is the only orientation where we know how the foil works. QBlade have already implicitly oriented the profile along the the flow, otherwise the mass travels sideways over unknown territory.
My only requirement is for QBlade to draw the profile where it belongs in the physical model. A straight line is invalid and has no meaning on the wing. It is an airplane flying flat in circles and QBlade have already committed to a plane with curved profiles for air not to leak between foils and has to show that image,
I get slim wings is not a problem because the QBlade "error" does not show. I understand industry may think of the foils as straight stings and the approximation is negligible. My point is QBlade is a great and flexible tool perfect for experimentation and it should not make assumptions about slim or wide wings and finalize with a "symbolic" straight line representing the curved foil.
Scientific Mode
I am now done planting the seed for flawless high resolution wing surface output. You can call the option "Scientific Mode" and switch to the mode automatically when required by geometry.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
I am not planning to implement such a festure (to warp the foild geometry around the curcular path of the blade) in QBlade. What you could try to do to get this result is to export the blade geometry as a .txt file and then perform the warping of the foil coordinates on a per foil basis in a CAD tool, such as SW.
The .stl file that is exported by QBlade is not really thought of as a final geometry for constructing the blades anyway as there are more problems associated with it such as dents and kinks on the surface - so most people use the .txt coodinate export function and post-process the data.
If you would like to inplement the aforementioned capabilities into QBlade I could also help you by giving you directions as to where in the source code you would have to apply the changes.
Cheers,
David
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Could not get a clear picture of how to configure the QT<>MinGW 64 bit environment so the Qt 5.7.0 32-bit was a better starting point.
Qblade 0.96 Compiled and executed ok. Changed checkbox logic to be able to see boundary layer and pressure arrows independantly and without diving into complexity made both thicknes and camber routines "pXFoil->tcset" and "pXFoil->hipnt" to execute on any change in the FoilGeomDlg. Maybe not how to do it but works better.
Great to be able do make small changes!
If you have some more info on how to obtain and configure a working 64-bit environment it is interesting but no panic at the moment.
Thanks!
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Tested is a minimal hack to make blades display with foils on same radius:
In BEM.cpp :: GLCreateGeom() I replaced all references to glVertex3d() with an intermedial glVertex3dX() that converts xyz to cylinder coordinates before calling glVertex3d() like this:
void glVertex3dX(GLdouble x, GLdouble y, GLdouble z)
{
double r = y;
double ang = x/r;
double xp = r*sin(ang);
double yp = r*cos(ang);
double zp = z
glVertex3d(xp, yp, zp);
}
Result is realistic blades with foils on cylinders
slim blades look like this..
Surface normal ignored in the test In the test, calls to glNormal3d() was not transformed. To be exact about illumination - within a glBegin(GLQUADSTRIP) block, the calls to glNormal3d() also have to be transformed using the same transform as used for the following glVertex3d(). The normal vector will affect illumination of the surface so transformed flat wing ends now need an explicit call to glNormal3d() for each surface vertex..
Something similar and simple can probably be made in the STL generator. I will keep track of changes made to the code in case anyone interested.
Happy foiling
Last edit: tofo 2016-11-21
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hi,
thanks for the info. Im glad you found the source code so easy to work with and got results that fast. The .stl generator is actually working with the same functions as the GLCreateGeom() function - so you should not have much issues.
But be aware that your modifications wont have any effect on the simulations, but just on the visualized or exported rotor shapes. The BEM and LLFVW models just cant work with profiles that are curved in the circumferential direction.
Cheers,
David
Last edit: David 2017-01-05
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Profiles are not made cylindric when applied in circular context.
All blade profiles I use come from cylinder sections of real life turbine blades collected at design operating angle to cut close to the core profile they may originate from. Profiles are then flatened from cylinder elements and normalized to xfoil coordinates with chord length 1.
In QBlade it looks like the profiles are used in blades without making them cylindric by the radius they are applied. For wide blades the curvature becomes totally false and the blade exported in STL 3D format consists of straight profile elements and do no longer, even closely, reflect the blade they originated from.
Profiles on slim or wide blades should be located with an offset perpendicular to blade axis, rotated to desired angle and then wrapped onto the cylinder they belong.
1. Profiles collected from original blade outside QBlade
2. Profiles used in a QBlade blade
3. QBlade STL output
As a newbie - maybe missed some option?
Hi there,
I dont exactly understand what you are explaining. Maybe try to explain the issue in other words?
