Questions tagged [turbulence]

A regime of nonlinear viscous flow characterized by random, rotational motion with a wide range of length scales. Its study is critical to many fields, such as aerospace, atmospheric science, chemical engineering, and astrophysics.

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Most effecient negative shape to create laminar flow

I was looking at laminar flow filters to aid in my mycology work I'm doing. Most filters use an aluminum extrusion with fins. I figured the options out there are pretty expensive for what you get and ...
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Problem about the hypothesis of turbulence from Kolmogorov (1941)

I'm actually studying the famous paper of Kolmogorov (1941) about incompressible turbulence (https://royalsocietypublishing.org/doi/abs/10.1098/rspa.1991.0075), but something struck me and I can't get ...
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Uncertainty Decomposition in velocity signal

I have a timeseries with repeated measured velocity signal (almost periodic signal). To find the mean time-varying velocity, I have decomposed the signal and computed the ensemble-average and the RMSE ...
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Turbulent flow in a pipe - how to compute the friction coefficient $\lambda$

Consider a pipe of diameter $D = 0.01$ m and Length $L = 1.0$ m represented in the figure underneath. At the in- and outlet, the pipe cross-section converges, respectively diverges smoothly. We will ...
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Physical Interpretation of Kolmogorov 5/3 law [duplicate]

The Kolmogorov 5/3 law says that in turbulent flow, the energy $E(k)$ contained in a certain wave number k is proportionate to $k^{-\frac{5}{3}}$. How should one interprete this result in physical ...
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How much will a hole in the wing of a bumblebee affect its flying? [closed]

let's assume the holes are round shape in the middle of both wings. if the size is 1% of the whole wing, how much will be the impact? i assume this is not linear, how much will be affected if the hole ...
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Is there a physical limit to silent quadcopters, and what are the parameters?

Quadcopters can now navigate fairly well indoors. One could imagine many possible uses, including telepresence and security, but which are limited because of the loud noise. Assuming zero 'motor ...
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What exactly sets the scale in Fusion power plants?

In fusion power plants, larger devices are said to achieve fusion more easily, next step tokamaks like DEMO are even larger than ITER. In a quantitative way, what exactly isn't scale invariant in a ...
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How should energy loss in a hydraulic jump be calculated?

The energy loss in a hydraulic jump is still calculated with the old equation of Bresse from year 1860; (I.e., equation 7 in this paper from 2017) $$ \frac{\Delta E}{E_1} = \frac{(\sqrt{1+8Fr^2}-3)^3}...
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Is that reasonable to use kinetic energy and potential energy of a fluid system to define the laminar, transition and turbulent region?

This is my assumption ( I don't know whether it exists or not ): I suppose a fluid system always contains two types of energy, i.e., kinetic energy and potential energy. The kinetic energy of a ...
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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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What is a precise definition for laminar flow that includes “laminar vortex-shedding”?

I can't find a definition for laminar flow that includes vortex structures. See paper: Numerical calculation of laminar vortex-shedding flow past cylinders and countless others when googled.
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What is the relation between incompressible flow and laminar flow?

I have a small question about dynamics. My textbook shows me the velocity profile for an incompressible flow, which has a parabolic profile. Does this automatically mean it's laminar flow? I don't ...
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Dimensionless properties of turbulence with law of the wall

The velocity profile is defined as law of the wall is defined as $u^+ = f(y^+)$, where $u^+ = \frac{\bar{u}}{v^*}$; $y^+ = \frac{yv^*}{v}$ and $v^*=\sqrt{\frac{\tau_w}{\rho}}$. How would one then non ...
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Laminar vs. turbulent boundary layer equations

The 2D boundary layer equations (continuity and momentum) are given by: Can these also be applied to turbulent boundary layers? These simply come from Navier-Stokes and are simplified with scaling ...
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Why do large eddies in turbulence break-up

This is probably a silly question. But, Why do large turbulent eddies break up into smaller ones? A possible argument Why can't they (large eddies) retain their size and gradually diffuse instead of ...
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Vortex ring solutions in General Relativity

Vortex rings are captivating toroidal self-reinforcing fluid systems that can happen in turbulent fluids. I wonder if something similar can exist as a solution to Einstein's gravitational equations
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Does the drag equation only apply to turbulent flow

I am doing an analysis of the motion of an object in air and so I'm first finding whether the flow is laminar or turbulent. From my research, I'm still a bit confused as to whether the drag equation ...
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At what critical Reynolds number does vortex shedding begin?

