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1answer
36 views

Application of Stoke's Law

I was looking at Stoke's law and it says that you use it to calculate the drag force on a sphere passing through a fluid. Can i also use this equation to calculate the drag force on a car going ...
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2answers
67 views

Viscous forces with asymmetric gradient velocity in fluid mechanics

In fluid mechanics, the stress tensor writes $\sigma = -p 1 + \tau$ where the deviatoric part $\tau$ corresponds to shear. The viscous (volumic) forces are $\operatorname{div}\tau$. For a Newtonian ...
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1answer
38 views

Derive drag coefficient of plate

There is any analytical way to derive drag coefficient of flat plate aligned perpendicular to the flow? Wikipedia says it's between 1.98~2.05 but I want to get this value in calculation, not ...
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1answer
28 views

Ratio of force of resistance due to liquid to that due to gravity

What is ratio of force of resistance due to liquid to that due to gravity? For any object for example a ball falling in a liquid with constant velocity, what will be the ratio?
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1answer
26 views

Without knowing fluid density, can it be correctly determined by measuring both kinematic and dynamic viscosity directly?

Without knowing a fluid's density, can its density be correctly determined by measuring both kinematic and dynamic viscosity directly, and then dividing these values? Can one determine cStokes and ...
2
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1answer
66 views

Can dynamic viscosity be measured directly and without knowing fluid density?

Can dynamic viscosity be measured directly and without knowing fluid density? If so, how? My understanding is that only the kinematic viscosity can be measured directly (with the devices that I am ...
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1answer
34 views

Velocity of liquid molecules in turbulent flow

I was solving some questions when I came across this: what is the velocity of liquid molecules in contact with the walls of the tube? and the answer was given that it can have any velocity and then ...
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0answers
27 views

How to determine which one is dominant shear rate vs. flow rate

I have a question for the image below. Now we have a pump connecting to a votator for transferring some slurry. The pump yields a flow rate Q, and the votator yields a shear rate 𝛾. I wanna ...
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0answers
55 views

Dissipative forces and reversible processes

A book that I have contains the following lines: For a process to be reversible, the dissipative forces such as viscosity and friction should be absent. My question is why?
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1answer
36 views

Shear stress in cylindrical coordinates?

In cylindrical coordinates the momentum flux is given by (in the $r$ direction): $$ \Pi=-\eta \frac{\partial (r\omega)}{\partial r}$$ Where $\eta$ is the viscosity. Therefore one would expect that the ...
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0answers
13 views

Plateau–Rayleigh instability according to liquids $Ca$ number

For examining whether viscosity or surface tension dominates each other effects, we can't refer to $Re$ or $We$ numbers because they just tell us about one of them ( surface tension and viscosity ). ...
2
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1answer
29 views

The validity of constitutive diffusive fluxes

In transport phenomena the diffusive fluxes for mass, energy and momentum are the constitutive laws: $$\boldsymbol{j}_c=-D\boldsymbol{\nabla}c \quad \boldsymbol{j}_T=-k\boldsymbol{\nabla}T \quad ...
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1answer
32 views

Plateau–Rayleigh instability for liquids with low $Re$ number

I'm working on a project about Plateau–Rayleigh instability for liquids. But I've a question. we can examine the fluids with high $Re$ number that the influence of viscosity is negligible, but what ...
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1answer
66 views

Why does my coffee stop?

As I was mixing my coffee this morning, wishing that it would do it on its own, I started wondering: What makes my coffee stop swirling? I mean what exactly? Is it the walls of the cup or the coffee ...
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3answers
650 views

Derivation of viscosity using basic kinetic theory?

This question has been asked in part before in the question Kinetic theory derivation of viscosity of a gas although the given accepted answer does not give the required detail for the part of the ...
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2answers
27 views

Viscosity forces and Depth of water

I was wondering if the viscosity force depends on the depth of water. I mean it is much more harder to swim in the ocean at a depth of 1km than swimming at the surface due to the viscosity forces ?
2
votes
1answer
77 views

Which formula is correct to find the terminal velocity of a sphere falling through a liquid?

