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

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50 views

Dyson air blade principle as a propulsion system for an autonomous underwater vehicle?

Any thoughts on applying this principle to an AUV (autonomous underwater vehicle) ? if the power source is a battery, would its efficiency be beneficial to that of a propulsion system?
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2answers
95 views

Spontaneous motion in a wind tunnel

Suppose that a hollow truncated cone is placed in a wind tunnel with a steady wind speed $V$. The cone is placed in such a way that it's base of area $A_1$ faces the wind (rather than the other side ...
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3answers
453 views

Dyson Air Blade as a propulsion system?

I've read from many sources that Dyson Air Multipliers are more efficient and quieter than normal fans. Now, with the proof of concept, is it possible to use its principles as a propulsion system for, ...
4
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1answer
173 views

How to calculate strength of wind speed in a von Karman vortex?

I am working on a project involving Von Karman vortices coming off of a mountain. I was able to calculate the shedding frequency (thanks to tpg2114 in a prior question), but now find it necessary to ...
3
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1answer
89 views

Pipe in a flowing river problem

I'm working on a certain problem in fluid mechanics, which isn't really my strongest area. The problem is as follows: Curved pipe is partially submerged in a flowing river so that one end is pointing ...
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1answer
298 views

Compressible fluid flow through a branched pipe junctions

Backdrop: Designing a dust extraction system (LEV) with a branched junction. What principles allow for the calculation of volume flow rate and pressure at the inlets if the volume flow rate and ...
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1answer
89 views

What makes an abstract physical system describable by a “fluid” equations of motion?

We can describe (some of) the dynamics of many systems using fluid mechanics. Of course these include classical fluids like water, more exotic fluids like photon gases and the universe as a whole and ...
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1answer
331 views

Lotus effect dust removal

I have found hundreds of papers describing the contact angle of water droplet sitting on hydrophobic surface and the change between Wenzel Regime and the Cassie-Baxter regime. Now, as I understand ...
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1answer
46 views

Laminar flow in low-permeability material. Which is faster, gas or a liquid?

I consider a simple low-permeability material $(k \sim 10^{-18}\;\text{m}^2)$. Now I either apply a gas (e.g. nitrogen) pressure or liquid (water) pressure of - let's say $10\;\text{MPa}$ - on one ...
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1answer
63 views

Can a long pipe stop the flow of a liquid from a pump?

If a pump is discharging a fluid into a pipe, is it possible to add a long enough pipe such that the flow of the liquid will be stopped and none will come out of the open end of the pipe?
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1answer
52 views

Speed of liquid being blocked at end of pipe

How fast would water go if at the end of of a 1 inch diameter pipe was closed by a valve? The system is as follows: 5 meter high source of water that feeds a 1 in pipe. The pipe goes straight down ...
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1answer
60 views

Vortex shedding

So I was reading about vortex shedding, and got to know that it causes the building to resonate. Is there any way to use this resonance to generate electricity (maybe use quartz?) I am trying to make ...
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1answer
53 views

Vortex Air Intake

Why is a vortex air intake in an engine cause the fuel to burn more efficiently within a vehicle. Why is this more efficient.
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16 views

Eckert number in incompressible flow

Most of the time, temperature evolution for incompressible flow is computed assuming the Eckert number is negligible, that is the viscous dissipation and work of pressure variation is negligible ...
0
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1answer
24 views

Measuring cross-section area of a flexible tube (5mm dia approx)

I want to measure the avg. inner cross-section area of a flexible tube of outer diameter 5mm. Since the cross-section isn't a circle exactly, use of vernier caliper to measure inner diameter fails. ...
4
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2answers
112 views

The velocity of a cloud?

I noticed an unusually fast moving cloud this morning. My questions: What is the average velocity of a cloud on Earth? What is the greatest ever recorded cloud velocity? What factors affect the ...
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2answers
20 views

Which temperature to evaluate fluid properties in pipe?

