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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 ...
Active learner's user avatar
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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 ...
Kevin Kostlan's user avatar
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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 ...
Erik Jurgens's user avatar
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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 $\rho$ ...
GedankenExperimentalist's user avatar
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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?
Devansh Mittal's user avatar
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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 ...
Ross Hayward's user avatar
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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?
CaptainAmerica Whyso's user avatar
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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. ...
CaptainAmerica Whyso's user avatar
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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). ...
procommania's user avatar
2 votes
2 answers
333 views

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 ...
Tayler Montgomery's user avatar
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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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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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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, ...
Tayler Montgomery's user avatar
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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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Continuity Equation for Steady State Flow vs Incompressible flow

Good day guys, I have been reading on the continuity equations on the slides of my fluid dynamics course. I was introduced to the following definitions: Steady state flow: $\forall f \in \text{Flow ...
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What is the pressure near the end of the siphon tube inside water?

Consider a standard siphon Tube as shown What is the pressure at point O in the figure? A continuous streamline is there from A to O to B to C to D (correct me if I m wrong) Applying Bernoulli’s and ...
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Modelling the number of times a gas tank can be filled

I'm currently working on a project where I need to estimate how many times a large, high-pressure gas tank can refill a smaller tank. For this purpose, I'm using a pressure regulator to manage the ...
Enzo 's user avatar
6 votes
1 answer
127 views

Why do jet engine vortices go toward the ground?

This image was shown to us to illustrate how a tornado forms due to a low pressure region (also see Jet engine vortices). I find it odd that the tornado always ends up at the ground, where it is a ...
AlphaLife's user avatar
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Can the air have to travel slower than the aeroplane for the plane to experience a forward force?

The speeds are relative to the ground. Firstly, I don't understand how the speed of the air adds onto the horizontal speed of the plane. Since, the air moves slower than the plane in the horizontal I ...
Devil's Advocate 2321's user avatar
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Why will the Coanda effect make a piece of paper bend?

There is an answer here that explains the Coanda effect very well in my opinion. To summarize, the Coanda effect is when a stream of air flowing will ‘pull along’ the air molecules beside it, mainly ...
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2D Stokeslet: a reference?

Consider the Stokes equation $$ \begin{cases}\Delta u = \nabla p - F \\ \operatorname{div}(u)=0 \end{cases} \text{ in } \mathbb{R}^2,$$ with $u$ a velocity field, $p$ a pressure and $F$ a point force ...
2 votes
1 answer
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Finite differencing for velocity cross terms?

In writing down the Navier-Stokes equation I have encountered two equations as follows: $$ 4\frac{\partial^2 v_x}{\partial x^2} + \frac{\partial^2 v_x}{\partial y^2} + 3\frac{\partial^2 v_y}{\partial ...
Raj Upadhyay's user avatar
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Would this modified Tesla Valve improve performance?

I'm wondering if adding more loops, perhaps even in increasingly smaller loops (like a fractal) could improve a tesla valve's performance, or would the difference be negligible? This is what I was ...
Thom Blair III's user avatar
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Difficulties understanding fluid flow claims in the context of animal physiology/cardiovascular networks

A topic that has repeatedly given me confusion is the notion of fluid flow through animal vasculature. I find that many of the 'physics 101' basic notions of fluid dynamics are not well-suited to deal ...
S.C.'s user avatar
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Why doesn't the Coanda effect pull fluid from the center of the streamline?

As explained nicely in this answer, the Coanda effect will pull air from the surrounding air outside of the streamline. This picture shows it nicely : So my question is what stops the low pressure ...
Wyatt's user avatar
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Time derivative of moment of inertia tensor

Suppose that I have some fluid in a fixed volume. Its moment of inertia is given by $I=\int\rho r^2dV$. The derivative of $I$ is given by $\dot{I}=\int\frac{\partial\rho}{\partial t}r^2dV$. Why do we ...
James's user avatar
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3 answers
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Does air create a high pressure zone once the low pressure zone is filled in?

So say you have a sphere of low pressure air (let's say a 0.5 atm sphere in a 1 atm environment). Air would rush to fill in the low pressure, therefore it would accelerate to the center of it. Wouldn'...
Wyatt's user avatar
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2 votes
2 answers
170 views

Direction of shear-stress on fluid element

This image is regarding flow of viscous fluid between two parallel plates. I don't understand how they determine direction of shear stress above and below the element. As the flow is towards right ...
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2 votes
1 answer
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How does the chain rule work in sound wave analysis using fluid mechanics? $\tfrac{d x}{dt}\neq v$?

Context: I am reading Landau & Lifshitz's book on Fluid mechanics. Specifically its section on Sound waves. In section 101, the book's authors discuss about nonlinear traveling waves in one ...
asal's user avatar
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Hot dust contribution to whirlwinds forming

My father observed an event with a whirlwind and had an aha moment on its forming. What he saw was a weak wind blowing over a sun heated patch of dust, and when the dust rose up, all of suddenly a ...
Nemanja's user avatar
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5 votes
3 answers
387 views

Bottle with a hole, with straw through the lid

Consider a bottle filled with water, with an air tight lid, with a hole at height h. It's well known that the water doesn't flow out when the lid is closed. Now, if a straw is inserted through the lid,...
vishvAs vAsuki's user avatar
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1 answer
64 views

Conduction in liquid and gas

Is this condition correct, "if liquid and gas heated from top, then it will be possible for 'conduction' to occur" ? One reason i can think is : when liquid or gas is heated from sideways or ...
Cerebral cortex 's user avatar
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Continuity of a quantity in a conical system to determine the velocity field

My research is on radar images and the images are collected in several conical surfaces. These conical surfaces have the same origin, the same maximum length (max flare or max range), but different ...
CfourPiO's user avatar
1 vote
1 answer
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Why are water bubbles created at the top of the bottle if the water level is higher?

Water bubbles created at the top of the bottle if the water level is higher: but water bubbles is not created at the top of the bottle if the water level is lower: This question is very different ...
Cameron Melvin's user avatar
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Why cornering wind tunnel rotate?

Why cornering wind tunnel rotate, why is not just curved? A curved wind tunnel has a radial pressure gradient, but this pressure gradient doesn't exist in a real turn, so how do you get zero pressure ...
22flower's user avatar
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-1 votes
1 answer
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How to make a parametric that matches a vector field?

So I have a vector field defined as $(X(x,y),Y(x,y))$ and I’m trying to make a parametric $(t,t)$ who’s derivative at a point is equal to the vector field at that point. for example the vector field $(...
GIORGI GOGIBERIDZE's user avatar
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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) ...
Wyatt's user avatar
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1 vote
0 answers
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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 ...
culebrón's user avatar
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Lift generated by airfoil and why does a flow with a positive angle of attack around a flat plate curve upwards instead of downwards?

I've recently been reading about what really causes lift on an airfoil and the article linked mentions that even a symmetric airfoil or even a flat plate generates lift as long as the angle of attack ...
Hadi Khan's user avatar
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