Design of Hydropowered Turbine Propeller for Mobile Charger

[TaylorHoward21]

TL;DR

Working on a picohydropower turbine propeller, what design considerations/equations are necessary to consider for low velocity streams?

I am currently working on a project for an undergraduate course in university. My team and I have decided to make a hydropowered mobile device charger, and I am responsible for the design and modeling of the turbine propeller. This turbine will need to be able to function in low velocity streams and rivers, so where can I find information on how to include the necessary blade curvature, pitch angle, blade twist, and other important design considerations? I've been perusing databases such as Google Scholar and EBSCO and have yet to find any resources.

 

[berkeman]

Summary:: Working on a picohydropower turbine propeller, what design considerations/equations are necessary to consider for low velocity streams?

I've been perusing databases such as Google Scholar and EBSCO and have yet to find any resources.

Fun project!

What about just Google searches with directed search terms? Have you been through most of the hits in this search, for example? I used Low Flow Water Turbine Design to get the search results:

https://www.google.com/search?client=firefox-b-1-d&q=low+flow+water+turbine+design

 

[TaylorHoward21]

Fun project!

What about just Google searches with directed search terms? Have you been through most of the hits in this search, for example? I used Low Flow Water Turbine Design to get the search results:

https://www.google.com/search?client=firefox-b-1-d&q=low+flow+water+turbine+design

View attachment 261884

Thanks for the quick reply!

Yes, I have done some more simplified research and it seems that most pico/micro hydro turbines are modeled with Kaplan and Francis turbines for stationary projects.
My group is going with fixed pitch so we don't overcomplicate the task or go over the budget.
There are already devices that accomplish the task at hand like this.

 

[berkeman]

Thanks for the link.

BTW, what freedoms and constraints do you have in this project? Are there some typical locations that this device might be used (like a local creek or something), where you may be testing or having the design graded?

I ask because in reading the DoE link in the search that I posted, several ideas come to mind for optimizing each of the potential generator schemes. Can you think of some of the things that I'm thinking about to try to broaden the scope of your project to get more energy out of your device?

 

[TaylorHoward21]

Locations will be small rivers and creeks most likely. The project is taking the form of a "product" that will have backpackers and outdoor enthusiasts as the target audience. So we are to imagine that the "product" would be utilized as such, in remote outdoor locations.

Our goal is to provide about as much power as a typical phone charger would require. The power will be stored in 18650 battery cells, but that is the responsibility of my Electrical Engineering colleague (I am M.E.).

I will be designing the turbine propeller in SolidWorks and another team member will be 3D printing it. Unfortunately due to COVID-19 we likely won't be able to test our initial designs more than once.

So for the sake of the following our tight timeframe I will have to run with theoretical analysis more so than experimental. With the fixed pitch design, I know that the fluid velocity will have be as low as around 1 to 2 m/s.
The turbine itself will have a diameter of around 6 inches, and will consist of three propeller blades as prior research has shown that 3 blades is more efficient than 2 or 4.

Hope this adds some context!

 

[anorlunda]

I agree, fun project. Simple paddewheels, and pelton wheels can work for that purpose.

On Youtube, a quick search shows several.







I would check out all such things as I can find before plunging into analysis and design. It would be embarrassing to find that my sophisticated analysis was out performed by a kid using parts from a dollar store.

It would also be embarrassing for my propeller design to be bested by a paddle wheel.

Good engineering also begins with numerical requirements. How many joules/sec does the electrical guy say he needs? Are there size or weight restrictions? As much as possible or as little as possible, are terrible requirements and likely to earn you a low grade for the project.

 

[TaylorHoward21]

I agree, fun project. Simple paddewheels, and pelton wheels can work for that purpose.

On Youtube, a quick search shows several.







I would check out all such things as I can find before plunging into analysis and design. It would be embarrassing to find that my sophisticated analysis was out performed by a kid using parts from a dollar store.

It would also be embarrassing for my propeller design to be bested by a paddle wheel.

Good engineering also begins with numerical requirements. How many joules/sec does the electrical guy say he needs? Are there size or weight restrictions? As much as possible or as little as possible, are terrible requirements and likely to earn you a low grade for the project.

