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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In turbulent flow, where is the friction of the pipe exactly? Is it between the laminar layer and the pipe walls or the turbulent layer and laminar?
In turbulent flow as we get closer to the pipe walls we encounter an overlap layer and then a layer of laminar flow.
Also at the walls of a pipe, in turbulent flow, the laminar shear stress dominates. ...
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Bernoulli principle (classic form) in irrotational viscous flow (a paradox?)
We derive the Euler equation for inviscid flow. Then, for irrotational flow, we use the Euler equation to get Bernoulli equation (classic form) and show it holds in the irrotational region (still ...
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How to conceptually explain diagonal elements of viscous stress tensor in a fluid?
How can the diagonal components of viscosity tensor be explained conceptually? In other words, how can viscosity affect the normal stress (pressure) on the cube element of the fluid?
$$\sigma_{ii} = 2\...
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Recovering the classical Navier-Stokes equation from Landau's relativistic tensor [closed]
I'm trying to get to the classical compressible Navier-Stokes equation from the relativistic tensors in the Landau/Eckart frame. I understand these have their own problems about entropy.
In several ...
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Is it necessary that a particle attains terminal velocity?
In a viscous medium, consider a ball travelling under the influence of gravity and viscous force.
Is it always necessary that during its time in air, the ball attains terminal velocity
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Green Kubo Relation for viscosity
I am calculating viscosity of WCA fluid using the Green Kubo relation. I am also following the paper of Zhang et al. for the Time decomposition method https://doi.org/10.1021/acs.jctc.5b00351 where, ...
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Difficulties understanding fluid flow claims in the context of animal physiology/cardiovascular networks
A topic that has repeatedly given me confusion is the notion of fluid flow through animal vasculature. I find that many of the 'physics 101' basic notions of fluid dynamics are not well-suited to deal ...
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Does air create a high pressure zone once the low pressure zone is filled in?
So say you have a sphere of low pressure air (let's say a 0.5 atm sphere in a 1 atm environment). Air would rush to fill in the low pressure, therefore it would accelerate to the center of it. Wouldn'...
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Direction of shear-stress on fluid element
This image is regarding flow of viscous fluid between two parallel plates. I don't understand how they determine direction of shear stress above and below the element. As the flow is towards right ...
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Low Reynolds number flow and Potential flow
In an experiment conducted in my lab, we observed a low Reynolds number flow between two parallel plates with narrow gap between them resemble Potential Flow which is quite counter-intuitive as low ...
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Can frictional force be un-aligned with flow direction?
There is a well known solution to Navier-Stokes equations for atmospheric boundary layer according to Ekman (see for instance PalArya's book "Introduction to Micrometeorology" or Holton's &...
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Where did the idea for the approach to solving this boundary layer problem come from?
I found the derivation of Blasius-Equations here: A free stream velocity hits a flat plate and the goal is to derive boundary layer behavior.
Everything in this tutorial is clear - but the most ...
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Name of Equation $Q = \Delta P / R$
A very fundamental equation in understanding fluid flow is $Q = \Delta P / R$. When the flow is through a cylindrical pipe of constant radius, $R=8\eta L/\pi r^4$ can be substituted to give Poiseuille'...
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Soap film retraction dynamics
Let’s say you have a planar soap film, which thickness increases linearly. If you burst it, the film will retrace and the retracing speed will decrease. How exactly does the velocity of bursting ...
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Can angular momentum be transported between scales in turbulent flows?
Consider a turbulent rotating flow. You are interested in its average features so you use the Reynolds-averaged Navier-Stokes equation. Now, conservation of angular momentum implies the viscous ...
