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

learn more… | top users | synonyms (1)

-1
votes
0answers
7 views

How may I compare the pressure between fluid with relative motions?

According to Bernoulli's principle, the air flows faster has lower pressure. However, this does not quite explain when it comes into relative motions. I had the following question. The air in Ring 1 ...
1
vote
2answers
149 views

Fluid speed and fluid density

How does fluid density affect fluid speed? Basically I am trying to figure out if, with all other quantities remaining constant, would an increase in fluid density cause the fluid speed to increase/...
4
votes
2answers
375 views

Viscous Burgers equation physical meaning

The viscous Burgers' equation: $$ q_{t}+q\:q_{x}~=~\nu\:q_{xx}, \mbox{ where } \:\:\nu >0, $$ combines the nonlinear propagation of $q(x,t)$ and the diffusion. What is this equation for? (in ...
1
vote
0answers
68 views
+50

Static vs Dynamic pressure

According to Bernoulli's law, the narrower the tube where the fluid is flowing the lower its static pressure and the higher its dynamic pressure. Does this make any difference? If the dynamic pressure ...
9
votes
8answers
307 views
+50

How to pour water from a bottle as fast as possible

When one pours water out of a bottle, it first flows smoothly but then a pressure 'blockage' develops and the pouring becomes interrupted and turbulent, so that the water comes out in splashes. This ...
0
votes
1answer
42 views

Solving for speed of water in a system composed of tube & disc [on hold]

The system consists in two parallel discs of radius $R = 80\ \mathrm{cm}$ separated by a distance $d = 5\ \mathrm{cm}$, connected to a vertical tube of height $H = 1.2\ \mathrm{m}$ and circular ...
0
votes
1answer
109 views

If I was to poke two holes in a water filled balloon would it lose water twice as fast a a balloon with one hole?

if I was to assume that the only force behind water coming out of the holes is the pressure i.e., the height of the water remaining which is constantly changing (declining) as water leaves the balloon,...
0
votes
1answer
105 views

The name of effect of liquid flow inducing flow to neighboring layers of liquid?

How do you call an effect, when liquid or gas stream is involving the neighboring layers of matter also move? Like on videos of rocket engines testing, when exhausting gas sucks an air and steam from ...
1
vote
2answers
44 views

Force of water hitting a wall [on hold]

If you had a 8" pipe with 500psi stream of water exiting it and hitting a wall at 90 degrees 8 feet away, what would the force of the water on the wall be? Thank you all. Non-mathematician.
1
vote
3answers
42 views

How does an hydraulic ram pump work?

Hydraulic ram (wikipedia)(youtube) uses the water hammer (wikipedia) to pump water. Please help me understand how it works. I understand that the check valve catches the pressure from the water ...
8
votes
3answers
130 views

'Slapping' sound when trains pass each other

I have noticed that when riding in a train travelling at over 100 kmh$^{-1}$, a loud 'slap' can be heard when another train travelling at a similar speed passes in the opposite direction, followed by '...
4
votes
4answers
181 views

Is there any electric current in a continuous medium of moving charges?

Consider a continuous charged fluid (unlike in real life where charge is carried in discrete chunks like electrons) in a bottle. Suppose that the fluid is stirred in a circular manner and then left to ...
1
vote
1answer
47 views

Bernoulli equation and pumps [on hold]

I have a doubt on the use of Bernoulli equation for pumps. Consider the situation in the picture. I marked different points: $1$ on the surface of first tank, $2$ in the exit from first tank, $3$ ...
1
vote
3answers
69 views

Pressure just before the hole in a draining tank

I get extremely confused in fluid dynamics problem where the pressure in some points is required. Consider the ideal fluid in the tank in the following picture. I would like to understand what is the ...
2
votes
3answers
63 views

Flame shape and size(length) depending on gravity

How would the shape and size of a flame(from a simple candle for example) depends on the gravity? Suppose all the relevant information is known, like candle dimensions and its chemical composition, ...
9
votes
4answers
11k views

What equation of state is needed for liquid states?

I'm familiar with the ideal gas law $$PV=nRT$$ but I don't think it applies to liquids like water. If I'm wrong, please correct me! If I'm right, then what equation of state applies to liquids such ...
0
votes
1answer
166 views

Equation of a water pump with a nozzle

If I have a small water pump with a flow f (L/s) and maximal pressure p (bar) and attach its output to a small tube having on the other end a nozzle with an area A (m^2). What is the equation that ...
2
votes
2answers
117 views

Why does pressure decrease as velocity increases?