We have already created design specifications, I can try to share it if you would like to see. The weight shall be less than 3lbs and should be less than 1.5lbs. Fixed pitch propeller provides lower weight than others. Printing will be done using PETG as it will outperform PLA and will be more resistant to corrosion and UV decay.

Fixed pitch also provides allows the design to be as compact as possible; our primary design priority. Electrical guy would like to see between 1 and 5 Watts.

Grading will also weigh heavily on aesthetics, our projects cannot look like it came from the dollar store.

 

[berkeman]

The project is taking the form of a "product" that will have backpackers and outdoor enthusiasts as the target audience.

Ah, "backpackers" kind of shoots down the idea that I had. The idea was to take advantage of the slope of a creek and use some tubing (like 1" PVC) to add length to the head that you could use to run the water through the turbine. If you could get an extra 6" to 12" of head by running 30 feet of tubing down the creek, that would make the turbine much more effective.

But there's no way a backpacker is going to carry that much tubing, even in flexible form.

Also, for the creeks that I'm familiar with, 1-2m/s seems a bit fast to me. As @anorlunda says, be sure to do some reality checks on the amount of power available from your water flow and the swept area of your generator, in order to see how close you are to being able to charge a cell phone battery.

 

[jrmichler]

You might throw a stick into a stream to measure the velocity. My experience with a kayak is that 0.3 m/sec is not too difficult to paddle upstream, much more fun to go downstream, and there is noticeable swirling around obstructions. At 1 m/sec, paddling upstream is a real challenge. At 2 m/sec/ paddling upstream is not going to happen, even if you work the slackwater to maximum. Getting the design velocity correct is critical because the power is proportional to velocity cubed.

Given a realistic velocity, your next challenge is to calculate the propeller diameter. The calculations are the same as for a wind turbine. Water just has lower velocity and higher density. My 8th Edition of Marks' Standard Handbook for Mechanical Engineers has a very good section on wind power.

 

[Baluncore]

@TaylorHoward21
You have low velocity water, low pressure, but high flow volume, so the terms you need to search are 'sailing hydro generator'. Hydro generators are used by cruising yachts to recharge batteries without starting the motor. Solar panels work during the day. Hydro generators work while the boat is moving through the water, or anchored in a tidal flow which is analogous to your situation.
https://www.sailmagazine.com/diy/know-how-hydro-generators

As the water flows, the turbine (not a propeller) rotates and "cuts" the volume of water. The optimum number of blades is inversely proportional to the flow velocity. 3 blades is probably too few, and would be more suited to a 4 stroke engine.
Too few blades, with shallow angles to get high RPM, will have high surface velocity, so very high drag which is proportional to the square of the surface velocity.

Once you have an optimum design the blade count, the blade angles and profile will resolve itself. If the turbine profile is asymmetric, it will be the opposite expected for a propeller.

 

[LT Judd]

Hi , You will probably find in these very small projects frictional effects will be just as important as turbine geometry. So really pay attention to your bearings and balancing.
If you can get your hands on a textbook "Fox mcdonald and Pritchard Fluid Mechanics 9th ed.", It contains some formulas and worked examples for blade and impeller geometry.
Also are you planning to have the electrical generator part out of the water or in it. Shaft sealing is critical , unless you have some sort of PMG drive that does require though shaft.

 

[AverageEngineer]

Summary:: Working on a picohydropower turbine propeller, what design considerations/equations are necessary to consider for low velocity streams?

I am currently working on a project for an undergraduate course in university. My team and I have decided to make a hydropowered mobile device charger, and I am responsible for the design and modeling of the turbine propeller. This turbine will need to be able to function in low velocity streams and rivers, so where can I find information on how to include the necessary blade curvature, pitch angle, blade twist, and other important design considerations? I've been perusing databases such as Google Scholar and EBSCO and have yet to find any resources.

Sounds like a fun project. I would read a lot of research papers on micro hydro. I too am working on a personal project involving micro hydro. I have got most of my information from reading textbooks or online, there is a lot of good information.