Complicated air flow in front of a fan
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- čas přidán 25. 08. 2024
- I started this video to show why a cowling around the fan wouldn't help, but as I experimented, things got more interesting.
More about my crazy 1 hp fan: woodgears.ca/si...
Experiments with the veturi effect: woodgears.ca/ph...
My other channel: / @matthiasrandomstuff2221
Seems like adding cowling could increase efficiency for an exhaust fan where there is concern for what air is being drawn in. There may be applications where you don't want to draw air from the sides, only from the back; maybe a concern of system efficiency versus local efficiency.
Good point, yes, if I want to suck air, the cowling, preventing air from being sucked in at the front, could cause more air to be sucked from the back. I was thinking in terns of the "leaf blower" application.
I wonder if a cowling would increase air speed at the cost of volume throughput? I'm thinking all that stationary air being sucked up into the stream must "steal" its energy from the air being propelled by the... propeller? Though I guess the cowling wouldn't have any effect on the air in front of the propeller, so probably negligible effect overall...
The blades have to be very close to the shroud and the length and shape of the shroud is important, but most of the time a ducted fan is more efficient at producing thrust (and they are quieter).
@@matthiaswandel the thing missing from your video is any consideration for the interaction between the total load on the motor at different speeds, and the specific characteristic rpm torque curve of the motor. Because by adding a coweling it would change the curve of the total drag vs airspeed / spindle speed. Which is a different curve. And it is the combination of those 2 curves together which determines the point of optimum efficiency of the entire system. Remembering that these are 2 opposing forces. Now you could postulate that the effect of drag due to the air and turbulence is not significant, or that it is below and within the performance of the motor and prop, being under driver in both cases. Or you could try to do come complex fluid dynamics calculations on a supercomputer. But most people in industry would instead do a 'small scale version' experiment or use a wind tunnel. And use other knowledge and experience. In this instance you have been thorough investigating the no cowling situation. However I do not feel that your assumptions were equally thorough or sufficient for predicting what the situation with cowling would do in terms of total air drag vs turbulence. Not without doing some further research or looking for nearby other real world examples. But perhaps in terms of deriving a maximum reactionary force then a good example would be something like a hovercraft or 'swap boat" like they have over in florida.... sorry I cannot think of any other good examples off the top of my head. Personally I really have no idea if some type of a cowling would be better or not. We could endlessly speculate. For example perhaps a concept like the nacelle 2nd chamber of a jet engine could serve to be more efficient at involving nearby airstreams but IDK, since the speeds and temperatures are hugely different in each cases. But I would not presume to know either way unless there were some existing real world experiments and examples to reference and read up on. It would be foolish to otherwise speculate upon such things. The calculations get out of control pretty quickly, and end up being far too complicated. Even for supercomputers.
Is it not the venturi effect that hsppens?
Hey Matthias, I believe you are seeing a venturi effect in front of that tube where as the flow across the tube opening causes a lower pressure within the tube. The faster the fan blows across the face of the tube, the lower the pressure inside... Drawing in the ribbon from the other end.
He even has the water-hose eductor from an older video showing this principle!
Yeah that's what I was thinking too, it's just a difference in pressure
This is related to the Bernoulli Principle. To measure what is happening in the air stream you would need some form of pitot tube.
He could make a giant carburetor
Yeah, Matthias is demonstrating his lack of knowledge when it comes to fluid dynamics. I would wager that the vacuum he was seeing was venturi effect but having worked in a wind tunnel for 4 years researching aero-thermodynamics I learned to never guess what is happening in turbulent air, test it. We've already seen that he has all the equipment needed for really high fidelity testing. Just rig up a test stand to take measurements in a 3d grid around the fan using his wind speed meter and water manometer (and an ammeter on the fan for efficiency measurements). Run the measurements with and without the shroud and he would have his answer right away, plus you can make some really fun charts with the data :)
Aerodynamicist here. Just wanted to help with some points to perhaps improve your understanding of your fan!
1. Yes, Bernoulli principle applies to turbulent flow; otherwise it would be quite useless. It doesn't apply to *compressible* flow, but the air speeds of you fan are way below sound speed (M
Careful, whenever a SME points out why he's come to the wrong conclusion on something he often ends up moving the goalposts like a true engineer :^)
Thanks for clarifying that the Bernoulli principle works for turbulent flow. How else would Pitot tubes work on airplanes? A question: is the correlation between pressure drop and velocity different for turbulent and laminar flow?
