The viscosity tag has no wiki summary.
15
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1answer
371 views
Minimum viscosity of liquids
In a lecture by Purcell he mentions that he notices that there aren't any liquids with viscosities much less than that of water, even though they go up seemingly unbounded. In an endnote (endnote 1 in ...
10
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2answers
264 views
Can vorticity be destroyed?
I have a professor that is fond of saying that vorticity cannot be destroyed. I see how this is true for inviscid flows, but is this also true for viscous flow? The vorticity equation is shown below ...
8
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1answer
486 views
Friction term in Navier-Stokes equation
The friction term in Navier-Stokes equation assumes that the viscosity coefficients are the same for the longitudinal and transverse directions. This doesn't seem intuitive, because the former is ...
7
votes
3answers
168 views
How do I intuit viscosity in a rotating fluid?
Suppose I have two plates with a viscous fluid in between. I slide them in the same direction (a direction in their own plane), one at $5 \,\text{m/s}$ and the other at $6 \,\text{m/s}$. Due to the ...
5
votes
2answers
253 views
Explanation that air drag is proportional to speed or square speed?
A falling object with no initial velocity with mass $m$ is influenced by a gravitational force $g$ and the drag (air resistance) which is proportional to the object's speed. By Newton´s laws this can ...
5
votes
1answer
225 views
Are coffee's properties different enough from water's to cause increased spillage while walking?
I recently found this article, which describes how...
It just so happens that the human stride has almost exactly the right frequency to drive the natural oscillations of coffee, when the fluid is ...
5
votes
4answers
290 views
Do we have viscous force acting between two layers
Frictional force between solids operates even when they do not move with respect to each other. Do we have viscous force acting between two layers even if there is no relative motion?
4
votes
1answer
212 views
Calculating Reynolds number for a viscous droplet
I'm trying to develop a very basic scaling law/unit analysis for viscous droplet formation, and I'd like to get some rough numerical values of the Reynolds number to play with. To be specific, I'm ...
3
votes
3answers
159 views
In the classic viscosity definition, why does doubling the plate gap cause the force to halve (intuitive)?
I am puzzled by an artifact of the definition of viscosity and need an intuitive picture to help explain it. I know $\tau_{yx}=-\mu{dv_x \over dy}$ but I am looking for an intuitive picture of the ...
3
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3answers
355 views
Equations of fluid dynamics and differential geometry
Where can I look for equations of fluid motion written in terms of nifty things from differential geometry like exterior derivative, Hodge dual, musical isomorphism?
Preferably both with and without ...
3
votes
1answer
450 views
Is there an analytical solution for fluid flow in a square duct?
I couldn't find one but assumed it must exist. Tried to find it on the back of an envelope, but got to an ugly differential equation I can't solve.
I'm assuming a square duct of infinite length, ...
3
votes
2answers
571 views
Does irrotational imply inviscid?
Let us consider a 2D irrotational flow, such that $\nabla\times\boldsymbol u =\boldsymbol 0$. Defining the stream function such that $\boldsymbol u =\nabla\times\psi \boldsymbol n$ where $\boldsymbol ...
3
votes
2answers
344 views
Strict general mathematical definition of drag
Is there a formal definition of drag, say, as some surface integral of normal and shear forces? There seem to be a lot of formulas for specific cases, but is there a general one?
I need to accurately ...
3
votes
1answer
131 views
How to write classical dynamics of solids in tensor form (relation of stiffness and viscosity tensor)?
This is a question about dynamics. If I have understood correctly there should be a tensor that describes the dynamics of a (solid?) body (= viscosity ?). I mean, tensor that includes the time ...
2
votes
1answer
506 views
What is the shear stress of a fluid?
One book defines the shear stress $\tau$ of a (Newtonian) fluid as
$$\tau = \eta \frac{\partial v}{\partial r} $$
where $\eta$ is the viscosity. There is not much context, so I've made some guesses. ...
2
votes
1answer
170 views
Water vs Milkshake being sucked through a straw
Consider water in a glass being sucked through a straw. The water rises up in the straw because of a pressure gradient introduced by the sucking action.
Now, change the liquid from water to something ...
2
votes
1answer
312 views
Velocity in a viscous fluid
The force $F$ to carry a plate of area $A$ with velocity $v$ in a fluid of depth $d$ is given by
$$\frac{F}{A}=\eta\frac{v}{d}.$$
Hence if the depth is $kd$, the force becomes $F/k$.
Do this ...
1
vote
1answer
355 views
Intrinsic Viscosity
I'm presently undergoing an Experiment for the determination of the viscosity of Ficoll-70 using Ostwald viscometer to calculate the time and a digital weighing balance to determine the weight of a ...
1
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1answer
118 views
Capillaries in series
The velocity of fluid of viscosity $\eta$ through a capillary of radius $r$ and length $l$ at a distance $x$ from the center of the capillary is given by; $v=\frac{P}{4l \eta }(r^2-x^2)$ (where $P$ is ...
1
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1answer
42 views
Are there dedicated instruments to measurethe viscosity of shear thinning liquids?
Googling around for ways to measure the viscosities of shear thinning liquids, it seems to me that most of the time viscometers are used at different settings to measure different apparent ...
1
vote
1answer
194 views
Reynolds number with hyper-viscosity
Is it possible to evaluate a Reynolds number when viscosity operator is substituted by hyper-viscosity operator at the power H (Laplacien to the power H) in the incompressible Navier-Stokes equations ...
1
vote
1answer
388 views
Determine viscosity using falling sphere (Stokes Law, Ladenburg correction)
Introduction
I am trying to determine the viscosity of a fluid. Therefore, I let a sphere of known mass m and radius r fall ...
1
vote
1answer
128 views
How to find out the maximum radius of a hole that can keep water stay in a container by water viscosity?
Assume I have a inverse cone which holds 200ml water. I am going to cut the tip of the cone to create a small hole. How to calculate the maximum radius of the hole that the water will still stay in ...
0
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1answer
439 views
Is water considered a substance with low friction or high friction?
Like, for example, rubber is a substance with high friction, as an object with neither high or low friction would easily stop on it, and wouldn't skid. Ice is considered an object with low friction, ...
0
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1answer
146 views
Modellng mechanical behavior of heat shrink film
Consider a heat shrink film (as used in shrink sleeves that decorate plastic or glass bottles).
These materials are produced by blow extrusion. When the film is heated (hot steam, hot air or ...
0
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0answers
20 views
Determine the maximum diameter value a glass particle must have in order to sediment [closed]
Speed rate sedimentation of a sphere made of a certain material in a given liquid grows along with the size of a particle. Determine the maximum diameter value a glass particle $(\rho_{\text{glass}} ...
0
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2answers
110 views
The viscous force between the layers of liquid is same, then why there is variation in the velocities of its layers?
I have learned in my textbook that when the liquid flows the bottom layer of the liquid never moves because of friction, but the upper layers move with increasing velocities how it is possible if the ...
0
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0answers
40 views
Viscoelastic materials parameters values
I am taking part of a theoretical research about viscoelastic material, in particular related to the Kelvin-Voigt model.
For some numerical simulation we need the values of the Lamé elastic and ...
