Questions tagged [flow]

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2
votes
1answer
66 views

What exactly happens to kinetic energy in the turbulent layer on an aerofoil?

Sources I've read contains contradicting information. As far as I know, when the laminar airflow breaks up, it becomes a thicker and draggy layer, causing a layer of what essentially is slowed air; ...
6
votes
2answers
2k views

Why do planes employ vortex generators if the laminar flows exhibit a far lower skin friction drag than turbulent flows?

I am a student and still relatively new regarding fluid flows. Our professor asked this and I can't find a source to answer this question.
1
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2answers
150 views

Is it possible to have the laminar flow above $Re=10^7$?

For pipe flow I came across the information that the onset of turbulent flow occurs at approximately $Re=10^3$ to $Re=10^4$, while for boundary layers on the airfoil the onset occurs in between $Re=10^...
4
votes
2answers
438 views

Why can't commercial aircraft have a wing boundary layer suction system?

I've read that NASA's boundary layer suction system on the wings can reduce drag by removing the boundary layer through the suction holes. If this can reduce a lot of drag (hence improving fuel ...
25
votes
5answers
5k views

Why does airflow separate from the wing during stall?

What causes the airflow separation from the airplane wing, that triggers a stall? To be more precise, what is the detailed explanation of the physics for why flow separation occurs at certain speeds ...
1
vote
1answer
767 views

Boundary layer momentum thickness

Could someone please explain the concept of the boundary layer momentum thickness and its difference to boundary layer thickness calculation? Some explanation about the application of the boundary ...
1
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0answers
90 views

What is subcritical and supercritical boundary layer?

What is subcritical and supercritical boundary layer? What is the difference between them?
1
vote
1answer
2k views

How to calculate the static pressure in a pitot tube?

In a pitot-static tube, we have two different pressure, the static pressure $p_s$ and the total pressure $p_0 = p_s + \frac{1}{2}\rho v^2$, which comes from the Beroulli equation for incompressible ...
9
votes
2answers
2k views

Is there a physical argument for the Kutta-Joukowski theorem?

I am doing the following exercise: Consider inviscid, incompressible, steady flow. The Kutta-Joukowski theorem $$L' = \rho_\infty V_\infty\Gamma$$ where $L'$ is the lift per unit span $\rho_\infty$ ...
4
votes
1answer
178 views

Does this formula hold true for a source sheet covering a closed body of arbitrary shape?

Let me explain the picture above: We have a uniform flow and a source sheet cover the the surface of an arbitrary closed body. Let s be the distance measured along the source sheet, λ=λ(s) is the ...
3
votes
1answer
357 views

How do I calculate the normal component of the velocity at the midpoint of a source straight panel?

I am reading "Fundamental of Aerodynamics " by J.D.Anderson Fifth edition. Now I am at the chapter 3. If you got the book, please go to the page 286, the part that says: "when j = i, the contribution ...
1
vote
0answers
328 views

What causes these losses in this propeller simulation?

While running a CFD simulation comparison of 2 vs 3 blade propeller versions (48" diameter, 23" pitch, 3570RPM), I've come up with: 2-blade: 347N of static thrust @ 110Nm Torque 3-blade: 220N of ...
7
votes
1answer
246 views

Why is the flow ahead of a shock wave chaotic?

Here is the image of a shock wave on a cone in a small supersonic wind tunnel, the white lines are the condensations formed in the test chamber due to flow expansion. Why are the condensations so ...