Consider a sphere of radius $R$ & density $\rho_s$, falling through a liquid having density $\rho_l$, attains a constant terminal velocity $V_t$ then in this case the net force acting on the ...
1
vote
1answer
41 views

Would a fluid with zero viscosity reach an equilibrium

My hunch is yes, but I can't think how to prove it. An argument against this is you have a box with a divider in the middle, one side is filled up higher than the other. The divider is removed, you ...
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0answers
48 views

Explanation of the liquid rope coil effect

I was recently introduced to the liquid rope coil effect by this video: https://www.youtube.com/watch?v=zz5lGkDdk78 I noticed while the video mentioned the equations governing the motion, it didn't ...
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0answers
20 views

Relation between weight and friction in fluid mechanics

In case of horizontal flow of a fluid,does its weight affect its velocity? Or just the coeffecient of viscosity is sufficient to express the increase in friction with the increase of the fluid's ...
2
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1answer
40 views

Friction in a fluid

when an object is moving in a fluid(air for example), the air will resist the object's movement: molecules of the air will collide with the surface of the object (no slip condition) and then we will ...
2
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1answer
38 views

Is there a conclusive correlation between viscosity and surface tension?

I'm working on a project and I need to know if the viscosity effects on the surface tension or not?
2
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0answers
45 views

Numerical problem on Viscosity [closed]

A horizontal tube of radius $1\ \mathrm{mm}$ and length $40 \ \mathrm{cm}$ is connected to the bottom of a cubical tank of sides $100\ \mathrm{cm}$ containing water of viscosity $0.01 \ ...
0
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1answer
21 views

How drag force relates to velocity in the air?

As you know in the formula of drag $$F=0.5 *d*A*C*v^2$$ in different velocities we have different Reynolds number. and the Reynolds number relates to coefficient of drag. my question is how can we ...
2
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1answer
72 views

How viscosity and velocity relate in a pipe?

Assume we have a pipe that there is a fluid stream in it. By increasing the velocity of the fluid the resistance will increase either (because of the viscosity I think). My question is how are these ...
0
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2answers
145 views

Derivation of Viscous Force

For viscous drag, the formula for the force is, $$ \mathbf F=\pm\eta A\nabla\mathbf u $$ where $\eta$ is the viscosity coefficient, $A$ the area and $\nabla\mathbf u$ the velocity gradient. How is ...
0
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1answer
35 views

Viscosity of Muddy Water

How do I calculate the viscosity of muddy water at 25 deg C and knowing the weight of undissolved solids either SiO2 or Al2SiO5 in H2O, grain size < 150 microns? Do I have enough information to get ...
2
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1answer
47 views

Suffocation in a granular medium

I read of a recent accident in Alberta in which three girls fell into an open bed truck carrying canola seeds and suffocated. In that situation would it have been possible to keep breathing by using ...
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1answer
89 views

How to Determine Viscosity using Damped Oscillations? [closed]

How does one find out the viscosity of a fluid, using viscous damping of an oscillating spring? Any help would be greatly appreciated.
0
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1answer
42 views

Why does the stiffness of organic polymers (plastic) change so much with small changes in temperature?

This is on the borderline between Physics and Chemistry, but I would like a Physics perspective. I am guessing that plastics are a glass-like phase, rather than a true solid.
0
votes
1answer
117 views

How is viscosity related to the forces in fluid?

I think it was that the forces are only perpendicular but do not know how this is related and from where it comes from. EDIT: I am asking for the difference between viscous and non-viscous fluid in ...
0
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0answers
11 views

Visco-elastic fluid | stress/strain relationship

I'm working on a moving visco-elastic fluid with a absorption law (against frequency) that can be represented by a Zener model (Gaussian quality factor). I try to make a numerical modeling of it ...
3
votes
2answers
113 views

Lift and drag coefficients on other planets

The question I'm trying to answer seemed simple: how hard would it be to fly on a planet with lower gravity but also thinner atmosphere compared to Earth. If the answer could hint me at how much ...
5
votes
2answers
322 views

What happened here in this Taylor-Couette Flow experiment?

I came across this video of Taylor-Couette Flow on YouTube. Originally I was looking for a visualization of the wavy Taylor vortices induced by the angular motion of the inner cylinder. However, I ...
0
votes
1answer
48 views

Will there be a drag for a solid body already dragged due to reaction?