In: "Fluid Dynamics", Chapter 3 (Turbulence), Section 26, Landau and Lifchitz analyze the problem of the stability of a steady flow past a body of finite size. The fluid is assumed to be ...
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Why naturalness is an issue in particle physics? It is not in fluid dynamics

I have often heard that naturalness is a strong argument in favor of Supersymmetry. They say that there must be energy scales not too far away the EW-energy so that the quantum corrections of the ...
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How does the transition to turbulence happen in incompressible fluids?

The question is difficult to understand unless I explain why I am asking it. I would not really be interested in Fluid Dynamics if the transition to turbulent flow were not, at least approximately, ...
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398 views

Is Navier stokes a turbulence model?

Is Navier stokes a turbulence model? If yes, what is the use of k-omega model.. if no, what does the Navier stokes equation got to do with the turbulence models ..? I am very new to fluid dynamics... ...
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How do speed and density change in a turbulent flow?

Suppose a fluid passes from having laminar flow, to having a turbulent flow (like when passing after an object). How do fluid speed and fluid density change after that?
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Circular flow in a bowl

Let us assume we have circular flow in a bowl or a tea cup. (1) If the velocity of the fluid in the bowl is low, we have laminar flow. (2) However, to my understanding turbulent flow is defined as ...
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How could I integrate the changing location of the midpoint of a streamlined body into either the drag or reynolds number?

Because the volume and surface area is constant I am not sure how to represent the change in flow dynamics - laminar to turbulent. (sorry if this is a stupid question, I am a biologist and I can't ...
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Mean velocity in unsteady flow

I'm starting hydraulic experiments, where I'd have to measure velocity in an unsteady flow with a device called Acoustic Doppler Velocimeter (acquisition rate: 100 Hz) . In DSP terms, I'd have a ...
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Slowing the late descent of an atmospheric probe in a gas/ice giant exploration [closed]

I remember the 1995 descent of the Galileo atmospheric module in Jupiter atmosphere. The robust casing made it withstand several dozens of bars of pressure before going out. What measures could be ...
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Difference between MHD turbulance and Alfvenic turbulence?

I'm quiet confused in reading literatures involved MHD turbulance and Alfvenic turbulence, it seems they are pointing to the same notion in most of the content. Please explain the difference of them?
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How can I calculate a Reynolds number if I do not know flow or the diameter of a pipe

I am a freshman student working on a capstone project. I am doing a microhydro feasibility study for a homesteader in my area. I am trying to optimize the size of the pipe that delivers water. I am ...
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What is the turbulent Navier Stokes equation for cylindrical coordinates?

I am looking for turbulent Navier Stokes equation for cylindrical coordinates. I know that RANS (Reynolds Averaged Navier Stokes) eq. is the solution, I understood the point of it but only for ...
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How would I calculate the speed passengers 'jump' based on the speed and displacement of a plane during turbulence?

I read recently that if I'm in a plane that hits turbulence, the plane might only move 1 to 20ft. However, due to the speed that plane is travelling at (say cruising at 550mph). The passengers in the ...
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Can I determine if the flow laminar or turbulent from the vorticity?

I made a 3D model and i get a numbers for the vorticity but i can't know if this numbers can used to determine if the flow is laminar or turbulent. and if yes what is the critical value of the ...
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RANS in cylindrical coordinates

Lets say we have a fully developed turbulent pipe flow. We consider the flow in cylindrical coordinates (x aligns in the streamwise direction). So $\bar{u_x}(r)$, we decomposition the flow as follow $...
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Mathematical description of Bernoulli equation and transition from laminar to turbulent flow

I am very interested in the mathematical description of the next topics: 1. Bernoulli equation 2. Transition from laminar to turbulent flow Could you help me ...
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Atmospheric turbulence and telescope resolution

I have this question asking me to decided whether we can view a a crater on the moon given the turbulence in the atmosphere turns a point source into an extended source of diameter 1". We also found ...
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Turbulence in fundamental particles

We know that when fluids move fast enough they create turbulence. So, my question is: Is it true for mass-less or negligible mass particles also, do they also show turbulence when accelerated to ...
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Are all Irrotational Flows Frictionless and Laminar?

