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.

Filter by
Sorted by
Tagged with
0
votes
1answer
13 views

Is it possible to determine the position of the laminar-turbulent transition of a boundary-layer?

Can the exact position of the transition point from laminar to turbulent flow be calculated when working with flat plates? Or can the position only be estimated based on the common Reynold's numbers ...
0
votes
0answers
8 views

Interpretation of wind power spectral density

I'm reading this article on Dryden Wind Turbulence Model, and also similar Von Karman wind model. The Dryden model gives power spectral densities of turbulent wind. But why is power spectral density a ...
1
vote
1answer
31 views

Which direction do whirlpools on a river eddy line spin?

In a turbulent flowing river, an eddy is created when water is forced upstream. The area where the upstream and downstream flows meet is called the "eddy line", and whirlpools often form ...
3
votes
1answer
29 views

Is there such a thing as laminar-turbulent transition in free flow?

Free flow in the sense of "without any objects or obstacles influencing the flow". High altitude wind or ocean currents could probably be real-world examples. There is the well known ...
0
votes
2answers
40 views

Free falling water from tap turns laminar to turbulent

Why does water flowing (falling freely) from a tap become turbulent after some distance? Radius at tap = 0.4 cm Distance from tap where turbulence start = 15 cm approx Radius where turbulence start ...
0
votes
0answers
24 views

Pressure in wake of turbulent vs laminar flow

I understand that a turbulent flow creates a smaller wake than a laminar flow, as explained here. Does the pressure inside this wake also depend on the flow regime (turbulent/laminar) or doesn't the ...
2
votes
2answers
72 views

Why is astronomy intensity interferometry immune to atmospheric turbulence?

I have read there is renewed interest in intensity interferometry in astronomy. I read that intensity interferometry is immune to atmospheric turbulence, which plagues astronomy and regular (amplitude)...
1
vote
2answers
58 views

Why does falling water become less and less focused as it falls down?

So, I was observing my water purifier fill up my water bottle and I noticed that the beam of water coming through it became less and less focused as it falls down more. Now, I do understand the ...
0
votes
1answer
31 views

Locality of the Turbulent Energy Cascade

Locality appears to be an omnipresent feature of physics, including within turbulent fluid dynamics. In 1941 Kolmogorov postulated that the turbulent energy cascade is driven by scale-local ...
1
vote
1answer
33 views

Wall shear stress definitions

Good afternoon everyone. In defining the shear velocity at the wall $u_\tau=\sqrt{\frac{\tau_w}{\rho}}$ for the incompressible turbulence, $w$ being the wall, I found in some literature that this ...
1
vote
4answers
596 views

Does flow separation starts earlier at higher airflow speeds?

At same AoA,will flow separation starts earlier (point of separation more upstream) at higher airflow speeds (=higher air inertia) compare to lower airflow speeds? High speed airflow has more air ...
1
vote
0answers
25 views

Understanding the Viscous Sublayer in Turbulent Flow

I'm slightly confused at how/why the viscous sublayer forms in a turbulent boundary layer. From what I understand, the boundary layer is a region where there is momentum transport through the planes ...
0
votes
0answers
14 views

Determining the Reynolds number from 3D velocity data

I have some 3D velocity data $\{v_x,v_y,v_z\}$ recorded over time at a very high frequency in an environment with anisotropic turbulence. I know that for a single (i.e. 1D) variable, we may use the ...
2
votes
1answer
23 views

Why is the production of turbulent kinetic energy maximum in the lowest layers of the turbulent boundary layer?

I have been studying the basics of CFD from a book titled 'An Introduction to Computational Fluid Dynamics' by H.K. Versteeg. In the turbulence modelling section, the author shows how the production ...
3
votes
3answers
720 views

Concept behind Reynolds number

I would be glad if someone can explain to me the concepts and the applications of Reynolds number in real-life. My handout has this explanation and I cannot understand it clearly... Reynolds number ...
2
votes
2answers
112 views

From where does irreversibility arise in the Navier-Stokes momentum equation?

A form of the Navier-Stokes momentum equation can be written as: $$ \rho \left( \frac{\partial \mathbf{u}}{\partial t} + \mathbf{u} \cdot \nabla \mathbf{u} \right) = - \nabla \bar{p} + \mu \, \nabla^2 ...
0
votes
1answer
31 views

What is instability in the context of fluid dynamics?