By learning Fluid Structure Interaction tutorials, I managged to simulate a 2d transient fsi simulation using Comsol fsi fully coupled module. A solid body due to motion in vertical direction ...
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5answers
4k views

What does air “feel” like to a flying mosquito in terms of viscosity?

If I go for a walk at, say 4 km/hour, unless there is a breeze blowing, I probably won't notice the air around me at all. If I go for a swim though, I will immediately notice the viscosity of the ...
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1answer
370 views

Height of Water 'Splashing'

Suppose from a height $H$, I throw a ball of mass $M$ and radius $R$ with initial velocity $u$ into a pool of depth $x$ having a liquid with density $\rho$ and coefficient of viscosity $\eta$. ...
0
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0answers
34 views

How do i calculate the amount of fluid flowing through a tube?

If I have a tube with an internal diameter of 3.5mm in inside diameter and 30cm in length with a viscosity of 1.77cp, and a pressure of 200kpa, how fast will the liquid flow through? It the tube is in ...
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votes
2answers
170 views

Velocity profile of a viscously damped wave

For a test case, I want to determine the velocity profile of a viscously damped standing wave. By linearizing the density ($\rho=\rho_0+\rho'$) and velocity ($ux=ux'$), the continuity and ...
0
votes
2answers
253 views

Calculating the drag force provided by a laminar flow [duplicate]

If I drop a ball into viscous fluid (e.g. oil), by calculation I know that the fluid flow is laminar. So which equation do I need to calculate the drag force provided by fluid? The drag equation, ...
1
vote
1answer
109 views

What is the cause for turbulence?

The transition from laminar flow to turbulent flow is usually told interms of Reynolds numbers. The Reynolds number is $Re=UL/\nu$ where $U$ is the speed, $L$ is dimensional length and $\nu$ is the ...
5
votes
1answer
94 views

What is the viscosity difference between a solid and a liquid

The pitch drop experiment, for example, shows bitumen as a liquid, even though it appears to be a solid, and then there is the "glass: solid or liquid" debate. Is there a numerical value in viscosity ...
1
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0answers
76 views

Cosmological Bulk Viscosity - is the universe a fluid?

I was trying to make heads of tails of both this paper and the press release about it. The scientists have used bulk viscosity (as opposed to shear viscosity) and popped it into a model and somehow ...
5
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0answers
64 views

Cleaning a dirty jar [duplicate]

I would like to wash the inside of an almost empty cylindric jar on whose walls there are remains of a sticky substance such as peanut butter. I do this by filling it up with water and then shaking ...
0
votes
0answers
25 views

Flow Rate Calculation from a drain tank through a pipe [duplicate]

I want to know how to calculate the flowrate (Q) of a drain tank flowing through a pipe (see the figure below) All I know is that Q=Velocity(V) x Area (A) V= sqrt(2*g*H)=sqrt(2*9.81*10)=14m/s. I ...
1
vote
1answer
72 views

Frictionless and inviscid

In the book Fluid Mechanics by Robert A. Granger, there is a study question, 4.10, asking "How can frictionless real fluids exist and inviscid fluids not exist?" Could someone please explain? ...
0
votes
1answer
691 views

Terminal velocity of a steel ball in water [closed]

I am investigating on the terminal velocity of steel balls moving in water. I used the balls with different diameters, such as 3.17mm, 6.02mm, etc. And I used a full-filled 1L graduated cylinder. I ...
1
vote
0answers
39 views

Volumetric flow rate as a function of radius of pipe [duplicate]

I have a container (assume open on top) with $1m^3$ of water. That water exits this container from an opening that has a cross-section area A e.g. $Ď€R^2$ = $1cm^2$. What is the volumetric flow rate ...
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0answers
89 views

Viscous drag proportional to $r$ or $r^3$?

When a spherical object is falling at terminal velocity through a fluid: $W=U+F$, where $W$ is weight, $U$ is upthrust and $F$ is viscous drag. Rewriting, using Stoke's Law, we get: $$\frac{4}{3}\pi ...
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0answers
146 views

Gauge potential for locomotion at low Reynolds number

I've been studying some approaches with gauge theory to some problems in Mechanics and I've found the problem of self propulsion at low Reynolds number a quite complicated one. The approach I'm asking ...