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31 views

Why the viscosity $\mu$ is called “dynamic” viscosity? [closed]

In fluid mechanics we have the co-efficient of viscosity $\mu$. Why is the adjective "dynamic" added to it?
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0answers
19 views

Dissipation depending on viscosity - where am I wrong?

Accodring to this answer to an older question of mine, dissipation in a fluid in W/kg is proportional to U³/L (U characteristic speed, L Length). I was wondering why this is independent of viscosity, ...
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1answer
31 views

Qualitative idea of viscosity [duplicate]

Suppose we are considering some fluid. As I currently understand, viscosity exists because of the following: supposing we draw one infinitesimal surface on the fluid, then the fluid parcels on either ...
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1answer
44 views

Vorticity versus Viscosity

For a work project I need to revive my aerodynamics knowledge again. Can somebody help me with the distinction between vorticity and viscosity. If a flow vorticity is not equal to zero, the flow is ...
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1answer
33 views

Say, a liquid is made to flow in a tube. Why does the layers of the liquid in contact with walls of the pipe have zero velocity?

Say, a liquid like water is made to flow in a pipe. Why does the layer of water near the walls of the pipe have zero velocity? Does that mean that the layer of water near the pipe is stationary and ...
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1answer
58 views

Which moves faster in a time $t$: $A$ or $B$? [closed]

Suppose we have two objects, $A$ and $B$, both made of the same substance. They also have the same shape (e.g. two spheres), but $A$ is larger and therefore more massive than $B$. Both $A$ and $B$ ...
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0answers
41 views

Can we take transport equation of imaginary quantity?

In the RANS equation we approximate the nonlinear fluctuating terms to eddy viscosity times strain rate. Then by using turbulence models like Spalart-Allmaras etc, we take the transport equation of ...
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3answers
33 views

Airway resistance greatest in tertiary bronchi

As the title reads, why is airway resistance greatest in tertiary bronchi? Primary and secondary bronchi have a lower surface area than tertiary bronchi so what makes resistance greatest at this ...
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1answer
148 views

Gas viscosity at high pressure, high temperature

EDIT 1 PER COMMENTS I am wanting to model nitrogen gas viscosity as a function of pressure and temperature OR learn of an existing equation that models nitrogen viscosity for the pressure and ...
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1answer
55 views

What causes a spacecraft entering the atmosphere to catch fire? [closed]

What causes a spacecraft entering the atmosphere to catch fire? A) surface tension of air B) viscosity of air C) high temperature of upper atmosphere D) greater proportion of ...
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0answers
38 views

How to calculate the ship resistance caused by water viscosity

If there is a ship going in the sea at 50km/h, and a length of 5m, width of 2m, how do I calculate the ship resistance caused by water viscosity? in other words I want to calculate the drag Force that ...
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1answer
757 views

What is a Physically Accurate Explanation for the Kutta Condition?

Countless arguments between highly intelligent people have been waged (on this very site in fact) as to exactly how lift can be explained in an experimentally and mathematically rigorous way. Taking ...
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0answers
104 views

Derivation of the equation of motion of a viscous fluid by Landau & Lifshitz

I am trying to follow Landau and Lifshitz, from the Volume 6 (Fluid Mechanics) of the Course of Theoretical Physics, on their derivation of the momentum equation for a newtonian viscous fluid, but I ...
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3answers
133 views

How is viscosity described on the molecular level?

What is the 'molecular' origin of the viscosity? The molecular origin of elasticity is almost clear for me: at the very bottom the 'elasticity' comes from the attraction and repulsion between atoms ...
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1answer
78 views

Viscous Burgers equation physical meaning

The viscous Burgers' equation: $$ q_{t}+q\:q_{x}~=~\nu\:q_{xx}, \mbox{ where } \:\:\nu >0, $$ combines the nonlinear propagation of $q(x,t)$ and the diffusion. What is this equation for? (in ...
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2answers
85 views

How can a gas support tensile stresses?

In working through a rigorous derivation of the compressible Navier-Stokes equations, I find that the momentum flux in the X-direction should be driven not only by the normal pressure gradient ...
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1answer
79 views

Is a non-Newtonian gas possible?

