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

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Can a submarine be powered by a wind turbine?

This is not intended as a realistic way for propulsion of submarines, it is just an interesting thought experiment. Say I want to travel directly towards the wind, only powered by the wind. This is ...
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7 views

Relativistic blast waves in medium of non uniform density

The relativistic outflow of a gamma ray burst drives a shock into the circumburst medium. This medium could have a uniform density $n_0$ or a density profile of the form, $n(r) \propto r^{-2}$. For ...
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20 views

Is this fluid-dynamics problem complete?

A wind tunnel test must be conducted to study an aircraft prototype with the following specs: $$ V_{prototype}=300\frac{Km}{h} $$ $$ \rho_{prototype}=1\frac{Kg}{m^3} $$ $$ MaxScale=1:5 $$ $$ ...
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1answer
14 views

Does moving air suck in air from left and right of its path?

When air is made to move (e.g. by a fan) it has a lower pressure than when it is still. Essentially, this moving air should become a low pressure zone relative to the static air around it and the ...
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34 views

What is meant by “surge” in fluid mechanics?

When reading about the action of opening a volume at vacuum submerged in a fluid at pressure, the fluid is said to "surge", i.e. to fill the void space (the vacuum). Per Google, surge is defined as a ...
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39 views

Basis for Derivation of Stokes Friction Law for Spheres

When deriving Stokes law one uses the Navier Stokes equation with the assumptions: low Reynolds number stationary flow in compressible flow leading to this version of the N.S : $$\nabla p = ...
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31 views

Acceleration of an bubble under the sea [duplicate]

An air bubble arises from the bottom of the sea. Find its acceleration if resistance force is proportional to $\rho Av$ where $\rho$ is density of water, $A$ is cross section area and $v$ is velocity ...
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32 views

Acceleration of an air bubble under the sea [on hold]

An air bubble arises from the bottom of the sea. Find its acceleration if: a) There is no resistance of water b) Resistance force is proportional to $\rho Av$ where $\rho$ is density of water, $A$ ...
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32 views

volume of the air bubble in the water

How does the depth affect the volume (the radius) of an air bubble in the water, if the temperature and density of the water are constant. Is there any relation combining this? Can I say that ...
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11 views

Hele-Shaw Flow/Hele-Shaw Cell Approximation

In the literature of microfluidics, the Hele-Shaw Flow/Hele-Shaw Cell Approximation appears often. Can someone briefly explain its origins and the related references for further reading? Thank you.
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Vortex in a Pipe / Solutions or approximations?

I want to study a vortex flow in a pipe; in other words helical flow. A couple introductory texts on fluid mechanics (e.g. Shames, Mechanics of Fluids) describe the solution to vortex flow in 2D: ...
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33 views

Origin of spin and direction in the magnus effect

If you solve the Bernoulli equation: $$p=p_0-\rho_0{v^2 \over 2}$$ using a complex flow potential for a flow around a cylinder: $$W(z)=v_0 z + {v_0 R^2 \over z} - {\Gamma \over 2 \pi } \ln(z)$$ you ...
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1answer
26 views

Is there a difference between solid-to-fluid convection and fluid-to-fluid convection?

I found an online calculator relating to convective heat transfer, but the calculator's description says it's for heat transfer between a solid surface and a moving fluid. However, the definitions ...
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116 views

Why do stellar boundaries exist?

What theorems or insights are available to decide wether a star with some given interdependence between its density, pressure and temperature distributions ought to have a boundary at a finite ...
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20 views

Prove thrust is double the dynamic pressure across area A [on hold]

Hey, I would be really thankful if someone could answer this for me. Prove that the value of the reaction thrust F equals twice the total dynamic pressure across the area A for an incompressible ...
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1answer
32 views

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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21 views

Liquid jet in the absence of gravity [on hold]

On earth, we have liquid jets which are falling and accelerating under influence of gravity ( this cause their radius to decrease ) My question is about liquids in the absence of gravity. Can we make ...
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11 views

Changing the Density of a liquid while its surface tension is constant

I'm working on Plateau-Rayleigh waves and I want to investigate the effect of density of the liquid on the wavelength of these waves How can I change the density of the liquid while its surface ...
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23 views

Water volume vs. pressure [on hold]

I have a pump that can deliver 14000 liter per hour. It is rated for a lift of 6m and a push of 36m. It has a 4m long 25mm hose as inlet(fed from a 30,0000l tank) and a 25mm outlet connected to 2m ...
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17 views

Vortex filaments in Stokes flow

Suppose that due to some sort of active process (like a moving boundary or an array of pumping source-sink dipoles) it was possible to create lasting vortex filament at low Reynolds number. While ...
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17 views

finding work done by the buoyant force on a submerged object [closed]

A flotation device is in the shape of a right cylinder, with a height of 0.500 m and a face area of 4.00 m2 on top and bottom, and its density is 0.320 times that of fresh water. It is initially held ...
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20 views

How to restict air flow without reducing pressure

I have a large volume of lightly pressurized air say 10000 cubic feet at 1 psi above atmospheric pressure. I want to move it to another area through a duct which is 20 in by 20 in. Airflow will be ...
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23 views

inlet velocity calculation from mass flow rate [closed]

I am struggling for following calculation, Could somebody please help me with this Mass flow rate and inlet velocity at 300 K and 40 mbar are 4.246 gm/minute and 32.8 cm/sec respectively, if the ...
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1answer
47 views

Tornado Vortex Low-pressure Force

If a tornado forms not contacting the ground and then moves over a large flat roof and contacts that surface, producing low pressure above that surface and having normal, higher atmospheric pressure ...
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66 views

Interpretation of Eigenvalues and Eigenvectors of an hyperbolic conservation law $\partial_t W + A \partial_x W = 0$

I read in a article dealing with a hyperbolic partial differential equations this statement : For any system of hyperbolic partial differential equations (pde), expressed as (1) ...
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1answer
78 views

Adding cinnamon to my coffee makes it stop whirling much faster: Why is thats?