I am always confused about which temperature to evaluate fluid properties at. Let's say I have a helical pipe and I know the inlet temperature, outlet temperature, and surface temperature and the ...
6
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3answers
534 views

Effect of water pressure on sinking objects

As I understand, water pressure increases as we go towards bottom of the ocean. So if an object* is thrown into water and it starts sinking with some speed, does the sinking object's acceleration ...
2
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1answer
25 views

Consequences of tensor form due to various symmetries

I'm reading a paper on 2D hydrodynamics, specifically on the drag of a rod in a 2D fluid. It is a low-Reynolds number regime, therefore linear hydrodynamics and the velocity of the rod can be ...
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2answers
399 views

Calculating Reynolds number for a viscous droplet

I'm trying to develop a very basic scaling law/unit analysis for viscous droplet formation, and I'd like to get some rough numerical values of the Reynolds number to play with. To be specific, I'm ...
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1answer
18 views

Darcy Flow in porous material - consider porosity in cross-section area?

According to Darcy's Law, the volumetric flow rate Q of a fluid occuring due to a pressure difference $\Delta p$ over a distance L and through a cross-sectional area A of a porous medium (volume V) ...
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2answers
28 views

Non-unique pressure for Navier-Stokes for incompressible fluid

The Navier-Stokes system for incompressible fluid says $$ \begin{aligned} \dot{\mathbf{u}} + (\mathbf{u}\cdot\nabla)\mathbf{u}-\nu\Delta\mathbf{u}+\nabla{p} &= 0,\\ \nabla\cdot\mathbf{u}&=0. ...
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1answer
52 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 ...
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31 views

Propeller Force & Momentum

An air stream is created by a propeller at velocity $\nu = 93.6\frac{m}{s}$ To calculate force applied by the propeller I used this formula: $$F=\frac{1}{2}\rho\nu^2A$$ where: $\rho = 1.29 ...
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2answers
66 views

Does space have a “radiation pressure” caused by subatomic particles?

If space is not actually a void, then there's something shooting around in it, I'm guessing a lot like molecules in a gas. Could we apply a $(PV/T = k)$ -like gas law to it. Obviously we're not ...
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4answers
11k views

Why can't helicopters reach mount everest?

Is there a reason why people can't just take the helicopter to mount Everest? Why is it that helicopters can't reach that high?
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1answer
163 views

How does a hinge affect the amount of a submerged material?

Suppose I have a rod that has a density of $X <1$. If I were to submerge that rod in water (density 1), I would expect $X$ of the rod to be below water and $1-X$ of it to be above water (simple ...
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1answer
37 views

Streamlines for steady flow problem

I need to calculate the streamlines for the steady flow given by the velocity field $$\mathbf{u}=(u,v,w) = \left( 0,\frac{y}{y^2 +z^2} , \frac{z}{y^2 +z^2}\right)$$ Now I've been able to notice that ...
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6answers
635 views

Tsunami dampening mechanisms

Encouraged by the zeitgeist let me ask the following: Is it feasible (now or in the future) to build systems a certain distance of a vulnerable coastline which can serve to dampen a tsunami before it ...
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0answers
7 views

Impact of Ag nano-particle size on OPV efficiency : simulation

I would like to simulate the impact of gold nano particles size on the efficiency of Organic photovoltaic devices(inverted ofcourse) looking for any simulation plateform where this idea could be done ...
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2answers
44 views

What causes drag in a fluid?

What causes resistance of an object to motion within a fluid like water? Please explain to me the molecular dynamics of the situation.
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1answer
76 views

Water falling, why does it spin?

I have noticed that water, when falling will rotate. Looking closely at a thin stream from a faucet and placing a flat object mid stream you will see the water is rotating. The further down the stream ...
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3answers
291 views

Home experiment question

I want to make a home experiment where I roughly explain the phenomenon of water remaining in a straw if you close one end of the straw. So I'm thinking that the weight of the water is pulling it ...
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4answers
71 views

In the formula for the mass of a drop of water on the end of a tube, is r internal or external radius?

