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

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2
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2answers
407 views

Air drag coefficient value

Is there any equation that calculates the $C_d$ value in the formula of air drag ? $$F_d = \rho C_d v^2 A$$ I have found that there are tables for this constant but I am looking for the equation that ...
2
votes
1answer
1k views

Rotating fluid under gravity, fluid dynamics question

An incompressible inviscid fluid is rotating under gravity g with constant angular velocity $\Omega$ about the z-axis, which is vertical, so that $u = (−\Omega y, \Omega x, 0)$ relative to fixed ...
0
votes
1answer
639 views

communicating vessels formula

i having trouble with this formula (asked first in math.Se, i Didn't know the existence of physics.se) $$ Z1(t) = Ze+(\sqrt{Z1-Ze}-\frac{2S0}{S1}\sqrt{2g(1+\frac{S1}{S2})}.t)² $$ Z1 and Z2 are ...
14
votes
2answers
1k views

Why doesn't water come out of tap/faucet at high pressure when I turn it on?

(tap=faucet) When I turn a tap on full and then put my thumb over the spout covering, say, 90% of it, then the water spurts out. If I turn it on to, say 10%, then the water dribbles out. What's the ...
1
vote
1answer
365 views

Boundary condition for water waves generation

I am trying to model water wave propagation in 2D with CFD. What would be a suitable boundary condition to generate the waves on the left boundary? Currently I vary the fraction of water above the ...
2
votes
2answers
4k views

Why is the unit of hydraulic impedance/resistance kilogram per second and hypermeter?

I'm trying to figure out the unit of impedance in the hydraulic analogy of electronic networks. Assuming $$Z=\frac{P}{Q},$$ with $P$ as pressure difference, $Q$ as volumetric flow rate and $Z$ as ...
4
votes
1answer
3k views

Why do steam bubbles increase in size as they rise?

In the following video (a customer's review of a glass kettle), we can observe water boiling: http://youtu.be/jByY5I7Xk7w?t=2m55s As the kettle starts to boil at around 2:55, we can see large steam ...
2
votes
1answer
544 views

How was this pressure pulse propagation speed be derived?

Some lecture notes I was reading through claimed that a pressure pulse propagates through a liquid-filled tube (blood in a vein) with the speed $$c=\sqrt{\frac{A}{\rho}\frac{dP}{dA}},$$ where $A$ is ...
-1
votes
1answer
189 views

Force on pneumatic cylinder [closed]

A pneumatic cylinder is kept vertically straight on a weighing scale, which is set at 0 for the setup. now a force of 1000 N is applied on the cylinder. what is the reading of scale. assume the ...
-1
votes
1answer
635 views

Ping pong ball levitation control system question, modeling as a damper? [closed]

I am building a control system to levitate a ping pong ball at a given height in a clear plastic tube using an arduino and implementing PID control. I have to come up with a transfer function... I am ...
2
votes
1answer
4k views

How does smoke move in the air and how can I direct it so it will go to a place I want it to go?

Let's assume a close room with 1-2 people who only one of them smoking cigarette. What is the equation describe the smoking spreading? is it diffusion? what are the parameters is so? Is there a ...
2
votes
1answer
399 views

Calculating spacecraft water leak flow rate

A large container of heated water is floating in space. How can I calculate leak rate if a small puncture is opened? I'm assuming the water is kept at 298K and in the liquid state inside the chamber. ...
0
votes
0answers
93 views

Can a wave propagate in an elastic fluid in the absence of volume forces?

A motion (wave) $\mathbf{x}: \mathcal{B}_0 \times [t_0,t_1] \to \mathcal{E}:$ such that $q-o = \mathbf{x}(p,t)=(p-o)+\mathbf{a}_0 cos(\mathbf{k}_0\cdot(p-o) - \omega_0 t)$ can propagate in an elastic ...
5
votes
2answers
124 views

What is it called when a fluid will “jump” to grab onto an object that comes very close?

I'm doing an experiment where I bring a probe very close to a well full of fluid and then very slowly lower it to obtain some force deformation values. The material behaves very much like a fluid and ...
1
vote
1answer
84 views

Speed of a dynamic hydraulic system

We all have noticed that changing the temperature of the water in the shower is not instantaneous, rather the result is felt when the water that was in the tap works its way up to the showerhead. ...
2
votes
1answer
120 views

How can I calculate the amount of bubbles needed to lift a submerged body?