I was wondering if it was possible to have a Non-Newtonian Gas. I was planning a science fair experiment to try to create one if its possible.
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1answer
80 views

Irrotational fluid

Often, when threating some problem of fluid dynamics I have read that people make the approximation of irrotational fluid, i.e. the velocity field is assumed irrotational: $$ \nabla \times \vec{v}=0 ...
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1answer
71 views

Torque required to turn the inside of a drum (Honey extractor) [closed]

I need to mount a motor with a variable speed drive(VSD) onto a honey extractor but need to know how much torque I need to start the extractor to start turning. The diameter is 700mm and the max ...
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1answer
47 views

What is the relationship between Q-Factor and viscosity for a Newtonian fluid based damper?

I am working with a rotary damper (paddle hanging off a shaft attached to the bottom of a rotary table and into a vat of fluid). I know the viscosity of the current Newtonian fluid, I know the flow is ...
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1answer
37 views

Deborah Number for harmonic excitation

I think I do not understand well the concept of Deborah number. It is presented in the sources available to me as the ratio between the relaxation time of a fluid and a characteristic time scale of ...
3
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2answers
79 views

How does the viscosity (besides density) of a fluid affects sinking

If water, air of whatever fluid had a different viscosity, but the same density, would things fall/sink differently?
3
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1answer
122 views

Explicit form of the entropy production in hydrodynamics

I'm trying to understand how hydrodynamics arise from a precise, mathematical formulation of thermodynamics, learning mostly from Landau's "Hydrodynamics". So Landau starts from formulating the ...
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2answers
61 views

Does the lift created by a wing change when the slats are deployed?

This is a conceptual question as much as an empirical one, but the question is: Does the lift of a wing change when the slats (or any other leading edge device) are deployed? I am stipulating that the ...
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3answers
116 views

Why does the tea in the middle of the cup spin faster when I stir it?

Try this: Make a cup of tea, add sugar, and stir it. Now add some milk, while it's still spinning. What I noticed is that the milk appears to move around a lot quicker in the middle of the cup of ...
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1answer
76 views

What causes the 'tears' in yoghurt drinks?

Fluid dynamical instabilities are present in many different everyday things. The famous tears in wine for example are a classical example of a Marangoni effect, where surface tension gradients due to ...
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0answers
65 views

An equivalent for the Bernoulli equation for viscous liquids

I was wondering whether there is any equation for viscous liquids (probably derived from energy and mass conservation principles) relating the pressure, rate of volume flow, area of cross section and ...
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2answers
208 views

Viscosity tensor in Navier-Stokes equation?

In my Hydrodynamics notes the viscosity term in the Navier-Stokes equation is of the form: $$ \nabla\cdot(\underline{\underline{h}}\cdot\nabla)\mathbf{u} $$ where $\underline{\underline{h}}$ is the ...
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2answers
71 views

What causes drag in a fluid?

What causes resistance of an object to motion within a fluid like water? Please explain to me the molecular dynamics of the situation.
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1answer
43 views

Atmospheric heating and the reduction in viscosity

The oceans are becoming less viscous as they are heated. I'd imagine a similar effect is likely occurring in the atmosphere as well. What, if any, effect would this reduction of viscosity have on ...
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1answer
83 views

Blood Viscosity

When measuring blood viscosity, the literature claims that we generally use a cone-and-plate viscometer. Why is this; is there any way to explain this mathematically in terms of the shear rate, etc? ...
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1answer
78 views

Viscous fluid flowing around obstacle: would it deflect earlier?

Consider a viscous fluid, flowing linearly (say, with velocity $\vec u = [1,0]$ everywhere). Then an obstacle is put in the flow. Would a highly viscous fluid start deflecting around the obstacle ...
3
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1answer
132 views

Why viscosity is diffusive?

I'm studying fluid mechanics in more depth during my Ph. D. and there is something related with the diffusive term that has been bothering me for a long time. Looking at the convection diffusion ...
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0answers
84 views

Determining The Coefficient of Viscosity and Diffusivity in an Estuary?