I used to work in electronics cooling, and we used commercial CFD software all the time. The results of these simulations seem to have been accepted as God's only truth by engineers.
@@paulkolodner2445 The specifics get quite complicated when you look at it in detail, the relationship between static pressure and velocity is nonlinear in general. It is only for low Mach numbers that you can approximate it with a linear equation, so for this first order approximation it is more about the Mach number than about whether the flow is turbulent or laminar.
So, changing the geometry/positioning/size of a duct would affect the thrust produced by a ducted fan? (thinking RC models here) This could be of value to model aircraft builders....
A few things you said are exactly what he said in the video, suggesting you just skipped through it waiting for a chance to talk about your field
0:33 "and even at the sides it seems to suck in"
That's the problem; the air that it sucks in there comes from the nearest area of high pressure: the front of the fan.
Cowling prevents the air that is pushed out at the front from just flowing around the blades to the back and get sucked in again.
That is why prestty much every kind of efficient design for a fan includes cowling.
Yep. Watch the sawdust at 5:40 when it goes off-center. the sawdust in front gets sucked back into the back of the fan.
Precisely!
Ditto what Vinny said. Efficient exhaust fans include a circular "collar" around blade tips to prevent recirculation of air that's supposed to get gone. This is particularly necessary if there is any obstruction in front of fan like a louver which (if no shroud) will actually direct much of the thru-flow back around the blade tips & into the space being exhausted as that's the path of least resistance. If it's just a comfort fan the shroud isn't important, Ur just moving air, so positive control of direction doesn't matter
This is a well known problem, it's a source of inefficiency for wings, also
I think this applies more at lower fan speeds.
With such high speeds I really doubt the lowest energy difference is between the just energized turbulent air compared to the ambient stale air.
"Now, people are going to argue Beronoulli principle and all that..."
Proceeds to demonstrate Bernoulli principle.
Spot on! Moving gas, lower pressure - Bernoulli principle
He did, but he still correct. Bernoulli's principle only applies to *laminar* flow, Matthias is experiencing turbulent flow.
labman.phys.utk.edu/phys221core/modules/m8/turbulence.html
@@FedoraSpunk incorrect. bernoulli's principle applies more or less to all subsonic (incompressible) flows.
@@SuperAWaC the paper I linked shows a good diagram most of the wag down, Bernoulli's principle doesn't account for all of the factors in play once turbulence is involved, it's simply a different flow type/equation at a certain point
@@FedoraSpunk of course flow is a complex problem with endless variables, but what matthias showed in the video is still bernoulli's principle, in addition to jet entrainment
Imagine all the things you’d witness if Matthias was your neighbor.
Imagine Colin furze!
I wish he was my neighbors call the cops on me for talking in my own back yard
I'd ask to help XD
Best comment yet!
You'd also have your yard covered in his leafs and sawdust at random times ;)
I can only imagine your wife and kids listening to you down in the basement screaming and air movement over an incredibly loud fan 😂
These ‘nerd out’ videos are by far my favorite videos threads of yours. Your genuine pleasure and interest (and knowledge) is just awesome. Keep up the happiness!!
3:43 - "Yes, it sucks!"
I got my engineering degree 45 years ago with my masters in hydrodynamics, I find these video experiments fascinating. In school we had a large lab and used various show & tell models to demonstrate the physics principles you are showing here. Turbulent air flow is difficult to model but you did a great job of demonstrating the effects.
The cowling reduces tip vortices, allowing the ends of the fan to contribute to air flow - this widens the stream and improves the efficiency of the fan.
Trust me I'm an engineer ;) (mech eng)
Now we really need so see experiments with a cowling - ideally fabricated on the big new bandsaw:)
Testing claims-even sensible and reasonable sounding ones-often leads to extremely interesting results. Love these kinds of experiments.
The efficiency a cowling imparts is specifically when you want the net flow of air to move in a single direction. By putting a cowling you won't restrict the airflow significantly you will simply restrict lateral air flow that is the pressure will be lower behind the fan for the same pressure in front of the fan. If you put a cowling I doubt you would notice more airflow, but simply more "thrust" for the same amount of airflow.
