My name is Olivier, student in mechanical engineering in Montreal, Canada. This is the third year that I am involved in a project of designing and fabricating a wind powered car. For those who are curious, you can check our instagram page : youtube.com/watch?v=KrwrcutnHdU&t=83s
This year, I am focusing on the wind turbine itself. It has been a few years that the team hasn’t change the blade’s geometry and the diffuser shape. Because of that, the knowledge hasn’t been transfered very well and I have a lot to learn. I have familiarized on the BEM by reading the book Aerodynamics of wind turbine. We have a Matlab script that incorporates these equations to compute the power generated of a blade.
Here are my interrogations so far:
How can I compute the power loss generated by the wind turbine drag? In our Matlab script, we have an equation to calculate the axial force on the blade element. I was thinking of applying Power = force x incoming wind velocity, but this results in a negative net power output.
What strategy could I use to maximize the net power output of the wind turbine? Our car goes against the wind, so our wind turbine needs to be optimized for the net ouput (Pnet=power-drag).
I understand that the main focus of the NREL is for large wind tubines, but do you have suggestions of airfoils that would be more appropriate for a 2 meter diameter wind turbine? As of right now, we have a thicker airfoil at the root (NACA 63(3)-618) and a thinner profil for the rest of the blade (FX60-100).
Feel free to give any other advice!
That sounds like an awesome project to work on! If I got things right, the car would run with an electric engine that’d be recharged by the wind turbine that would be put in motion by the relative wind created by the movement of the car?
And if the blade geometry hasn’t been changed for the last couple years, I think it would be quite useful to do a quick check as to learn whether there were new discoveries in this domain, such as new polymer or fibre materials that would be lighter and thus easier to put in motion.
Anyways, I hope that your research will result in something applicable to “real life” cars, because these days, I feel like we’re witnessing the birth of the car of tomorrow, with new energy sources, autonomous technologies… Hell, even the private sector (here, the real estate market) is preparing for these to become the norm: https://tranio.com/articles/how-self-driving-cars-will-change-the-property-market_5386/
Oh, and by the way, since that’s my domain of research and since you’re located in a country which pretty much has the same climate as my homeland, Russia, double check (and even triple check) every piece of data you can find in terms of temperature. We ran into a couple issues because of that, since we shared some of our research with partners from other countries with radically different climates in terms of temperatures and humidity (our main partner team is in India) and tried to apply them to our research…
Here are my answers to your questions:
When using BEM theory, the aerodynamic power can be calculated by integrating the ( in-plane aerodynamic force ) x ( local radius ) x ( rotor speed ) along each blade. The first two terms multiplied together are the local aerodynamic torque of a blade airfoil. Drag and nonoptimal rotor design will reduce the power from the theoretical optimal (Betz limit).
While I have little experience with wind power cars, my understanding is that an optimal rotor for a wind-powered car is different than for a normal wind turbine. That is, in a wind-powered car, while you’ll want to maximize power, you’ll also want to minimize thrust for the car to be able to travel upwind.
I’m not really an expert at selecting airfoils; hopefully someone else on this forum can provide better guidance. But in general, you’ll want to pick an airfoil that has high lift and low drag at the Reynolds numbers the airfoil operates in. Because your rotor will not operate 24/7, my guess is you do not need to worry about sensitivity to surface roughness (from erosion and bug build-up) that would be important for conventional wind turbine airfoils.
Sounds like a fun project…best of luck!
To Feliks :
Our car is purely mechanical. So a driveshaft goes down the mast, into a clutch, then in a 14 speed gearhub (Rohloff bicycle hub) and finally to the rear wheels. As of right now, our blade are made out of two composite skin with resin poured in the middle to add inertia as we need it to start the car from standstill without stalling the wind turbine. The downside of this manufacturing technique is that the leading edge and trailing edge are sanded by hand, with is not good. This year, we want to try printing the blades with a composite reinforcement in the middle.
To Jason :
Thanks for your input. When I use the in-plane and normal aerodynamic force to calculate the the power generated and the power lost by the drag force, I end up with a negative net power output. I’ll try to figure what I am doing wrong.
Thanks for the answer, I hope I wasn’t digging too much into the secrecy of the research! It does sound like an awesome project, is it destined to be a pre-production model or a technology demonstrator? Because in the case of the former, it will need an auxiliary engine to get through tunnels or just windless days. But as a demonstrator, it’s perfect and I’m waiting to see an article about this!
This project is not a research, it is regroupment of students that design and fabricate a wind powered car on their spare time. This is not a course nor do we have professors helping us. This was the 8th iteration (8th year) that the team participated in Racing Aeolus competition, which is the goal of our project. The objective is mainly develop our skills to become better futur engineers.