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Questions tagged [viscosity]

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Scaling law or order estimation for turbulent viscosity in a rectangular cavity

Is there any recognized scaling law for the eddy viscosity inside a rectangular cavity? Indeed, that should mean some sort of homogenized value, since the quantity is spatially dependent. I have made ...
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2answers
193 views

Why is oil called more viscous than water when we slip on oil more than we do on water [duplicate]

If we were to throw some water on the floor then walk over it we may or may not slip but it wouldn't that be difficult to walk. If we repeat the same thing with oil we it would be harder to walk as me ...
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Calculating Reynolds number in a water tunnel

I am trying to calculate the Reynolds number of a flow that I will be creating in a water tunnel. Reynolds number ($RE$) is given by the following where $\rho$ gives fluid density, $u$ gives velocity ...
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Why bicycles' rims are bent after winter? [closed]

I've noticed that the rims of many bicycles which are parked in the street during the whole winter are heavily bent. I'm wondering what causes this deformation? Typically, this happens to rather cheap ...
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Time scale for steady flow to occur in parallel disk viscometer

Hey to whomever is reading this! I'm currently trying to solve a problem given to the class in a hydrodynamics course. I have to main questions. The following describes the problem: We are ...
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1answer
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Small amplitudes and Stokes drag law

Why is it that on a damped harmonic oscillator or a pendulum in a fluid, the Stokes drag law in the fluid only applied to small amplitude oscillation compared to large amplitudes oscillations? Dose ...
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1answer
31 views

Taylor Couette Bernoullis

Has anyone studied a Taylor-Couette flow in the presence of a varying diameter pipe. Is there any research that i can be pointed to to understand how the pressure differences develop in a purely ...
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23 views

Theory or method on how to calculate the pressure needed to push a viscous fluid through a narrow slit

I need to calculate the minimum amount of pressure I need to apply to a piece of molten glass to start making it pass through a narrow slit - think 1 kg of glass and a 0.2 mm slit. At this point I ...
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3answers
149 views

How to start moving in at $Re\ll1$

I find it difficult to see how something can accelerate (and therefore increase its velocity, e.g. start to move) in a $Re\ll 1$ situation. It is customary, at low Reynolds numbers, to ignore ...
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Does bernoulli's principle explain the suction by an emerging air stream?

Consider flow exiting a nozzle into atmosphere, its static pressure will decrease through the nozzle as the molecules vectors align with the direction of the exit. However, as soon as it exits the ...
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2answers
90 views

How does viscous dissipation influence fluid temperature in pipe flow?

I'm looking at viscous dissipation of an incompressible fluid in fully developed pipe flow. I'd like to generally derive the bulk temperature variation as a function of pipe length due to viscosity, ...
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48 views

When can viscosity be ignored?

I am working on understanding the motion of a solid ball in an infinite elastic (or possibly viscoelastic) medium when subjected to a sinusoidal driving force. The frequency-dependent complex wave ...
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What Is The Lowest Temperature At Which A Fluid Will Flow?

I’m studying Hydraulics, and this week we’re talking about viscosity and fluid properties and I came across this question but I can’t find the answer anywhere in my books. Please help.
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Viscoelastic Constitutive Relation

In the Mori-Zwanzig formalism, the following identification for the generalised shear viscosity $\eta(t)$ is given: $$ \eta(t) = \frac{V}{k_B T} \langle \sigma(t) \sigma(0) \rangle, $$ identified as ...
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1answer
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Non-conservative forces in Lagrangian mechanics

In the Lagrangian formalism with a dissipative frictional force $F$, we can write $$\frac{d}{dt}\frac{\partial\mathcal{L}}{\partial\dot{q}_{k}}-\frac{\partial\mathcal{L}}{\partial q_{k}}=Q^{(nc)}_{k}...
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Is the velocity gradient of a homogeneous viscous fluid constant?

The formula for the viscosity of a fluid (or even a gas) is equal to \begin{align*} \frac{F}{A} =\mu\frac{du}{dz} \end{align*} where $F$ is the force applied to the top layer of the fluid, $A$ is the ...
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Viscous fluid equivalent of hyperelasticity

A hyperelastic solid is defined as one for which the stress tensor $\sigma$ can be written as the derivative of some stored energy function $W$ w.r.t. the strain $\varepsilon$: $\sigma = \frac{\...
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Where does this equation come from?

