while I was writing my bachelor thesis I simulated modelplanepropellers with qblade v0.6-r68. The BEM method is working for propellers as well as for turbines.
For simulating a propeller I wanted to change the direction of rotation. By deactivating the lines 122, 127, 151, 154, 157,190, 193, 196, 200 and 203 in „SimuWidget.cpp” (stored in the „XBEM” folder) it is possible to enter negative rotational speeds.
If you change the direction of rotation without changing the coordinate system the angle phi has to be bigger than 180°. Because this is not considered by the trigonometric functions used for computing phi I changed it to:
// the angl e phi i s computed
i f (m_lambda_local . at ( i )>=0)
{
phi = atan ( (1−a_a) /(1+a_r ) / m_lambda_local . at ( i ) ) /2/PI *360;
}
e l s e
{
phi =180−atan ( f abs ( (1−a_a) /(1+a_r ) / m_lambda_local . at ( i ) ) ) /2/PI*360;
}
The sign of lambda is used to find out the direction of rotation, because with negative rotational speeds lambda also gets negative.
With the modified phi the solidity becomes negative, which is not correct. So I added a fabs function to get the amount only.
im happy you could find your way around in the source code and thanks for sharing your modification. Just two question: why did you want to change the direction of rotation - did this affect the performance in any way? And have you heard of JBlade? J. Morgado from the University of Beira Interior developed it as a QBlade branch for propeller design with some additional modifications.
Regards,
David
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Hallo,
As I learnt turbines and propellers are working a bit different. While turbine blades are deflecting the incoming airflow away from the rotation axis to drain out energy from the airflow. Propeller blades are deflecting the incoming airflow towards the rotation axis and put energy into the airflow. So I wanted to change the direction of rotation to get a proper AoA for propellers.
I do not really know how to explain that, but it might become a bit clearer with the added picture showing the velocities at the blades.
An have not heard of JBlade. At first sight it seems to do exactly what I wanted QBlade to do. I think this would have made my work much easier. Thanks for that hint. I will give a closer look at JBlade.
regards,
Christian
hello everyone,
while I was writing my bachelor thesis I simulated modelplanepropellers with qblade v0.6-r68. The BEM method is working for propellers as well as for turbines.
For simulating a propeller I wanted to change the direction of rotation. By deactivating the lines 122, 127, 151, 154, 157,190, 193, 196, 200 and 203 in „SimuWidget.cpp” (stored in the „XBEM” folder) it is possible to enter negative rotational speeds.
If you change the direction of rotation without changing the coordinate system the angle phi has to be bigger than 180°. Because this is not considered by the trigonometric functions used for computing phi I changed it to:
The sign of lambda is used to find out the direction of rotation, because with negative rotational speeds lambda also gets negative.
With the modified phi the solidity becomes negative, which is not correct. So I added a fabs function to get the amount only.
At last negative power and thrust should be allowed so I deactivated the lines 470 and 483:
For me this modifications worked fine and the results matched pretty good the results I got from the propeller simulation PropCalc.
From the following link you can get the modified code. I marked the modifications I made with my initials CW.
https://www.dropbox.com/sh/mkir32bik1t7vpm/AADomyKBBeCwA65BqmuA4704a
regards,
Christian
Hi Chris,
im happy you could find your way around in the source code and thanks for sharing your modification. Just two question: why did you want to change the direction of rotation - did this affect the performance in any way? And have you heard of JBlade? J. Morgado from the University of Beira Interior developed it as a QBlade branch for propeller design with some additional modifications.
Regards,
David
Hallo,
As I learnt turbines and propellers are working a bit different. While turbine blades are deflecting the incoming airflow away from the rotation axis to drain out energy from the airflow. Propeller blades are deflecting the incoming airflow towards the rotation axis and put energy into the airflow. So I wanted to change the direction of rotation to get a proper AoA for propellers.
I do not really know how to explain that, but it might become a bit clearer with the added picture showing the velocities at the blades.
An have not heard of JBlade. At first sight it seems to do exactly what I wanted QBlade to do. I think this would have made my work much easier. Thanks for that hint. I will give a closer look at JBlade.
regards,
Christian
hi chris! I can t open your modified code.Can you help me please?
Last edit: giuseppe 2017-03-20