# Questions tagged [flow]

The motion of fluids (gases, liquids and granular material).

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### Differential 1 form problem in 2 dimensional fluid flow

Problem: Consider a fluid flow emerging from origin at a constant rate and flowing uniformly out in all directions. If we assume that the fluid is incompressible then the rate at which fluid flows ...
1 vote
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### What are some good resources to learn fluid mechanics? [duplicate]

I know that there are a lot of resources out there to be explored and I have gone through several of them. What I want is some resource where fluid mechanics is treated, from a geometric viewpoint, ...
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### Is vorticity in ordinary liquids such as water quantized?

In superfluid helium, vortexes are quantized. A whirlpool of superfluid helium contains an integer number of these individual vortex quantas. But all physics comes from quantum mechanics. So it would ...
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### Open or closed windows in a tornado? [closed]

Should one have the windows open or closed when a tornado is nearby? B.S. in Physics but very rusty in this day and age. I have always been taught that one should keep windows cracked open because of ...
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### Granular Material Piles on an Inclined Plane

Consider a conical pile of sand (or any other granular material) that is placed on a flat surface. This conical pile has a given radius and height (r and h, respectively). What would the effect be on ...
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### Why will low pressure pulling higher pressure air towards it make "thrust"? [closed]

Low pressure air means a lack of air molecules. Normal pressure air means a normal amount of air molecules. Say you have a stationary (can't move no matter what) cube of say steel, with low pressure ...
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### Is air resistance truly linear in surface area?

Air resistance is generally said to be linear in the surface area of the moving object. Out of pure curiosity, I am wondering to what degree this is an approximation, i.e., when this assumption begins ...
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### Incompressible flow condition intuition

The derivation of the continuity equation leads to $$\frac{D\rho}{Dt}=-\rho(\vec\nabla\cdot\vec u)$$ as shown in this wiki article. If we assume that the flow is incompressible, it implies that $\rho$ ...
33 views

### Is Steady Flow necessarily Streamlined Flow? or Vice Versa?

Is Steady Flow necessarily Streamlined Flow? What about vice versa? What is the difference between the two? What conditions should be satisfied for a flow to be streamlined?
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### Does Pipe Temperature Directly Correlate To Water Temperature? [closed]

I need to know if just by taking a boiler flow pipe temperature that will tell me the water temperature that is flowing through the pipe. For example if the water from the boiler travelling through ...
1 vote
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### Where exactly is the friction with the pipe walls and the fluid? [duplicate]

Is the friction between the walls of the pipe and the no slip layer? Or is it between the no slip layer and the rest of the fluid above?
1 vote
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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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### Given the same cross-sectional area, is fluid velocity constant?

I'm currently studying a introductory section on fluids and was given this principle of continuity: $$A_1 v_1 = A_2 v_2$$ I understand the logic behind it (viz. the conservation of mass and whatnot). ...
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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 do I find the absolute maximum and minimum values of the Lamb-Oseen Vortex?

For an angular velocity function derived by Navier-Stokes, $$\omega \left(r,t\right)=\frac{\omega _0R_0^2}{R\left(t\right)^2}exp\left(-\frac{r^2}{R\left(t\right)^2}\right)$$ from which the azimuthal ...
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### Can supersonic flow be achieved without converging diverging nozzle?

Can supersonic flow be achieved without the presence of a converging diverging nozzle if sufficient pressure difference is available? https://www.tomshardware.com/desktops/pc-building/an-ordinary-...
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### Direction of force by fluid on convergent nozzle

If a convergent nozzle is placed at the end of a pipe, then, since mass must enter and exit the nozzle at the same rate in the steady state, the exit velocity is greater than the entrance velocity. ...
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### Does Navier-Stokes equations get correct result for complex turbulent flow without turbulence model?

Does Navier equations (1822 formulation) get correct result for complex turbulent flow without turbulence model? Is this 1822 formulation?
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### Location of Vena contracta

Is it possible to calculate the location of vena contracta downstream of an orifice? I am interested to see if for a fixed geometry, the location of vena contracta depends on the flowrate (velocity)? (...
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1 vote
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### Output of ventilator and air friction

Imagine you have a ventilator with straight rectangular ventilator blades which are rotated at some small angle from a perpendicular line to the rotating axis. The ventilator has 100% efficiency (all ...
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1 vote
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### Is this assumption about a vortex's angular velocity reasonable?

I am deriving a velocity flow function $\psi(r,t)$ that could be derived by (1) establishing the relation between two vortex area functions, $a(t)$ and $A(r)$, using the disk method of integration, ...
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### What are the differences between Navier and Stokes versions of equation?

What are the main differences between Navier(1822) and Stokes(1845) versions of equation? If I understood correctly, original equations formulated Euler, what did they invent that they deserved to ...
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### Where is the reaction force $F_2$ of $F_1$ applied?

Suppose there is a spherical container with high-pressure air inside, and there is a small hole on its left that sprays air outward. We all know that this will generate a left thrust F1. I believe ...
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### Transition from laminar to turbulent and vice versa

Let's imagine a viscous fluid flowing horizontally through a cylinder with inner diameter $d$. The Reynolds number for that setting is described as: $$Re=\frac{u\cdot d}{\nu}.$$ The fluid is first ...
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### Does high pressure make drag on a wing?

Say you have a plate facing the airflow right over a wing. Not attached, but just right over it. If flow separation and drag on the rear side of the plate (rear meaning the trailing edge of a wing) ...
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1 vote
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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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### Does (and how) a shark fin on car top (or fan blade) reduce drag?

I've heard this kind of shark fin on the roof reduces drag by breaking the wave that forms behind, where the roof bends into rear window. image source The story goes that it's similar to these fins ...
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