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

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Why Velocity is referred as momentum? [closed]

In many text books the velocity is referred to as a linear momentum which is being convected. For example the table in the following page My old conception is that the momentum or more precisely ...
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1answer
38 views
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1answer
64 views

Ideal shape of a water clock

The ancients undoubtedly discovered the ideal shape of a water clock by trial and error. In examining some ancient water clocks I notice the shape is different depending on the size. For example, a ...
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1answer
242 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 ...
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2answers
38 views

Is the force exerted by the container on the fluid and the force exerted by the liquid on the container equal?

I came across a question where i was asked to find the force exerted by the walls of a frustum shaped bucket on a liquid inside it . I found the force exerted by the liquid on the walls of the bucket ...
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1answer
33 views

Karhunen-Loeve transform of a repeating process

This question is inspired by measurements of an unsteady flow. I have some doubts about interpretation of principal component transform using Karhunen-Loeve theorem. I have (centered $\equiv$ zero ...
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1answer
204 views

How to calculate fluid(oil / hydrocarbon) loss under pressure

I'm trying to calculate the amount of fluid that would flow through an area dependant on the amount of pressure that there is. I'd also like to know the rate at which it would flow. Essentially I ...
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1answer
36 views

How to model terminal velocity as a function of gravitational acceleration?

Taking the most simplistic form of terminal velocity, $v=\sqrt{\frac{mg}{c}}$ I want to try and derive an equation that models the velocity as g changes in height.. Because obviously the terminal ...
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1answer
26 views

Without knowing fluid density, can it be correctly determined by measuring both kinematic and dynamic viscosity directly?

Without knowing a fluid's density, can its density be correctly determined by measuring both kinematic and dynamic viscosity directly, and then dividing these values? Can one determine cStokes and ...
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386 views

Lifting a wet object off a table

When there is a film of water in between an object and the tabletop it rests on, it is difficult to pull the object directly upward. However, when you slide the object, it comes off easily. What is ...
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1answer
65 views

What shape is a vortex?

When I see a whirlpool form around the drain in my tub, or see a hurricane on the radar, to my naked eye it looks pretty much circular from above. Is it a perfect circle? An ellipse? If not, ...
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1answer
29 views

How do you calculate force in a cone full of fluid? [closed]

I have no idea how to calculate the force the sides of the cone exert to the fluid (when the cone is at least partly filled with fluid) Can someone help me? A link or a short explanation will do
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Effect of water pressure on sinking objects

As I understand, water pressure increases as we go towards bottom of the ocean. So if an object* is thrown into water and it starts sinking with some speed, does the sinking object's acceleration ...
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2answers
172 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 $v$ ...
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1answer
432 views

Solve unsteady state Bernoulli equation for flow in a pipe

I am an engineer studying an unsteady-state flow through a pipe. The Pipeline has been cleanly cut into two halves, without deforming the cylindrical form of the pipe, exposing the contents to ...
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1answer
193 views

Bernoulli's Equation for flow of gas and changing area

My task is to determine the size of piping needed in a system. In this system, hydrogen gas flows horizontally in a $\frac{3}{4}\,\mathrm{inch}$ pipe and into a vertical pipe of a larger diameter. My ...
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2answers
610 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 ...
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1answer
172 views

What's the corresponding symmetry of enstrophy conservation?

In fluid mechanics, especially 2D turbulence study, people talk about conservation of enstrophy. But I can't really understand enstrophy very well, and what's the corresponding symmetry of enstrophy ...
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1answer
33 views

What is the difference between agglomeration and aggregation of nanoparticles?

I've been working with colloidal nanoparticles. Most of papers are about nanoparticles' aggregation while most of people I know use the term "agglomeration". Reading wikipedia convinced me that both ...
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1answer
40 views

How long it takes till the gas reservoir is empty?

We have a gas reservoir of internal pressure $p$ filled with an ideal gas of volume $V$. The gas is leaking to outer atmosphere till the internal pressure equals atmospheric pressure $p_0$. The ...
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1answer
20k 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 ...
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1answer
34 views

Velocity of liquid molecules in turbulent flow

I was solving some questions when I came across this: what is the velocity of liquid molecules in contact with the walls of the tube? and the answer was given that it can have any velocity and then ...
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1answer
77 views

Reconciling $Q=PR$ and $Q=vA$

Say we have a closed loop system, where the flow $Q$ is constant through a pipe. Then, at one segment of the pipe, we make the radius smaller. This causes the resistance $R$ to be greater, so the ...
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2answers
69 views

How to move a bubble which is trapped by the capillary pressure?

I have a question about how to move a trapped bubble in a tube. If we assume to have a horizontal tube, with water on each side of the bubble. The point to the left of the bubble is point 1, while ...
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1answer
204 views

Rayleigh-Plateau instability and optic [closed]

Let a liquid jet fall onto a surface. If the contact point is illuminated by a lase beam, rings of light around the jet can be observed . (pic.1) and we know it that the reason of this phenomenon is ...
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2answers
147 views

Derivation of Viscous Force

For viscous drag, the formula for the force is, $$ \mathbf F=\pm\eta A\nabla\mathbf u $$ where $\eta$ is the viscosity coefficient, $A$ the area and $\nabla\mathbf u$ the velocity gradient. How is ...
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62 views

How does an anti-g overall work?

