How to apply ducted fan theory to real world fans
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- Опубликовано: 30 апр 2021
- Placing a propeller in a duct increases efficiency and maximum thrust. But how much? Do you need complex computer simulations to calculate this? This video explores applying Newton’s second law to ducted fans. I try practical experiments to learn about the physics that goes into developing a math model for describing ducted fan aerodynamics. Hopefully in the next video we can explore more about Bernoulli's theorum and the Coanda effect, but I do touch on it in this video.
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Hi, I really enjoyed your video. I'm a mexican aeronautical engineer and I have made some simulations on this phenomena. I can tell you that, in principle, the effect of a duct on propeller efficiency can grow up to 30% in static thrust. However, the effect is faded away when the system is travelling with respect to air, mainly because the drag of the duct. On the other hand, the calculation that you are doing with Newton's 2nd law is called in aeronautics the 'Rankine Froude approximation'. For a better approximation one needs to use the 'blade element theory'. In that case, you will need the lift and drag curves of the airfoil (or airfoils) used along the blades. Indeed, the 'lost power' in your calculation is due to drag on the airfoils: Rankine Froude approximation cannot take that into account. I offer my help if you desire to learn about blade element theory. Congratulations for the great work!
I would assume at higher power levels for small EDFs air compressibility also applies, in what conditions you expect it to be noticeable?
@@hailstorm7868 Compresibility only becomes important with high speed flows. When the air travelling over the aerofoils is greater than mach 0.3 compressibility of air should be considered for greater accuracy.
Testing a static fan, you probably want to think about putting a "bell-mouth" inlet in front of the fan. When the fan is stationary the capture area (the area at which the amount of air flowing through at the flight speed of the fan) goes to infinity (pesky divide by zero thing). Of course you can't put an inlet on it with infinite area, but you can put an inlet on it that has a shape that follows pretty close to what the streamlines relatively close to the inlet. This type of area smoothly accelerates the air as it moves from the stationary room air (very very low velocity at very big area) to the inlet of the fan (higher velocity and smaller area)
You can actually see the streamlines if you put a little smoke from a small source in the air in front of the fan. A great way to do that is with an incense stick (as long as the air isn't moving so fast that the smoke is stretched out so much you can't see it. Smoke is the best way to visualize the flow field since the smoke particles follow the curvature of the streamlines and allows you to see the entire flow field by introducing smoke just along the outer edges of the area you want to visualize the flow field.
Another way is to put a short (L/D of maybe 10) tuft of yarn on the end of a very thin stick (so as to disturb the airflow as little as possible) and then move the stick at a range of axial distances from the fan and radial distances from the centerline. When the air is moving relatively quickly the tuft of yarn will follow the streamline pretty closely. Fluff up the yarn to decrease the density and increase the drag so that it follows the streamlines at lower velocities. At some lower airspeed the weight of the yarn is such that the drag from the moving air isn't enough to keep the yarn in line with the streamline.
Either with smoke or yard on a stick, mount a camera at a stationary location perpendicular to the plane of the fan and in front of the fan by 1 fan diameter. Then move the incense stick along the perimeter or the tuft of yard in a raster scan across a 2-D slice starting at the centerline about 3 fan radii in front and then move upward to about 2-3 fan radii above the centerline. To visualize the flow field grab individual frames and superimpose them and you should end up with a visualization of the entire flow field in front of the fan inlet. If you make an inlet that follows the shape of the streamlines going into the tip of the fan you should end up with a bell-mouth inlet.
Here is a picture of a bell-mouth along with sizing information. forum.ih8mud.com/threads/1hd-t-intake-manifold-modifications.651365/page-4
I hope this was helpful.
We’re still here and lots of us, haha! Your humility and candor are refreshing as you give us a peek into what researchers long ago had to go through to develop the fantastically efficient ducted fans which power every airliner with massive bypass engines; most of the air doesn’t even go through the combustion chamber. It’ll be super to see what principles lead to powerful fans with more than four blades.
After another month of poking around the internet, this is still the best resource I have found for calculating the pitch along a swept blade. Keep it up.
Nothing wrong with metric, but the statement that all these calculations need to be done in metric units or that the formulas only work in metric are flat out false. The relationship "f = m x a" works for all units of force, mass, and acceleration. Mixing measurement systems adds a touch more work, but is also fine. Physics works the same, regardless of the arbitrary naming and magnitudes used in measuring it.