I teach all these concepts in my aviation courses at a technical education school. It’s cool to see you excited about it enough to learn about it and teach others. Not too many people are educated about these things. Keep up the great videos!
You can increase the efficiency of your fan by installing a nose cone (also called a Spinner).
The fan plays a B Flat from the musical scales, in case you wanted to know.😂
I work in a Lab where we have vibrating plates and motors similar to his. As a musician, I have noticed they all produce a B flat. I think it has to do with the 60hz cycle of AC power. 58.27Hz would be B flat, 61.74Hz is B.
@@eyesopen45 Well that makes sense. Induction motors try to spin at line frequency. But as the rotor speed nears target speed the torque falls so it never quite reaches full speed if loaded.
As a side note induction generators are physically the same except the shaft is spun slightly faster than line speed. The generator wants to spin at exactly line speed to it converts the extra into electricity.
@Jason Hall @@eDoc2020 ...Common 4 pole induction motor on 60 Hz line has synchronous speed = 1800 rpm, but slips to typically 1760 rpm under load, which is 1760/1800 = 97.778 % --> 0.9777 * 60 = 58.6667 Hz note ~= B flat [pretty closely]. Nicola Tesla invented the AC induction motor ~ 1887 & the rest is history...
I would spent way less times reading comics in science class if I was taught like this!
Definitely! And this happens with so many subjects! I was in an engineering class and the teacher did not manage to get control systems explained properly. I was fed up with his bad explanation and bought a simple thermistor, fan and heater and explained the class to control the heater temp with the fan. Using this direct approach made the class get the issue and solution very easily!
You are learning now. It's never too late.
4:10 what you call vacuum is just the static pressure (air is moving, so static pressure is lower because of bernouilli : height + speed + pressure = cste)
Has fancy air flow meter
*Uses crazy strings hanging on a stick to measure air flow*
Those are *science* strings, thank you very much!
Strings visualize it much better for video.
If you go back and watch any aircraft analysis videos from the 1950s or before you will find them scotch-taping lengths of knitting wool to the back of the wings and side of the airframe so that they could take pictures and see how the air was blowing.
Multimillion $ sailboats have telltales too.
Before the advent of large scale wind tunnels and computational fluid dynamics they would affix tufts of string to a surface so they could observer how the flow interacted with it, the surface.
Bernoulli , moving air has less pressure so die outside compresses it
I think the only way to find out is to make a cowling. I am wondering if the pipe in the airflow is a flawed test. If you pass air across a pipe like that it will always vacuum.
He just stated that Bernoulli's Principle does not apply in turbulent conditions, and the Venturi effect is built on Bernoulli's principle. So it also does not apply during turbulent flow.
@@Tomasu321 that is not an accurate statement, Bernoulli’s can still apply to turbulent flow.
That would be a good test. I like paramotors and RC planes. How would centrifugal force, vacuum 'and' the weight of the cowling affect efficiency?
@@JamesSeedorf Please elaborate more when just offhandedly dismissing statements. You're not being helpful.
@@Tomasu321 Should maybe take your own advice then? "This is so because he said so" is just as dismissive and not proving anything.
Dear Matthias,
Love your channel. I think you should count on the Venturi effect on your experiment: the more you increase flow speed, the more you decrease pressure. I think what's happening here is that the high-speed flow in front of the blade is a low-pressure spot and the ambient pressure of static air push and narrow it as you going farther from the fan. That's also why your pipe is always sucking air wherever you place it in the flow. As long as one end is in the flow, the pressure drops.
About the fact that the flow seems to go closer to the ground, it could be ground effect: it's less turbulent for the flow to run closer to a surface because the vortices are smaller. So it chooses the easiest way.
I like your yelling voice. You should yell the Lord of the rings unabridged for an audio book with the fan going in the background.
"Yes it sucks!" 😂
Next follow up video: A collaboration with Destin from Smarter Everyday.
You still need to put an airfoil on your prop. I think you will be amazed at the improvement in air flow.
what's an airfoil? I was thinking how about making the ends the same as all the newer wingtips on aircraft these days? those are supposed to provide smooth air flow right
@@johngreydanus2033 A prop is flat on one side and curved on the other giving the airplane lift. You can get air movement by the angle of attack of the blade but it is not as efficient as an angled blade with an air foil.
