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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Physical intuition for Lamb vector

In many aerodynamical descriptions involving vortex structures (e.g. the Crocco's theorem) there is a useful physical quantity called Lamb vector: $$ \vec{\omega} \times \vec{v} $$ where ...
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320 views

Why does a propeller suck in air from the front?

A rotating but fixed propeller sucks in air from the front. What is the cause for this acceleration of air particles? Since propeller blades act like rotating wings, my best guess is that the blades ...
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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?
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165 views

Could a bladeless “Tesla Turbine” type air compressor be used as a high vacuum pump?

I have a wacky idea for a new vacuum pump, I'm trying to figure out why it shouldn't work. I'm interested in learning about Tesla Turbines, specifically when used in reverse as compressors or vacuum ...
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567 views

What shape has the highest drag coefficient?

This image from NASA illustrates drag coefficients for several shapes: It is generally accepted that some variation of the teardrop/airfoil shape has the lowest drag coefficient. I was wondering ...
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81 views

Why is an airplane propeller so different from a boat propeller in shape? [closed]

Examples: Airplane propeller Source:http://www.sensenich.com Boat propeller Source:http://www.nauticexpo.com It is obvious that the airplane propeller is drastically different from the boat ...
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72 views

Boeing 737 Homework Problem [closed]

I have done the above problem, but have come out with a rather large surface area. Could someone point out my mistake(s)? Given/Assumptions: I assume $\sum F_y=0$ because it's level and straight. ...
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35 views

Simulating supersonic flight in game

So this question about how to implement a good looking simulation of super-hypersonic flight of a rocket from launch point to orbit. I have an idea how to implement a good looking aerodynamic on ...
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0answers
32 views

How is egg shaped ball different from a spherical ball, aerodynamically?

I don't know whether this is the right place to ask this question or not but, how is an egg shaped ball aerodynamically different that the spherical ball? What advantages could one have over the ...
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1answer
28 views

Power vs. Speed - Indoor rowing

In the sport of indoor rowing (and probably others) I know that to double your speed you must increase your power output by a factor of eight. I am wondering why this is the case. The indoor rower ...
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1answer
33 views

Aircraft Thrust to weight ratio contradiction with energy conservation

Usually, airliners have (Thrust/Weight) T/W ratio in the range of 0.2 to 0.8 and for steady flight W = lift My question is, for example, that Antonov 225 has Thrust/weight: 0.234 for max takeoff ...
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64 views

Are raindrops actually “shaped like tears” when they fall?

Raindrops are always pictured like this, people imagine they have this shape when they fall, but is this true? Doesn't this shape create too much drag? What shape do they really have? It would also be ...
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Why is an Aircraft Runway NOT like a Teaspoon?

If the aircraft runway were like a teaspoon (by this I mean, flat in the beginning, then curving downwards and finally upwards), would it not work in favor of the propulsion of the aircraft? In spite ...
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1answer
47 views

rocket vertical landing [closed]

SpaceX has published a couple of videos that show one of their heavy-lift rockets landing vertically in a highly specific location. How is it possible that they are able to control so many ...
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4answers
8k views

Number of blades in a helicopter rotor

I was wondering how it is possible to determine what is the optimal number of blades in a helicopter rotor. I think that the length of the blade is involved as a longer blades would have to spin ...
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4answers
401 views

Aerodynamics of two objects closely following each other

On bicycles.se a question came up about whether one cyclist drafting another causes the lead cyclist to be slowed down. A contributor suggested that the opposite might be the case, that the leading ...
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2answers
41 views

How to estimate wind speed from a pressure difference?

Does a formula (or a rule of thumb) exist to estimate the wind speed between a high pressure area and a low pressure area given the pressure difference between the two areas? Only the wind resulting ...
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2answers
8k views

Position of aerofoil force moment, center of pressure, aerodynamic center

I'm confused by wikipedia's page on aerofoils, the aerodynamic center, and center of pressure; it seems to contradict itself. The airofoils page says the center of pressure is at the same position as ...
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1answer
75 views

Can the Arcaboard fly?

Recently, BBC news had a video that claimed to show a "real" hoverboard: As far as I can tell, there are 36 small fans on this device, and it seems to be flying just a few inches off the ground. ...
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1answer
67 views

What is the difference between the Method of Characteristics being formulated in terms of theta & alpha and theta & nu?

So I'm doing an MSc thesis involving the method of characteristics in rocket nozzles. My lecture notes have the MoC formulated such that the positive characteristics are defined as: C+ = Tan ( ...
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3k views

What exactly is the 'lift' of a sailboat as explained by Bernoulli principle

I have heard that when a sailboat is sailing against the wind, it operates on the principle of 'lift'. I am unable to understand the explanation, based on Bernoulli principle, completely. My question ...
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3answers
3k views

A spinning bullet

I know the rifling in a gun or rifle puts a spin on the bullet along the axis of trajectory. Now I don’t understand exactly why does it make the trajectory more stable and allow for greater travel?
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4answers
47 views

How do I figure out the totally airborne height for a given machine?

Technically "airborne" can just mean to move through the air, but I would like to know how high you have to be before you are entirely supported by air in a helicopter-like machine, as opposed to ...
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1answer
31 views

Equal transit fallacy in viscous materials

Does the equal transit theory work in viscous materials? It would seem here that if one were flying through something like gelatin the particles would come together at the tail end of the wing.
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926 views

How does a converging-diverging nozzle not violate conservation of energy?

