What Causes Stall/Flow Separation? Adverse Pressure Gradient Explained

[@unverozkol]

Nice and very informative presentation. Just a quick note; Flow around the corner creates a very sharp pressure drop (rather than pressure increase) right pass the corner. Since pressure has to come up to normal ambient levels, that have to occur with a very high adverse pressure gradient causing a flow separation. A very similar thing happens also in the airfoil, following the stagnation point. Turning flow accelerates and pressure initially drops. That very low pressure dip should not be forgotten.

[@jameswright4732]

Nice Video. Never quite understood the physics behind adverse pressure gradient and this cleared a good bit of confusion. I think what I always missed was the positive pressure pushing the airflow back to (approximately) free stream velocity.

[@KYLEENGINEERS]

Glad I could help! Thanks for watching!

[@Sherlock_MacGyver]

Yep, I hadn't considered that aspect in my head. Good video.

[@0Freguenedy0]

I'm reviewing your aerodynamics videos while having the classes at the university. Thanks a lot, hope you are doing well in F1.

[@vaibhavhiwale]

Mercedes F1

[@0Freguenedy0]

@@vaibhavhiwale he is no longer there

[@falconbanshee]

I would absolutely love a more detailed look into this phenomenon, aimed at a junior engineering level. I have a final year engineering project on the effects of attack angle on a symmetrical wing (NACA0012) under turbulent conditions, and have been trying to get a thorough understanding of the boundary layer physics occurring at separation, as I believe it is the downfall of CFD programs at turbulent conditions

[@md.mizanurrahman4477]

Acceleration and deacceleration over the body → adverse pressure gradient → slowing of boundary layer → at sufficient adverse P gradient fluid layers adjacent to surface flows backward → separation boundary layer.

[@jacocardi6488]

Great video. You have the ability of explaining clearly also the hardest notion. Here i understood everything. Thanks for making videos

[@KYLEENGINEERS]

Thanks for the compliments!

[@addieroxrev09]

Very clearly explained without equations and complex jargon. Thank you

[@africanviolet4773]

This video about to blow up

[@aniketkumarsingh6478]

Bhaiya, you explained this concept in suchhh A great way! I'm so thankful this resource is on KZbin! This feels like it was so easy! I visualised the things. Thank you so muh🎉 (Bhaiya is a term used to refer to elder brothers in India)

[@EC-ol8nz]

The diagram was good. Should have left stalling out had to watch twice to separate the concepts. Great explanation!

[@myminnyvids]

Can you explain why the velocity is fastest at the bottom of the wing (or the top of a wing on an airplane)? You said that like it's a given, but I didn't follow that assumption. (2:33)

[@balupakki4995]

Either apply Bernoulli's theorem or just think that it has more x-direction velocity,while crossing surface some of its x-velocity is converted into y-direcn velocity but on top of the surface there will be no curved surface so the velocity is high

[@abhishekkumar-bl7in]

Thank you for clearing our concept behind this.. also upload more videos

[@mdfahim9513]

what factors determines the pressure gradient on the surface of the body?And please make some video about Center of Pressure

[@pikachus.4281]

brilliant video thank you

[@kotlarattila]

Thank you! It's really useful for my PPL (Aeroplane) theory

[@gbolagadeolajide6091]

Nice video. Thanks

[@Angel_F1]

Great video, but i don't really understand one thing, the boundary layer is pushed back and that means it gets sucked away from the wing surface and turbulent air occurs? Thank you.

[@jesalkotak5595]

great video please make a video of same stuff with turbulent and laminar flows

[@TechTrader108]

Brilliant explanation Mate.....thank you very much.....very helpful indeed

[@pinchentertainment8551]

could you please explain the effect of surface roughness of blades on the flow efficiency

[@hmabboud]

@03:00 Where is here and where is there? Iti is not clear from your pointing to which part are you pointing to exactly.

[@PerSon-xg3zr]

This is important for lifting body aircraft since those aircraft fuselages are mimicking a very thick airfoil compared to their wings.

[@cimfur]

Thank you, any chance we can see how this works on different car shapes as an examples. Specifically slotted spoilers on hatchbacks. I get all cross eyed trying to understand.

[@mohamedelmalah6716]

Thanks a lot for the video and your efforts. very helpful.Thank You. Could I ask a question please, there is a statement which I read but do not understand it "In compressors flow is against an adverse pressure gradient."

[@malfinzhang]

Thank you KYLE.ENGINEERS, thumbs up! subscribed!

