Questions tagged [viscosity]
The viscosity tag has no usage guidance.
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Viscous Force On A Rotating Cylinder
In this question asked in Irodov, it is taken that the friction force acting on a unit area of a cylindrical surface of radius $r$ is given by $σ = ηr(∂ω/∂r)$.
A fluid with viscosity $η$ fills the ...
8
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1answer
90 views
Viscous flow through a concave tube
Consider gravity-driven incompressible flow through a concave tube with known radius $R(z)$, where pressure is atmospheric $P_a$ on both ends:
How does the viscous pressure distribution $P(z)$ ...
0
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1answer
45 views
Do viscous and inviscid flow have opposite effects on pressure?
Consider flow through the converging and diverging portions of a tube with varying radius:
In inviscid flow, Bernoulli's equation states that velocity at the throat will be the highest, so this area ...
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0answers
17 views
Viscosity from terminal settling velocity of a sphere
I don't have an attempted answer to this question because I don't really know where to start. The Tip says to start from a force balance for the sphere, but I'm not sure on how to do that.
I know ...
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1answer
58 views
How to find drag of a cylinder?
How can I find a drag on the cylinder placed in uniform water flow, if I know a velocity field around it?
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0answers
93 views
How to calculate the viscous damping coefficient of a viscous layer between an inner sphere and an enclosing outer sphere?
In this article by Rahn and Barba, a flat-spin transition manoeuvre is investigated. For this it is assumed that a rigid spacecraft contains a spherical, dissipative fuel slug of inertia $\boldsymbol{...
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0answers
16 views
Scaling law or order estimation for turbulent viscosity in a rectangular cavity
Is there any recognized scaling law for the eddy viscosity inside a rectangular cavity? Indeed, that should mean some sort of homogenized value, since the quantity is spatially dependent.
I have made ...
4
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2answers
246 views
Why is oil called more viscous than water when we slip on oil more than we do on water [duplicate]
If we were to throw some water on the floor then walk over it we may or may not slip but it wouldn't that be difficult to walk. If we repeat the same thing with oil we it would be harder to walk as me ...
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0answers
45 views
Calculating Reynolds number in a water tunnel
I am trying to calculate the Reynolds number of a flow that I will be creating in a water tunnel. Reynolds number ($RE$) is given by the following where $\rho$ gives fluid density, $u$ gives velocity ...
2
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0answers
41 views
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 ...
0
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2answers
36 views
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 ...
0
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1answer
26 views
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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0answers
27 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 ...
2
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3answers
154 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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0answers
15 views
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 ...
0
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2answers
135 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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1answer
55 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 ...
0
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2answers
39 views
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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1answer
37 views
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 ...
1
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1answer
90 views
Non-conservative forces in Lagrangian mechanics
In the Lagrangian formalism with a dissipative frictional force $F$, we can write
$$\frac{d}{dt}\frac{\partial\mathcal{L}}{\partial\dot{q}_{k}}-\frac{\partial\mathcal{L}}{\partial q_{k}}=Q^{(nc)}_{k}...
0
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1answer
67 views
Is the velocity gradient of a homogeneous viscous fluid constant?
The formula for the viscosity of a fluid (or even a gas) is equal to
\begin{align*}
\frac{F}{A} =\mu\frac{du}{dz}
\end{align*}
where $F$ is the force applied to the top layer of the fluid, $A$ is the ...
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2answers
32 views
Viscous fluid equivalent of hyperelasticity
A hyperelastic solid is defined as one for which the stress tensor $\sigma$ can be written as the derivative of some stored energy function $W$ w.r.t. the strain $\varepsilon$:
$\sigma = \frac{\...
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0answers
44 views
Where does this equation come from?
I am investigating about viscosity of fluids and I found the following equation to calculate the viscosity:
$$\nu = \frac{2(\rho_s-\rho_l)\cdot g \cdot r^{2}}{9\cdot\Delta v} $$
The experiment ...
0
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0answers
16 views
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 ...
2
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1answer
63 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
38 views
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
85 views
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 ...
2
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2answers
55 views
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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2answers
69 views
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
167 views
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
197 views
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
128 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
95 views
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 ...
2
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1answer
68 views
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?
0
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1answer
357 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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2answers
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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
38 views
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
50 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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2answers
54 views
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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2answers
117 views
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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0answers
122 views
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
52 views
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
62 views
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 ...
3
votes
2answers
125 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....
22
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1answer
252 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 ...
4
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2answers
157 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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2answers
68 views
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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1answer
56 views
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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1answer
117 views
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 ...