@@dillonpapa You still didn't enlighten me on an AIRFOIL, let me go to Google. I thought it was wings that are flat on one side and curved on the other giving the airplane lift.
@@johngreydanus2033 yes... that is an airfoil. Curved on one side flat on the other on both blades.
"Airfoil" is a particular shape, evidently
Thanks for all your recent uploads! You’ve been missed. Wish you and your family a Happy Christmas 🎄
I came to the comments to introduce the idea of Venturi Effect. The pipe "sucking" is the effects of the air rushing past the end of the pipe causing low pressure.
Come for the woodworking, stay for the fluid dynamics.
I was wondering when the prop would fail being just a piece of pine. That whirling and vibration. Awesome work as always.
The cowel(?) might yet reveal some mechanics that you have not considered, remember, the pressure does create a faster flow, and eliminating part of that flow create more energy for the flow to go. Such as in the case of the floor blocking out vacuum which made faster flow to that area... Give it a try. Would love to see it!
A book I had to study, “Propeller Theory and Fluid Dynamics” was pretty dry reading but solved your problems by having more twist near the hub compared to the tip.
That’s a Venturi effect. The tube will have a lower pressure because the opening is perpendicular to the stream lines. Not because there’s “vacuum” in front of the blade.
Also the shroud will make the fan more efficient by stopping the recirculation at the tip of the blades.
The tip being where a lot of the work gets done. I'm sure Messr Wandel would figure this out on his own.
I think the effect you're measuring at 4:00 is the venturi effect of air rushing past the end of your pipe, drawing air into it and creating a vacuum in the pipe. The fact that the vacuum in the pipe persists until you angle it into the fan I think is consistent with the venturi effect. I don't think you're actually measuring the vacuum at the centre of the prop, but rather the speed of the air rushing past the end of the pipe.
Lol'd at the part where the air moves through the pvc conduit and you shout, "Yes it Sucks!", over the obnoxiously loud fan noise.
Fluid dynamics are complex enough that I hesitate to trust predictions of what would happen if you add a cowl. Would be nice to follow up with a video where you add a cowl and see if your predictions are accurate. Shame the propeller broke, but maybe you want to remake it anyway (not sure I would trust glue to hold for a repair). If so, consider this an additional justification for doing so.
Regarding, from about 2:30 onward, the business of the "stream" being narrow at first, fluids sustain abrupt boundaries between regions of turbulent flow and regions of laminar flow--- sustained by entrainment of the laminar fluid into the turbulent region (which Matthais notes leads eventually to widening the turbulent stream). And the turbulent core, the "stream" as Matthais is calling it, cannot sustain steep changes in the axial velocity in the radial direction due to the turbulence involving radial mixing. But the surrounding laminar flow CAN sustain steep changes in the axial velocity as it lacks the turbulent mixing. That's why and how the stream can initially be narrow.
This bloke is fantastic. I love how enthusiastic he is about finding the stuff out. ANd, of course, he is so good at making the apparatus. I wish I had his skill and know how, but then he's spent all those years earning it. Great job, fella.
- I understand this is supposed to be a leaf blower (near the ground) but for propeller efficiency test, test should be conducted high above the ground. (jet engines are tested on a pylon with a bell mouthed entry to provide a smooth transition between still air and moving air).
- Google translation doesn't offer two nouns for this but in French this would be called a "moulinet" and not an "hélice" (propeller) because the blades are not warped to ensure constant angle of attack along the radius. Moulinets are used to test aircraft reciprocating engines on the ground.
- as somebody already commented, shaping the blades like an airfoil would greatly improve the efficiency.
With the pipe pointing into the middle truly shows the vacuum.
Man. That fan blade + 1hp motor is very terrifying to watch.
All very neat analysis. My own thoughts about a shroud weren’t about efficiency, I assumed there would be some reduction in air flow, but I was thinking more of concentrating the outflow at a point.