In the formula for the mass $m$ of a drop of water forming on the end of a vertical capillary tube, $$m = \frac{2\pi r \gamma}{g},$$ does $r$ refer to the internal or external radius of the ...
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33 views

Fluidic gravity, TOE, what's your oppinion on this research? [closed]

It's interesting because we don't normally consider the "vaccuum of space" as a fluid, but it's becoming more apparent that it's an ocean of subatomic stuff. Here's a link to a book: Unified Fluid ...
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3answers
137 views

Particles scattering on fluids: breakdown of the effective continuum description

When does the macroscopic continuum description of a medium like a fluid break down? Say I'm interested in a scattering process of some particles with momentum $p$ and energy $E$ off a fluid of ...
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0answers
15 views

Modeling viscous fluid flow in the curved pipe

I want to know if there is any simple (results don't have to be very precise) way of modeling viscous fluid flow throught the curved pipe with elastic walls. I need to gather preassure values and ...
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1answer
27 views

Calculating water flow as function of the height of water above the inlet pipe

The Source of Water is Pond where the water level do change randomly . A pipeline of 200mm pipe diameter run for around 2500 m . The Height difference between the level of the inlet pipe and the ...
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2answers
1k views

Reynolds number and inertial force

The Reynolds number is defined as the ratio of ´inertial´ forces to viscous forces. $$ Re = \frac{\text{Inertial Forces}}{\text{Viscous Forces}}$$ Now, viscous forces make sense to me. They are ...
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23 views

What's the shocks mach number in this specific problem?

The shock wave I'm interested in occurs for a special Riemann problem, known as 1D Noh's problem. It means basically that two streams of air (equal density) are colliding at $x = 0$ for $t = 0$; I ...
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0answers
33 views

Translation symmetry and the non-conserved momentum in Viscous fluids

Even though a viscous fluid has a translation symmetry (invariance) for its Lagrangian , it still 'waste' Linear momentum. How come ?, isn't the rule that every symmetry yields a conservation law ?
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1answer
13 views

Backspin in outer space i.e. in a liquid with no viscosity: not changing direction?

No viscosity means no friction between neighbouring particles. I think outer space is such a place. So a golfball or a tennis ball traveling in space with a large spinning such as backspin would not ...
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3answers
1k views

Reducing the Tsunami impact using Nuclear bombs [duplicate]

I am a novice on this topic. However, I wonder if we use nuclear bombs against the tsunami, will it reduce the speed and impact of the tsunami. Is it possible to break the massive wall of waves using ...
3
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1answer
66 views

Why is the water on one side of a bridge choppy?

My daily commute take me across the Evergreen Point Floating Bridge on Lake Washington. I have noticed on several occasions that the water on the southern side of the bridge will be quite choppy ...
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0answers
131 views

How fast would a truck have to go to pull a pedestrian onto the road?

Let's suppose a pedestrian P is walking or standing next to a highway. Suppose a truck T will drive by the said pedestrian at speed V leaving distance L between the two. How fast would the truck have ...
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2answers
66 views

How much force is required to compress air?

How much force (Newtons) is required to compress normal air in a chamber to 2 atm? For example, if I had a sealed piston pump, how much force would need to be exerted in order for the air to be ...
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1answer
57 views

How quickly does air return to a vacuum chamber?

I know there are a lot of variables that affect how quickly this would occur. Any information on the topic would be highly appreciated. For sake of argument, lets say 1 square foot chamber, lets say ...
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2answers
291 views

Addes mass forces: can a force depend on acceleration?

My friend and I had a little discussion about added mass forces. I always interpreted "F=ma" as a cause-effect relationship, so I find rather uneasy to accept that the cause can instantaneously ...
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2answers
44 views

Is it possible that Cauchy stress be asymmetric?

According to conservation of linear momentum and angular momentum, one can derive that Cauchy stress tensor is symmetric and hence has only 6 independent components. Is it possible that, when breaking ...
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1answer
52 views

How does a ducted fan suck in air?

I am thinking of a simple ducted fan with a single set of rotating blades, no stator vanes behind. If the effect of the fan is to raise the pressure of the air, how is there flow into the fan against ...