Assuming that a human being would be exposed by 10g in a jetplane. This g-force will cause health risks without a proper g-protection. But with an anti-g vest such health risks can be minimized. One ...
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1answer
134 views

References on De Broglie-Bohm pilot wave theory

Are there any good books related to the not much popular De Broglie-Bohm pilot wave theory and its application in hydrodynamics, walking droplets concepts?
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3answers
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Do objects sink in ice?

The title explains it all. Do objects suspended in ice sink over time? You may remember the story of World War 2 planes that were found 260 ft under the ice which would be anachronistic with seasonal ...
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1answer
36 views

Direction of surface tension

consider the capillary tube shown in the diagram. According to my book the direction of surface at the point of contact is towards the surface as in diagram 2, but shouldn't it be away from as in ...
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1answer
24 views

Hot water tank elements [closed]

In a 2 element hot water tank, is there a kilowatt power usage increase if only one heating element is operating correctly?
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Physical intuition on bivector in fluid dynamics

Reading the M. S. Howe's Theory of Vortex Sound I've ran into this exoression and equation: Let $v_A$ denote the fluid velocity at a point A at $x$. The velocity $v_B$ at a neighbouring point B at ...
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2answers
44 views

Volume integral of pressure interpretation

If you have a fluid with with pressure field $p$ what is the physical significance of the the volume integral of the pressure $\int_V p dV$?
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115 views

Numerical model for a Air core Vortex, why it's still so limited? [closed]

The Question can be Formally presented as follows; How is the Numerical Model (CFD, Navier Stokes) of fluid dynamics for Vortexes at in it's limits? At this Publication from 2013 at page 48 is ...
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58 views

Why is the no-slip condition valid for fluids but not for solids?

You can obviously move a solid at a different speed along the surface of another solid, so how come the velocity of the fluid at the fluid-solid interface must be equal to that of the solid? What ...
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3answers
632 views

Why don't we talk about angular momentum at all in fluid mechanics?

People usually talk about similar (or maybe not?) things like vorticity or enstrophy in fluid mechanics, but no one talks about angular momentum, why?
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1answer
67 views

Air core Vortex; Physical explanation of the “air Entrainment Hook” at $F_{co}=0.7$

This question was originally asked in the Outlook of this study (page 197)1 $F_{co}$ combined Froude number, [dimensionless], and can be calculated $F_{co}\thickapprox v_D/ \sqrt{gh}$ where $v_D$ is ...
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1answer
216 views

How deep can a whirlpool descend?

My question is based around comparing the physics of a tornado against, what I imagine/assume to be the marine equivalent of a tornado, that is a whirlpool located either at sea, in a tidal region or ...
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1answer
134 views

Is it possible to generate one half of a Karman Vortex Street?

The Karman Vortex Street is a type of phenomenon which is generally illustrated by examples in which a long, solid, smooth circular cylinder moves at constant velocity through a fluid. The long axis ...
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2answers
86 views

Why does the pressure of fluid increase when the diameter of the pipe increases?

Assuming mass flow rate doesn't change and it's a closed system. Why does going from a smaller pipe to a large pipe cause an increase in pressure? What is the kinetic energy converted to as the ...
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4answers
128 views

Mass flow rate: Intuition of it being a product? [closed]

I'm looking for a good intuition for understanding the mass flow rate and specifically why it's a product. The mass flow rate is: $$density \text{(of fluid)} \times area \text{(of a face)} \times ...
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416 views

Why does this capillary action generator not work?

So I was doing a bit of reading. Apparently the the obstacle to generating energy from the forces driving capillary action is breaking the surface tension at the top of a capillary tube. It is just ...
3
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1answer
64 views

Cauchy stress tensor in different coordinate system

The general form of the cauchy stress tensor is given by the dyadic decomposition $$\boldsymbol \sigma = \sigma_{ij}\,\,\mathbf{e}_i \otimes \mathbf{e}_j$$ I want to know how this can be expanded in ...
3
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1answer
62 views

Intuitive explanation for subsonic Fanno flow

In most situations in physics, the effect of kinetic friction is to reduce the macroscopic kinetic energy of a system and convert it into heat, thereby increasing its temperature. but in the case of ...
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1answer
76 views

Evolution of normal of material surface moving at a steady velocity

I need some help with the following question: A material surface moves with the fluid with a steady velocity $\mathbf{U_{o}}$. Show that the unit normal $\mathbf{n}$ to the surface evolves ...
3
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1answer
179 views

Worthington jets explanation: fluid phenomenon

I don't understand the reason behind the formation of Worthington jets I've been reading a bit about Worthington jets Video 1, this phenomenon is caused when something is thrown to the water as we ...
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2answers
222 views

Why is the solution to the Blasius boundary layer problem self-similar?

In every course or textbook that I encountered so far, the authors transform the Navier-Stokes equations of the Blasius boundary layer problem into the Blasius ODE. The problem with many of those ...
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0answers
55 views

Reverse-engineering an equation of state

Suppose we have a fluid of some kind with a (let's keep it simple) barotropic equation of state: $p = p(\rho)$. Typically, I see that one starts with a function $p$ and $\textit{then}$ solves the ...
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1answer
1k views

Finding surface tension of water at certain temperature and pressure

The question is: Using the Young-Laplace Equation (if applicable), find the surface tension (dynes/cm) for water at 20 degrees Celsius with 2.5 psi. Round to the nearest tenth. ...
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1answer
67 views

What is the difference between the Method of Characteristics being formulated in terms of theta & alpha and theta & nu?

So I'm doing an MSc thesis involving the method of characteristics in rocket nozzles. My lecture notes have the MoC formulated such that the positive characteristics are defined as: C+ = Tan ( ...