1. ### I Laminar-turbulent transition and Reynolds number

Hi all! This is my first post here, so hopefully I am not in violation of any rules or etiquette. I'm looking to derive an equation for Reynolds number as function of pressure for a pinhole leak in a pressurized gas line. The line is regular air and is pressurized to 1 atmosphere and is leaking...
2. ### Diffusion or turbulence?

<Mentor moved to Physics> My teacher talks about turbulence (2D and 3D), but I don't quite understand this. How is the turbulence different in the two buckets, and why does my teacher talk about turbulence but not diffusion? Is not diffusion the reason why the dye spreads in the water? I have...
3. ### Average velocity in a turbulent flow tube

hi guys I'm really struggling to get the expression for average speed in turbulent flow The book explains absolutely nothing about how the integration is carried out, in addition to the fact that the logarithmic term becomes undefined when r = R what I did was carry out the integration up to...
4. ### I Turbulence Required For Lift

For the wing of a plane, as an example, I think that the circulation around the wing due to faster flow on the top is balanced by the circulation of a vortex which is formed off of the tail. Since the greater speed on the top is necessary for the lift, would that also mean the turbulent flow...
5. ### Requesting recommendations for specialized journal for....

A physicist I know is looking to publish a paper on a special case of the Navier-Stokes equation; he submitted it to Physics Review Letters, who rejected it for two reasons: (1) it was too specialized, so not suitable for the broad readership that PRL targets, and (2) the physicist had made used...
6. ### Flow Quality Impact on airfoil pressure distribution

I have collected velocity data for a 3-D grid of test section of a low speed wind tunnel.I have tested airfoils for pressure distribution in the same test section for similar free stream conditions. How do I calculate the impact of flow quality in the test section on the test results of pressure...
7. ### A Speed of fluid 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?
8. ### I How does a fluid behave inside of a spherical cavity?

Suppose you have a spherical cavity, with a flow of a fluid ( in particular water), entering it from one side. What will happen to this flow? Will it create turbulences? Will speed increase? Will eventual waves entering the cavity be reflected, so creating waves with bigger amplitude? Suppose...
9. ### I Would there be turbulence around objects w/o boundary layers

According to wikipedia "The onset of turbulence can be predicted by the Reynolds number, which is the ratio of inertial forces to viscous forces within a fluid which is subject to relative internal movement due to different fluid velocities, in what is known as a boundary layer in the case of a...
10. ### What causes pressure in form drag?

Consider a ball flying through the air. When there is turbulence, and the flow separates, say on a SMOOTH ball, then in the rear, there is circulation in the wide wake. There is pressure on the front, but no pressure on the rear due to the fact that the fluid is "busy" circulating around. So...
11. ### A Boundary vs. Flow Separation

Could someone please go here... https://en.wikipedia.org/wiki/Flow_separation And explain to me the difference between Flow and Boundary Separation discussed in the opening. Because this explanation makes no sense to me. I have the problem. I just don't understand the difference.
12. ### Laminar to turbulent flow transition

Is it true that the laminar to turbulent flow transition has been finally solved? From what I've read, it seems to be well described by the Directed Percolation Model. I can hardly believe it since I haven't seen the news in the press (from my point of view, it's a long standing unsolved issue...
13. ### I Golf ball and Tennis ball turbulence

So I have read many articles on tennis ball fuzz and golf ball dimples and I am more confused than before. Here is one that says that the dimples make the golf balls go faster: https://entertainment.howstuffworks.com/sports/golf/basics/question37.htm And just when it makes all sense, I read...
14. ### CFD Modeling of Flue Gas Pollution Dispersion

I've previously studied and used the k-epsilon turbulence model within Ansys to model water in a small stirred vessel. I am now interested in CFD models appropriate for modeling flue gas dispersion. I'd like to know: What additional considerations are required for modeling a gas as opposed to...
15. ### Inviscid flows and the turbulent (eddy) viscosity

Hello, After Favre averaging the momentum equation for an inviscid flow, the following can be obtained: \frac{\partial}{\partial t} \left(\overline{\rho}\tilde{u}_i \right) + \frac{\partial}{\partial x_j}\left( \overline{\rho}\tilde{u}_i \tilde{u}_j \right) + \frac{\partial...
16. ### Geophysical Dynamics

Why does the planetary boundary layer velocity profile shows a sinusoidal variation with height? Reference: Fig:14.10 Page 576 Fluid Mechanics - Kundu and Cohen 2nd edition
17. ### I Structure function in turbulence

Hey guys, I need your help. I have to write a homework and we are actually looking at structure functions (Kolmogorov 41 and so on), but I have no clue what it does. So I have formulas, but I do not understand what a structure function is. Is it something in the "real world" or is it just a way...
18. ### Integral length of turbulence

. ##\require{color} \color{white} \colorbox{crimson} {Mod Note: to see images in this post displayed correctly, click on Reply and view this in editor}## Hey guys, I need your help. It is about the integral length of turbulence flow. So we got data from some wind measurement, recorded at...
19. ### Why Reynolds Stress vanishes on boundary of closed volume?

The rate of working of the Reynolds Stress can be written as: where ui is the fluctuating velocity and Ūi is the time-averaged velocity. It is stated in the textbook that, if we integrate the above equation over a closed volume V, the divergence term on the left integrates to zero since τRij...
20. ### I Why is DNS more computationally expensive than k-ε?

In the modelling of turbulent flows, DNS is often too computationally expensive. Therefore, we take a 'statistical' approach and use mean flow equations, which require closure on account of the Reynolds stress. One way to do that is through the Eddy Viscosity Hypothesis, and one of the ways of...
21. ### Chaos & Scales in Turbulent Flows

Suppose you want to solve the Navier-Stokes equation for an incompressible turbulent flow. This is, in principle, possible. However, for higher Reynolds number, this isn't really feasible since the smallest eddy sizes are really small. First question 1) Why would this prevent you from...
22. ### I Why Prandlt Mixing Length Theory works at all?

There are several unreasonable assumptions in the formulation of the Prandlt Mixing Theory. However, it works reasonably well for simple 1-D flow. An attempt to explain why is given by Davidson in his book 'Turbulence', on page 122 - 124, section 4.1.4. It's stated that it still works because...