One option you might find helpful though is the "Advanced blade design" tab in the HAWT blade designer. There you can assign an offset to each individual blade station and also change the point around which the airfoil is rotated due to the twist angle.
CHeers,
David
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Mark all as spam, and block user from posting to "Forums"
Hi David
Thank you for the attention to user activities!
If you design a 3-blade rotor with short straight blades with six equal foils you see the foils packed side by side:
If this rotor would be put in use in real life conditions a thin air stream would not travel mainly along one single airfoil wich is the assumtion of airfoil analyzis made earlier. It is probably the asumption in QBlade calculation too. Who would analyze a foil for straight travel and then put it in a rotating motion without bending it to the probable path of the flow across the blade?
If a rotor is made of the STL file exported it would have profiles lined up for travel along a streaight line but rotated in circular motion.
New feature: Airfoils on bent blade axis and oriented with the wind
As this is corrected - a cool feature would be if Qblade could use calculated path across the blade and physically line up profiles upp that way when constructing the blade. Near rotor center it would be more cylindric/conic and furher out the blade cross sections have foils tilted inwards and even scewed to stay with the airstream and in all cases appear to the wind as in the straight airfoil analyzis.
That would make blades where you know air travels mostly along the airfoils of your design and you could predict the behaviour based on airfoil data and calculations made.
New feature: Spline to locate foils on blade axis
Tilted foils mean thinner blade cross section so the another thing to add is the blade axis being a spline to make curved blades easy to experiment with wing tip losses and blades bent against the wind direction. Wind interactive flow vectors by radius would give designer a sense of what the wind would do given the blade profiles and axis "curving".
Ok, I understand the point you are making now!
One of the main assumptions of the BEM and LLFVW simulation methods in QBlade is that the flow is 2D over the airfoil sections of the blade(s) (and there is no crossflow). This is also the reason why we can use 2D airfoil polars for the simulation of a 3D rotor.
For most realistic wind turbine blades this assumption holds true as the chordlength of the airfoils is rather small compared to the circumference of the rotational blade path. This ratio between the circumference and the chord at a blade station is called the local solidity. At the root section of blades (as in your example) the solidity can be quite high at times - however, as the airfoils used here are cylindric and dont contribute to the performance significantly, this does not have a large impact on the results. All turbines that are in operation today have been designed with a BEM method, under the assumption of 2D flow at the airfoils - so this is common practice.
If you want to look at "wide" blades, as in the picture above - you might lose accuracy and need to switch to a different, higher order, method such as CFD to accurately represent blade crossflows and other 3D effects.
Regards,
David
View and moderate all "Bug Reports" comments posted by this user
Mark all as spam, and block user from posting to "Forums"
Thank You David
My point is that the real world will automatically aproximate a circle to a straight line where needed.
I will argue below for the straight profiles being an aproximation that should not be performed at all.
In HAWT configuration the basic asumption is the foil is wraped to a rotating cylinder or even better aligned to the actual flow. Staying exactly on the same radius or something similar is a great starting point of observation and makes you stay close to what you know about the airfoil from data.
The "objection" is puting straight profiles on a square blade is just mathematically wrong and has no connection to the amazing calculation just peformed by QBlade. No matter how many decimals you need the transformation choosen is wrong given the model used by QBlade.
As profiles are twisted and chordlength varies throughout the blade, adding the real profile cylindric or else curved, would not add to final complexity to the product - just make it mor accurate.
Conclusion.
1. HAWT blades are circular by nature - they just look square when blades are long
2. Display wings with profiles following the same path as used in flow calculation.
3. If user desires a straight corner wing - terminate the blade with straight edges.
4. It is ok to chop the blade in straight elemts for convenince or practice, but blade curvature is allways defined from curved foils.
That would serve all users: ignorant, pragmatic, stubborn or picky. What do you think?
Hi there,
using 2D airfoils in a 3D simulation is of course a large approximation - but amazingly it gives very accurate results for slender blades, even when compared to real life measured wind tunnel data or CFD simulations that naturally take the curvature into account.
Changing the approach to curved foils would require a a completely overhaul of the used methodology - and simple 2D airfoil polars could not be used in the simulations anymore - so the whole common practice of how to design WT blades would need to change.
Also, this assumption is not the only simplification and assumption that the BEM or LLFVW models inherit. Again, to get the full picture use CFD - if you want to have quick results use the simplified methods and take results with a grain of salt.
Cheers,
David
View and moderate all "Bug Reports" comments posted by this user
Mark all as spam, and block user from posting to "Forums"
I am not so great at explaining.
