Tagged Questions

A subset of [tag:fluid-dynamics] concerning primarily forces such as lift and drag generated on bodies as they move through gasses or as gasses move through the body (typically air).

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0answers
9 views

Influence of paper lantern shape on burning behaviour of candle [on hold]

I am wondering what would be the most significant factor in designing a paper lantern, as to keep the candle inside burning even at strong wind. I am thinking of a simple lantern design, with a hole ...
-2
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0answers
8 views

Prandtl's equation - Calculating coefficients [closed]

I don't even know how to get started. Could you please give me a clue? I haven't seen a similar problem before.
2
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1answer
65 views

Why do vapour cones form around jet fighters?

Apparently this phenomenon has nothing to do with jets breaking the sound barrier and has something to do with the Prandtl-Glauert singularity as described on Wikipedia. But, the Wikipedia article ...
2
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1answer
228 views

what kind of wings would a person need to fly?

I heard from a teacher in school that in order to fly, he would need a wingspan much wider than the wood shop where he was standing. Thinking back on it, I assume the number of times you can beat your ...
5
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3answers
514 views

Benefits of rear spoiler in cars

What would be the benefits of rear spoilers in cars, like this one:
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0answers
28 views

If i had a aero-nautical object [closed]

If i had a aero-nautical object with a span of 10 feet and a weight of 40 pounds with a strong gale blowing do you think i could make it off a cliff with out plummeting to total utter death?
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1answer
28 views

Delta wing flow patterns (straight and yawing)

I was wondering the differences between fluid patterns and their consequences when a delta wing is straight and yawed slightly.
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1answer
53 views

What causes a spacecraft entering the atmosphere to catch fire? [closed]

What causes a spacecraft entering the atmosphere to catch fire? A) surface tension of air B) viscosity of air C) high temperature of upper atmosphere D) greater proportion of ...
5
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2answers
266 views

How does train back draft work

Quoting platforms and stations : Fast trains can create a vacuum called a ‘back draft’ that can blow you over or suck you under a train. How does that work ? I thought that the volume of air ...
3
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1answer
48 views

How to design windy area - what variables?

When you're walking around malls or parking structures, or a building corner, you'll sometimes notice areas with consistent windiness. I was wondering what positions, angles, wind direction, ...
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0answers
28 views

Why does a brand new cricket ball swings? [closed]

Why does a brand new cricket ball swings? Both the sides of seam are equally smooth. None of them is rougher than the other. Can someone please explain the exact physics behind it?
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3answers
61 views

Propellers and the Speed of sound

I was reading this website that described a novel wind turbine technology and it has this quote: In the mid-20th century, open propeller-driven planes with piston engines reached performance ...
6
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1answer
664 views

What is a Physically Accurate Explanation for the Kutta Condition?

Countless arguments between highly intelligent people have been waged (on this very site in fact) as to exactly how lift can be explained in an experimentally and mathematically rigorous way. Taking ...
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1answer
68 views

How a fan moves air? [duplicate]

How does a fan moves air towards you (I mean in 1 direction). Also propeller and fan have different shapes, does it mean they work different?
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3answers
2k views

What is going on in front of and behind a fan?

Why is it that when you drop paper behind a fan, it drops, and is not blown/sucked into the fan, whereas if you drop paper in front of a fan, it is blown away?
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1answer
100 views

Why Are Normal Shock Waves Unstable in a Converging Channel?

While learning about shock waves in an introductory Gas Dynamics course, it was revealed that normal shocks are unstable if formed in a converging channel. Even if the local conditions ostensibly ...
4
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2answers
70 views

Number of blades in a fan

How does the number of blades in a fan affect the flux of air? I read that 3 blades are the best option but some companies uses more blades because there's a misconception among people that more ...
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0answers
41 views

Static,total and velocity pressure at a point

I have a past exam question that I am stuck on. $200$m$^3/s$ of air is entering a shaft of $5m$ diameter, the density is $1.18$kg/m$^3$, and I have shock loss of factor $X=.5$ I want static, ...
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1answer
57 views

Is the flow in a ducted fan really incompressible?

