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

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Inertial force of fluids [duplicate]

Reynold's number is the ratio of inertial force to viscous force.I also know the definition of inertial force.but where does a fluid get this force from?what are the factors responsible for this ...
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2answers
39 views

Equations describing a counterflow heat exchanger [closed]

One of my experiments has a water-cooled apparatus. I plan on building a heat exchanger to keep the apparatus cool. However, I am not very good at thermodynamics and could use a hand. Also, from a ...
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48 views

What is the psi at the bottom of different tubes filled with water filled at the same height

if I have a 1 inch square tube with 144 feet of water I know I have about 63 pounds of water (63lbs ft**3) and 63 psi at the bottoms off the tube. If I have a 1/4 inch sq tube filled with water at ...
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69 views

Fluid Mechanics Paradox

This is a deceptively simple problem in fluid mechanics that I can't quite figure out because it produces a paradox. Suppose that there is a straw and a small column of water inside the straw, such ...
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Mechanics around a rail tank wagon

Some time ago I came across a problem which might be of interest to the physics.se, I think. The problem sounds like a homework problem, but I think it is not trivial (i am still thinking about it): ...
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Submerged water jet

I am trying to calculate at what pressure and speed water from a high pressure water jet will hit an object 100 millimeters away from the nozzle opening, but i can't figure it out. The nozzle will ...
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Why does the higher pressure of air underneath an aeroplane wing keep it flying?

With aeroplane flight, the wings are shaped so that the air that goes over the top of the wing has to travel faster than the air that goes below the wing. This means that the air below the wing has ...
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60 views

How long time before all the water in a lake has been replaced? [closed]

Studying hydrology, and in that context we've seen some information about lakes and the times it takes for the water to renew completely in them. This got me interested in finding out how this is ...
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26 views

Pressure required to overcome surface tension

Imagine I have a vertical straw, and that it is partially filled with water. If I were to decrease the radius of the straw at the bottom end, eventually surface tension would allow the water to remain ...
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23 views

Recommended books about vorticity

Could anyone suggest a good introductory book or any online resource about vorticity? I just now started to learn physics but I have a good mathematical background.
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flow rate measurement of a fluid

I had an experiment related to piping networks in my institute. In the experiment there was a device that was measuring flow rate based on rotations of a fan-like system. This created a doubt in my ...
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9answers
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Are eductors working on the Bernoulli principle?

This is a picture of an eductor. The wikipedia article claims that it works on the Bernoulli principle. The Bernoulli principle is famous due to the misconception about how aeroplanes fly and ...
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71 views

Atmospheric pressure changes on plastic bottle containing a liquid

We have a problem at work and I need some help on a theory. We ship a liquid in plastic bottles using a pump closure. Recently some of the bottles have been arriving to customers having leaked. The ...
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174 views

Continuity Equation in Differential Geometry

I'm looking for a derivation of the mass continuity that applies in general on symplectic manifolds. In particular the "the amount of change in the mass in a volume is just amount that flows in or ...
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1answer
39 views

Wall Shear Stress

I have the solution of a Navier-Stokes simulation with an incompressible, Newtonian fluid with laminar flow. Now I compute the wall shear stress (vector) as $$\tau_n = \mu (\nabla u) n,$$ where $\mu$ ...
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1answer
48 views

How does capillary action work in tubes which are closed at the top?

In all textbooks the examples and descriptions use tubes which are open at both ends. Our teacher remarked that if it were closed at one end like a test tube (albeit a thin one) even then capillary ...
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21 views

Rankine Oval is oval shaped

I'm studying Rankine oval and I have a question. How do you prove the equation for its zero streamline curve is in fact oval shaped? Is there some family of oval shaped curves including Rankine Ovals? ...
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1answer
17 views

How much load does an aqueduct support?

