# 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 ...
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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. ...
• 11
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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 ...
• 2,421
1 vote
48 views

### 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 ...
• 2,421
183 views

### 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 ...
• 2,421
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. ...
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 ...
183 views

### 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 ...
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....
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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)...
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1 vote
72 views

### 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 ...
• 111
687 views

### 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 ...
1 vote
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?
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1 vote
159 views

### 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, ...
• 1,958
165 views

### 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 ...
• 1,958
1 vote
207 views

### 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 ...
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### 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 ...
• 1,958
1 vote
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?
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### 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 ...
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 ...
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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 ...
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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 ...
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