[@Serenelove520]

Dude, I am going to be a boring addition here, SO WELL EXPLAINED! Thank you. I have a request. I want to understand how aerodynamics react to the underside of the chassis, its relation to ground clearance, etc. is it possible to building an off-road vehicle with great aerodynamics? And how do you define great in this context in comparison to other non off-road cars?

[@Sherlock_MacGyver]

Considering there is a boundary layer of stationary fluid, why does surface area and therefore friction drag cause any problem at all? It seems that friction is holding the boundary layer stationary, and beyond that, it is energy transfer and minor gas related friction of the air itself, not contact with the wing surface that would cause drag. If that made sense, maybe you could explain it better. Thanks!

[@gisolu492]

Thank you ! Did you noticed like me that this teacher really looks like Ryan Gosling 😂

[@Sherlock_MacGyver]

I totally got that, thanks.

[@ericpreposi3226]

do I have to read the 1st graph for the airfoil if I am doing lift for an aeroplane

[@gilangw595]

wow i just knowing this phenomenon, is it somehow related to my experience of buying cheap mini fan that seems have bad design? because everytime i try block some airflow from behind, it wont blow forward air again

[@kotlarattila]

Good video, but I still don't get why with extended plain flaps the adverse pressure gradient is steeper, and with slats the adverse pressure gradient is reduced. They have the same suction peak over their surface.

[@Rb-fj8zo]

how do you know that there is flow separation on a graph of pressure coeff in function of an angle of a cylinder?

[@xBIGMUSCLEx]

What would happen if vortex generators are installed underneath a wing? Could the angle of attack be slightly increased without the wing stalling then?

[@KYLEENGINEERS]

Yep! Check out 5:50 onwards in this video: kzbin.info/www/bejne/b4jLlZKBo9h_gac

[@Hypersonik]

I believe that's what they aimed for with the Mig-29 wing roots

[@martinliza4811]

In the case of a turbulent BL, the pressure gradient needed to generate flow separation should be higher than the pressure gradient needed for flow separation in the laminar BL case? I’m purely looking at the thickness of the different BL’s. However, I’m not sure if I’m missing something, because in a turbulent BL, you do have some pressure fluctuations.

[@fattahrosady7845]

do you know why if water flow through expansion, let's say in the lower side of expansion, the recirculation zone is very large, but in the upper side, the recirculation zone is smaller because of the presence of stationary air accumulation, will the center streamline is pointing a little bit upward? could you tell me in detail? any answer would be appreciated, thank you

[@JK-ql2yp]

Kyle,the equal argument theory is wrong isn't it.then how does decreasing pressure increases velocity

[@JK-ql2yp]

Bernoulli's principle doesn't apply to multiple stream lines

[@hu5116]

Hi: I really liked how you were starting out talking about the step. And so I thought you were going to carry that over as an analogy to the wing, which would have been cool! But then you didn’t! You never linked the step to the wing, but it appeared you were going to do that! But didn’t :-(. So I have my own mental model. But it does not overtly include the vacuum generation mechanism (have to use Bernoulli or momentum for that). But the way I think of it is you have that vacuum at the crest of the camber, and a vacuum suck (literally). So the air tries to go flying (via momentum) over the top of the wing, which being tapered moves away from the air stream (maintaining the suction). But this suction pulls on the moving air, slowing it down and trying to drag it towards the wing. At some point the suction has slowed the air down so much that it stops and even reverses. This reversal is detachment and the reverse flow initiates a vortex that then having angular momentum takes on a life of its own. That is how I mentally model detachment and vortexes. Thanks for the vid still!

[@sam90o48]

how Does Flow separation affects downforces

[@pavankumarkoratikere7045]

Nice Video. Only one doubt is there that why does the air accelerates at its tip of the wing ?

[@SriMukesshSubramainan]

no, it slows down i.e. decelerates

[@sharvenarshavin5895]

Does the wind driven turbine ventilator stall ? i am doing a FYP project on that , will be glad if you could explain about it. Thanks alot

[@shortclips7052]

Why is the flow seperation undesireable, is that due to the flow at seperated region is trying to push it down finishing the lift because of pressure is high than atmospheric pressure just like below the airfoil or anything else?

[@pilot_ricky]

Why does the separation point on the upper part of the wing come closer to the leading edge when the AoA increases?

[@claudiolettieri4513]

Nice effort. Perhaps it would be better for the example to talk in terms of streamline curvature effect on pressure gradients and apply Kutta condition at TE

[@arthikalexander316]

does the pressure increase on hitting the obstruction because the velocity reduces?or is it something else?