The interesting bit here is that the column of movement produced by the fan has its own physical properties. You were spot on with your analysis of the Column creating its own vacuum. That’s why it appears to be pulling air from the sides of the propellor blades
Vena contracta is caused by the fast moving air. Its total pressure remains constant but has a static and dynamic component. The static pressure outside the moving airstream is higher, pushing the airstream from the sides. Torricelli noticed the same effect when emptying a wine cask.
came for the woodworking tips stayed for the random projects
6:40 I KNEW that was gonna happen without a shroud on it! I KNEW it would happen! 😂
Matthias, perhaps the negative pressure when doing the test with the pipe is due to the mechanism behind a Venturi meter: fast moving air PAST the opening of the pipe causes low pressure in the pipe.
Don't take this the wrong way but it was great seeing you be wrong. Credit for stating a hypothesis, testing it and then sharing the results even when it demonstrated your hypothesis was wrong. Well done. Either way though, it was super fascinating to see how complex this was.
Does he have room in the basement for a wind tunnel? Someone sponsor him. I need more Matthias yelling over the noise of the fun.. I mean fan.
What you really need is stator vanes... I built my own fan snowgun and it didn't have very far throw, but when I added stator vanes to eliminate the swirling of the air stream, it went significantly further. However, stick with either a prime number of stator vanes, or at least not the same number as there are fan blades, or you will create a sweet air raid siren with the resonance...
Air flow characteristics are highly dependent on the shape of the blade. The blade on the oscillating fan is quite different from the propeller. My dad has a very old 2-blade floor floor fan with curved blades. You can set it a couple of feet from the doorway of a room and it will close the door, leaving it open just a couple of inches - moves a lot of air at a low static pressure.
You will have a vacuum everywhere the stream moves. Venturi effect is used for different technical applicaions
Fascinating. You have inspired science projects everywhere.
this video really BLOWS :P always fun learning these things with people that are excited about science
An intake cowling with aerodynamic shape reduces intake air drag resulting in an increased air flow of 15-20% approximately as compared to a straight intake pipe.
To measure relative air pressure differential even in the modest manner of your approach with the pipe it must be aimed directly into the air stream - see pitot tubes. Since you are so fascinated with this experiment please consider adding an inlet cowling, then outlet straight section (3x diameter of fan minimum), making the blade from hardwood (safer), and since you are so computer/electronic savvy measure the rotation of the the pickup prop. No need for high accuracy, just relative readings.
On a smaller scale also make a cowling for the inlet of a vacuum hose.
Still, nothing like a lot of horsepower - watching the effect on clearing the driveway is impressive!
I don't know if a cowling would help as a leaf blower but I would still love to see how it changes the airflow of your fan
Neighbour: Damn! That kid next door is playing with saw dust again. Can't he do it inside his house?
Back to the roots! I love it!
The reason why you were getting suction on the pipe was due to the Venturi effect. Namely, a high velocity fluid (air) passing over a small orifice will pull from the orifice. This is the principle carburetors are based on. So that is not a good method to measure the vacuum.
Great video!!
I frickin' love Matthias. Real life mad scientist...
It might be worth looking closer at what happens on the inlet side of the fan, rather than the outlet. Where turbine engines are used in static applications, they normally have some kind of trumpet-shaped duct on the inlet to give air coming from the sides a smoother transition to flowing along the axis.
a cowling is useful for ensuring that more flow is directed through the prop for useful work instead of being lost off the end of the prop. I'm told that this is more useful for props on slower boats (at least on sailboats like mine). Don't ask me why- I'm not a mechanical engineer.
An interesting experiment would be to see if you are experiencing a prop ground vortex. A ground vortex is the reason why power loading is destructive to a boat ramp, and why it's problematic to spin up your Cessna while standing still on the runway- it creates little tornadoes of low pressure which suck up all sorts of junk. You could design an experiment to visualize this using fine wood dust. You'd have to experiment with the distance between the prop and the floor, but that's half the fun!
The Vaccuum you massured with that Pipe in front of the Fan is originates from the "Venturi Effect".
This principle is why rear-thrust prop aircraft absolutely *must* have a tailcone. The cone compensates for the immediate vacuum, which would otherwise vastly reduce available thrust. The same sort of applies to a conventional prop, but the impact is not quite as severe.
If you wanted to truly optimise airflow, I would suggest that you look at a duct, rather than just a cowling, in combination with a "nosecone" of sorts. It would also be beneficial to create a cone around the rear of the motor (sans overheating concerns), which would reduce turbulence. To even further reduce turbulence, you could profile the edges of the duct at each end to create a smooth transition between the inside and outside of the duct, although that's now nitpicking and wouldn't be necessary for anything other than being an interesting experiment.
