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

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130 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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1answer
238 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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2answers
637 views

How much of the forces when entering water is related to surface tension?

When an object enters water with high velocity, (like in Why is jumping into water from high altitude fatal?), most of it's kinetic energy will be converted, eg to accelerate water, deform the object ...
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152 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 ...
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1answer
57 views

Minimum amount of fluid to experience turbulence?

Turbulence is a challenge to model and simulate: "When I meet God, I am going to ask him two questions: Why relativity? And why turbulence? I really believe he will have an answer for the ...
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1answer
84 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. ...
2
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1answer
32 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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1answer
66 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
63 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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44 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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1answer
52 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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12 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
105 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 ...
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1answer
64 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 ...
4
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1answer
133 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
355 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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0answers
51 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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2answers
79 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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2answers
91 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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0answers
30 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
205 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 level ...
2
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4answers
216 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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0answers
41 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
48 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
36 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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1answer
113 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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1answer
253 views

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

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. Assuming L is a reasonably ...
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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 ...
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2answers
261 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
66 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
101 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
158 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 ...
2
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0answers
55 views

Is there any connection between “Lagrangian and Eulerian formalism of fluid” and “Heisenberg and Shrodinger picture”

Is there any connection between "Lagrangian and Eulerian formalism of fluid" and "Heisenberg and Shrodinger picture of Quantum mechanics"? Thanks!
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1answer
146 views

Have I calculated the air flow of this fan correctly?

To calculate air flow capacity of a fan in cubic feet per minute (cfm): multiply the average air speed you measured in feet/minute (fpm) by the area of the fan face in square feet. (Area of circle =þ ...
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1answer
44 views

Atmospheric heating and the reduction in viscosity

The oceans are becoming less viscous as they are heated. I'd imagine a similar effect is likely occurring in the atmosphere as well. What, if any, effect would this reduction of viscosity have on ...
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3answers
99 views

What is sound in terms of acoustic sources?

Sound is nothing more than small amplitude, unsteady pressure perturbations that propagate as a longitudinal wave from a region in space which created it (called the source region) into a quiescent ...
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2answers
150 views

Does vortex shedding exist along the surface of an object?

Vortex shedding occurs due to the detachment of flow. The typical example is for the oscillating wake behind a cylinder, and has a frequency related to the size of the object. I want to know, if a ...
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4answers
2k 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 ...
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1answer
513 views

free falling object with air resistance?

we already know that if we plot speed vs time of free falling object it will be y=gx graph because we know the acceleration is gravity. If it have air-resistance acceleration will be change right?. ...
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0answers
42 views

How to get discretization coefficients of matrix $A$ in Finite Volume Method (FVM)? [closed]

First we have Discretization of the Transport Equation $$ \frac{\partial \rho \phi}{\partial t} + \nabla(\rho U \phi) - \nabla (\rho \Gamma_\phi \nabla \phi) = S_\phi (\phi) $$ In Finite Volume ...
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2answers
152 views

Can an extremely small force lift a mountain in a hydraulic system? If not, then why not?

As you see in the picture, a car can be lifted with a small force F1. Here it is shown that 'F1 . A1 = F2 . A2'. What will happen if A1 is of the size of a pin's cross-sectional area. Can a child ...
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0answers
24 views

Explicit solutions to simple one-dimensional fluid flow problems? [duplicate]

In order to test and verify numerical simulation results, I'm looking for explicit (or approximate) solutions to simple fluid flow problems to recalculate (like e.g. the pressure development during ...
6
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4answers
250 views

If I bury a cylinder (top end sealed) in sand, how much force do I need to pull it out?

Let's say the cylinder has a diameter equal to its height of $25\;\mathrm{cm}$ the cylinder is sealed at the top and filled with sand the cylinder is also buried in the sand at sea at a depth of ...
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3answers
452 views

How do birds generate thrust?

I have been watching this video carefully and I want to know how the wings of birds generate thrust. This is because the wings are more or less flapping up and down --- generating the lift. But I do ...
2
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1answer
2k views

What is the difference between dispersion and diffusion?

What is the difference between dispersion and diffusion? Currently I believe, that diffusion is the mixture of molecules due to Brownian motion. So I read everywhere, that it happens with magnitude of ...
3
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2answers
142 views

Speed of Sound/Push in Supersonic Flight

I've learned from things like the Veritasium Slink Drop and the old "break the speed of light by pushing on the end of a very long pole" thought experiment that objects have a "speed of push" which is ...
2
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1answer
156 views

Can a human body supercavitate to survive water impact?

Inspired by this analysis of a human (OK, Captain America) hitting water feet first at terminal velocity, I'm wondering if supercavitation would be possible and whether it would improve your chances ...
3
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1answer
77 views

Mathematically impossible for a vortex line to have loose ends?

Could someone show the math behind it? Source : "A vortex is a bunch of air circulating around itself. The axis around which the air is rotating is called a vortex line. It is mathematically ...
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85 views

Why does air circulate on an airfoil — The Kutta Condition

Why does the air circulate on a flowing airfoil, thus giving rise to increased velocity (circulation + relative airspeed) above the wing and hence decreased pressure.
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0answers
60 views

Why do floating objects attract? [duplicate]

Objects floating on the surface of calm water seem to be attracted to one another and tend to come together in a drift. Is this attraction like gravity?