Excellent video and theory description! Experiments and searching the truth are amazing.
Thanks to you,I finally figured out the twist of propeller’s blade!
Simple. Easy. 100% correct.
Awesome job,man!
Awesome build dude! Great explanation and transition to the various topics. I really liked how you went in deeper than pretty much everyone else
Great job. Not only made it all the way to the end but I watched it three times!!!!
Wow! Not only is your content really interesting, but it also has really intelligent comments posted from some obviously well-tenured individuals. Big respect to you and your commenters!
"If the ball park is big.. it will get you in the ballpark" love this.
This video is so well made! Awesome stuff dude!
I’m a bit of a scientist myself! Thank you for all the data you were goin off of. Someone may not be doin the same project as you but every piece of info helps. Thank you.
What a great opening sequence! Yes! I already love you - a nerd, an entertainer, a comedian, a cinematographer, well done!!!
Dude, this is an awesome video!! Well done, I have a feeling you’ll have a few more subscribers soon.
Would be interesting to measure air pressure inside the duct, pressure sensors are relatively cheap. Most iPhones have one now
this is a great video. making mistakes, finding and breaking them down is the best way to learn something - and the best way to teach something. I do hope you continue this project. It'd be fun hearing about the problems in more detail (Especially after reading some of the informative comments on this video)
Bro we have been waiting... I think this is the second time RUclips has recommended this video to me and i watched it all again, it's that good🔥
these vids are amazingly edited, hopefully this channel will soon become huge, great experiment
I loved this. Watched it twice over the last year. So funny and well explained. Thank you!!
I'm grateful that I stumbled upon this. What a lucky day...
Great explanation! Its cool to see how far this basic physics will get you, even with something as complicated as aerodynamics
Still here. I’ve been looking for this video for a while now. Thanks for making it.
Good video, I may have watched this to get ideas for fans for the Fan Showndown. Definitly learned me some napkin aerodynamics.
Love stuff like this! Wish RUclips had more of this content. Nice work! By the way, in order to get the motor RPM up did you consider gearing reduction? In aviation, especially turboprops, extensive gearing is used to reduce the RPM of the turbine to the propeller. Curious how that would have impacted your experiments (notwithstanding the added friction and heat losses from the gearing)
Nice , came to this vid having missed the previous ones, so was a bit behind the facts for a bit, but you showed how the math and physics worked quite well, good illustrations of the various calculations. I don’t remember all the physics I got but it made sense, well done.
As a fromer duct fan designer, I can only tell you one thing : Welcome to the rabbit hole :D d'ont worry there is no bottom to this one, you'll just be falling from now on.
Also congrats, these models and the way you make hyphothesis is really nice and a really "hand on engineer" approach I like it :D ofc you're making mistake even though some make me grit my teeth, mistakes are fun as long as you're trying to find them or checking your math with experiments.
And last thing ^^', Is you're motor ok? 400W of power loss... this thing might have been burning in there?
this is such a fantastic and charmingly made video and i really enjoyed it! i'm now back a few months later, and see that you haven't posted again since, so i really hope you're doing ok and tat you might find the time eventually. wishing you all the best, and thank you for the interesting experiments!
I realize I'm late to this design party, but I have a intense interest in ducted fans, and have 3D printed quite a few of my own up to 200 mm diameter, and I got some very useful information from this video. .so my question to you is, could you publish your formulas in a spreadsheet format.? Is that would be extremely helpful to us backyard designers. Thanks and keep up the good work
The diffuser inlet slows down the air and thus increases the static pressure before the fan. As a result the air density and mass flow increases. Something as simple as a pitot type inlet raises the pressure at the inlet enough to raise the pressure differential between the inlet and outlet.
Have you ever heard of the pc fan showdown?
@@seldoon_nemar yes i sub to his channel
@@JazAero I just watched this video, but there is no follow up video as expected :(
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FYI. I have watched every single videos of the Fan Showdown :D For those who do not know, the videos can be found here >>> ruclips.net/user/MajorHardware
I just found this randomly and it's great. I subscribed and immediately looked for the follow up.
I like this video. I was thinking about fun home projects. I thought more propellers were better. After this video, not only is the number of propellers very important to take into account but getting the right pitch. Good stuff.