Our teacher had us come up with our own thermodynamics experiments, so I put a glass of water inside a vacuum-capsule. Inside the glass of water I have placed a non-floating object, a small plastic ...
2
votes
1answer
305 views

Reynolds number with hyper-viscosity

Is it possible to evaluate a Reynolds number when viscosity operator is substituted by hyper-viscosity operator at the power H (Laplacien to the power H) in the incompressible Navier-Stokes equations ...
2
votes
1answer
559 views

Rough diffusion rate of sugar water through a larger volume of water

I hope this a question that can be answered and isn't too vague. I'm also only after a very rough answer. I'm adding a small amount (~500mL) of sugar solution into a carboy with a much larger volume ...
3
votes
2answers
805 views

Why are continuum fluid mechanics accurate when constituents are discrete objects of finite size?

Suppose we view fluids classically, i.e., as a collection of molecules (with some finite size) interacting via e&m and gravitational forces. Presumably we model fluids as continuous objects that ...
1
vote
0answers
59 views

Why tea dust in a cup of tea seems to concentrate in the bottom center? [duplicate]

Possible Duplicate: Vortex in liquid collects particles in center Sorry for my bad English. :-) Hello ! Here is my question : If you enjoy some cup of tea, you may see that there are some ...
1
vote
0answers
81 views

Discharge of a propeller in a yield-stress liquid

What form does the discharge stream of a propeller take in a Herschel-Bulkley fluid, chracterised by having a certain yield stress, shear between layers only occurs beyond that stress. This situation ...
6
votes
0answers
374 views

What's the efficency of a steam jet pump?

Jet pumps or venturi pumps are often stated as having a "terribly low" efficiency, steam jet pumps specifically are usually describes as "only justifiable when there's an abundant steam supply anyway" ...
0
votes
1answer
490 views

Examples of immiscible or wall-climbing liquids

I am very interested in the physics of immiscible fluids. I would like to ask you if you know any source or list of experiments done by others, with two or three liquids. I am interested in the final ...
-1
votes
1answer
495 views

Dyson fans in ceiling? [closed]

Will it be feasible to use Dyson fans in the ceiling since it has to draw air from the back to "push" towards the front?
12
votes
3answers
540 views

Occurrence of turbulences in Fluid Dynamics from the equations of motion?

How can it be shown that turbulences occur in Fluid Dynamics? I think poeple imply that they develope because of the $\text{rot}$ terms in the equations of motion, i.e. the Navier-Stokes equations, ...
2
votes
3answers
2k views

What is the velocity area method for estimating the flow of water?

Can anyone explain to me what the Velocity Area method for measuring river or water flow is? My guess is that the product of the cross sectional area and the velocity of water flowing in a pipe is ...
1
vote
1answer
130 views

Surface tension of N non-mixing fluids

I am a mathematician, not a physicist, so please be gentle with me if I write something wrong. Consider a bounded, regular container $\Omega$, which is filled with the fluids $F_1,...,F_N$ which do ...
2
votes
1answer
1k views

What is the shear stress of a fluid?

One book defines the shear stress $\tau$ of a (Newtonian) fluid as $$\tau = \eta \frac{\partial v}{\partial r} $$ where $\eta$ is the viscosity. There is not much context, so I've made some guesses. ...
4
votes
2answers
192 views

Autocorrelation of sound in liquids vs gas

This is just a curiosity and you need to bear with me as my math skills were always sub-par and so is my English academic language. My specialty is Electronics but I have always been a programmer. ...
2
votes
1answer
116 views

Clouds in closed hydrosphere

Is possible estimate the needed size of an geodesic dome (like in the Eden project) for creating an real hydrosphere - especially clouds (and rain)? With other words, under what circumstances can ...
0
votes
1answer
15k views

To calculate pressure at point in a vertical water pipe of given diameter

Is it possible to calculate pressure at a point in a pipe, where a solenoid valve shall be placed, given that the pipe carries water (utility supplied, regular water) from an overhead tank (at a ...
1
vote
2answers
366 views

Horizontal Speed of Descending Parachute

I understand how to get the vertical (descent speed) of a parachute and its payload, but how could one find the horizontal speed/velocity of this parachute depending on the speed of the wind? (yeah I ...
6
votes
1answer
438 views

Free surface of inviscid fluid flow

The following problem seems like it should have a definite solution, but I've been thinking about it for months and haven't got anywhere. It might not be a well-posed problem, but if it isn't I'd ...
-1
votes
1answer
136 views

Air simulation environment [closed]

I will preface this with the fact that I am not a physicist...I am an engineer by trade. I am working on a research problem that will involve flight of an organism with varying shapes, and I am ...
4
votes
1answer
243 views

Effect of rotation on turbulence threshold for Reynolds number?

