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Questions tagged [viscosity]

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12 views

Is Coefficient of viscosity frame dependent? Why/Why not?

Is Coefficient of viscosity frame dependent? Why/Why not?
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23 views

What is the drag coefficient of a tetrahedron? [on hold]

I would like to know the drag coefficients of all of the Platonic Solids. However, I am more interested in that of the tetrahedron.
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43 views

Does the viscosity of oil increase with rising temperature?

In order to calculate the viscosity index of a lubricant, apparently you need two input parameters. The kinematic viscosity (mm²/s) at 40°C and at 100°C. If I got it right, mm²/s means the distance ...
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1answer
37 views

Shear viscosity in an acoustic plane wave

In the absence of bulk viscosity, $\eta_b = 0$, in Landau and Lifshitz book and many other places, the viscous stress tensor is defined as: \begin{equation} \sigma'_{ik} = \eta_s\left(\frac{\partial ...
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About stoke 's formula

Why does the acceleration decrease whereas velocity increase for a freely falling spherical body inside a viscous liquid
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Bernoulli's law for turbulent flow

Is Bernoulli's law valid for turbulent flow for a non-viscous, non-compressible, non-rotating fluid with isoentropic flow? An ideal fluid has coeffieicent of viscosity=0,which implies that it's ...
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Modal filtering with Vandermonde matrix - Artificial viscosity

I am trying to implement a 2D shock detector for an artificial viscosity model to control strong nonlinearities in compressible fluids. The method I am relying on is originally from: Yu, M. L., ...
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33 views

What is the theoretical flow rate of water through a tube leaving a container?

The question comes from this image: There is a container with $h$ amount of water above a hole of diameter $r$. This hole leads to a tube that the water exits through. Using the pressure on both ...
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12 views

Viscous forceand it's relation with velocity gradient

How is viscous force directly proportional to velocity gradient??,lyk if consider a layer of water that is near the ground say 1st layer and a layer of water that is above 1st layer,if the velocity ...
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40 views

External force in the Navier-Stokes momentum equation

The Navier-Stokes momentum equation is $$ \rho\frac{\partial \bf{v}}{\partial t}+\rho(\bf{v} \cdot \nabla\bf{v})=-\nabla P + \nabla\cdot \bf{\tau} +\bf f $$ where $\tau$ is the deviatoric stress ...
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Derivation of Stokes Formula using stream function

I need help with derivation of Stokes Formula. I have found derivation on Wikipedia (https://en.wikipedia.org/wiki/Stokes%27_law), but I don’t know how can I get from equation (1) to equation (2). How ...
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1answer
61 views

Why doesn't mercury flow in the thermometer?

Nowadays digital thermometers are used, but in the past mercury based thermometers were used. From my experience the mercury does not flow in the thermometer tube. Mercury is a liquid, so it must have ...
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1answer
51 views

How does viscous heating arise?

Viscosity arise because of fluid deformation, which causes shear within it. Momentum is then diffused down the velocity gradient. What I can't seem to understand, is how the heating arises. I'm not ...
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1answer
24 views

What is the reason for the presence of a developing region in a boundary layer?

Why does a fluid first flow as shown in the entrance region before flowing as shown in the developed region ? In other words, why wouldn't it flow in developed region from the beginning ?
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Bird Transport Phenomena

in the book " transport phenomena" (Bird) when obtaining the famous equation of hagen poiseuille Bird defines a variable that involves the pressure, but when doing an exercise a term magically ...
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1answer
48 views

Why do we consider the viscous force to be tangential?

Is it that since it is a friction force, it needs to be tangential as other friction forces like kinetic friction and static friction forces are?
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0answers
31 views

Is it possible to find the exact value of the dynamic viscosity of a fluid by applying Stokes' law?

I am a high school student who is investigating the dynamic viscosity of a fluid. Typically, high school physics model the dropping of a spherical object vertically into a viscous fluid with the ...
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3answers
115 views

Can the flow be irrotational if the viscous forces act on fluid?

