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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14
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1answer
659 views

Kolmogorov/Energy spectrum for turbulent boundary layer

Previously, I have calculated energy spectrum for 3D isotropic turbulent flow data which is equally spaced in all three directions and then to compute the energy spectrum, one performs Fourier ...
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256 views

Are there known turbulent nonlinear equations where the cascade is a thermal gradient?

In a recent answer (here: The equipartition theorem in momentum space ), I suggested that if you have an appropriate first order equation (in the answer I used a second order equation, but it is more ...
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133 views

Where else in physics does one encounter Reynolds averaging?

Reynolds-averaged Navier–Stokes equations (RANS) is one of the approaches to turbulence description. Physical quantities, like for example velocity $u_i$, are represented as a sum of a mean and a ...
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79 views

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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135 views

Time scale turbulence flow -distance between two particles

I want to estimate the time interval, $\tau$, during which the original distance $L$ between two fluid particles become much larger. I assume that the motion takes place in the inertial interval. I ...
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123 views

Turbulence forming between the coaches of rail

is there any specific reason why rail coaches are connected by a rubber sheet; not of any other material ? I watched a documentary on trains (Discovery Channel) which said it connecting coaches by ...
2
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1answer
658 views

Reynolds number in a wind tunnel

I would like to understand how to calculate the Reynolds number in the test chamber of a wind tunnel. It is known that the Reynolds number for a pipe is: $$Re = \frac{UL}{\nu}$$ where $U$ is the ...
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105 views

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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142 views

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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67 views

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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228 views

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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125 views

The Optics of the Vortex (in Water): why there is a bright ring also in reversed flow?

This question is closely related to this one; The optics of vortex (in water): why there is a bright ring? In this case "physics girl" gives somehow an plausible explanation, and it's only debatable ...
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107 views

$L^p$-weighted enstrophy calculations

Mathematician here, only somewhat familiar with physics, but finding myself involved in a research project on fluid dynamics. I'm studying a 3D simulation of turbulent fluid flow, and we are currently ...
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31 views

Why hydrodynamic turbulence without heat terms matters?

A lot of research is made on turbulence in "pure" Navier-Stokes equations (NSE). There is a notion of energy cascade when energy comes from larger scales to lower scales and than dissipate. However ...
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250 views

Similarities between laminar-turbulence transition and others like BCS-BEC crossover, quark-hadron transition etc

From my limited readings on fluid dynamics, my understanding is that as the system changes from near-laminar flows to full turbulence, the dimensionless Reynolds number changes from $ R << 1$ to ...
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28 views

Regarding formulation of a multipoint model of fluid dynamics

Suppose I am trying to formulate a multipoint model of fluid dynamics. I have a procedure for doing so the details of which is not important to this question, but only that it is based on a series ...
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96 views

What is the relationship between complex time singularities and UV fixed points?

In this paper it is described how the turbulent kinetic energy spectrum and the flatness (a measure for intermittency) are governed by the position of the (dominant) singularities of the solutions of ...
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40 views

Turbulence and the symmetries of Navier-Stokes

I am reading the book "Turbulence - The Legacy of A.N. Kolmogorov" by Frisch. He begins the book by introducing the different stages of fluid motion when the Reynolds number increases. In particular ...
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55 views

Reynolds number in General Relativity

Does the relativistic counterpart of the Reynolds number exist, and how can find it? And what is the dissipative term in Einstein equations?
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42 views

Good resource for Drag Coefficient vs Reynolds number (various shapes)?

The Wikipedia page on Drag Coefficient has a nice chart a little way down that shows the Drag Coefficient vs Reynolds number for a sphere, derived from experimental data. I am interested in looking at ...
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172 views

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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22 views

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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1answer
690 views

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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44 views

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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1answer
36 views

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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54 views

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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85 views

Stratification vs Compressibility

This is a rather peculiar question to ask because as far as I know these two have sort of independent definitions, i.e. stratification is not necessarily associated with fluid motion on the other hand ...
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109 views

What is the physical interpretation of Rayleigh's inflection point theorem?

