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

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finding equation of a water droplet

I have a water droplet which is falling down through its gravity. I've supposed that my droplet is an ellipsoid and I want to find the equation that represents this ellipsoid in XYZ coordinate system. ...
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1answer
96 views

Kinetic energy of fluids in Venturi Injector

Since the cross sectional area is smaller in the middle the water flows faster and experiences a smaller hydrostatic pressure. Additional mass is sucked in from the middle tube and gets accelerated so ...
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1answer
68 views

Which moves faster in a time $t$: $A$ or $B$? [closed]

Suppose we have two objects, $A$ and $B$, both made of the same substance. They also have the same shape (e.g. two spheres), but $A$ is larger and therefore more massive than $B$. Both $A$ and $B$ ...
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1answer
410 views

I would like to know what variables to consider when I experiment with pouring from bottles and the “glug” effect?

I am a middle school science teacher and want to model a science fair project for my students. Specifically I want to investigate using a vent in the top of the handle of a gallon milk jug to ...
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51 views

Can we take transport equation of imaginary quantity?

In the RANS equation we approximate the nonlinear fluctuating terms to eddy viscosity times strain rate. Then by using turbulence models like Spalart-Allmaras etc, we take the transport equation of ...
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766 views

How to calculate the centerline velocity inside a pipe?

Well, I was reading about fluid-solid/structure interaction models for make a simulation in COMSOL, and in few papers about it [1] I find an expression about the centerline velocity. I understand the ...
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2answers
110 views

How stable are Benard Cells when the thermal gradient begins decreasing?

I've found lots of information on the formation of Benard Cells and convection currents but very little information about what happens to the self-organized structures when the energy gradient being ...
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1answer
103 views

Does this type of equation for an airfoil exist?

In a common airfoil, such as a plane's wing, diminished pressure over the top of the wing and increased pressure under the wing, generally speaking, will cause the wing to lift. Now, a man standing ...
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3answers
244 views

Airway resistance greatest in tertiary bronchi

As the title reads, why is airway resistance greatest in tertiary bronchi? Primary and secondary bronchi have a lower surface area than tertiary bronchi so what makes resistance greatest at this ...
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1answer
480 views

Pressure inside a plastic bottle filled with water and squeezed by X weight?

I'd like to know how it'd be possible to calculate the pressure inside a plastic bottle filled with water and squeezed by say 20 kg sitting on the bottle, which is lying on its side (so that ...
7
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1answer
585 views

Does Liquid Immersion protect against G forces?

I'm under the impression that if an object is immersed in water it can be protected from the effects of Gravity - or in other terms appear to be in a 0G enviroment. Typical examples of this include ...
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1answer
103 views

Is there an equilibrium for water and air in a tank?

I'll try my best to explain my question with examples because I don't have much knowledge on the theory. So say that I had a block of water in air, a cube of water, that is dropping. If the cube wasn'...
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1answer
78 views

Can a Newtonian fluid have a non-linear speed distribution?

As far as I know, a Newtonian fluid follows the equation: $\frac{du}{dy}=\frac{\tau}{\mu}$ (where $u$ is $x$-axis speed and $y$ the height from the contact surface fluid-solid.) This leads to the ...
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1answer
3k views

Flow Resistance and Pressures in Split Pipes

I am doing some simple flow experiments and my instruments are giving me strange results - I think they are broken, I need a sanity check for my understanding of the flow in my system to confirm it. ...
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1answer
88 views

Bernoulli Equation Reference Frames

I'm trying to understand an example on page 107 of "Fundamentals of Fluid Mechanics" seventh edition by Munson, Okiishi, Huebsch, and Rothmayer. The setup of the question is: Consider a flow of air ...
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90 views

Should the liquid come out of the tank if a hole is drilled in the vertical wall?

This is a tank filled with water kept on ground. The points $A$ and $B$ are at 'same horizontal level', hence, as per an interpretation of pascal's law, pressure at $A$ must be equal to the pressure ...
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1answer
93 views

In a column of fluid does density vary?

In a column of fluid does density vary?
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2answers
1k views

Gas viscosity at high pressure, high temperature

EDIT 1 PER COMMENTS I am wanting to model nitrogen gas viscosity as a function of pressure and temperature OR learn of an existing equation that models nitrogen viscosity for the pressure and ...
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1answer
72 views

Delta wing flow patterns (straight and yawing)

I was wondering the differences between fluid patterns and their consequences when a delta wing is straight and yawed slightly.
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1answer
44 views

Does blowing bubbles at the front of a ship increase efficiencies?

Would this make an air envelope that the hull could smooth past with less friction?
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910 views

What could be added to tap water to reduce air bubble formation on a submerged object?

Submerge your hand in a bucket of water. Some air bubbles appear immediately and others add to the surface of the hand over time. Is there anything that could be added to the water to reduce the ...
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0answers
128 views

Vortex doublet in 2D

I am not from physics background and I am looking for some easy source for learning vortex doublet related theory. Can anyone suggest me something please?
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2answers
287 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 ...
2
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2answers
226 views

Kernel normalization in Smoothed Particle Hydrodynamcs

I am trying to write some code for a fluid simulation. I have read about Smoothed Particle Hydrodynamics (SPH) and my question is related to the properties of the smoothing kernel. How do I set the ...
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128 views

Determine flow rate of side outlet from known flow rate in river

What reading is recommended to determine the initial flow rate of water through an intake from a river, given known intake diameter, and angle of incidence. I am aware that Bernoulli's equation and ...
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2answers
4k views

How Reynolds number was derived?