I tried to answer the question only using the definitions and the Navier-Stokes equation: $$\rho \frac{Dv}{Dt} = -\nabla P +\rho g -\mu[\nabla \times(\nabla \times v)] $$ In my opinion if the ...
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1answer
21 views

A viscous liquid moving from different holes

Say, we have bottled viscous liquid - such as a dishwashing liquid. There are two different caps for the bottle. One with a smaller hole, one with slightly bigger hole. Both holes are very small ...
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1answer
55 views

Deriving the Navier-Stokes Equation in Fluid Dynamics

I am trying to understand the derivation of the following equation which describes the motion of Newtonian viscous fluids: Equation 1: $\rho \dfrac{D u}{Dt} = \rho g_x - \dfrac{\partial p}{\partial x}...
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1answer
49 views

Find the expression for $η$ (coefficient of viscosity). For the given condition [closed]

A cube is sliding from wedge with a constant velocity and on liquid of $η$ coefficient of viscosity.The perpendicular distance between cube and layer of liquid is $x$ and the Length of cube is $a$. ...
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Effect of carbonation/nitrogenation on viscosity

What would the effect of heavy nitrogenation or carbonation have on the viscosity of a fluid? Would there be effect be different on dynamic vs kinematic viscosity?
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1answer
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What is the significance of kinematic viscosity? [duplicate]

We know that kinematic viscosity is defined as ration of dynamic viscosity to the mass density of a fluid. $\nu = \frac \mu \rho$ But I want to know the significance of that physical quantity of ...
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29 views

Poiseuille’s Law and viscosity type

Is kinematic or dynamic viscosity meant to be used in Poiseuille’s Law? What's the reason behind this? I have seen contradicting information online and they seem to use the same sign.
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1answer
44 views

Liquid nitrogen physical properties

I am looking for a reference containing the physical properties of liquid nitrogen, in particular density $\rho$ and dynamic viscosity $\mu$ as functions of temperature and pressure. This is for a ...
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30 views

Motion of an Object in a Viscous Fluid

Let us say that an object in a liquid is subject to a drag force proportional to its velocity -bv. What would be the graph of its vertical velocity as a function of time, taking into account the ...
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2answers
104 views

Why does a torpedo travel farther than a bullet underwater?

We know that to move in water we require more energy. Even shooting a gun, the bullet travels a very small distance. But how could torpedoes move so fast inside the water? If they have such an energy ...
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Viscous losses in loop helical flow

Imagine flow of the following kind. The flow line for each flow particle is a helix with its axis bent so that the beginning attaches to the end. How can I determine the viscous losses in this flow ...
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2answers
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Formula of viscosity

viscosity formula = η = F̅/A(shear stress)=Δvx/Δz but i noticed that viscosity depends upon temperature too.Shouldnt there be temperature variable too in the formula ?
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1answer
104 views

Is there a uncertainty relation between viscosity and volume in fluids?

If I make no mistake, dynamic viscosity $\eta$ is measured in $ \rm kg /(s\, m) $. And volume is measured in $\rm m^3$. The product of the two has the same units of Planck's quantum of action $\hbar$...
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39 views

What is rate of heat produced in terms of radius $r$ in viscous liquid under gravity?

what is the dependency of the rate of heat produced in terms of radius $r$ after the drop attains terminal velocity when A small ball of radius $r$ is falling in a viscous liquid under gravity? My ...
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What would be the Creep Response by using Boltzmann superposiition at t>t2

For detail see attach picture.. Under stress is σ, the creep response is given by , use Boltzmann superposition to estimate its creep response at t>t2 after the following stress history. [![enter ...
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74 views

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 ...
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1answer
104 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 $P(z)$ ...
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1answer
67 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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22 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
138 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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162 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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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
399 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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100 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 ...
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0answers
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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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2answers
38 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 ...
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1answer
30 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
35 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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28 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
158 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
292 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
64 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 ...