The quantitative study of how fluids (gases and liquids) move.

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251 views

What is the theoretical justification for a fluid flow's being irrotational?

I am not a fluid dynamicist, and I really just began thinking about this problem as my curiousity drew me into building an answer for the question What really allows airplanes to fly?. It is very ...
0
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1answer
368 views

How to calculate the energy required to generate a vortex? [closed]

I am looking for the formula to calculate how much energy it requires to create a vortex. Can anyone assist please?
7
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1answer
731 views

How to make the bubbles in my soda drink last longer?

I would like to make the bubbles in my soda drink last longer. For example, one good thing to do is to keep the bottle shut when you don't drink. But what else I can do? Should I try to minimize the ...
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vote
1answer
213 views

May I know how a vortex tube works? [duplicate]

From my point of view, high gas pressure input creates air rotation inside the tube. Due to the rotation, the kinetic energy in the air change to internal energy. The internal energy release as heat ...
0
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1answer
246 views

Derive conservation law using divergence theorem

Material scientists have discovered a new fluid property called "radost" that is carried along with a fluid as it moves from one place to the next (just like a fluid's mass or momentum). Let ...
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0answers
221 views

Waves produced by a mass of water on the calm sea surface

Suppose we have a parallelepiped shaped box full of water on the surface of the sea. Suddenly the box disappears. What is the shape of the waves vs. time caused by the fall of the water contained in ...
4
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2answers
265 views

What explains the effect of water's path falling around a ball/curve?

Disclaimer: I'm not a physicist. If you take an apple or a ball (or a cylinder works too) and put it under a tap such that the water falls down the side (not the centre) of the sphere, you get water ...
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1answer
329 views

Why is there a space between the flame and the nozzle on the space shuttle?

Why is there some space between the flame and the nozzle on the space shuttle? (see above picture)
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2answers
763 views

Example of inviscid flow with drag

This was my engineering viva question and I couldn't think of any example, for I am totally convinced that there cannot be drag in a inviscid flow. It also bothers me whether it is possible, a ...
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2answers
421 views

Water level difference by pumping [closed]

Open tank is partially filled with water and is divided into two equal parts by the wall. The wall has pipe that connects both sections. Obviously, water levels are equal from both sides (Fig.1). ...
18
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1answer
294 views

What are the equations of motion of a hole in a soap bubble?

Imagine the following situation: I have a thin stationary water film, like a soap bubble, suspended inside a large ring. I throw a small loop of string onto the film and punch a hole inside it. How ...
3
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1answer
172 views

Nonlinear waves and shock formation

In the cases of nonlinear acoustics, why is shock formation unlikely when the dispersion is strong when compared to the nonlinearity of the wave?
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2answers
406 views

Aerofoil Theory Project [closed]

I'm doing a project (dissertation) on the mathematics of Aerofoil Theory. I wonder if I could get some advice on a possible structure. I'm new to fluid dynamics, so it's quite hard to know where to ...
3
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1answer
144 views

Mysteries of the water meter

Recently, I got an exceptionally high bill for water consumption. I went to check my water meter, and saw that it rotates in a pace of about 200 cc per minute, even though all the faucets in my home ...
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1answer
311 views

Ship wake height

It is well known that a ship traveling in a deep water produces wake. Far from the aft of the ship, these wake are called a Kelvin wake. I found the mathematical expression of the shape of the wake, ...
4
votes
2answers
891 views

Finding Stagnation Points from the complex potential

I am trying to find the stagnation point of a fluid flow from a complex potential. The complex potential is given by $$\Omega(z) = Uz + \cfrac{m}{2\pi}\ln z.$$ From this I found the streamfunction to ...
0
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3answers
335 views

Does the ceiling fan make the air and dust spiral in?