You would need to check out a heatmap of the fan's airflow to get the proper dimensions for the cone, but to be honest it could be fun just doing a bit of trial and error.
Venturi effect?
Have you seen the Fan Showdown series on channel Major Hardware? People send in every design that comes to mind for blades, they are 3D printed and tested. He's worked out a way to pour smoke to show the airstream and tests by cooling ability of flow.
Thank you for the video. It was very interesting. I don't want to correct anything, I just want to throw an idea in.
I believe the first test, when air was sucked into the tube is caused by a low pressure area in the center of the propeller. I believe this area is formed like a cone with its tip pointing away from the motor. But I really think, the other test results with the tube could be caused by the Venturi effect. Just an idea.
I'd like to read your thoughts about this.
Thanks
Matthias doing his best weather channel audition!
The cowling helps, because the low pressure in the back of the blades sucks the high pressure from the front; this generates wakes that dissipate energy and slow down (drag) the propeller. Is the same effect why there are winglets at the ends of airplane wings. en.wikipedia.org/wiki/Ducted_fan I'm not sure if it means "more airflow" though...
The problem is that blade design is better for a propeller application rather than a fan. For a fan design look at computer fans, they're curved in a way to maximize airflow and then yes, having a cowling helps.
I love your videos but to say a cowling wouldn't work without actually trying it seems premature.
Cowled fans produce more thrust in a quadcopter. The cowl has to be very precise in order to work properly.
Bruce does a good job talking about this topic on RCModelReviews *How ducting a propeller increases efficiency and thrust*
He is not trying to generate thrust.
Once again a lesson by Professor Wandel. Thanks teach
As the fan spins, high pressure builds up on the front of the fan blade while there is a lower pressure on the back of the fan blade. The spinning fan blade also throws air radially outwards due to centrifugal force. The high pressure on the front of the fan blade tends to move radially outward due to this centrifugal force and it slips around the point of the fan blade to meet up with the low pressure on the back of the blade. That reduces the efficiency of the fan rather substantially because the pressure difference on the blade is lost. A cowl, if it fits the outer diameter of the fan blade with a very small gap, prevents the high pressure from moving to the back of the blade and joining up with the low pressure. That prevents the loss of pressure across the blade and increases the fan's efficiency. The gap between the cowl and the point of the fan blade must be small for the cowl to work properly. Just a small increase in this gap size and the high pressure will still move through the gap and join the lower pressure on the back of the blade. Which means the cowl won't work nearly as effectively if the gap is large.
You've not stated your inquiry well. "Why a cowling wouldn't help" leaves unstated what and where the "help" would occur. A cowling definitely "helps" concentrate and direct the airflow, and helps reduce the amount of sheer entropy whirling fan blades interacting with uncountable "air molecules" create.
Hi Matthias, for analysis on the performance of a cowling, please search "ducted fan". It is a very popular teaching problem in fluid mechanics.
You are right that Bernoulli's principle does not apply to turbulent flows. However, I would consider the flow in front of the fan to be weakly turbulent. Also, Bernoulli can certainly be applied to the flow behind the fan. So we know that there is relatively low pressure before the fan. Then we can use thermodynamics to determine the increase in pressure across the fan (use the power draw of the fan). Assuming it is adiabatic, the specific enthalpy will increase and the increase in pressure is relatively small, and the pressure remains less than ambient.
Another interesting thing to note is that flow coming in the side implies that the flow is speeding up as it crosses the fan (since the flow is not even close to being fast enough to be compressible). However, for a ducted fan, this means that the flow does not accelerate across the fan. Yet this does not necessarily imply a difference in performance. It points to the main purpose of a fan: to create a pressure difference.
Yes u r right about the vacuum, the cyclone effect is the same at the centre of tornados, probably caused by the angle of blades at centre is too shallow
Please give us more of these experimental type videos
It doesn’t suck from the side of the propeller. The blades act like a wing, and at the tip there is a vortex which tries to unite the front and the back of the fan. That’s why you see air going backwards.
The cowling would limit the vortex and make the blades more efficient. The air you see getting sucked back is a loss. It would ideally be propelled forward with the rest.