A I understand, Irrotational flows are also inviscid (have zero viscosity). This would lead me to assume that these kind of (purely fictional) flows would be well ordered (Laminar) and be frictionless....
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Von Karman mixing length $l=k \frac{du/dy}{d^2u/dy^2}$

In a fully developed turbulent flow of an in-compressible fluid inside a pipe of radius $R$, velocity at the center is $U_m$. If we define $U^*=\sqrt{\tau_0/\rho}$, where $\tau_0$ is the wall shear ...
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2D Uniform Flow Inclined Plane - Reynolds Averaging: Leads to no Turbulence?

We're looking at a fully developed flow along an inclined plate, the $x$ coordinate is along the plate and the $z$ coordinate is perpendicular to it. In 2D, uniform flow I end up with the continuity ...
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How to prove the formula of energy spectrum of strain rate in turbulence?

From Pope's turbulence book, for homogeneous isotropic turbulence, how to prove the following relation for strain rate energy spectrum $$\langle S_{ij}S_{ij} \rangle = \int_{0}^{\infty} k^2 E(k)dk $$ ...
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Cascade vs Inverse Cascade: Energy flow in 2D and 3D turbulence

We know that vortices tend to coalesce in 2D(inverse cascade) as opposed to 3D where they 'break down' into smaller vortices(cascade) ie. energy flows fro larger to smaller scales in 3D and opposite ...
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Are any advanced Reynolds-averaged fluid models used in astrophysics?

Reynolds-averaged Navier-Stokes equations allow to split the description of a turbulent fluid into an averaged (typically laminar) flow on some length and/or time-scale and separate equations for the ...
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What is the “sweeping velocity” of a turbulent flow?

Background: While reading Rubenstein and Zhou 1997 I encountered an unfamiliar term, "sweeping velocity". To quote the authors (pg. 3): ...the sweeping hypothesis makes the decorrelation depend ...
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277 views

Spectral analysis of turbulent flow

I have the "energy spectral density" curve for a specific location in a turbulent flow. My curve is based on turbulence frequency (w) rather than wavenumber (k). The mean kinetic energy can be ...
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Will cigarette smoke show an onset of turbulence in vacuum?

In this video one can see how cigarette smoke changes from laminar to turbulent flow. The conditions, though, are far from ideal (by which I mean that the air in which the smoke flows has no common ...
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Would $\nu/k$ be a meaningful timescale in turbulence?

If we consider kinematic viscosity $\nu \, [\text{m}^2/\text{s}]$ and turbulence kinetic energy $k \, [\text{m}^2/\text{s}^2]$, we can form a timescale $$ \tau = \frac{\nu}{k}. $$ Is it a ...
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Simulating atmospheric turbulence

This problem comes from simulation of atmospheric turbulence. It starts with the following transfer function in the frequency domain: \begin{equation} G_v(s)=\sigma k_1 \frac{1 + k_2 s}{\left(1+k_3 s\...
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291 views

Acoustic power spectrum of a natural turbulent flow

For a long time I've been curious about predicting the acoustic power spectrum of river sound from hydrodynamic measurements. What got me started thinking about this topic was repeatedly observing ...
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Model for sound generated by air flowing through pipe

I'm trying to write a program simulating the sound of an petrol car engine, just for fun. As a part of this, I'm trying to model the sound of air escaping the combustion chamber through an open ...
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Turbulence Model on Unsteady Navier Stokes

I am asking you if the Unsteady (Time-Dependant) Navier-Stokes Equation is able to predict accurately the Flow Turbulence? I know that the RANS (with different Turbulence Models like Spalart–Allmaras, ...