When I stir my coffee in a cup, the fluid spins a long time, but when I pour cinnamon into the cup, the spinning fluid slows and stops very rapidly - why?
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44 views

What is the difference between vortexing and centrifuging?

I understand that vortexing will result in mixing / re-suspension of particles, and that centrifugation will result in the separation of particles. However, what is the difference in the physics that ...
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1answer
18 views

Fluid diodes for use with cryogens

My aim is to measure the pressure difference across a fluid diode (a tube which allows a fluid to flow easily in one direction and with difficulty in the other direction). Is there an equation which ...
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9 views

Is there a relationship between maximum flow rate of a fluid through perforations in a cavity and the flow rate of the fluid in the cavity itself?

I have a scenario where water is flowing horizontally through a (rectangular) cavity. The underside of the cavity has a set of perforations that look something like: and I need to determine the ...
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1answer
45 views

Physical meaning of multipole moment

Is there a physical interpretation for multipole moments? For a quantity governed by the Laplace equation ($\nabla^2 \omega = 0$), I understand that the general solution is given by the multipole ...
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1answer
83 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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63 views

Why does water flowing from a tap become thinner as it flows down

When I opened the tap, water flowing out from the openening became thinner as it flowed down. The same thing also happened when weather came out of a bottle. What is the reason for this? Is it ...
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31 views

Is flow speed between two pressures dependent on absolute or relative pressure difference?

Imagine you have a pressure chamber which is divided by a removable wall in two equal parts. Scenario A) Air pressure on the left side is 1 bar, on the right side it is 2 bar. Scenario B) Air ...
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65 views

Helmholtz decomposition allows incompressible flow with an irrotational component?

A vector field can be written in terms of irrotational and a divergence-free components. Using a 2D velocity field as an example, $ \vec v = -\nabla \phi + \nabla \times \vec \Psi$ Where $\vec \Psi$ ...
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1answer
36 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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3answers
276 views

Effect of initial suction power on siphon performance

Background I have a flooded crawl space and I'm using a long hose to siphon the water out. I do this as follows: One side of the hose is in the crawl space, and the other side down a hill in the ...
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1answer
49 views

A model for constant temperature of water in a container

I put some water in a container with initial temperature $T_0$ in a room, and the room's initial temperature is $T_a$. Now the container is filled to the maximum, so any more water coming in will ...
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1answer
52 views

How does water at different temperatures behave when they are mixed? [closed]

If I were to inject a constant flow of water at T1 into a reservoir of water at T2, how does that effect the temperature of the mixture at different points in the reservoir? In other words, what ...
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38 views

How do the Americas Cup Yachts sails work?

With the vast majority of sailing boats its pretty evident how the sails work to harness the energy of the wind to propel themselves forward. However on the modern Americas cup foiling yachts i can't ...
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Misunderstanding about Reynolds number

I am confused about Reynolds number. I am trying to use the formula to see if NASCAR cars have laminar or turbulent flow. But I am not sure how exactly to use the equation in order to do such ...
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1answer
36 views

Application of Stoke's Law

I was looking at Stoke's law and it says that you use it to calculate the drag force on a sphere passing through a fluid. Can i also use this equation to calculate the drag force on a car going ...
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1answer
29 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
45 views

Determining intake pressure of a cannula returning blood to an ECMO circuit

What are we trying to figure out: We want to know if it is possible to determine the pressure of the inlet for the catheter that returns deoxygenated blood to the ECMO system to help prevent ...
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0answers
23 views

Could a hydrophobic surface increase a liquid's resistance to compression/displacement?

Imagine a quantity of an aqueous (yet slightly viscous) solution is resting on a hydrophobic surface with a contact angle around 100°. A downward force is then applied as a (repellant) surface is ...
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70 views

Viscous forces with asymmetric gradient velocity in fluid mechanics

In fluid mechanics, the stress tensor writes $\sigma = -p 1 + \tau$ where the deviatoric part $\tau$ corresponds to shear. The viscous (volumic) forces are $\operatorname{div}\tau$. For a Newtonian ...
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9 views

Hydraulics: Booster bore variance - pedal travel (car)

I want to install an inline (remote) VH44 booster (vacuum assist "brake booster"), which has a 5/8" bore. My master cylinder (in this case, I'm installing it on the clutch line) has a 3/4" bore. ...
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3answers
67 views

How does the cross section of a stream of falling water decrease

Consider a continuous stream of water flowing down from a tap. Since the water flow is continuous, by equation of continuity, the cross sectional area of the stream decreases. But what makes the water ...
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35 views

What fluid dynamics equations are like in zero gravity?

I don't know if this is a proper question. I am not so familiar with fluids. I am just curious about what Navier-Stokes equations for fluids will look like in zero gravity. Are they stay the same? If ...
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43 views

What is actually the characteristic length in fluid dynamics description?

In many fluid-dynamics models and quantities (Reynolds number, Strouhal number... generally various turbulent flow descriptions) there is a parameter (usually $L$ or $\ell$) descripted as ...
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Extension of the advection diffusion equation with diffusion perpendicular to the flow

Assume you model particle flow in fluid in a cylinder by an advection-diffusion equation, thus taking into account both diffusion and bulk flow. What would happen to the model if you would, at some ...