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

learn more… | top users | synonyms (1)

1
vote
1answer
36 views

What causes fizz?

When you go to a soda fountain and pour some soda into your cup, frothy fizz is generated at the top of the cup. What causes this? Obviously has something to do with carbonation, but when my cup is ...
0
votes
1answer
37 views

How do I find a stream function given a volumetric flow rate?

How do I find a stream function given a volumetric flow rate? The flow only occurs in one direction, between 2 plates, and I have no knowledge of velocity. I know that volumetric flow rate = ...
1
vote
1answer
33 views

External v.s. internal Reynolds number for cylindrical pipe

When calculating Reynolds number for cylindrical pipe, we were taught: $Re=vd/\nu$, where $v$ is the fluid velocity, $d$ is diameter, and $\nu$ is kinematic velocity. If you reorient the cylinder so ...
4
votes
1answer
58 views

Why does wind sound the way it does?

You can obviously hear wind. From everyday experience, the stronger the wind, the louder its sound. But this sound is always similar, and quite distinctive, noise-like. Can one compute the spectrum ...
2
votes
1answer
103 views

Normal Modes for Standing Waves in 1-D Acoustic Ducts with Arbitrary (but real) Impedance Jumps

Let's say we have a 1-D duct, such as this: Where $Z_i \equiv \frac{P}{US}$ is the acoustic impedance, L is the length of the duct in question, and S is the area of the cross-section. In general, ...
0
votes
0answers
23 views

Pulse wave velocity

I heard that the pulse wave velocity is higher than the speed of blood flow through the arteries. This is obviously due to the ellastic properties of vessel walls. I would like to have the most ...
1
vote
1answer
51 views

Derivation of Kelvin's circulation theorem

In the derivation of Kelvin's circulation theorem, I take the material derivative of circulation, or \begin{align} \dfrac{D\Gamma}{Dt} = \dfrac{D}{Dt}\oint_C \vec{u} \cdot d\vec{\ell}. \end{align} ...
0
votes
1answer
34 views

What is the force exerted by a fluid on the corner of a right-angled tube? [closed]

It is to be considered that the water is entering and leaving at the same velocity v. I have found a solution but cannot understand it as it is using a term dM/dt which I cannot understand in this ...
1
vote
2answers
95 views

Is surface tension characteristic of a fluid?

Does surface tension depend only upon the nature of the fluid or on other factors too like the liquid-solid or liquid-gas interface? I saw in my book definition that $$S = U/A,$$ where $U$ is the ...
0
votes
1answer
45 views

Entropy in ideal fluids [closed]

Can you derive a conservation law for entropy per unit mass? I know that there is a proof for this conservation. My assumptions are: $(\nabla p)/n = D \vec{v} + \vec{v} \cdot \nabla\vec{v}$ (Euler ...
1
vote
2answers
37 views

How many water wheel can fit on a river until another one produces zero energy?

Mostly what I'm after are the factors I need to know to do the problem. Imagine we're in the days of Leonardo Da Vinci. And pizza is everyone's favorite food. And there's a river that goes on ...
0
votes
1answer
48 views

Would a Tesla Valve create a pressure differential?

Start with two sealed boxes that are the same in every way. Then connect them by a tesla valve so that air could flow between them. Over time through entropy would the one-way preferential flow of ...
1
vote
1answer
44 views

Reconciling the Temperature and Pressure Relationship in Gasses vs Fluids

I've been trying to wrap my mind around this for the last couple of days to no avail. I suspect that much of my confusion comes from the fact that I have not yet taken a class specifically focused on ...
0
votes
1answer
41 views

reynold's transport theorom contradicting bernoulli equation

I am considering a funnel with two areas $A_1$ and $A_2$ with velocity at the interface as $V_1$ and $V_2$ respectively. let pressures at those areas be $P_1$ and $P_2$ . For simplification we assume ...
0
votes
2answers
131 views

If I Blow smoke out my window, will any come inside my room?