Bernoulli's principle states that as velocity increase pressure decreases. But higher the velocity, greater is the temperature and pressure must be high. Can you explain the situation in both the ...
0
votes
0answers
46 views

Inverted Bottle Physics - Bubble in, water out

With all due respect, I would like a practical answer, hopefully, to point my untrained brain in the right direction as to understand the variable elements of such system. I am not looking for the ...
3
votes
2answers
763 views

Force required to move a fluid out of piston at depth

I have a cylinder filled with water in it at the bottom of the ocean. Say 100 meters down. In this cylinder is a piston that moves up and down. Its job is to squish the water out the bottom of the ...
3
votes
0answers
34 views

Fluidics and surface tension

If a one cent coin is set carefully onto the surface of water horizontally (flat side parallel to the water surface). What are the relevant forces to determine if it would sink.
3
votes
2answers
274 views

Bernoulli's equation for flow between cylinders

Let's consider the situation bellow noting that the water cylinders aren't equal and there will be water flowing to the right (As indicated by the arrow) Taking Bernoulli's equation at the tip of ...
1
vote
1answer
251 views

Position based dynamics constraint scaling factor

Reading through Müller et al., Position Based Dynamics, 2007 I got lost when passing from equation (5) $$\Delta p = \frac{C(p)}{|\nabla_pC(p)|^2}\nabla_pC(p)$$ to equation (6) (and applying the ...
0
votes
1answer
33 views

Matching Bernoulli equation and Hagen Poiseuille law for viscous fluid motion

I thought that Bernoulli equation could be used only in the case of non viscous fluid. But doing exercises on 2500 Solved Problems In Fluid Mechanics and Hydraulics (Schaum's Solved Problems Series) ...
6
votes
2answers
276 views

Rayleigh-Taylor Instability dependence on acceleration direction

I'm trying to bolster my understanding of the Rayleigh-Taylor instability, and I've gotten stuck on the point of which fluid (more or less dense) is being accelerated into the other. Cases of uniform ...
8
votes
1answer
86 views

What is the physics behind “mocha diffusion”?

A friend shared a video on Facebook of a process for glazing pottery called "mocha diffusion." A light-coloured glaze is applied to a pot and then, while it's wet, a black liquid is dripped into it. ...
4
votes
1answer
56 views

Is the flow of a viscous fluid in free space under no pressure gradient always laminar?

Consider a (Newtonian) incompressible viscous fluid in three spatial dimensions, whose velocity field $\mathbb{v}=\mathbb{v}(x,y,z,t)$ moves according to the Navier-Stokes equations $$\tag{1}\label{...
0
votes
0answers
12 views

Scalar form equations for Non-Newtonian fluid

I am having trouble to write down the scalar form equations for this special class of non-Newtonian fluid (Oldroyd-B fluid), I really appreciate your input.
2
votes
1answer
528 views

Equilibrium between two water tanks

I've been reading about hydrostatic theory, however I couldn't find a similar case/exercise about my basic problem. I have two water tanks (same size) filled with different water heights, and ...
3
votes
2answers
75 views

What is the velocity in the Navier-Stokes equation?

I have been looking at the Navier-Stokes equation, and can't seem to find anywhere a clear description of what velocity it represents. From what I have read it could be any of the following: The '...
0
votes
2answers
57 views

Pressure due to weight of the fluid in fluid dynamics

In Bernoulli equation, the only term which corresponds to what one usually calls "pressure" is $p$, the other are still pressures dimensionally but their meaning is linked to kinetic and potential ...
0
votes
2answers
240 views

Viscosity for steam in the Reynolds number

In calculating the Reynolds number for a flow of steam in a pipe, this is the general formula I am trying to use: $$Re=\frac{\rho d v}{\mu}$$ with density $\rho$, pipe diameter $d$, flow steam $v$ ...
1
vote
1answer
42 views

Why does viscosity effect the normal component of stress in a Newtonian fluid?