Somehow, in an extremely sleep deprived state, ended falling down the 3D printed EDF RUclips rabbit hole and landed here. This was AWESOME!
I made it to the end and subscribed, but when I went to check your other videos, noticed this was the last one you made. :(
I get it, though. This project must have taken an utterly absurd amount of time and money to put together, which might have burnt you out early. Or... you know, maybe life happened and you haven't had the time or motivation. Still, I subbed and will look forward to a new video if we ever get one! :)
Don't know why, but fan design fascinates me so much. Especially 3D printed ones.
Great stuff, had some similar ideas pop into my head and nice to see someone else mathing over some of the concepts. I see a lot of RC plane EDF's are optimized for high power/high rpm but thought a larger, lower rpm, high efficiency EDF's could be appealing for a glider type RC plane or even a solar plane (rctestflight style). Next episode soon please :) I know at least the wikipedia page mentions having very small clearance between the blades and duct can be a large factor for efficiency. Also i imagined multi-stage/multi prop ducted fan may have some more thrust gains too potentially? Thinking like, running on the same motor axis a larger high volume intake fan at the front with a second internal blade optimized for high static pressure a bit like a turbofan engine? Or even just another of the same blade internally may extract slightly more efficiency from the same input power. The next step would be to 3d print or redo the duct frame in a lightweight material and see what kind of thrust/weight ratio you can get from the whole thing.
WOW. I love you actually get to "calculate" the parameters, even if it is at "napkin" precision. Thank U greatly.
That was really cool! On next iteration try to keep clear the distinction between power and energy and their symantics. Great work! I look forward to the next one!
this is why i love research. i don't work on this type of project, but it is discovery that is good.
according to shannon, when something new is not learned, nothing has been done. his concept was if a project is worth doing, success or failure, learning, or new unknown information is adduced. (shannon information for anyone that is interested in his ideas)
Also be very interesting to compare your real world with a CFD program like sim scale which has a free public version
Thank you. Like the delivery.
Very simple and informative. I stayed to the end of your Video. Good one 👍
Awesome video! The explanation of the design methodology is great!
Put together well thanks for sharing.
Fantastic video. You do a great job teaching, really helps me on my project, thank you.
Feel like I stumbled upon a future million sub channel before it took off.
We need more projects! This is great!
Good video! hope to see more content. It's inspired me to put my all ready printed variety of fans/blades/pitches I printed onto my test bench finally!
this was really nicely done!! thanks!
Great work and interesting results. Thank you!
a lot of effort went into this video, thanks it was interesting.
Wyman : It is a pleasure to hear your explanation...sounds well thought out ! Best Wishes towards success .
Please keep up, i love your scientific approach!
Is this the best video about a ducked fan EVER?
I want to design and test a variety of 3D printed propellers with my students and this video has been an incredibly useful resource. Thank you!
Watch these >>> ruclips.net/user/MajorHardware
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All of the designs are free to download, use and share.
I enjoyed this! You earned my sub. Thank you for this.
Very nice and good explained video. You got me hooked immediately. Let's raise your subscribers to infinity!!!
you could do a variable size exit cone and empirically check for best speed / thrust, also the increased speed in a reduced duct is a venturi effect (speed increased, pressure decreased) and this is used in the ICE engines throttle bodies etc.
You, sir definitely deserve my subscribe, absolutely awesome
having had an airplane with a three bladed propeller, subtracting the drag of the air-frame, at speed, about 82% efficiency could be achieved, i.e. keeping the air-frame aloft at something like 125knots forward airspeed. Fans have one advantage, that is the solidarity of the disc, as they can go over solidarity and create a compression of the air, and that usually there are stator blades (another advantage, but requires power) after the fan, essentially another set of fan blades that 'straighten out the twisting motion that the fan blades exert on the air. In a low speed mode, one also has to model in the total induced Bernoulli effect, which even propellers have, that greatly reduces the overall efficiency, so it is not unrealistic to get the 'just starting efficiency being very low and increasing to the potential with a fixed pitch blade, even to the point that forward stator blades make sense (see older turbine jet engines) S back to Solidarity, and the formula usually produces a 1.12 increase effect for a totally solid blade configuration, but can be higher at optimization, so as you look at the 7 to nine stages of a gas turbine with the rotating stages and stators, you see the compression significantly increasing.. but then add in the loss of pressure at flight altitudes.. bla, bla, bla.. (why take-off takes so much fuel and maybe all runways should have a catapult and big jet aircraft should be towed to the end of the runway and into take-off place, or why high speed, well 1/3rd of flight speed, rail makes sense.. slower acceleration, no lifting force).