Let $\boldsymbol{u} = U(z)\,\mathbf{e}_x$ be the velocity profile of an inviscid parallel flow. Rayleigh's inflection point theorem states that this flow may be linearly unstable to perturbations only ...
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212 views

About the aerodynamic force on a rotating maple leaf seed

Every matured (ready to fall), wing-shaped seed of the maple leaf tree ends up in a rotating motion, no matter what it's initial position is (the seed follows the path of least action, or in more ...
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100 views

Onset of turbulence

Does every fluid undergo a transition in the presence of disturbances? Even if we could isolate the disturbances entering the boundary will the fluid still undergo transition and become turbulent ...
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108 views

Optical distortion caused by a vortex: “gravitational lensing” in a swimming pool?

Falaco solitons were accidentally discovered by professor R. M. Kiehn while he was visiting a friend's swimming pool. He describes them as [...] a pair of globally stabilized rotational ...
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2k views

About the definition of boundary layer

I've a question regarding the definition of the velocity boundary layer. The boundary layer is defined (correct if I'm wrong) as the region close to the body where viscous effects are important and ...
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75 views

How is zonal flow defined and computed?

The transition to turbulence in pipe flow was recently observed to be in the same universality class as directed percolation. This was done by reinterpreting the turbulence and laminar flow in terms ...
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1answer
238 views

Turbulence in gravitational waves

I want to understand physical meaning and possible implications of few terms often used in physics specially with regards to gravitational waves / space-time fabric Space-time fabric is disturbed by ...
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63 views

Dependence of the magneto-rotational instability (MRI) on thermal relaxation?

The MRI is the most efficient driver of turbulence in accretion discs (as measured by the effective scalar stress). The magnetic field, being properly coupled to the gas (weak coupling), connects the ...
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71 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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178 views

Can a hierarchy of fixed points potentially be used to describe a kinetic energy spectrum which is composed of multiple scale invariant subranges?

Making use of a nonequilibrium functional renormalization group (Berges and Mesterhazy, 2012) are able to investigate a whole hierarchy of fixed points that explain the successive evolution of a ...
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314 views

Physical interpretation of an intermittency definition

A random function $v(t)$ is said to be intermittent at small scales of its "Flatness" $F$, given as $$ F(\Omega) = \frac{\langle (v_{\Omega}^{>}(t))^4\rangle}{\langle v_{\Omega}^{>}(t))^2\...
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Need advice on bluff-body aerodynamic research

I am from civil engineering, I am doing simulation and analysis (CFD and other statistical method) on flow around bluff bodies as in a wind tunnel. Different from in aerospace aerodynamics, our ...
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1answer
38 views

Difference between alfven waves and magnetic fluctuations in solar corona

I have read in this paper https://arxiv.org/pdf/1911.07973.pdf about particles being accelerated in the solar corona either by Alfven waves (to my understanding when the turbulence is weak) or by ...
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27 views

How do we determine the flow regime during condensation without knowing the Reynolds number?

Condensation occurs in the mixed flow regime of a condensate film on a flat vertical plate. How does one determine the flow regime during condensation without knowing the Reynolds number? I know that ...
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23 views

Modification of Mixing Length Damping Function to include Surface Roughness

Surface roughness has been incorporated into the van Driest damping function in studies by van Driest himself (1956) and more recently by Krogstad (1991) and Crimaldi et al (2006). These models ...
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Behavior of parachutes in Crew Dragon launch escape experiment

When watching deployment of parachutes in SpaceX Crew Dragon Escape experiment, I noticed that sometimes parachutes collides with each other and later- separates. (Btw, you can watch this movie here, ...
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11 views

Estimating (or Modelling) an opening of vertically hinged door due to air flow

I am solving a simple looking, but actually difficult fluid dynamics problem. As shown, a hinged door is placed at the bottom of the box-shaped duct. Here, it is possible to assume any friction at ...
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48 views

How do I determine the shape of steam?

When you dip a fork into a plate of hot food right off the stove and pull it out again with a forkful of food, it generates water vapour steam from the temperature difference. I am wondering how the ...
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29 views

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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1answer
26 views

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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31 views

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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67 views

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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91 views

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 ...