Recently, I found out about /r/InfrastructurePorn, and I found a particularly interesting photo of the Gouwe Aqueduct in Gouda, NE: It seems like the bridge that is supporting the boat wouldn't be ...
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2answers
127 views

Must flow be supersonic for disturbances not to affect upstream?

I'm studying oil production and found a fact that puzzled me. It states that fluid flow downstream of the wellhead must be supercritical in order not to disturb the flow upstream of it. From ...
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1answer
64 views

Explaining the shape of a raindrop and a drop of mercury

I saw on wikipedia that the shape of a raindrop is explained by using Laplace pressure. But why? Since the drop is in motion, we shouldn't be able to use an hydrostatic law, am I wrong? ...
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1answer
13k views

What is Convective acceleration of flow velocity?

I know that $\frac {dv}{dt}=a$ is acceleration, but: What is convective acceleration of a flow velocity? What is difference between $(v\cdot \nabla) v$ and $v\cdot (\nabla v)$?
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1answer
26 views

How does a fluid force behave at different angles?

I have a mock exam problem that deals with fluid forces acting at different angles. Here are the scans: Based on the description of the systems, I know that in (a) and (c), F is going to equal the ...
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1answer
32 views

How does the viscosity of a non Newtonian fluid (ooblek) affect its resistance to electricity?

I know the conductivity of water is based on whatever is dissolved into the solution, hence pure water does not conduct electricity. However, these ions in solution must also be free to move around. ...
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2answers
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Efficient way to move water pumping vs circulation [closed]

I have a basic question about efficiency of pumping. If I have a well of 100 meters depth, but water filled till top, and I want to circulate the water. What will be most energy efficient. A) ...
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1answer
48 views

I want to increase pressure of water in a closed vessel [closed]

I am trying to make a high pressure water jet using DIY hand pump which pushes water into a sealed vessel with non-return valve at the inlet. I am planning to do it by first closing the valve to the ...
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Why is a controlled shear test compared to the natural flow?

Looking for the areas where contolled shear stress (CSS, where force is fixed while rate of deformation is measured) and controlled stress rate (CSR, where conversely the force is measured while ...
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20 views

Phase diagrams and critical pressure

If a solid substance is pressurized past its critical pressure, what happens? Is the critical pressure only a factor when a substance is over the critical temperature also? On another note what makes ...
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22 views

Formula relating Pressure and Radius of a fluid in a pipe?

Let's say I have a section of straight pipe whose radius varies along its length with some sort of ideal fluid flowing through it. Is there an equation I can use to calculate the pressure of a fluid ...
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2answers
36 views

Why does an ideal gas not consist of identical molecules? [closed]

since the mass , temperature , and number of particles are the same , shouldn't the molecules be the same so that the pressure of the gad is inversely proportional to the volume.
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74 views

Why do water waves with longer wavelengths travel faster?

When wind blows over the sea, it excites a range of wavelengths. Why do longer wavelengths travel faster?
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Scale analysis for the vertical component of the Boussinesq equation to obtain a complete hydrostatic relation

This is actually an exam question which i have been trying to solve for my studies. Consider the Boussinesq vertical equation: \begin{align} \frac{\partial \widetilde{w}}{\partial t} = - ...
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41 views

Plane landing into a tunnel

Typical action movies cliché is landing a plane in a tunnel or even a flight in a tunnel. Let's drop any doubts about supreme heroic piloting skills of the characters etc. and focus on aerodynamics. ...
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1answer
599 views

How much more effective is it to stir in both directions?

I have been told that industrial mixing machines (say, for cake batter) switch directions periodically, first stirring in one direction, then the other, because this mixes the material more ...
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79 views

If a hole is drilled at the bottom of a vessel, why is the pressure of the liquid leaving the vessel equal to atmospheric pressure?

My question is similar to this one : Should the liquid come out of the tank if a hole is drilled in the vertical wall? , but I still don't understand why the pressure within a free jet of ...
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Which paramteres in the Weber number belong to the object and which to the fluid?