I have a long duct with a fan in the middle of it. The fan causes a steady airflow in the pipe which is at low speeds (incompressible) the mean flow in the pipe is about 10 m/s. However the fan blades ...
2
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1answer
340 views

Calculate flow rate of air through a pressurized hole

I was wondering about this: If there is a pressurized container, like a tank of compressed air at some pressure that is greater than the ambient air pressure, and this tank of air has a hole in it, ...
1
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1answer
53 views

What does centre of lift depend on?

I've read in many places that centre of lift is about quarter chord of the wing and that post-stall lift (the part developed on lower surface) has centre midchord. The later makes sense; the pressure ...
2
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2answers
108 views

Confused about the theoretical origin of quadratic air drag [duplicate]

Though the mathematical concepts underlying quadratic air drag are quite straightforward (a single variable differential, just like the linear drag equation), my text book (and online text books) ...
2
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1answer
72 views

How to calculate the drag coefficient using terminal velocity?

I was wondering if it were possible to calculate the drag coefficient by allowing an object to reach terminal velocity. Can you rearrange the terminal velocity formula to give the drag coefficient?
8
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2answers
1k views

How much more efficient is a road bike than a mountain bike? [closed]

What would be a good estimate on the difference of efficiency between a road bike and a mountain bike? A number of links cite all the usual reasons: thinner tires, better aerodynamics... But I'm ...
3
votes
1answer
48 views

Why does a piece of paper travels up when inserted into a kite's thread?

When I was young, I would insert a piece of paper into a kite's thread. The paper would travel upward till it reaches the head of that kite. What makes it to go up against the gravity even if the ...
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0answers
89 views

Could the phenomenon of vortex bursting be exploited to reduce wake turbulence?

One of the classic stories in the annals of aerospace engineering is the development (and subsequent redesign) of the F-18 and its Leading Edge Extensions (LEX) due to fatigue problems, problems that ...
9
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2answers
726 views

Why do co-rotating vortices coalesce, but not counter-rotating ones?

In studying the aerodynamics of modern aircraft equipped with high-lift devices, I have discovered that quite a number of distinct trailing vortices are present in the immediate wake of an airplane in ...
7
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2answers
199 views

How should I throttle my rocket to reach highest altitude? [closed]

"Real world" problem. Suppose we want to launch a rocket equipped with an engine which can be throttled as we prefer. Suppose also that the amount of fuel burnt per time is directly proportional ...
27
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13answers
2k views

What does a wing do that an engine can't?

This isn't a question of how a wing works -- vortex flow, Bernoulli's principle, all of that jazz. Instead, it's a question of why we need a wing at all. A wing produces lift, but why is that ...
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2answers
58 views

How laminar or turbulent is air?

Consider an outdoors scenario, with good weather and no sensible air currents at the floor level. How turbulent or laminar is the air surrounding this environment?
1
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1answer
96 views

How much wind does it take to tip a sign over? [closed]

Or said another way - how much counterweight does the base of a sign need to keep it from tipping over given a specific max wind? Assume the sign does not let wind through Assume the base of the ...
2
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2answers
54 views

Maximum helicopter height [duplicate]

Helicopters or dual/quadcopters stop rising after reaching some height from the ground. What causes that? And what one should do if he want to prevent this, if he want the helicopter to keep rising ...
4
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2answers
72 views

Are Mach Diamonds radially symmetrical?

