Questions tagged [fluid-mechanics]

Fluid mechanics is the branch of physics which involves the study of fluids (liquids, gases, and plasmas) and the forces on them. Fluid mechanics can be divided into fluid statics, the study of fluids at rest; and fluid dynamics, the study of the effect of forces on fluid motion.

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Is a stream of air / jet exhaust low pressure?

Inspired by this answer, is a moving stream of air (Jet exhaust, rocket plume, etc) low pressure? I’ve always thought that a higher pressure area (say the combustion chamber of a rocket engine) will ...
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86 views

Why does the density decrease equal the speed gain at Mach 1?

In this answer, it says : "At small Mach numbers, changes in speed cause negligible changes in density, but as Mach approaches unity, both are of similar magnitude. With Ma>>1 , changes in ...
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378 views

Determination of a Joukowski airfoil chord (demonstration)

I'm currently studying Aerodynamics, and one thing that I noticed is that the maximum and minimum $x$ coordinate of the airfoils (which are necessary to compute the chord) on the transformed plane (...
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1 vote
80 views

Why does the angle of a shock change when the flow leaves the influence area of an object?

In this (great) answer, it says: "far enough" from the Concorde's nose, the path followed by the airflow is not affected by its presence and it's just a straight line. Close to the nose we ...
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1 vote
68 views

Calculating Lift-To-Drag ratio of a rotating propeller with zero forward velocity

I'm simplifying some blade element theory problems by assuming that the propellers are perpendicular to the ground and their motion is constrained to being purely vertical (without forward velocity). ...
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1 vote
88 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 ...
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1 vote
185 views

How much lift can be generated by the intake lip of a duct?

How to calculate the extra lift gained by the intake lip of a duct? Aside from improving efficiency by preventing tip vortices, if a duct has a bell-shaped intake, this lip around the edge creates ...
• 149
80 views

Why doesn’t the air expanding behind a shockwave reverse the effects of wave drag?

Wave drag is (from my understanding) the difference in pressure between the front and rear of an object due to shockwaves, making an opposing force. This needs higher pressure in front of said object ...
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117 views

Why doesn't the Coanda effect also pull air from inside the jet / streamline?

As explained nicely in this answer, the Coanda effect will make a streamline of air draw from the surrounding air outside of the streamline. This picture shows it nicely : So my question is what ...
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60 views

What causes the oscillation in vortex shedding?

When studying this video, I was wondering what actually causes the oscillation? Any source online that I found said that it was from oscillating low pressure zones, but what causes that?
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32 views

Will supersonic flow return to subsonic through shocks over a flat surface?

Will supersonic flow return to subsonic through shocks over a flat surface? Imagine supersonic flow over a plate. Will it always try to return to subsonic through a series of normal shocks? (Pretend ...
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40 views

Are oblique shocks formed at the leading edge-top surface of a wing?

Do oblique shocks form on the leading upper surface of a wing? I know bow shocks are formed there, but is that the same thing as I’m talking about? Oblique shocks would have to form there because the ...
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117 views

Does lift decrease in hypersonic speed?

In John Bertin's Aerodynamics book, it is said that when the thickness of the boundary layer is low, the displacement thickness of the boundary layer is also low, and therefore the curvature of the ...
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98 views

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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95 views

Is winglet height equivalent to duct height?

Winglets increase effective wingspan by causing vorticies to be generated further away from the wing root in proportion to the height of the winglet (if vertical), likewise with winglets on propellers....
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76 views

What is the speed and temperature profile of the boundary layer at the stagnation point?

At the statgnation point where the air velocity is zero, what is the shape of the velocity and temperature profile of the boundary layer? Is the velocity profile of the boundary layer in the form of a ...
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