The Weber number (We) "can be thought of as a measure of the relative importance of the fluid's inertia compared to its surface tension" (Wikipedia): $$\mathrm{We} = \frac{\rho v^2 l}{\sigma}$$ So ...
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23 views

Difference between droplet and sphere?

So I was reading a section in a book(Advanced transport phenomena, Gary Leal), that was analyzing the equation of motion of a sphere, that is pushed by the action of an applied force F, toward a solid ...
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2answers
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How to quantify the spreadness of beam of air molecules as they escape from a capillary to a vacuum?

Consider a tube from an oxygen cylinder attached into a vacuum chamber. When the cylinder is opened, the molecules escape out into vacuum chamber. What makes the molecules spread out when they escape ...
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38 views

Excess corn starch in a non-newtonian fluid

I'm currently performing a high school experiment regarding non-newtonian fluid. And as a further exploration, I am aiming to figure out whether excess corn starch in the solution will cause a ball to ...
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In a flowing fluid, why the particles are gathering together under critic distance and separating above this distance?

In a flowing fluid has an inner pressure which gives it some abilities. So this fluid is flowing from narrow gates, the speed of flow is increasing while the pressure of fluid is decreasing. If we ...
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Fluid dynamics: valve and pressure drop [closed]

I have a question regarding valves: Let's assume a district heating system where you want to control the mass flow in a sub-station with a valve. Is (in normal cases) the diameter of the valve ...
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1answer
263 views

Why does (potential) fluid flow bend around a solid surface in the flow?

Potential flow obeys Laplace's equation with certain boundary conditions (i.e. no fluid penetrates the solid body in flow, and far away from the body, the flow is uniform with a given velocity and ...
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659 views

Liquid wave faster than sound in the above gas: possibility implications

I recently heard that tsunamis (meaning "harbour wave") can travel over 800 kilometres per hour (500 mph), not so far from the speed of sound in the air. May it happen, in general, that a wave in a ...
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4answers
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Why airplanes fly: the final truth

The questions about the reasons the aircraft fly are frequent among scientist, since the high school until now, even if I work on the other side of fluid mysterious world (the Low Reynolds numbers ...
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Definition of Buoyancy Flux

I've seen in some papers the definition of buoyancy flux as follows $$B = g \frac{\rho_a-\rho_0}{\rho_0}Q$$ where $g$ is the gravity acceleration, $\rho_a$ is the density of the ambient fluid, ...
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62 views

How to survive a direct hit of a Tsunami?

It's probably a question too general for this forum, but I'm not sure. The other day, I was in the beach, near the sea, and a big wave came towards me. So, instead of running from the wave, I decided ...
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How to predict the group velocity of the waves in the liquid?

The question appeard in the book. The phase velocity of the waves on the liquid surface is given by $$V_{ph}=\sqrt{\frac{2*\pi S}{\lambda \rho}} $$ where S is the surface tension and $\rho$ is the ...
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Why Flow meters are some times showing -ve fluctuating Values in Pressurized Pipe lines [closed]

In our Underground Water reservior we are pumping water by Hydro-pneumatic pumps to maintain same pressure till last connection. in order to measure the flow we have installed precise electromagnetic ...
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4answers
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Propellers and the Speed of sound

I was reading this website that described a novel wind turbine technology and it has this quote: In the mid-20th century, open propeller-driven planes with piston engines reached performance ...
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What would be an appropiate shape for a parachute?

I'm trying to design a parachute that minimizes the descent velocity, but I'm not sure what shape I should use. From what I've read, ellipse-shaped parachutes are too aerodynamic and minimize drag, ...
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Finding the inner rotational velocity of a vortex incrementally

This is for improving accuracy in a prototype hydro design spreadsheet. Hypothetically: In a 6.6m tank, water enters tangentially at 0.575m^3/s with a velocity of 0.7m/s. The height of the resulting ...