I am investigating about viscosity of fluids and I found the following equation to calculate the viscosity: $$\nu = \frac{2(\rho_s-\rho_l)\cdot g \cdot r^{2}}{9\cdot\Delta v} $$ The experiment ...
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Kelvin solid and deformation in transverse direction with Poisson ratio

A Kelvin-Voigt material is a material with such a behavior : I'm wondering if there is a way to model in a similar way the deformation in the transverse directions $y$. Meaning we have for the ...
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1answer
52 views

Flow through a hole in a sphere

I have a sphere of diameter $D$ (radius $R$) with a small hole of diameter $d$ (radius $a$) in it, with air flowing through the axis of the hole: I am trying to estimate the drag force due to ...
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1answer
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How does a viscous fluid flow?

In all problem involving viscosity, while applying $f=nA \frac{du}{dz}$ why do we consider velocity of the bottom layer to be zero?
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3answers
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If the molecular collisions are elastic will there be any dissipation in a fluid?

Viscosity arises due to collisions of the molecules of one layer of a fluid with another in contact. But viscosity is a dissipative element leading to heating and dissipation. Where does it heat come ...
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How does the velocity of the fluid layers gradually increase towards the axis of a tube?

For a fluid moving through a cylindrical tube in a streamlined motion, a fluid layer in immediate contact with the wall of the tube remains effectively at rest. The layers away from the wall has ...
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Why does a viscous fluid tends to cling to a solid in contact with it?

My textbook says that a viscous fluid tends to cling to a solid in contact with it, and also gives a consequence of the same: "Dust particles cling to blades of a fan even when it is rotating rapidly."...
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3answers
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Are there any cases where Stokes law does not apply in viscous fluids?

A friend of mine and I are conducting an experiment to find the relationship between terminal velocity and radius of a sphere (i.e trying to confirm Stokes law). We are using spheres ranging from 1....
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4answers
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Why can't liquids oppose tangential forces acting on them?

Also, when a glass of water is inclined at a certain angle, why does the surface of water continue to remain parallel to ground?
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1answer
108 views

How to improve this simple Brownian motion simulation by adding viscosity?

I've written a 0th order Brownian motion simulator to envision how a particle of smoke might appear to move under a microscope. There will be missing $\sqrt{2}$'s and $\frac{\pi}{2}$'s since I haven'...
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2answers
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Stressing Over Stress Tensor Symmetry in the Navier-Stokes Equations

How do we know that the stress tensor must be symmetric in the Navier-Stokes equation? Here are some papers that discuss this issue beyond the usual derivations: Behavior of a Vorticity Influenced ...
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How can a vortex be created?

i have seen this video. https://www.youtube.com/watch?v=pnbJEg9r1o8&t=96s It is not completly clear how a difference of velocity can cause a vortex, can you explain me?
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1answer
240 views

How does one mathematically derive the damping coefficient of a theoretical viscous dashpot?

I am very well aware of how to get the damping coefficient experimentally by observing a system in action. Given the dimensions and fluid properties of a theoretical viscous fluid dashpot, how does ...
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Can a water vortex (whirlpool) be used to efficiently store energy?

Either a large, constrained cylinder of water or a large volume of open water (perhaps in the ocean) could be persuaded to form a vortex by pumping energy in. The body of water would be acting as a ...
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0answers
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Formula for volume of liquid residue in containers after pouring [closed]

When trying to empty the filled containers by pouring, we will find that this is impossible to reach the "real empty" as some residual liquid should exist in the containers. Have some mathematical ...
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1answer
47 views

Why do we use $m\frac{dv}{dy} = -b(v-v_{ter})$ while determining how the terminal velocity is changing for an object falls down in linear drag force?

Why do we use $$m\frac{dv}{dy} = -b(v-v_{ter} )$$ while determining how the terminal velocity is changing for an object falls down in linear drag force . I was Jr Taylor's classical mechanics. In the ...
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Why doesn't the object slow down more after attaining the terminal velocity in liquid?