[@Donniekabab]

Does this phenomena always happen to airfoils even if it is just flying straight forward??? Generally speaking if an airfoil is in stall, this seperation point moves further upfront to the leading edge, but if it is in straight normal flight is this separation point always present, but more located close to the trailing edge?

[@nixonx360]

what would happen if you added tiny dimples to the surface of the wing like those seen on Zipp carbon bicycle clinchers? how does dimples work on a surface when interacting with air flow? I've seen an example applied to a car on the pescarolo 01' where there are big bulges and serrations on the second element of their wing. i cant seem to grasp that concept. i hope you could make a video on this. cheers!

[@wweisfake100]

THANK YOU

[@97naanu]

Is it that way due to low pressure in that particular point and high pressure comparatively beyond that point tends air to flow from high pressure to low pressure causing separation .

[@jkotka]

Its difficult for me to make the jump from the pressure graph to the flow profile going negative on the boundary layer towards the end of the wing. Can try to elaborate on that bit more? Which part of the graph, which gradient am i looking at here ? I feel like there is part missing here that would allow me to actually connect the two.

[@zacmac]

Hi.. fluid always moves from a region of high pressure to a region of low pressure.. because the pressure gradient is positive, the pressure INCREASES as the particle is moving towards the end of the wing. At this point, the force on a fluid particle caused by the pressure gradient acts in the opposite direction to its velocity.. so as its going along it keeps slowing down and slowing down until it runs out of speed and separates from the body.. Now, the flow reversal at the tip of the wing is caused by fluid particles moving from a region of high pressure (at the tip of the wing) to a region of lower pressure (in the middle of the wing)

[@jkotka]

Ok, this makes sense, thank you for the explanation!

[@jacksonshiek1486]

Why does the boundary layer end up being pushed back down the wing to cause recirculation?

[@allesklarklaus147]

Because down the wing there is very low pressure due to the high velocity

[@shortclips7052]

alles klar klaus Why is the flow seperation undesireable, is that due to the flow at seperated region is trying to push it down finishing the lift because of pressure is high than atmospheric pressure just like below the airfoil or anything else?

[@nickamarit]

So stall is undesirable because it decreases the efficiency of the wing due to flow separation?

[@KYLEENGINEERS]

Depends, in something like F1 they deliberately stall the rear wing with DRS so that the total drag drops (the induced drag is very high otherwise) as they don't care about the downforce down the straights. But in most cases yes, stall is undesirable.

[@nickamarit]

KYLE.DRIVES Ah, I see. Thanks!

[@Sherlock_MacGyver]

I didn't know they did that, I always wondered about whether or not they controlled it for different effects at different times.

[@manishsharma-dg7wf]

Why shear stress is zero at the point of boundary layer separation

[@sudharsanvenkatesan1805]

Would the top and bottom of the wing have different pressure graphs? If yes, how do they affect each other?

[@Sherlock_MacGyver]

Naturally, yes, due to the wing profile. Pressure differences on one side of the wing will transmit through the vehicle, affecting the suspension and fluid dynamics below the vehicle, but the pressure on top of the wing shouldn't have an effect on the pressure under it as they are separated by the wing. I suspect that the varying pressures do matter once the air leaves the end of the wing and the streams combine, where they create turbulence and an adverse pressure region behind the wing. This is where Micro VG's I believe are used as well on the aft of a wing, about 30% of the distance before separation, in order to create a vortex to minimize the AP behind the wing. But, I really just started studying aerodynamics online for fun the other day. This guy should know much better. I may have also messed that up, I'll have to read it again.

[@falconbanshee]

I think by the trailing edge the pressures both return to near atmospheric, so the effects are minimal. It's one of the reasons for aerofoil's shape. The bigger issue is with spillover off the side of the wing, where the high pressure fluid tries to flow over to the low pressure side, creating what's known as wing tip vortices. If you image search that, you can clearly see the effects of it on aircrafts (quite pretty). It's why wings generally have a plate on the side, or a bent up wing section at the end in the case of some aeroplanes

[@shortclips7052]

Sherlock MacGyver Why is the flow seperation undesireable, is that due to the flow at seperated region is trying to push it down finishing the lift because of pressure is high than atmospheric pressure just like below the airfoil or anything else?

[@shortclips7052]

Zander Meiring Why is the flow seperation undesireable, is that due to the flow at seperated region is trying to push it down finishing the lift because of pressure is high than atmospheric pressure just like below the airfoil or anything else?

[@manikantaginni7240]

Due to an adverse pressure gradient, in what way it will affect the motion of the plane? Thank you

[@JettyBuilder]

that is the stall condition

[@NAMANSACHDEVABME]

Why stalling does not depend on speed of air?, as if the of air is increased then there will be more negative pressure at the leading edge of an airfoil and hence there will be more pressure difference and flow should separate earlier. Is this right or wrong?

