Questions tagged [flow]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
0 votes
1 answer
198 views

Why will air keep accelerating in Mach 1+ flow, when it would decelerate in subsonic flow?

So I was clarifying a few things in a comments section of an answer, and I had quite a few questions so I thought I'd ask my main one in a separate post. In the second comment on this answer, it says ...
Wyatt's user avatar
  • 1,345
2 votes
1 answer
145 views

Does speed affect the pressure and lift distribution at the wingtip?

So I was wondering if speed affects the pressure distribution at the wingtip. The second comment on this answer says (if I interpret it correctly) that speed doesn't change the pressure distribution ...
Wyatt's user avatar
  • 1,345
1 vote
1 answer
144 views

Forces acting on ram air parachute (for pulling ships)

I recently stumpled across this question about the ram-air parachutes for use in pulling ships. In this answer it is stated that the parachute needs to travel perpendicularly to the ship's motion in ...
pat3d3r's user avatar
  • 219
26 votes
5 answers
5k views

Why a kite flying at 1000 feet in "figure-of-eight loops" serves to "multiply the pulling effect of the airflow" on the ship to which it is attached?

In CNN's June 30, 2023 Giant kites could pull cargo ships across the ocean – and slash their carbon emissions “What differentiates it from other wind solutions,” says Bernatets1, “is that the wing is ...
uhoh's user avatar
  • 5,808
2 votes
3 answers
87 views

Is contact between flow and inner walls of nozzle required for thrust generation?

I uploaded a picture below explaining over-expanded flow/nozzle condition with regards to thrust. This aviation source tells that “extra nozzle walls don’t generate any additional thrust because flow ...
Jawel7's user avatar
  • 244
1 vote
0 answers
85 views

How can over-expanded flow go out of nozzle when it has less pressure than ambient pressure?

We know that over expansion in flow means that nozzle exit pressure of flow is lower than ambient pressure at specific altitude. It gets narrower while exiting nozzle causing loss in efficiency. My ...
Jawel7's user avatar
  • 244
3 votes
3 answers
399 views

What is the most efficient way to reduce interference drag when surface imperfections are unavoidable?

Interference drag can start to appear when there’s imperfections or excrescences on an aircraft outer surface. For example the following image shows some of these typical imperfections: Source of ...
Frank's user avatar
  • 415
6 votes
2 answers
367 views

Do tufts show boundary layer flow or outer flow?

Outer flow and boundary flow are often different. Do tufts at the wing surface show boundary layer flow or outer flow? Picture source. Paint shows boundary layer flow. Picture source
user707264's user avatar
  • 1,722
2 votes
2 answers
224 views

why normal surface pressure over wedged cone is greater than freestream pressure

I came across this question in "Fundamentals of Aerodynamics" by John Anderson, although I knew how to solve the question, I didn't understand why we had the surface pressure on the wedge 1....
Allaw Hussein's user avatar
2 votes
1 answer
196 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; ...
De_'s user avatar
  • 43
7 votes
2 answers
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.
Aircraft Enthusiast's user avatar
1 vote
2 answers
200 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^...
Darjan's user avatar
  • 1,145
4 votes
2 answers
773 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 ...
Johnson's user avatar
  • 1,703
25 votes
5 answers
6k 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 ...
user avatar
1 vote
1 answer
1k 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 ...
Guha.Gubin's user avatar
1 vote
0 answers
112 views

What is subcritical and supercritical boundary layer?

What is subcritical and supercritical boundary layer? What is the difference between them?
Darjan's user avatar
  • 1,145
1 vote
1 answer
4k 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 ...
Josh Pilipovsky's user avatar
9 votes
2 answers
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 $\rho_\infty$ ...
Dat's user avatar
  • 990
4 votes
1 answer
200 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 ...
Dat's user avatar
  • 990
3 votes
1 answer
568 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 ...
Dat's user avatar
  • 990
1 vote
0 answers
383 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 ...
FlegmatoidZoid's user avatar
7 votes
1 answer
278 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 ...
Davide's user avatar
  • 773