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

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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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37 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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79 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
80 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
39 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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21 views

Formulation of blood flow dynamics under pressure

If external pressure is applied and maintained on the upper arm, the blood flow to the forearm slowly decreases. If at this point of time, the pressure is suddenly released, blood will gush through ...
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1answer
69 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 ...
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1answer
103 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
43 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 ...
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45 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
99 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
27 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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44 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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66 views

In a column of fluid does density vary?

In a column of fluid does density vary?
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193 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
29 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
39 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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24 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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40 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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1answer
72 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 ...
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1answer
52 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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55 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
248 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
85 views

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

I vaguely understand the continuity equation (at least its integral interpretation), but I don't really understand the differential interpretation of the continuity equation. I'm having trouble ...
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2answers
77 views

Bubbles of Different Size

Suppose that I have 2 bubbles of different sizes located in a liquid, and assume that both of those bubbles are close to one another. What exactly will happen to both of those bubbles? From a ...
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38 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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1answer
86 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?
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1answer
104 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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27 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 ...
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1answer
91 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
92 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 ...
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4answers
180 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
58 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
118 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. ...
3
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0answers
103 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
120 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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291 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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32 views

Equation of acoustic pressure in moving fluid: derivation

I'm looking for a detailed derivation of the equation of acoustic pressure with harmonic time dependence (of type $p(t,{\bf r}) = \psi({\bf r})e^{i\omega t}$) in moving fluid and under assumptions ...
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2answers
68 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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29 views

Fill and drain tank (same time) [closed]

Consider an open tank with cross section area A, into which liquid can enter at the top through one pipe and leave at the base through another. If the liquid enters at the constant rate of a volume of ...
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76 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 ...
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33 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 ...
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1answer
43 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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25 views

flow through an orifice [closed]

The surface area of a first orifice with 2 mm diameter is 3 mm$^2$. The surface area of a second orifice is 5 times bigger from the surface area of the first orifice (15 mm$^2$). How much would be ...
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48 views

Isn't it impossible to make a theoretical model to describe the behavior and the statistics of a turbulent flow? [closed]

Why mathematicians are interested to smooth solutions of Navier Stokes equations? For the three-dimensional system of equations, and given some initial conditions, mathematicians have not yet proved ...
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3answers
93 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
49 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, ...
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69 views

Calculate surface pressure due to forced vibrating plate using wavenumber space [closed]

My problem lies in the field of acoustics. I have a given complex velocity distribution. The velocity is the velocity in the normal direction to a rectengular simply supported vibrating plate. I now ...
3
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4answers
406 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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3answers
102 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 ...