Does the rotation of ceiling fan makes air circulate in a spiral, circular motion beneath the radius of fan or the air from outside is also mixed with it and replaces the air in room? A ...
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3answers
5k views

Why should fluids be confined for Pascal's Law to be applicable

When is Pascal's law about fluid pressure propagation applicable? Is it applicable to a closed circular pipe with a pump rotating the fluid, but not to a tub of water. Most statements require only ...
2
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1answer
68 views

A way to track a gas's expansion

I was wondering if there is a way to see, empirically, how a gas behaves. Perhaps the most natural way is to use fumes with color, but they quickly disperse, rendering partially useless. Are there ...
0
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1answer
56 views

Non-uniform field pressure on fluid

I have been studying fluid mechanics and currently I was trying to understand Euler's equation for fluid flow. For that purpose, I was following this webpage. My problem is in understanding Eq.(12). ...
0
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1answer
299 views

how to reduce pressure drop in a 5/16 ss tube

I have a fluid line which passes high density fluid at $60 \text{psi}$. At the end there is a valve. I have a $30 \text{psi}$ dynamic pressure drop in the line valve itself creates a back pressure of ...
4
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1answer
199 views

Bubble in a pipeline

I am just thinking about this phenomenon: We have a horizontal pipeline with a flowing liquid, which contains a small bubble of gas. How do the dimensions of this bubble change when it reaches a ...
2
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0answers
58 views

Realistic Ocean Shears

I was wondering if anyone could point me to published data on the vertical structure of strong ocean currents, such as the Gulf Stream. I am primarily interested in the mean current profile as a ...
13
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5answers
4k views

Why planes have propellers in front but watercraft have them behind?

Why do propeller airplanes mostly have their propellers in front (of the fuselage or wings) while ships and boats mostly have them at the back? I realize that there are aircraft with pusher ...
0
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1answer
159 views

What happens (in terms of pressure) when there is a leakage in a horizontal pipe? [closed]

Consider a horizontal pipe that has water being pumped continuously through it, with a leak at a given point. What will the leak's effect be on the pressure in the pipe, both above and below it in the ...
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2answers
3k views

What does the Froude number represent?

While reading on Wikipedia, I read the following The Froude number is defined as: $$\mathrm{Fr} = \frac{v}{c}$$ where $v$ is a characteristic velocity, and $c$ is a characteristic water ...
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0answers
48 views

Nuclear Weapon Effects: Cloud Rise [closed]

I am interested in modeling the rise of a nuclear cloud to stabilization height post detonation. I am interested in any ideas you may have on the approach. I have collected some research on the topic ...
5
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1answer
277 views

Are electrodynamics problems in the complex plane relevant to real life?

This is a question I asked in Maths SE, and it was suggested I ask it here. This is a direct copy of that question. I have been reading Tristan Needham's excellent Visual Complex Analysis. The end of ...
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0answers
186 views

Horizontal Capillary Question

I have a fluid mechanics question, that I think is caused by a lack of understanding of some key concepts. Suppose we have a horizontal capillary with a radius of 10um. The fabrication process has led ...
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2answers
649 views

Boundary between supercritical fluid and gaseous phase

As far as I understand, going around the critical point, it is possible to transform a liquid into a gas without seeing a phase transition. Does this also mean that there is no clear separation ...
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1answer
321 views

Blasius boundary layer solutions

I'm trying to understand the Blasius boundary layer solution, but I'm having some difficulties. Using wikipedia, I wonder how they get the first formula: ...
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0answers
112 views

Boundary layer equation

I was trying to understand the derivation of the boundary layer equations at p.145 of http://www.unimasr.net/ums/upload/files/2012/Sep/UniMasr.com_919e27ecea47b46d74dd7e268097b653.pdf. : the ...
3
votes
1answer
590 views

Question about streamline in boundary layers

I was wondering what the streamlines look like in a boundary layer. I found a picture that shows this: I would like to know if this presentation of the streamline is correct. I don't think that it ...
4
votes
1answer
213 views

Can Smoothed-Particle Hydrodynamics (SPH) be used to simulate porous media flow and deformation?