My girlfriend and I have got into a lively debate about whether or not my flatmates can smell the smoke I blow out my window. Can you help us? Here is the scenario. The smoker, places himself ...
0
votes
1answer
44 views

Total energy of the fluid

Consider a one dimensional system with fluid in it. Mass and momentum balance equation of the system are (in the absence of external forces and assuming Newtonian behaviour valid for viscocity), ...
1
vote
0answers
30 views

What is the definition of governing equation? [closed]

What is the exact definition of the governing equation? What is its purpose? What makes it different than other equations of physics? Why they are necessary?
1
vote
0answers
25 views

physical constraints on fluid models based on shannon entropy/information

Is it possible to use the idea of entropy to constrain mathematical objects meant to describe physical fluid motion which is virtually incompressible and virtually without friction. More precisely ...
0
votes
0answers
20 views

Drag in Free Fall [duplicate]

I was recently thinking about how I might go about describing projectile motion with air reistance. The problem I encountered was that air resistance might cause some acceleration for a short period ...
1
vote
0answers
60 views

Mathematical understanding of vortex solitons

I am wondering if anyone has ever come up with a mathematical description of something that (to me, and I am no expert) look like soliton vortexes. The example I can think of is if you create two ...
0
votes
1answer
32 views

Diffusion (2 species) versus advection (1 species)

Why do we see diffusion with 2 species but advection with a single species if both cases involve molecules spreading to increase entropy? To take a physical example: Let's say I have a box with two ...
2
votes
1answer
62 views

Velocity of water column

If an air filled tube 5 km long with a diameter of 20 m was submerged vertically under water one end 5 km underwater and the other end at the surface, how fast would the water column rise if the ends ...
0
votes
2answers
68 views

When I open a window to air out the room, how does the smell disperse?

Let's say I'm in a room with some kind of noxious stink, possibly of flatulent nature. The quickest way to right the world that comes to mind is to open a window. When I open a window, how do the ...
0
votes
0answers
35 views

What is the use of thermal boundary layer and velocity boundary layer?

In heat transfer by convection, why must we show the thermal boundary layer and the velocity boundary layer. What do they signify? Also how are these terms related to the Prandtl number? And what is ...
0
votes
0answers
12 views

How does submerging tubing affect 'airflow' when the tube is filled with water also?

The question probably isn't asked well and I feel sort of stupid asking it but... So I have a small piece of tubing connecting two chambers (where both the chambers are partly filled with water and ...
1
vote
0answers
24 views

What is the “flow area” for a screen/mesh? [closed]

I'm trying to find out, for a given duct area, how large an area of woven mesh (like bug screen) do I need for minimal pressure drop? Is there a rule of thumb or approximation for "effective flow ...
0
votes
0answers
60 views

Flow in a cylindrical pipe

A cylindrical pipe is, at the left of section A, divided by a plane passing through its axis. The upper half is supplied with water at a velocity $V_1$, the lower half is supplied with water at a ...
1
vote
3answers
77 views

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 ...
1
vote
1answer
27 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 ...
0
votes
0answers
31 views

Is this fluid-dynamics problem complete?

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

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

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 ...
1
vote
2answers
140 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 ...
0
votes
1answer
65 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 = ...
0
votes
0answers
33 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 ...
0
votes
1answer
78 views

Navier Stokes : what about angular momentum?

I play with CFD for a while, and suddenly, a transcendantal question raises: :-) Navier Stokes is basically Newton applied on a continuum in Eulerian. For solids, we would consider linear, but also ...
0
votes
2answers
120 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 ...
0
votes
0answers
21 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.
1
vote
0answers
35 views

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: ...
2
votes
0answers
48 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 ...
1
vote
1answer
74 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 ...
6
votes
2answers
157 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 ...
3
votes
1answer
71 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 ...
1
vote
0answers
27 views

Liquid jet in the absence of gravity [closed]

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 ...
0
votes
0answers
16 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 ...
0
votes
0answers
36 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 ...
1
vote
0answers
27 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 ...
3
votes
2answers
79 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) ...
1
vote
1answer
92 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?
0
votes
2answers
139 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 ...
5
votes
1answer
20 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 ...