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Questions tagged [boundary-layer]

Use for boundary layer related topics, including laminar and turbulent flows

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Does the pressure recovery on an airfoil cause separation more with turbulent BL’s?

If you have a turbulent boundary layer going through pressure recovery on an airfoil, why is it more likely to separate than a laminar boundary layer? From my research/intuition I think turbulent ...
Wyatt's user avatar
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1 vote
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Intersecting Boundary Layers in XFLR5

I am analyzing an airfoil called RevE-HC. While doing a type-1 analysis, I encountered that the BL is intersecting towards the trailing edge. The panels are refined and the geometry is also smooth. ...
Hellbat's user avatar
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How is the pressure constant across the boundary layer but density isn't?

In $P=ρRT$, ρ is density, R is the gas constant, and T is the temperature in Kelvin. In the boundary layer, the temperature and density varies, so why doesn't the pressure? If you have a slip line in ...
Wyatt's user avatar
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1 vote
1 answer
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How do boundary layers and shocks interact?

How do boundary layers and shocks interact? What difference is made with thinner and thicker BL's? I've recently been researching this topic, but at least for me there are no good search results on ...
Wyatt's user avatar
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1 answer
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What causes the lambda shape in a shockwave?

What causes the λ (or lambda shape) in a shockwave? I heard it had something to do with the interaction between the shock and the boundary layer. If so, how do they interact and why does it make the ...
Wyatt's user avatar
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4 votes
2 answers
202 views

Why Critical Angle of attack doesn't change with an increase of IAS/TAS?

I am trying to understand this topic that is not letting me sleep. I am a private pilot and I am studying for the CPL, if someone could give me a simple explanation of this I would be very grateful. ...
Alex Gallegos's user avatar
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2 answers
120 views

is it necessary for the velocity distribution profile over a flat plate to have that kind of parabolic shape?

A wind tunnel boundary layer experiment was done for a flat plate with 5 stagnation probes distributed horizontally (each probe has 5 vertical sensors) and a variable flap, for 2 different free stream ...
I.ham's user avatar
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1 answer
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How to calculate boundary layer thickness?

So I have a flat plate with a surface of 7sqm and an aspect ratio of 12 with air blowing straight at it (like a wing) at a speed of 50km/h. I would like to manually calculate the thickness of the ...
Vincent Cerowski's user avatar
5 votes
1 answer
213 views

Effect of leading edge contamination wing performance

When a wing accumulates irregularities such as insects or dirt on the leading edge, its performance decreases. There are two main effects of this which are explained in https://aviation.stackexchange....
lWindy's user avatar
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Streamwise Pressure Gradient on Curved Walls

Could someone help me to understand how can a wall generate differents streamwise pressure gradients just by its curvature? I can understand how it works in cross-flow (perpendicular to the streamline)...
Josue's user avatar
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Is it expected to see transition from laminar to turbulent BL at low Reynolds numbers?

I have used XFOIL to do the following analysis: NACA0018 airfoil. Reynolds number $2\times 10^4$ (low Reynolds number). Critical Amplification factor, $N_\mathrm{crit} = 3.54$ (corresponding to a ...
Amazigh_05's user avatar
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2 answers
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Temperature profile for a boundary layer

So I was reading the textbook today, and I see this picture for the temperature profile through the boundary layer. And I was confused on why the shape looks like this? Should it not look more like ...
Yihong Zhu's user avatar
1 vote
2 answers
207 views

Is flow attached in the center of delta wing?

Is flow attached in center of delta wing or only on the edge where two vortices operate? Any video of delta wing vs AoA with smoke?
22flower's user avatar
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1 vote
1 answer
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Can vane delay flow separation? [closed]

In general is a slat better than a vortex generator to delay flow separation, for high AoA or extremely curvature wing/objects? Does this "roof vane spoiler" works same as slat at wing, ...
22flower's user avatar
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What is max angle of surface without stall?

AoA is by defintion angle between choord line and airflow, here is 25°. But max effective AoA here is 60°, so flow will separate for sure here.. What is max lets call it "effective AoA" that ...
22flower's user avatar
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1 vote
1 answer
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Examples for the benefits and importance of having a Boundary Layer

I understand what a boundary layer is and how it is formed. Mostly these boundary layers are related to increasing skin friction drag of the body. Please could you give some examples that show the ...
RNG's user avatar
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3 votes
1 answer
417 views

How can a small airflow that passes through a slots redirect all the outer flow?

If this is normal wing without slots behind wing will be huge wake; airflow will separate, which is very easy to predict. Why would the outer flow follow the wing's couture; how can a small airflow ...
22flower's user avatar
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1 vote
3 answers
881 views

How does the turbulent boundary layer thickness affect separation?

I read that for a turbulent boundary layer, a thicker (turbulent) boundary layer separates earlier than a thinner (turbulent) boundary layer? Why is that? Or is it the other way around?
RNG's user avatar
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2 answers
463 views

Does flow separation starts earlier at higher airflow speeds?

For same AoA,will flow separation starts earlier (point of separation more upstream) at higher airflow speeds (=higher air inertia) compare to lower airflow speeds? High speed airflow has more air ...
user avatar
15 votes
3 answers
4k views

What is the difference between flow separation and turbulent flow?

For air flowing over a wing, both flow separation and turbulent flow involve disturbed flow next to the surface and smooth flow further away. At what point does one say "oh, this flow has changed ...
Guy Inchbald's user avatar
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What causes the adverse pressure gradient that leads to flow separation?

When reading about flow separation I generally see a diagram like this: imp source: Wikimedia commons This shows that the boundary layer slows as it passes over the wing, eventually creating an ...
TomMcW's user avatar
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7 votes
3 answers
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What is the effect of flow separation on lift, pressure distribution and drag?

Consider an airfoil (a wing) in an airflow. When angle of attack increases, at some point the flow start to separate from trailing edge. By increasing the angle of attack more, this separation area ...
S.Serpooshan's user avatar
8 votes
2 answers
639 views

How much noise does flow separation cause?

I recently found the following image showing the different sources of noise in vehicles. I notice that Aerodynamics is actually quite a big part of vehicle noise, as shown below by the blue line: ...
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