When an object falls down in a liquid it has two forces working on it one gravity and another is viscous drag . Now when these forces are same the object attains the terminal velocity in liquid. Now ...
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Why does Anderson ignore a derivative of a normal viscous stress?

I am reading "Fundamentals of Aerodynamics" 5th edition, J.D.Anderson. In part 15.6, he said: Consider a steady two-dimensional, viscous, compressible flow. The x-momentum equation for such a ...
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What is the relationship between coefficient of discharge, Cd and the viscosity of the fluid flow?

Will an orifice’s coefficient of discharge depend on the viscosity of the fluid being used to measure it? Is Cd a geometric property or will it change for different fluids of different viscosity? ...
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1answer
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A viscosity unit [closed]

Does the viscosity unit "$\mathrm{ps}$" exist or is it a misprint and refers to poise "$\mathrm{P}$"? Thank you A liquid of $0.014\,\mathrm{ps}$ viscosity and $1.4\,\mathrm{g/cm^3}$ density ...
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1answer
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Viscosity Vs Conduction

Viscosity of a moving fluid (e.g. a gas) is commonly related to the exchange of momentum between layers of such fluid moving at different velocities. Intuitively, one could think that in a gas such ...
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2answers
109 views

Stokes's law proportionality to radius

Is there a logical explanation why Stokes's drag $F_d=6\pi R \eta v$ is proportional to the radius, $R$ of the sphere? Naively I would have expected that it is proportional to the cross section, i....
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1answer
240 views

Melted chocolate forming fractal branches

Tree-like structure in chocolate Today I let some melted chocolate solidify in a smooth bowl in my fridge. When it had settled, I gently heated the outside of the bowl with warm water to unstick the ...
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149 views

What causes viscosity of a fluid?

Consider a fluid like water. Intuitively I would say that its viscosity is caused by intermolecular interactions among its molecules. But the Einstein-Smoluchowski relation (and the Fluctuation-...
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Force absorption properties for various fluids

I'm a high school student and we have to research a topic in physics as part of our school curriculum. Essentially, I am unable to find any text online relating to this topic, so I was wondering if ...
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Derivation of Maxwell viscoelastic material stress

I have a problem with understanding of derivation of stress equation $\sigma(t)$ for Maxwell rheological model. Below is the classic equation: $$\dot{\sigma}(t) + \sigma(t) \, \frac{E_0}{\eta}=E_0 \,...
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What properties of liquids determine the shape of the meniscus?

I recently purchased a little e-cig type device that operates on these "pods," they look like this: Now, as you puff on the device, the liquid is consumed and starts to go lower in the pod, at which ...
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1answer
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Tracking down a citation for the dynamic viscosity of sea-water

I inherited some computer code that estimates the dynamic viscosity of sea-water from the water's temperature. The formula in the code uses is $$\mu = 2.414 \cdot 10^{-5} \cdot 10^{\frac{248.8}{T+133}...
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1answer
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Applied physics to “fill the jar” problem [closed]

I think that the most of you are familiar with similar kind of problems / riddles: I always said that it depends upon the velocity with which the fluid comes out from the faucet. It doesn't seem ...
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Can the effective viscosity perpendicular director of a nematic liquid crystal be smaller than that in the parallel direction?

For common nematic liquid crystals (LCs), e.g., pentylcyanobiphenyl (5CB) and p-methoxybenzylidene-p-butylaniline (MBBA), the ratio of the effective viscosities $\eta_\perp^\mathrm{eff} / \eta_\...
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1answer
170 views

Drag Force VS Stoke's Force

Drag force reads $$F_d = \frac{1}{2}\rho_F v^2 \mathcal{C} A$$ Where the letters have the usual meaning (respectively: fluid density, velocity relative to the fluid, drag coefficient, front area of ...
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394 views

Are all Irrotational Flows Frictionless and Laminar?

A I understand, Irrotational flows are also inviscid (have zero viscosity). This would lead me to assume that these kind of (purely fictional) flows would be well ordered (Laminar) and be frictionless....
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Viscous force and it's proportionality constant

"Introduction of Mechanics" states: $F_v = −Cv$, where $F_v$ is viscous force and $C$ is a constant that depends on the fluid and the geometry of the body. For objects of simple shape moving slowly ...