For the airstream going towards the floor, take a look at the Coanda Effect. Moving air tends to "stick" to surfaces that it moves along. That's actually very important to getting HVAC systems to work properly.
congratulations for reading the text on the screen
@@matthiaswandel Ha! I totally missed that. Was watching your pencil demonstrate it.
***********As an HVAC professional, I find people don’t realize the cowl is for inlet control, NOT outlet control. If you look at a car radiator, the cowl is to make the only air entering the fan, air that has come through the radiator. If it doesn’t matter where the inlet air comes from, no cowl needed....like a common box fan.***********
agreed. But the original comments were about adding a cowling to make it blow better, and a cowling would not help with that.
@@matthiaswandel I actually meant the comment about the box fan as a response to the unnecessary requirement of a front cowl. On a side note, I found your temp recording and trend analysis of the house and of the freezer pretty interesting.
Now I would like to see you make a giant airfoil ring from wood. Like a giant dyson shop fan.
I love these physics experiments you're doing. And even though I'm not sure if all your observations are explained with the correct theories, it gives so much more insight...
I built a simple box air filter with a desk fan as the air moving apparatus. Efficiency was horrible until I used a bottomless plastic bucket to make a tight cowling to make sure the fan *pulled* air only from the box, rather than keep it spinning around at the edges of the propeller. Maybe it's different when you just want to push a lot of air, idk.
you can’t direct suction so you needed the bucket to suck thru the filter. but if you were blowing at the filter, it would not have been so bad.
I suggest you read about KORT Nozzles. They are used around boat propellers to increase thrust and efficiency. The inside facing the prop is shaped like an airflow, benefiting from the same effects as an airplane's wing. If you design one, maybe Frank H. would cut it out on his router. It could be done with a larger pantograph mechanism [e.g. your phone cutting machine] or a giant version of a pantorouter (with some control over the stepping forward). I tried to make a Kort Nozzle for my boat by casting. I gave up when I could not make a suitable wax wax version for the molding process.
Some pressure measurements using an inclined (for better resolution at low pressure) water column and pitot tube would be interesting to see.
Fascinating! Maybe do a mini series on fluid dynamics?
How have you not made an old school wind tunnel. Would make for some interesting dust collection experiments!
The phenomenon is known as tip inversion. And, yes, a cowl will help alleviate it but it needs to be close to the blades.
Very close.
What about touching the blades? Like those props with circles around them you see on kid's toys
@@allencummings7564 that's a lot more mass.
unducted fans are more efficient than ducted fans at lower speeds due to their "infinite bypass ratio", a good example being the General Electric GE36. There plenty of other advantages and disadvantages, but two of the main disadvantages is that there's nothing keeping the fans from going through an airplane fuselage if they let go, and there's no noise attenuation, both of which are huge deals for the airline industry. I think my main concern is the longevity of your blade and where it might go if it lets go.
I think it's worth noting that your propeller has a constant pitch while most modern propellers have less pitch at the ends of the blades. Just because your fan isn't more efficient ducted doesn't mean most aren't.
this is why I also demonstrated with the oscillating fan.
after the post on IG i have wait this video to see how was the propeller crash 🤣😭 but no camera rolling! I'm still fascinated for all your work Matthias, keep doing the great job!
luckily you were not injured!
It would have been nice if you could have measured the amount of vacuum at different points with your tool as for your dust collector.
Very interesting indeed.
A strong air flow blowing at an angle into the pipe opening will cause the air inside the pipe to be sucked out from it along with the fan stream. Like a pump. You could use smoke to visualize how the current's going. White smoke and UV lights could make for a cool effect ^_^
The pucker factor is high with this one!
There's another reason you don't need a cowling: it works fine without it and adding it would be extra work. Not that laziness is always the answer but if it gives you time for more meaningful projects...
Like you discovered, a cowling would increase the air velocity, but not the total airflow or total energy imparted to the air. That's why airplane propellers(slow ones anyways) aren't shrouded, I guess.
So a cowling would make for little difference, but maybe a cowling with opposing stator vanes? That would certainly keep the airflow less turbulent and maybe increase the pressure but would likely reduce the total volume. If your clearing leaves, volume is really what your after.
Am I missing something, it looks like you are detecting the venturi effect