I'm studying fluid dynamics and recently the formula $Re=\frac{\rho vd}{\eta}$ was presented to me. I'm curious to know how Reynolds came up with this relations between this different variables. Did ...
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1answer
633 views

How does the divergence theorem justify the integral form of the continuity equation?

I vaguely understand the continuity equation (at least its integral form), but I don't really understand the differential form of the continuity equation. I'm having trouble understanding how to ...
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3answers
189 views

In terms of scale, where does the concept of Reynold's number cease to have meaning?

The Reynolds number is classically described in terms of pipe geometries but its use has also been usefully extended to other more complex surface geometries to predict transitional flow behavior. But ...
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2answers
392 views

What is atmospheric stratification?

In the context of atmospheric stability, what are the meanings of stable or unstable stratification? What is stratification?
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1answer
135 views

Is turbulence due to the inertia of the fluid?

Turbulence is the time-dependent chaotic behavior seen in many fluid flows. Why is it generally believed that turbulence is due to the inertia of the fluid?
5
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1answer
435 views

Variational form of Euler's incompressible fluid equations?

I am trying to derive Euler's incompressible fluid equations in terms of a variational stationary principle. Given Euler's flow equations: $$\frac{\partial v}{\partial t} = -\nabla p$$ $$\nabla\cdot ...
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0answers
65 views

Boundary Conditions for axisymmetric stream functions in a pipe

I'm solving the equation $$ \frac{\partial^2 \psi}{\partial r^2}+\frac{\partial^2 \psi}{\partial z^2}-\frac{1}{r}\frac{\partial \psi}{\partial r} =-\omega_\phi $$ in a cylindrical pipe, where $\psi(r,...
2
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1answer
191 views

Rigorous definition of pressure in a fluid

We briefly introduced some terms at the start of my Fluids class, and one of them was pressure. I'm looking for a rigorous definition of pressure. Wikipedia gives this definition for pressure: $p = \...
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1answer
413 views

Physical Meaning of Divergence of Convective Velocity Term

When taking the divergence of the convective velocity term, I get the following: \begin{align} \nabla\cdot\left[\mathbf u\cdot\nabla\mathbf u\right]&=\frac{\partial}{\partial x_i}\left[u_j\frac{\...
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4answers
673 views

Why does a bubble take a spherical shape?

I suspect this has something to do with thermodynamics and the isoperimetric inequality and I'm interested in a mathematical derivation of this result.
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1answer
254 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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3answers
2k views

How long does it take to equalize pressure of two gas containers?

I'm looking for an equation that will tell me how long it takes for two gases at two different pressures to equalize their pressures. As a more concrete question, Container 1 has gas at pressure P1. ...
5
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1answer
298 views

meteorite-like impact of a drop of yogurt

When I throw a drop of Yogurt (through spoon) into a dish of Yogurt, it caused something like a meteor hitting the earth and something occurs similar to the place a meteor hitting the earth(Barringer ...
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1answer
313 views

Bernoulli Equation Paradox

Imagine a funnel with an extremely wide mouth, filled with water. Attached to the stem is a water pump that pumps water upwards (into the funnel). Water is being pumped in at the rate of Q. The cross ...
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2answers
842 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
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2answers
2k views

How does train back draft work

Quoting platforms and stations : Fast trains can create a vacuum called a ‘back draft’ that can blow you over or suck you under a train. How does that work ? I thought that the volume of air ...
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2answers
268 views

Time for water levels to equalize

Suppose that someone dumps some quantity of water into the ocean somewhere. Also, assume that no other water level changes are occurring. How long does it take for the change in water level to "...
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1answer
216 views

Can one model a spiral galaxy with a similar manifold to one for a whirlpool?

My question is more of a phenomenological question than literal, since the forces involved are very different. When one looks at the distortions (or wrinkles or whatever you wish to call them) in the ...
3
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0answers
95 views

What is the relationship between the angular speed and the diameter of the eye of a water vortex?

In a water vortex formed in a plastic bottle, what is the relationship between the angular speed of the water and the diameter of the hole in the cap? I would have expected that according to the ...
2
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1answer
75 views

Estimate the maximum distance of water spatter

There is a faucet dripping water from height $H$ onto a smooth, horizontal ceramic surface, and I need to give a upper bound of the maximum distance between the water spatter and the point directly ...
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3answers
120 views

If a body is floating in a static fluid, then the volume of the displaced fluid equal to the volume of the inmerse part of the object (proof)

Suppose an arbitrary body is floating in a static fluid, either totally or partially immersed in it, then the volume of the displaced fluid equal to the volume of the immersed fraction of the object. ...
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1answer
114 views

How to design windy area - what variables?

When you're walking around malls or parking structures, or a building corner, you'll sometimes notice areas with consistent windiness. I was wondering what positions, angles, wind direction, pressure,...
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4answers
692 views

Is a causal relationship implied by Newton's 2nd Law?

Throughout my time learning physics I have been imbued with the notion that forces cause accelerations, period. Accelerations don't cause forces, and they aren't merely correlated phenomena. By ...
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4answers
2k views

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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0answers
32 views

What is “full clutching flow” in fluid-dynamics with regards venturi design?

As the title says, what is "full clutching flow" in fluid-dynamics with regards venturi design? I came across this reference a few times and can not find any further info on it, I'm currently ...