This will go a long way to winning your doctorate! Great job.....
You deserve much more views. Subbed and shared
Wow amazing video learnt a lot .
First visit to your channel. Got as far as "the short answer" and subbed. 😁👍
Great vid, I love this stuff.
It looks like you are getting into the realm of some rotating compressible flow characteristics. You might want to consider that to account for the higher output. It's been a while since I've done those calculations myself, but I'm sure there is open source CFD code that could easily be used to make (more detailed) calculations and get you a precise anwser.
I made it to the end, thanks for that. FYI, I'm watching because I have a very limited knowledge and my full home HVAC system sucks. So, I'm trying to make it better, thinking I'm going to put in an inline duct booster.
I basically can't imagine living in a wind tunnel with temperature hot spots though, so I ain't going to be happy till the mailman has trouble putting paper in my mailbox though. Thanks for fueling my crazy adventure.
Subscribed
Killer video. I'll have to think about this one.
Great video, I hope to learn more.
I learned something today! Thanks
May 2022 checking in. Super looking forward to part 3 :D
If you want a very easy way to check your RPM measurement you can simply install a free app like decibels, or any other that gives you the instantaneous sound spectrum of the fan noise emissions. Indeed, a fan emits discrete tones at the blade passing frequency (BPF) and harmonics. The BPF is defined as BPF = B Omega/60, where B is the number of the blades, Omega is the rotational speed expressed in revolutions per minute (rpm). So, you can look at the dominant tone and derive the rotational speed Omega with very high precision from the formula above. This works if the blades are (almost) equally spaced.
I am one who watched the whole thing - and enjjoyed it. I know that the running time of the video is 19:16. Very interesting and a good example of the pursuit of the science. As for interest to me, it maybe is something abpout my background. I have had a lifelong interest in aviation, but a one point I was medically disqualified from flying. My father was an aerospace engineer, and his father spent 30 years in the RAF. In my military services, I spent three years with a USMC fighter squadron, and six years as an aircraft maintainer in a USAF heavy airlifter wing. I also worked for a while with a major airline. And I retired from a career in measurement science. So yes, this is VERY interesting to me! Very well presented. Thank you.
It’s a precious, thank you for video
Gave you a thumbs up for figuring out something as minuscule as the hz rate of the electricity in your lights 🤣 genius
Hi, very interesting video! Love how you tackle the physical problem from a very experimental point of view.
In one of my project I use a commercial EDF to generate a kind of vacuum cleaner to apply a tuned suction force on a plane below the EDF, playing around with the RPM. I would like to estimate this "vacuum suction force" as a function of the rotation speed. From your opinion, would you say that such suction force is equivalent to thrust? Or is it something different?
Thanks a lot in advance,
Jules
loved it man your entertaining af
That was excellent. Good, straightforward application of Newtonian physics to a low speed ducted fan! You might want to look up momentum theory and try to analyse it that way as well, for comparison?
That's a great video!
Really excellent work.
Great video, love it
Great Video! I made it all the way. Subscribed at the end, BTW.
I cant beleive this has only 370 vies, this is MONEY! nice work guy nice work
Thanks so much, I appreciate it
@@WymansWorkshop i am new here...
I have watched 100% of the video and genuinly enjoyed every second of it... you got my sub now
It would be amazing if you share an excel sheet where we just plug in the numbers for our application and get the results in the "ballpark"
Fantastic video and I'm hoping to gain some additional knowledge here. I have been playing around with bldc ducted fan as a form of forced induction on combustion engines and I am far from an engineer but understand enough to get in trouble. My question is how to calculate/estimate how much if any, pressure generated. I figured in some format thrust would convert or be part of pressure however I have yet to find a direction. I would like to find some baseline to begin testing "plumbing " configurations as well as utilizing the ducted fan in a compound turbo configuration feeding a "dormant " standard turbo. Again, awesome work!
