All language subtitles for 2020-10-13_17-01-51-f75dd59e4ea58ada123e8c1eb6facb10 (1)

This flow effects on Airfoil hello, everyone, in this lecture's will talk quieter, the viscose and

the more specific boundaryless effects on the airfoils.

So this lecture is going to be different from the introduction lectures because here we have a close

look to the airfoil and what the effects are doing to it.

So what you can see in front of you is an airfoil inside viscose flow.

And you can see that there is some displacement of the surface of the oil.

So this displacement is due to the boundary layer.

And this is done because the stream lines immediately external to the boundary layer on each surface

of the airfoil are shifted normal to therefore surface.

And the distance of which this streamlines are shifted is proportional to the displacement thickness

of the layer.

So you can imagine that the last line is actually the border of the boundary layer and the flow over

there for oil is shifted because of this layer.

And another thing you can see is that the thickness of the boundary layer increases with as long as

we go to the heart of the airfoil and this is normal because the flow gets retarded and for that reason

that this thickness increases of the bone layer.

And this is on the air for about what happens behind the airfoil.

So behind airfoil, both bonder layers from the upper and the lower service march in the wake.

The tired air in the wake is.

A manifestation of a drug sold drug is created from this week, and this is the drug war, therefore,

is directly dependent.

So the drug in this week is directly dependent to the momentum thickness of the bone layer of the trailing

cage.

So here in front of you can see the precious modification due to the boundary boundary layer presence

on an airfoil.

And on the graph you can see Envisat or flow that does not have the viscose effects versus the viscose

flow.

And you can see the difference.

So this is the pressure coefficient over there, foil over the court of their file.

So what effects we can find here?

So the first thing that we can notice is because of the presence of the viscose layers, the pressures

are slightly modified and you can see that there is a loss of lift.

And because of that, the shock.

Is further forward in the case of the viscose bandoleer, so when we have a close bond earlier, the

shock is slightly forward.

And also, we can see that when we have four floors, the shock is also weaker than the one of the Envisat

floor, and this is because the reduced expansion over the effective upper surface.

So as the surfaces of their foil are modified, then it's normal that also the shock will be modified.

If I remember, we're talking that the shock is produced because of the expansion and the compression

waves, which are dependent on the curvature of the airfoil.

So as we have viscose effects or the effective surface of the Air Force change because of the Bonta

layer and the curvature there has changed, then the boundary layer and the.

Shockwave will also be changed, so as we have changed the effective chamber, then the shock wave will

be smaller or weaker in the case of the viscose floors, or what we can also notice is in the US and

what we can see on the trailing pressures that are in the end of the graph is that the trailing edge

of the displacement surface or the one that has the effects is much lower.

Pressure, so the pressure there is much lower, but everything that we are talking about was only for

Airfoil, that he has a zero angle of attack or zero incidents.

But what is happening when we increase the incidents?

So when we increase the incidence, the Envisat and the viscose shape of their foe could match, and

this could increase the shock strength drastically.

So when we increase the angle of attack or the incidents, then the shock strength is increased.

The shockwave will also produce local thickening of the boundary layer so it will get thicker local

to the shock.

And this is going to be due to the imposed adverse pressure gradient.

The boundary layer may even separate if the shock strength is sufficiently high.

So we could have a flow separation.

This depends on the shock strength.

And this means that the shockwave, as well as the produced wave drug will result, increased the viscose

drug and possibly flow breakdown.

So, as you know, sometimes when we increase the angle of attack, the lift increases, but considerable

increase.

The angle of attack is not very beneficial.

Exactly.

Because of these effects for floor separation and for us is very important that the flow is always located

on their foil.

So it doesn't separate when the flow separate from the airfoil, then therefore is not effective.

So it doesn't develop lift force and it doesn't lift the aircraft in the sky.

And these are the viscose flow effects on the airfoils.