I am curious and eager to discuss about the experience of determining viscosity and diffusivity coefficient for our coastal or estuary model. I myself, just start to use the range of: ...
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0answers
163 views

Shape of the “flow head” in Laminar flow in pipe

Laminar flow is a streamlined steady flow with a uniform gradient of velocity across the diameter of the pipe. I am familiar with the elementary treatment of laminar flow, like basic velocity ...
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2answers
66 views

Estimating parameters to Falkenhagen equation for viscosity of solutes

In this answer to a question about viscosity of water in the presence of solutes, the Falkenhagen relation is given: $$\frac{\eta_s}{\eta_0}=1+A\sqrt{c}$$ where $\eta_s$ is the solution ...
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2answers
126 views

Dynamics of Honey in hot water: Honey accelerates like it is falling through air?

Here is a Video showing the honey accelerating in the hot water. As you can see, there are also dynamics. Since the water started stationary, I guess the dynamics arise because of convection flow. ...
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1answer
85 views

Motion of Object in Rotating water [duplicate]

Water inside bucket is rotated (by spoon or something) to flow in circular motion. An object kept in the bucket tends to be at the center of the bucket. Why is that?
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0answers
49 views

Is this explanation for the no-slip condition at a pipe wall correct?

The standard boundary condition for a fluid in contact with a surface is to enforce matching velocities at the interface. The explanation I was given is that contact forces between the wall and the ...
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1answer
129 views

How to calculate fluid(oil / hydrocarbon) loss under pressure

I'm trying to calculate the amount of fluid that would flow through an area dependant on the amount of pressure that there is. I'd also like to know the rate at which it would flow. Essentially I ...
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2answers
181 views

Why do some beverages stay cold longer than others?

For my daughter's science experiment, she placed six beverages (cola, diet cola, milk, chocolate milk, apple juice, and water) in the exact same amount in the exact same type and size of plastic cups, ...
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1answer
102 views

Viscosity of water in the presence of solutes

Some physical properties of water change in the presence of solutes: vapor pressure, boiling point, freezing point and osmotic pressure. In particular, these four properties are called colligative ...
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1answer
83 views

Shaking water inside bowl causes waves but why does the water stabilize?

Suppose you shake water inside a container, then at first the waves goes up and down strongly but they gradually dissipate. What makes them dissipate?
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1answer
221 views

Velocity of a viscous fluid through a tube

When a viscous liquid flows through a tube in a laminar flow, why is its velocity highest at the center? I understand the concept of shear viscosity and why the liquid in contact with moving plate ...
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2answers
317 views

Water doesn't flow above the rim, one reason is surface tension. Is another reason viscosity?

According to Surface tension, water molecule don't get the force from outside and get little bit outward. Is one reason viscosity? Let's look at the water in a fully filled glass. No part is outside ...
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1answer
571 views

What is the buoyant and viscous force acting on a ball in free fall?

I was thinking about a situation were I have a long cylindrical jar with some viscous liquid in it. I also have a spherical ball with me. I drop the ball into the liquid inside the jar with some ...
2
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1answer
2k views

What is bulk viscosity and how does it affect the flow? [closed]

What is bulk viscosity and how does it affect the flow? Explain the idea of introducing such a term in the Navier-Stokes equation. What are the consequences if not taken into account?
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2answers
416 views

$\gamma$ in Newton's Second Law of Motion in Differential Form

I am teaching myself Differential Equations from a website. In the website I am up to Direction Fields and an example of a differential equation is Newton's Second Law of Motion. It is written on the ...
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1answer
422 views

Plastic bottle floating and sinking

I was doing this experiment: i take a plastic cup, put in a container of water, it floats – then when I put a coin in the water, it sinks and rests at the bottom. So to make the cup sink, i fill it ...
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1answer
224 views

Conditions of applicability of potential flow about an airfoil

In many cases the flow about an airfoil is calculated by solving the Laplace equation, (for example in the Hess-Smith panel method). If the velocity field is irrotational and its divergence its zero, ...