7:00 Another way to express the second law is momentum change per time. Also, the velocity change is of the air, not the fan. Obviously the air speeds up when entering the fan, however not as much as airspeed increases
Amazing work 👏
I liked how you tried different number of blades. I wonder what the correlation is between the number of blades vs rpm vs power vs efficiency. Since you have all those fans made up why not? I learned a lot from this video, great information, thanks
It's not just the Coanda effect that makes an inlet flare a Good Thing. A sharp-edge inlet forces separation at the inlet. Good picture of the resulting flow is that of a Borda mouthpiece, which essentially reduces flow area to below that of the actual passage. Superb treatment of the instrumentation that you created! Skepticism combined with keen observation produces very useful results.
Awesome job!
Brushless motors would be an excellent addition to this project. For about $250, you could get a decent quality motor and controller like a vesc or odrive. Those two both connect to your computer for exact rpm commands and will measure power for you too. If you don't have a battery big enough, a switched mode power supply would be pretty cheap. It seems like the ability to measure power and thrust across a range of RPM gives you enough extra information to warrant the additional dollars. Plus, learning new stuff is fun.
indeed, you can then test the setup over a range of motor velocity and make a curve where the max power of the motor is reached. Another variable to think about: when making a test setup, how accurate is the power meter? When doing a test setup, you'll want to control every aspect - so measuring current and voltage in stead of measuring power with a 'cheap' power meter.
Great video.
Remember that the diffuser at the inlet increases the mass flow because it slows down the air raising its pressure and density, the greater pressure difference between the inlet(before the fan) and outlet(after the fan) adds the mechanical displacement of air from the fan. In other words, with a diffuser, air begins to pile up before it interacts with the fan.
Yaa.. i still here😂 i love your videos😊
Good video (got my vote) and as other comments have said it opens up a whole new set of possibilities of parameters/variables to be investigated.
Awesome video! Need more
Thanks!
It would be interesting to see how blade tip clearance affects things. I know that ducted fans running as close to 'zero' clearance as possible will perform better, but I do wonder how much that extra trouble is worth it then it comes to efficiency.
Or have a band connecting all the blades, with a cutout in the housing to accommodate the band. Then the only thing that can slip by is not in the stream has to find it's way out.
great video thanks
Great video! Subbed
Great video! Didn’t even realize it was 20min hahaha. Are you a aero / related field engineer? Can’t wait for the more concise explanation vid!👍
Not an engineer... just a pilot who loves physics, ha
Hey. First of all two things: Congrats & thanks. I adore napkin math because it shows up that "vital few & trivial many". I read in the comments about drag and air density inside the cone and many other things, but for measuring coanda effect maybe you can add some measurements of the velocity of the back flow around the duct at a certain distance. Then you could average the speed over the "influence ring" around the duct and calculate the change in momentum (vectorial mv). That wouldn't be too hard or too complicated and could give you the theoretical deviation / validation of your measurements without the duct. You can also check the results against the Bernoulli given impulse due to differences in static pressure.
In your calculations you dont include drag it seems so that is where the additional power goes. the propeller is like a wing that rotates so there is a drag there and the acceletaed air in your tube has friction with the inside of the tube. in both cases the power used to fight the drag grows like the cube of the speed. by running one setup at different RPM you should be able to derive the drag "constant" ( of course an oversimplification but a good approximation ). my 2 cents
I would wager that a significant portion of the drag comes from when the accelerated air mix with more stationary air at the back of the fan.
@@tykobrising5339 OOOOOOOOohhhh god bless your wagering and god bless drag becase without it everything would just work so god bless friction and gases becases without them how would we breathe so god bless god for making gas and fans to blow away foul gasses ohhhhhhhhhohaaahhhhhhhhhhhhhhhhhhhhhhhhh
I made it to the end but I wasn't subscribed... But I am now!
Really enjoyed this
Thanks
Nice video, thanks :)
The HVAC guy used to take account of static pressure and dynamic pressure in working out air duct flow performance.
Local moving air has a lower pressure (density) than ambient air, with or without ducted.
the inlet is helping redirect normal atmospheric pressure (even in all directions) into the fan. It provides a gradually curved surface the air can "hug" as it starts moving radially inward in the plane of the fan and has to accelerate at 90 degrees to this to actually enter the fan. The curved inlet prevents flow separation, same as the top curve of an airfoil.
Please continue to improve this design! I would love to make something like this one day for mounting on my bike