# Questions tagged [viscosity]

The viscosity of a fluid is a measure of its resistance to flow, or be deformed, stirred, and changed shape.

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### Fluid dynamics of a balloon

This is a question which might not seem relevant to physics, but I was always curious if the shape of the balloon were to be not the shape that we all know of, when we release the tip will air flow ...
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### Experiment about a sphere in a tube in presence of viscous resistance

Recently, I carried out an experiment at home with little equipment, but I can't get to the bottom of it. Consider a fluid-dynamic resistance force of intensity $F_L$ ($\vec F_L = - \alpha \vec V$) ...
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### How to mathematically derive the pressure contribution to drag force over a with viscous contribution determined?

I've looked in a lot of books on how it would be possible to derive the drag force over a sphere using PDEs. I've also learned in my fluid dynamics class how to derive the drag force of a rotating ...
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### How to mathematically derive the pressure contribution to drag force over a sphere after the viscous stress is determined? [duplicate]

I've looked in a lot of books on how it would be possible to derive the drag force over a sphere using PDEs. I've also learned in my fluid dynamics class how to derive the drag force of a rotating ...
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### Sphere submerged in a thin layer of gel (fluid with yield stress) that is spread on a vertical wall

Imagine a uniform thin layer of a viscous gel sticking on a vertical wall. A small sphere is submerged in this gel. The gel has a yield stress (Bingham model). How can I calculate the yield stress ...
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### Force exerted by water flowing in a pipe bent into a circular arc

my school teacher told me that when water flows in a pipe, it exerts a force equal to $ρAv^2$ where $ρ$ is density, $A$ area and $v$ velocity. he further said that when the liquid enters the pipe, the ...
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### Is the wing drag of induced drag + 2d drag at 0lift still accurate for cambered airfoils?

I have some work at uni that requires some aerofoil analysis to create a wing, but from the polar plots its clear that the cambered aeros have lower total 2d viscous drag (from xfoil) at the cl its ...
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### Can an ideal fluid undergoes a turbulent flow?

I have read before that the existence of viscosity is the main reason for the appearance of vortex. However, by definition, an ideal fluid has $\eta=0$. So, can an ideal fluid undergo a turbulent ...
1 vote
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### Unexpected result: flux using Poiseuille greater than using Bernoulli

I have a simple, easy to solve, Poiseuille type of problem, to which I added a second question, in which viscosity is zero, so I can solve it using Bernoulli. I am arriving a greater flux using ...
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### How can the panel method be used to find drag and lift if it is for invicid flow?

If simple CFD softwear like XFoil and OpenVSP use the panel method to find an estimate of the drags and lifts/pressure distributions. How do they find drag and lift if the panel method works based on ...
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### Terminal velocity of two raindrops

Question: "Consider a small (less massive) raindrop, and a large (more massive) raindrop (consider both to be spheres), falling with air resistance (drag). Which will have a larger terminal ...
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### Can direction of frictional force be opposite to velocity?

The frictional force in incompressible Navier-Stokes equation is given by $$\vec F = \nu \nabla^2\vec v$$ Lets assume simple 1D-flow along $x$, where $v$ depends on $z$: $$v_x = v(z)$$ Then the ...
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### In the derivation for Poiseuille’s formula for laminar flow through a cylindrical tube the speed parallel to the central axis increases. Why?

To start off with, I'm a first year undergrad and do not have much knowledge at all about fluids, and am simply working with context that has been provided to me from a lab script (of a lab I did not ...
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### Why friction increase subsonic speed through pipe?

I know equations of Fanno flow but can anyone explain physically how friction increases subsonic velocity and decreases supersonic velocity through pipe ? is that for sake of boundary layer ...
1 vote
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### Pitch drop experiment with (poly/mono)crystal

In 1927 a piece of pitch was placed in a funnel and since then pitch flowed at rate of about 1 drop per 10 years. Obviously we can repeat experiment with any amorphous solid. Viscosity of water is ...
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### Can contact stresses become independent of the rolling velocity in a viscoelastic rolling-contact?

In nonlinear viscoelastic rolling contact problems (assuming a viscoelastic wheel rolling/slipping with zero slip angle on a rigid body with friction), is it possible that the contact stresses (...
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### Is the slip condition equivalent to the zero velocity condition for the Euler equations?

When doing an inviscid fluid simulation, one typically uses the Euler equations. With these equations it is important to specify that there may be no normal velocity on the surface of an object (e.g. ...
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### Fluid viscosity, mass diffusion and Navier-Stokes equation

With the increase of fluid viscosity, mass diffusion of a fluid decreases. Then how the diffusion term in Navier-Stokes equation has a dominant effect at high viscosity? Also how the mass convection ...
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### Simplifying 2D Navier stokes equation over the top and bottom part of an airfoil - assumptions incompressible, steady, very high viscosity

I am trying to simplify the Navier-Stokes equations with my assumptions, to be able to solve them numerically: I'm trying to model an airfoil flying through a very viscous fluid at relatively low ...
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### How does inertia affect an object suspended in a fluid?

When I asked my physics teacher how fully submerged objects are suspended in fluids, she told me it was because the object's density was equal to that of the fluid's as a result of the net force ...
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### Why is a viscous drag produced due to relative motion of layers of fluids? [closed]

When two layers of fluids move over each other, a viscous drag is produced. Could you please elaborate on this?
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### Are closed streamlines necessary to have vortices?

I am studying fluid dynamics, and all the examples I have found so far about vortices show closed streamlines rotating around an axis. All these examples suggest that having closed streamlines is a ...
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### Will the velocity gradient be zero if there is no adhesive attraction with the bottom surface?

(Above is a representation of what I currently understand of viscosity). My question is, if the bottom layer and the floor didnt interact with adhesive forces and hence the motion of bottom layer of ...
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### Is viscosity caused by 'electric charge interaction' between molecules, or its just like friction and caused by 'roughness' of molecular structure?

When I hear that viscosity is the "internal frictional force between layers of fluid", Iam being guided to imagine the usual friction where a rough surface's irregularities are hindering the ...
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### How does Viscosity of the Sun varies as we go from core to the convective zone?

How does Viscosity of the Sun varies with its radius? For. eg, Here is the graph of the Density of the sun v/s radius. I am looking for the Viscosity v/s radius plot.
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### Speed of objects travelling down liquid-filled tubes of different widths

Consider I have two tubes filled with water: Tube A and Tube B. Tube A has a diameter of 20mm and Tube B has a diameter of 10mm. A marble ball with a diameter 8mm is dropped down both tubes. Why does ...
1 vote