Videos like this show a form that suggests a radial symmetry in the gas jet. The same is reinforced by schematic illustrations. But other images, like this, look like there is a twisting structure ...
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4answers
352 views

Experiment - Measuring final velocity of a parachute

I'm working on a project that involves a scale parachute. It is vital for the project to get a good measurement of the speed it has when it lands. We still haven't built the parachute, but we need a ...
3
votes
1answer
50 views

Stagnant Air Deep Inside Vintage Mines

This is really a question more about mining ventilation than true "physics." I occasionally explore a southwest desert mine, but am aware of the hazards - typically passing over half a dozen vintage ...
2
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0answers
64 views

Why air above airplane's wing moves faster? [duplicate]

One explanation I read: Because of the wing's geometry, the "upper" side of the wing is longer, so the air has to travel faster: My wondering: Who said (and what was his/her explanation) that ...
2
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1answer
84 views

Uses of the Reynolds number

I have seen a lot of places talking about the Reynolds number and how it is calculated, but I have never seen an equation that actually made use of this number to calculate lift, drag, or other ...
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2answers
143 views

What's the advantage of NASA's flying saucer over traditional aerodynamic models?

NASA has recently tested a saucer-shaped spaceship. What's the advantage of this new design over traditional aerodynamic designs? The test launch was performed from within atmosphere which would ...
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2answers
57 views

Does the lift created by a wing change when the slats are deployed?

This is a conceptual question as much as an empirical one, but the question is: Does the lift of a wing change when the slats (or any other leading edge device) are deployed? I am stipulating that the ...
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2answers
77 views

Cause for Power Transmission Tower “Breathing”

OK, this question is not your usual one: Last night while hiking solo from the mountains back to my car at the mountain/desert interface (Lone Pine, CA), I had a rather bizarre -- and downright spooky ...
4
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1answer
188 views

Effect of Earth's magnetic field on aeroplanes?

As an aeroplane accelerates through the Earth's B-field, it experiences a changing flux $d\phi \over dt$ and a potential difference is induced along its wings. Given the wings are made of metal and ...
4
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1answer
154 views

What is the exact cause of flow separation in a viscous fluid?

I recently got into a lengthy debate about the exact nature of boundary layer separation. In common parlance, we have a tendency to talk about certain geometries as being too "sharp" for a viscous ...
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3answers
104 views

Why doesn't this model plane fly? [closed]

I have been designing a model plane for Design Technology for the past month or so, and today I laser cut my final design and assembled, it then tested it. Upon testing the plane does not get any ...
6
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1answer
253 views

Why aren't airplanes like golf balls?

Ok this is a silly question but here it goes Although it is good to have a laminar flow of the air around the object for low drag but the laminar flow is prone the phenomena called separation (sounds ...
5
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3answers
68 views

Why do tropical cyclones not tear themselves apart?

A tropical cyclone is the generic term for a hurricane, typhoon, or tropical storm. Tropical cyclones derive their energy from evaporation of water at the ocean surface which ultimately recondenses ...
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2answers
1k views

Does it make sense to open one window all the way when the other window is much smaller?

I can't wrap my head around this idea because I don't know much about air flows. Say we have this imaginary apartment with two windows, one of which is two times smaller than the other: Will the ...
3
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2answers
173 views

Why Don't Birds Stall?

I often hear about planes stalling when they lose lift due to low airspeed/too high angle of attack. Why don't birds stall? Does it have to do with the structure of their wings and their flexibility, ...
15
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5answers
4k views

Why isn't jumping from a high altitude fatal?

After seeing this answer claiming that displacing matter "In a very short time", "no matter whether the matter is solid, liquid, or gas" (even though he concludes that falling from a high altitude is ...
28
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6answers
6k views

Why is jumping into water from high altitude fatal?

If I jump from an airplane straight positioned upright into the ocean, why is it the same as jumping straight on the ground? Water is a liquid as opposed to the ground, so I would expect that by ...
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2answers
232 views

Does the wing-propeller plane or jet-plane struggle up at the high altitudes because of low pressure?

We all know that wing-propeller planes rely on air to create a thrust. They suck the air in and push them back hard that it's opposite reaction pushes the plane (Newton's law). Does that mean ...