I am trying to use Smoothed-Particle Hydrodynamics (SPH) to study fluid flow in and around porous media. The aim is to observe how it causes erosion and failure. For this, from my understanding, there ...
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0answers
253 views

Efficiency estimation for small-scale (~15cm) propellers

First up, apologies if this isn't quite the place for this; Aerospace is still in Area 51 so there doesn't seem to be a better place for it. If it helps, feel free to give theoretical answers and I'll ...
0
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1answer
317 views

What is physics of Collision between solid and liquid (or gas)? [closed]

My mind has been busy recently by this question: What is physics of Collision between solid and liquid (or gas)? What is Conservation law's of such Collision? Why, when we drop a solid object in ...
2
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1answer
1k views

Shear stress in directions other than the flow direction

Consider the flow of a newtonian fluid in a rectangular pipe. Consider a 3D coordinate system with the property that.that the flow of the fluid in the pipe is parallel to the x-axis. Let ...
2
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0answers
319 views

What is the drag coefficient of an open wedge?

To check my two dimensional CFD calculation I am looking for reference data on the drag coefficient of an open wedge. The geometry is shown below, together with the flow direction. I have found ...
6
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1answer
565 views

Question about the Bernouilli equation

There are some things I encountered, studying the Bernouilly equation, that I don't understand. I was studying in the following book: ...
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0answers
2k views

From Navier–Stokes equations to Euler, Bernoulli, etc [closed]

How can one go from the 3D compressible Navier-Stokes equations to the simpler Euler equations, Bernoulli's equation and other fluid dynamic equations?
0
votes
1answer
597 views

Is there a way to let water pour out of bottle without letting air inside? [closed]

Is there a way to let water pour out of bottle without letting air inside? i understand that air needs to enter the bottle to ensure water flow, but i do not want to the water to be exposed to air. ...
9
votes
2answers
5k views

Why do ice cubes stick together or to the edges of a drinking glass?

I was drinking iced-water from a drinking glass (made of glass) at a restaurant yesterday when I was taking a drink, I noticed that there is very little ice water coming out and then suddenly, the ice ...
42
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8answers
4k views

Explaining to a five year old - why don't bubbles run like water

My five-year old daughter was asking about astronauts the other day and why they float in space. After me showing her a few bits on the kids section on the NASA web site I started explaining about the ...
0
votes
1answer
2k views

Finding the Center of pressure of a body immersed in liquid

I came across some problems related to finding the center of pressure. Please guide me how to go about them. Posting them all so that I can find out the intricacies involved when there are so many ...
2
votes
3answers
11k views

About an upside down cup of water against atmosphere pressure

There is an experiment we learned from high school that demonstrated how atmosphere pressure worked. Fill a cup of water and put a cardboard on top of it, then turn it upside-down, the water will not ...
3
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0answers
149 views

seemingly impossible query

While on an expedition to a lake, it was noticed that the wind speeds gusted violently in seemingly periodic wakes and the proposed explanation was Von Karman vortex shedding off of nearby mountains ...
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1answer
767 views

Is the convective heat coefficient always dependent on heat flux and delta T?

I'm having a difficult discussion with a colleague because I'm running heat flow simulations for a small heater (5 mm^2 area), and I insist that if we're going to run more electrical power through the ...
2
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1answer
1k views

Equation to estimate droplet volume falling from a needle of a known orifice diameter at a given flow rate

I am doing some research to see if there is a simple equation (or an equation that can be simplified) to estimate the volume of a drop of liquid falling due to gravity based upon the approximate flow ...
6
votes
2answers
1k views

How to calculate air velocity in a fan?

How to calculate air velocity in a fan and what data should I know ? So if I have a fan motor, fan blade and a battery, what data should I get from these items ? I think I will need to know the ...
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1answer
285 views

Isentropic vs Total pressure

I am confused between these two quantities: Isentropic pressure and Total pressure. Are they the same?