I have been reading a paper about the production of respiratory droplets in human respiratory tract and learned that they are produced due to instabilities, which includes the Rayleigh Taylor ...
1
vote
0answers
63 views

$C_d$ is bigger at laminar or turbulent flow?

Bodies can be subjected to pressure drag or friction drag. But let's consider the overall drag coefficient $C_d$. My question is: $C_d$ is bigger at laminar or turbulent flow? This image represents ...
0
votes
1answer
20 views

A technique to distinguish the mean magnetic field from the fluctuations in the solar wind?

My question is: Is there a technique to distinguish the mean magnetic field from the fluctuations in the solar wind? Thanks
0
votes
0answers
14 views

Can we differentiate flows with identical Reynolds numbers but with different turbulence intensities?

The Reynolds number is given by $$\mathrm{Re} = \frac{v_{rms} L}{\nu}$$ Now imagine we fix $L$, $\nu$ and $v_{rms}$ - so the Reynolds number is constant. Imagine two different flows: $$(1): \bar{v} = ...
2
votes
4answers
88 views

Transition from laminar to turbulent flow

Is there a mathematically rigorous definition of turbulent or laminar flow? As far as I understand, laminar flow - means, that the velocity fields varies smoothly along the distance and time. Layers ...
0
votes
0answers
11 views

Turbulent boundary layer development

I'm currently working on my bachelor's thesis about the numerical simulation of a turbulent air flow through a rectangular channel. As part of that I'd like to compare my results to empirical ...
1
vote
1answer
33 views

Why is turbulence dissipation $\epsilon$ defined this way?

When deriving the turbulence kinetic energy equation $k$ by taking the trace of Reynolds stress transport PDE, this term appears : $$ 2\nu \overline{\frac{\partial u'_i}{\partial x_k}\frac{\partial u'...
1
vote
1answer
31 views

In turbulence what to we mean that an eddy has a wavenumber k?

In turbulence what to we mean that an eddy has a wavenumber k?
0
votes
0answers
16 views

Converting a turbulence spectrum in frequency to wavelength

So, I have a spectrum calculated from an underwater sensor, $S_{vv}(f)$, and want to convert it to $S_{vv}'(k)$, where $k$ is wavelength and $f$ frequency. I assume Taylor hypothesis for frozen ...
0
votes
1answer
15 views

Explanation of figure:turbulent magnetic field lines + spatial distribution of out-of-plane electric current density

The following graph is supposed to present turbulent magnetic field lines along with the spatial distribution of out-of-plane electric current density. However I am not sure I completely understand ...
14
votes
4answers
3k views

Can a Styrofoam box bounce back into a moving van?

I just came across this video. A styrofoam box falls out of a moving van, bounces off the road and lands back in the van. How can the box land back so precisely inside the van?! Usually, I would ...
0
votes
0answers
12 views

Initial Conditions for no-slip velocity (Walls)

For CFD initial condition, I want to know if i have to apply a very high velocity gradient on the wall of a pipe (internal flow) as it's the case when you study the freestream flow which surrounds an ...
1
vote
0answers
21 views

Is there a non-dimensional argument for a fluid’s characteristic force?

What the characteristic force is Dimensional analysis has an interesting result in fluid mechanics: the quantity $\chi=\eta^2/\rho$ has the units of force, where $\eta$ is the usual dynamic viscosity. ...
0
votes
0answers
17 views

Is there any relation between turbulent energy dissipation and pressure loss?

It is known that pressure loss depends on viscosity of fluid. However I learned today that energy dissipation rate in turbulent flow is independent of viscosity. It sounds like there is a ...
1
vote
0answers
29 views

Is it possible to solve for pressure loss in turbulent flow along a pipe purely analytically?

I understand it's possible to find pressure loss using formulas such as the Darcy Weisbach equation works with turbulence - but to my knowledge the friction factor is derived using empirical means. Is ...
56
votes
4answers
6k views

Why are aerodynamic / streamlined shapes always stumpy at the front?

I'm building an autonomous boat, to which I now add a keel below it with a weight at the bottom. I was wondering about the shape that weight should get. Most of the time aerodynamic shapes take some ...
0
votes
2answers
74 views

Reynolds number determines turbulent or laminar but Moody Chart has different interpretation

One can calculate the Reynolds number to determine whether or not flow is turbulent or not inside a pipe with circulating water. The formula is: $Re = \frac{\rho VD}{\mu}$ Let's say one gets $Re = 10,...
0
votes
1answer
29 views

Why does turbulent mixing result in a reduction of pressure and an increase in temperature?