If the significance of the Reynolds number is: Then what is the effect of angular momentum on the transition from laminar to turbulent as in a convective vortex? Waterspouts, in particular, seem ...
3
votes
2answers
366 views

Hydrostatics: Log floating in water near a dam

So I am studying for a final and can't seem to solve this. There is a log floating in water and I need to find its weight. The question I have is what parts of the volume of the log count when summing ...
2
votes
1answer
1k views

Free Body Diagram of Fluid Statics Problem

I need help determining the forces, and the direction of them in this fluid statics problem. A hollow cylinder with closed ends is 300mm in diameter and 450mm tall. It has a mass of 27kg and a tiny ...
1
vote
0answers
765 views

Do the properties of two streams flowing into an engine add together when they mix?

Let's say I have two stream supplys that have separate mass flow rates, enthalpies, and velocities that flow into an engine. Upstream of the engine's inlet, the two streams mix to form one stream that ...
6
votes
2answers
493 views

Given a terrain, how to draw the stream flow path?

Assuming I have a terrain, as usual the terrain has ridges, creeks and all the characteristics that you can find on a real life map. Water flows from the top of the mountain into lower area, the path ...
4
votes
1answer
615 views

Is there something like the Poynting vector for hydraulic circuits?

The Poynting vector is a representation of the energy flux in electromagnetics, showing the amount and direction of power flow at different points in space. In electric circuits, the energy is not ...
0
votes
1answer
854 views

The shear stress assumption in Navier Stokes

Viscous fluid mechanics starts with the assumption that shear stress is linearly related to velocity by $$\tau = \mu\frac{du}{dy},$$ but it later turns out that some forces in high speed situations go ...
1
vote
1answer
2k views

Constant velocity in siphon?

I was recently reading the explanation for the behaviour of a siphon on Wikipedia, which uses Bernoulli's equation in its proof. The argument is generally pretty easy to follow, except for one key ...
2
votes
2answers
835 views

Can you please help with our water tank and spray system?

For our design project we are working with a client in Wisconsin to help them remove snow from their roof-mounted solar panels in the winter. We are designing a system to spray water a vertical ...
3
votes
2answers
207 views

Timber floating in the river

There's an old puzzle (but the physical it is): Lumberjack chop wood and float it down the river. He noticed an interesting feature: in the spring, when the water is comming, timber is nailed to the ...
0
votes
1answer
2k views

Is the static gauge pressure of a free jet always atmospheric?

Let's say I have a free jet of air leaving a pipe into the atmosphere. I know that the static gauge pressure at the pipe exit is equal to the atmospheric. But what about the static gauge pressure 10 ...
1
vote
1answer
272 views

Is the pressure at the outer hole on a pitot static tube equal to atmospheric pressure?

I'm looking at a pitot static tube question right now and I just need some clarification. There is the outer hole on the pitot static tube, not the hole that the air stream goes through, but the other ...
1
vote
0answers
161 views

How do I determine where the maximum air velocity around an object is?

I have a freestream of air directed at an object. Is there a way to find where the maximum air velcoty occurs with only having initial air speed and static pressure at the object?
4
votes
2answers
220 views

At what size will self-gravitation contribute more to stability than surface tension?

The governments of Earth have embarked on an experiment to place a massive ball of water in orbit. (umm... special water that doesn't freeze) Imagine this to be a fluid with a given density, $\rho$ ...
2
votes
0answers
1k views

What's the meaning of a pressure coefficient in fluid mechanics?

I have a jet of air leaving a contraction from a pressurized tank at a velocity of 28.8 m/s and it's being directed towards a small object equipped with static pressure holes on its surface that give ...
3
votes
1answer
337 views

Fluid Dynamics: Bernoulli Air Tunnel

I have the following question as part of a lab intro to explain the more complicated stuff I'l actually have to submit in the lab. I put all the questions here just to show my thought pattern/what ...