[@JettyBuilder]

as the air speed increases the point at which the flow reverses advances towards the leading edge and initiating the stall.. at very high air flow velocity the wing with the curved surface just stops producing any lift and becomes an object of drag. that's why supersonic planes have almost no shape to the upper wing surface and have to take off with full flaps and max power but once they are flying can achieve their high speeds.

[@srushtitavare9968]

I have doubt . In case of car , suction is present in rear of car . As velocity of air which is nearest to car roof slows down and comes to rear of car , it's potential energy will also decrease and pressure will increase according to Bernoulli's . Why won't that high pressure air moves into suction cause pressure difference causes fluid movement . Fluid moves from high to low

[@lukassteininger8211]

late reply: because the bernoulli equation is an energy conservation equation. in a boundary layer, the shear stresses reduce the kinetic energy, but the pressure (which in itself is sort of a potential energy) remains constant. this also applies in the wake of, say, cars: because of high turbulence caused by the flow separation, the velocity at the back of the car is actually quite low, even though the pressure is lower too.

[@chalkywhyte8585]

Do thte concepts presented here apply to water flow? I'm trying to separate very fine gold from heavy iron (magnetite) sand. Great video by the way

[@falconbanshee]

Waterflow occurs at much lower reynolds number, and so I believe the flow better sticks to the wing, and doesn't separate as easily. Depends on the operating conditions though

[@francescolossiorebaza1422]

Nice video, I would like the videos to have the Spanish translation to be more understandable in this language, thanks kyle

[@250lmferrari]

I watched your vortex generators video and was wondering if they would be benifitial with a lip style spoiler? my car has a 10" tall spoiler (because of race class) so would generators make it more effective?

[@KYLEENGINEERS]

Honestly, it's impossible to tell precisely without knowing the exact specifics of your car/performing CFD modelling. Adding VGs will almost certainly shift the centre of pressure rearwards, and might increase your total downforce, but even then we would only be talking a percent or so at most. If you are interested in knowing for sure you can always check out the CFD services at www.jkfaero.com

[@250lmferrari]

+KYLE.DRIVES I don't really have the money to do proper aerodynamic engineering. my race car is just hobby. I really enjoy watching your and greys garage's videos about aero tho. thanks for the feed back!

[@KYLEENGINEERS]

No problem! I think you would be surprised by how accessible CFD is for hobby racers though, if you do your own CAD work it is only $250USD a run from JKF, just in case you ever decide to go down that route.

[@AndyRRR0791]

Does a $250 run come complete with a free can of worms...?

[@mikesymons3646]

great video and explanation, terrible arrows hahaha

[@jeremyduke4955]

I didn't know Bernardo Silva was a physicist

[@affanahmedkhan7362]

jazakallah ❤️

[@mafulsuranto5451]

how to excample calculate

[@michaeljohn8905]

I’m surprised you Formula 1 and driver guys don’t use a multiple cambered or a flexible cambered wing like a flaps on wings. Maybe you do and I’ve just never seen it. I think you car guys should take a few lessons one day and invert that wing and show them how it works on a plane. Seems a little easier to understand. I’m going to go check out your Vortex gen. Video . No offense but this video seems a little difficult to understand even said to somebody who knows it like me.

[@Daniel-qy5hj]

apruebame raquel

[@danielberry777]

Ok but how do you fix this if a wing you designed has detached airflow 😂

[@minamaged264]

If you already have it try to Increase its surface roughness

[@JerseyMikeP]

Need a Gurney Flap on that wing;-)

[@thomasnappo6309]

Don't know what your saying..with this diagram

[@Chris-eo5zs]

You need to work on your presentation, video editing, and your 'physics tutorial' ability. I enjoyed it as it was intended, but I have had a bottle of whisky (I'm Scottish), so please don't take offence at my critique: The name of the video is more complex than the content... For example, we assume a knowledge of boundary layers initially, though strangely, there is no mention of other videos that explain the concept... It's almost as if this knowledge is implicit... When talking to the layman, we bring up the subject of high pressure circulation before the wall. This circulation generates a separation point, as is logically observable, to those who know. How many average obververs of this youtube channel, actually know about stall/flow separation? For the general pops, I'll point you all to a CFD analysis we did for our course. This shows the high pressure regions referred to earlier. i63.tinypic.com/2r5fdrc.png I wanna drink whisky now, ut if anyone wants to discuss this, feel free!

[@ItGetsOrganized]

4/10