The constitutive law for a Newtonian fluid is $$ \boldsymbol{\tau} = 2\mu \mathbf{D} + \lambda\left(\nabla\cdot\mathbf{v}\right)\mathbf{I}$$ where $\mu$ is the dynamic viscosity. Assuming we have a ...
0
votes
1answer
46 views

Why does laminar flow turn turbulent(*) in external fluid flow and why doesn't a fully developed laminar flow turn turbulent in flow through pipes?

(*:with increase in distance from the leading edge.) I would appreciate if you give detailed explanation for the first question and then apply the same logic to answer the second.
2
votes
0answers
35 views

Water floating on water [duplicate]

In the video made by the slo-mo guys as shown here, at time 1:47 comes a moment when a water droplet(almost completely spherical), is seen to 'float' on the surface of the water for a while. So why ...
1
vote
0answers
14 views

Modelling a flow due to an oscillating hemisphere?

Say I have a long cylinder filled with air, closed at one end and open at the other. Now say I place a compressible hemisphere at the closed end and make it oscillate (compression and expansion of the ...
2
votes
2answers
810 views

Dynamic water pressure from flow and diameter

I have to test some fire hydrants and need to get the dynamic pressure. For that I know I can use a Pitot tube but, I don't have one. After Googling a lot, I found two formulas allowing to compute the ...
5
votes
4answers
134 views

Could you filter coffee back to being pure water?

Okay, so coffee filters remove solid matter from the beverage, whilst leaving the remaining coffee intact for caffeiney goodness. But it's got me thinking. Is there a way we could filter the coffee ...
0
votes
1answer
358 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 ...
0
votes
6answers
75 views

Can I recirculate water from an open reservoir to the bottom of a bigger, closed one, without a pump?

A fountain head pumps water out of the main tank into a 'pond' reservoir. Can the water recirculate back into the main tank without the help of another pump? I'm sorry if this a dumb question. I'm ...
3
votes
3answers
74 views

Fluid mechanics paradox: The force needed to 'balance' a fluid using a piston

We know that the pressure in a fluid (like water) is dependent on the depth. Consider this example: For the first setup, solving the pressure at the bottom yields $P_1 = \rho gh = 1000kg/m^3 \bullet ...
1
vote
2answers
34 views

Conditions for flow incompressibility

The condition for flow incompressibility is usually stated as: $$ \frac{D\rho}{Dt}=0 $$ This sort of vaguely makes sense intuitively. However it seems more natural to me to understand ...
0
votes
1answer
150 views

How does a water-steam mixture behave?

Namely, if I mix a flow of steam that has density $\rho_s$, velocity $v_s$, and pressure $P_s$ with a flow of water that has pressure $P_w$, velocity $v_w$, and density $\rho_w$, how can I find the ...
-1
votes
0answers
20 views

general solution of biharmonic equation in polar coordinates [closed]

biharmonic equation appears in the fluid flow. I want to get the general solution of biharmonic equation in polar coordinates.
-1
votes
0answers
15 views

Difference between turbulence and instability

One of the tasks of my current research is to study the instability of a viscoelastic fluid in a co-rotating cylindrical system. I have observed some patterns but cannot say if they are unstable or ...
5
votes
1answer
282 views

Sum of forces with liquid in rotation

It's not homework (I'm teacher). I would like to compute sum of forces on this study : The shape is symmetrical like that I'm sure the center of gravity is in the center of the shape. I compute ...
0
votes
3answers
27 views

Application of Bernoullis identity for problem concerning hole in a container

Consider the following problem: We have a container of water with a hole on the side, and we want to determine the velocity of the stream coming out of the hole (at $S_2$): If we suppose $S_1>&...
3
votes
2answers
35 views

Prevention of fluid vortex formation

I've been looking for a way to prevent Vortex (whirlpool) formation in a pressurized vessel as it drains, but I am not having any luck finding the parameters at which vortex formation occurs. Is there ...
2
votes
2answers
40 views

Different locations of a pump in a tube

I'm confused about pumps in fluid dynamics. As far as I understand, the basic effect of a pump which deliver a power $\mathcal{P}$ can be described with modified bernoulli equation between a point $A$...
-1
votes
1answer
52 views

Buoyancy and natural convection in a stratified water tank

I'm working on a simple calculation-model for a hot-water-storage. At the moment I'm stuck on implementing natural convection. To calculate the temperature I've implemented a simple 1D-model in ...