The origin of flat 2D world
In my world the 2D world originates from the idea of a thin section of an infinite wing where the same mass volume enters and exits the profile. To produce a similar setup with a rotating wing we can normally relocate the foil to a cylinder concentric with the turbine shaft.
After the the foil is transformed we notice if rotor spins in zero wind the air travels along the foil in a similar way it does with a linearly moving wing in zero wind speed. In the new 2D world the foil travels at constant radius with the speed v = ωr. In the simplest model it is now a plane with curved profiles running in circles.
The exact location of the airfoil?
So what I try to get across is the profile from the flat airfoil has a mechanical representation in the physical world of the rotor. It is located along the flow because that is the only orientation where we know how the foil works. QBlade have already implicitly oriented the profile along the the flow, otherwise the mass travels sideways over unknown territory.
My only requirement is for QBlade to draw the profile where it belongs in the physical model. A straight line is invalid and has no meaning on the wing. It is an airplane flying flat in circles and QBlade have already committed to a plane with curved profiles for air not to leak between foils and has to show that image,
I get slim wings is not a problem because the QBlade "error" does not show. I understand industry may think of the foils as straight stings and the approximation is negligible. My point is QBlade is a great and flexible tool perfect for experimentation and it should not make assumptions about slim or wide wings and finalize with a "symbolic" straight line representing the curved foil.
Scientific Mode
I am now done planting the seed for flawless high resolution wing surface output. You can call the option "Scientific Mode" and switch to the mode automatically when required by geometry.
Hi,
I am not planning to implement such a festure (to warp the foild geometry around the curcular path of the blade) in QBlade. What you could try to do to get this result is to export the blade geometry as a .txt file and then perform the warping of the foil coordinates on a per foil basis in a CAD tool, such as SW.
The .stl file that is exported by QBlade is not really thought of as a final geometry for constructing the blades anyway as there are more problems associated with it such as dents and kinks on the surface - so most people use the .txt coodinate export function and post-process the data.
If you would like to inplement the aforementioned capabilities into QBlade I could also help you by giving you directions as to where in the source code you would have to apply the changes.
Cheers,
David
Ok
Objective is to compile the current 0.963 64-bit version for Windows.
From what I read the Qt mingw compiler toolchain is recommended but the Qt windows online installer has a 32-bit option only.
What is pathway to compile the 64-bit version?
Hi,
you have two options:
Cheers,
David
Last edit: David 2016-11-17
Hi David
Could not get a clear picture of how to configure the QT<>MinGW 64 bit environment so the Qt 5.7.0 32-bit was a better starting point.
Qblade 0.96 Compiled and executed ok. Changed checkbox logic to be able to see boundary layer and pressure arrows independantly and without diving into complexity made both thicknes and camber routines "pXFoil->tcset" and "pXFoil->hipnt" to execute on any change in the FoilGeomDlg. Maybe not how to do it but works better.
Great to be able do make small changes!
If you have some more info on how to obtain and configure a working 64-bit environment it is interesting but no panic at the moment.
Thanks!
Hi David
Tested is a minimal hack to make blades display with foils on same radius:
In BEM.cpp :: GLCreateGeom() I replaced all references to glVertex3d() with an intermedial glVertex3dX() that converts xyz to cylinder coordinates before calling glVertex3d() like this:
void glVertex3dX(GLdouble x, GLdouble y, GLdouble z) { double r = y; double ang = x/r; double xp = r*sin(ang); double yp = r*cos(ang); double zp = z glVertex3d(xp, yp, zp); } Result is realistic blades with foils on cylindersslim blades look like this..
Surface normal ignored in the test
In the test, calls to glNormal3d() was not transformed. To be exact about illumination - within a glBegin(GLQUADSTRIP) block, the calls to glNormal3d() also have to be transformed using the same transform as used for the following glVertex3d(). The normal vector will affect illumination of the surface so transformed flat wing ends now need an explicit call to glNormal3d() for each surface vertex..
Something similar and simple can probably be made in the STL generator. I will keep track of changes made to the code in case anyone interested.
Happy foiling
Last edit: tofo 2016-11-21
Hi,
thanks for the info. Im glad you found the source code so easy to work with and got results that fast. The .stl generator is actually working with the same functions as the GLCreateGeom() function - so you should not have much issues.
But be aware that your modifications wont have any effect on the simulations, but just on the visualized or exported rotor shapes. The BEM and LLFVW models just cant work with profiles that are curved in the circumferential direction.
Cheers,
David
Last edit: David 2017-01-05