For example, if i have a horizontal orifice plate in a tube and i'm pushing flow through it, there will be significant turbulent mixing downstream of the orifice plate. E.g. https://www.youtube.com/...
0
votes
0answers
5 views

What does near field shear layer mean?

I'm reading a research paper and the abstract is as follows... Ignition initiation by a turbulent hot jet involves complex transport and chemical processes with disparate and sensitive time scales. ...
1
vote
0answers
20 views

Some question regarding turbulent eddies

There's several concepts I don't have a clear understanding of: Plots of the turbulent energy cascade have a wave frequency as the axis - yet I see definitions of this "frequency" as the ...
1
vote
1answer
38 views

Turbulent Energy Cascade - Scale Between the Integral and Kolmogorov Microscale

I have seen derivations of the the length scale, time scale and characteristic velocity of eddies in the inertial or large-scale range and in the diffusive or Kolmogorov scale range. I'm interested ...
1
vote
0answers
38 views

How does water move out of the way/around an object moving under water?

Let's say a torpedo moved under the water. Water is virtually in-compressible right? So what happens to the water in front of the torpedo as it pushes forward? It has to somehow move out of the way, ...
-1
votes
2answers
45 views

What is the structure on SUV's top back edge? [closed]

I see a lot of SUV's that has the structure as shown in the picture .I am talking about the the top back edge (right above the back window). Wont't it worsen the streamlined design and causing more ...
0
votes
1answer
27 views

What is the function for the magnitude of air resistance/drag?

In John Taylor's Classical Mechanics, he gives a basic treatment on air resistance/drag. In order to do this, he models air resistance as $\mathbf{f}=-f(v)\mathbf{\hat{v}}$, and then Taylor expands $f(...
1
vote
1answer
129 views

Why friction losses depend on velocity squared?

This is the reason that suction pipes of centrifugal pumps are most of the times much wider than the discharge pipes and that restriction of blood flow in arteries is always an alarming event. Does ...
1
vote
4answers
64 views

Confused about the direction of the Magnus effect force

From what I've read, the cause for the force acting as the result of the Magnus effect is the formation of a bended wake behind the moving sphere. Take a look at that picture: From that picture, it ...
3
votes
2answers
779 views

Can a theory of everything solve the oldest problem of turbulence? [closed]

Can a theory of everything solve the oldest problem of turbulence? Can we have unified theory of universe without solving the problem of turbulence?
1
vote
2answers
60 views

Is theoretically possible to have the laminar flow above $Re=10^7$?

The onset of turbulent flow ranges greatly, for pipe flow I came across the information that the onset of turbulent flow occurs at approximately $Re=10^4$, while for boundary layers on the airplane's ...
0
votes
0answers
22 views

How to simulate salinity gradient in experiment?

I feel like the question is probably fairly fundamental. I have to recreate oceanic turbulence in terms of salinity and temperature gradients. Temperature is easy - heater. What should I do with the ...
0
votes
1answer
71 views

Energy cascade in turbulence

I have studied that energy is transferred from larger eddy to smaller eddy and so on until that energy is converted into heat via viscous dissipation. 1. What i am not able to understand is why is ...
4
votes
1answer
45 views

Why turbulence is non-equilibrium?

I've encountered this notion many times that turbulence is non-equilibrium (e.g., Falkovich & Sreenivasan, Physics Today, 59, 2006). However, I am confused about what does it mean by "non-...
-1
votes
1answer
75 views

Why does a running fan causes some soundproofing in the room?

I notice that when I switch on my fan inside my room, the room becomes soundproof to a great extent to the outside noises. The greater is the speed of the fan, the greater is the soundproofing. When ...
0
votes
0answers
31 views

Approximation of air resistance of rectangle with angle alpha

my problem is not that hard to explain, but maybe hard to model, because I couldnt find anything appropriate on the forum or internet..;D I need approximate the air resistance force of a rectangle ...
0
votes
0answers
17 views

Correlation function definition in hear transfer (statistical theory of turbulence)

I am trying to reproduce the approach in the paper by Nikishov. Since the paper is not easy to get I will just write out the statements here. They write the heat transfer equation for averaged ...

1
2 3 4 5 6