Disclaimer: I know absolutely nothing about fluid dynamics, and very little about physics in general. THis may be a really dumb question. Now, at subsonic speeds, converging and diverging nozzles ...
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1answer
73 views

Why do throwing knives need to be balanced?

Indeed, unbalanced throwing knives are used, but I have read that balanced throwing knives are easier to use, because due to their geometric center being the same as their center of mass. Why would ...
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10answers
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What really allows airplanes to fly?

What aerodynamic effects actually contribute to producing the lift on an airplane? I know there's a common belief that lift comes from the Bernoulli effect, where air moving over the wings is at ...
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27 views

Lift provided to an aeroplane [duplicate]

We say that aeroplanes find lift due to an effect explained by Bernoulli's theorem. But isn't newton's third law of motion applicable along with Bernoulli's theorem? otherwise, an aeroplane wouldn't ...
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1k views

Paper plane between two fans - is this possible?

The setup: two fans facing each other, distance around 1m. Both are turned on. In between them, place a simple paper plane and according to this video, it will fly. ...
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2answers
64 views

Conflicts between Bernoulli's Equation and Momentum Conservation?

The well known Bernoulli's equation states that $P+\frac{\rho V^2}{2}=c$ However, a simple momentum conservation considering $P_1$ and $P_2$ acting on two sides, and velocity changes from $V_1$ to ...
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1answer
63 views

How can we calculate the maximum height of a fountain? [closed]

There are two limiters in this question. First is drag of air. Second is the viscous forces of pipe.(belong to the tube where water hitts up) The question is how can we calculate the maximum height ...
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1answer
21 views

How drag force relates to velocity in the air?

As you know in the formula of drag $$F=0.5 *d*A*C*v^2$$ in different velocities we have different Reynolds number. and the Reynolds number relates to coefficient of drag. my question is how can we ...
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30 views

Simulation physics software for air blowers [closed]

Anyone know a physics simulation software for air blowers or where you can simulate air lifting objects? I want to simulate a lottery drawing machine.
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2answers
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Difference resultant aerodynamics force on an airfoil and a flat plate

From basic airfoil theory the following free body diagram can be determined for a two dimensional asymmetric airfoil: Here the direction of the resultant force is governed by the geometry of the ...
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Deriving equation for skipping stones over water

Why can rocks skip over water (stone skipping)? For instance, if you conduct an experiment where you drop both rocks from the same height, but give one considerable acceleration in the $x$-direction, ...
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5answers
899 views

Do objects have a tendency to fall in their most aerodynamic position?

In one of my physics classes, we are using slow motion video to analyze the falling motion of an object and then find out the drag coefficient of that object etc. I noticed while doing this that if I ...
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3answers
350 views

Why don't surfboards fly out the back of a utility truck when driving on the highway?

I have never had it happen myself and every time I throw my boards (shortboards not malibus) in the back of someone's ute, with no cover on the tray, they always assure me they'll be alright( the ...
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3answers
109 views

Can Bernoulli fly a car?

I need to settle an argument. How much influence, if any, does the Bernoulli principle have in sending a stock car traveling at 200 MPH sailing through the air when the air pressure unexpectedly ...
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2answers
83 views

Can a glider maintain a constant forward velocity component?

I have a puzzle which asks me to consider a (engineless) glider descending at a constant rate and flying at a constant forward velocity (in still air). The question asks how to derive sink rate, $v_s ...
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1answer
31 views

How does a nozzle behave differently at different velocities of flow?

A converging duct acts as a nozzle for subsonic flows while the same nozzle acts as a diffuser (decelerator) for supersonic flows? How does this actually work?
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Gliders in a trailer

Everybody has heard I the old thought expirement of the birds in the trailer where the man hits the trailer the birds take flight and the trailer gets lighter. This has been disproven by the ...
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1answer
105 views

How does wind cause a wind turbine to spin? [duplicate]

How does wind cause a wind turbine (pictured) to spin? I cant find a good source on google to explain this to me. This question should help me understand better how a turbine is spun in a jet engine. ...
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1answer
66 views

How does gas spin the turbine in a jet engine?

I am confused about how the energy from the ignited gas spins a turbine in a jet engine, as pictured below ...
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1answer
48 views

Speed limit to air travel? [closed]

Is there a hard limit on the speed of air travel on earth? That is, if you consider the way the human body reacts to gravity. Is there active research ongoing in this area?
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1answer
49 views

Why do papers fly off the wall when you run past?

Another example is walking past a book and the pages of the book will fly forward. When you run, why do you blow air to knock over papers off the wall or turn pages of a book?
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1answer
62 views

Is it possible for something to travel at supersonic speeds in a tunnel?

Is it possible for items to travel at supersonic speeds in a tunnel, as opposed to unconfined spaces? The particular scenario I had in mind was a bullet train travelling faster than the speed of ...
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3answers
76 views

How does a boomerang behave in microgravity?

Let's say I have perfected a boomerang throwing machine - in Earth surface conditions the boomerang is always thrown the same way, and always returns to the throwing arm. And let's say I've sponsored ...
3
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1answer
120 views

How do propeller blades rotating through air accelerate it to provide thrust?

I have a good understanding of how a propeller works. An engine turns the blades resulting an increase in velocity. But how do the blades accelerate air to result in thrust?
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2answers
113 views

Lift and drag coefficients on other planets

The question I'm trying to answer seemed simple: how hard would it be to fly on a planet with lower gravity but also thinner atmosphere compared to Earth. If the answer could hint me at how much ...