Gap needed for two adjacent aerodynamic blades to be useful

[T C]

TL;DR Summary

Want to know how correctly the ANSYS simulation have shown the torque generated by the flow.

I have designed a new kind of wind turbine and recently I have tried an ANSYS simulation of the machine. The photo above is from the ANSYS report. In the photo, you can see that all the flow passing through the turbine has got a bend. The blades are aerodynamic airfoils and is set at 10 degree 15 minutes angle of attack for highest lift generation that is around 1.5. The frontal projection area of each blade is 1.76 cm and the gap between the camber lines of two adjacent blades is 3.1923 cm. The diameter of the ring shown is 18.3 cm and the number of blades is 18. There the gap between the last point of contact and first point of contact of two adjacent blades is around 1.43 cm. I want to know whether the gap is too narrow for generating a linear flow at the lower part of the blades. In that case, can the aerodynamic properties of the blades be useful again by reducing the number of the blades? Will wait for expert comments in this matter.

 

[Baluncore]

At that 10.25° angle of attack, it will produce a good torque at zero RPM.
But if it rotates, it will no longer produce that torque.

What moves relative to what?
Is there something you are not telling us?

 

[T C]

It's not rotating, it has been done just to find out the torque. But, problem is that the torque generated shown in the simulation is much lower than what is expected. My main objective is to find out whether the gap between the blades are sufficient for getting the desired aerodynamic lift or not.

 

[Baluncore]

Think of the separation between the wings of a biplane. There is an optimum separation where the wings work with each other. That requires the upper wing be forward of the lower wing. That generates a slot effect, as seen in close-hauled sailboats.

The optimum RPM of a propeller, is inversely related to the number of blades. The air must be cut by a blade, just ahead of the disturbance caused by the previous blade. Too close, and it will cause noise and vibration, too far, and it would benefit from more blades or higher RPM.

The area of wind intercepted needs to be maximised. There must be a pressure and/or velocity reduction across the turbine to extract energy. It looks to me like your design restricts the working airflow to only a small area, but it has a huge wetted surface area.

 

[T C]

Just searched net as per your suggestion and found that the gap should be at least 1.5 times the chord length. Here the chord length is around 10.2 cm. But, those blades are fitted at the periphery of a cylinder and therefore a little away from each other and at an angle of 20 degree instead of 0 for exactly parallel airfoils.

 

[T C]

Here is the latest ANSYS simulation results after just one modification. The basic structure and shape, angle of blades remains the same. Just an outer rim is added. And, just see the change in torque and lift after just adding the outer rim. Can anyone explain the reasons?

 

[Baluncore]

Can anyone explain the reasons?

Placing a turbine or propeller in a duct, (a ducted fan), reduces the "induced drag", that normally occurs at the end of the airfoil, where air can flow around the end.

 

[T C]

That's the simulation result of a concentrated wind turbine in full i.e. together with the venturi section and the turbine afterwards. Anyone can check the results.
But afterwards, the blades has been given a different angle and only the turbine is put into a simulation where the flow velocity will be the same as the flow velocity inside the venturi. The result of this simulation is shown in thread no. 6. I want to know, if the new turbine has been fitted inside the same venturi where the velocity will be same as the velocity of the flow shown in the file below, will it produce the same results as the simulation of thread 6?

 

[Baluncore]

It struck me that, when modelling turbines, you should not model the blade, but model the duct between two blades, because that is where the fluid flows.

 

[T C]

Ok. Thanks for your reply. But I want an answer to my query.

 

[T C]

Here is the latest ANSYS simulation result of this turbine. But, one thing isn't clear to me whether the force and torque shown is for a single blade or for all the blades. Requesting for comments from experts here.