Questions tagged [fluid-dynamics]

The quantitative study of how fluids (gases and liquids) move.

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50 views

Why the total temperature remains constant through shock wave?

We know that total temperature is sum of static and dynamic temperature. If static temperature increases through the shock wave, then how total temperature remains constant? It must increase and not ...
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Find a general solution for gravitational potential, $\Phi(r)$ in a uniform, Newtonian universe, to derive Friedmann equations with $v_r = rH(t)$

I want to derive the Friedmann equation in a Newtonian regime, but properly. So, I am supposed to consider a cold fluid with density $\rho$, velocity field $v$ and gravitational potential $\Phi$. By ...
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Why does Drag force equation contradicts the relationship between Reynolds number and drag coefficient?

The drag force equation is described as: Where the surface area of the front of the sphere is = 2πr^2, so we can deduce that the radius and drag coefficient graph will look similar to this (the ...
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Intuition behind hydrostatic force/pressure being applied laterally

I can understand how the downward vertical force is being applied: due to the weight of the water column directly above it. However, I cannot understand how the lateral and the upward forces act. How ...
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Organized structures in rapid flows: Vortices, Rollers, Air Entrainment (Reference request)

Water flows in rivers show a wide variety of organized structures due to the interaction of the flow with its boundary. In whitewater, people give these features names like rollers, vortices, holes, ...
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What caused the 3rd shock wave in this nuclear explosion?

In 1958, the United States conducted a series of nuclear tests at the Pacific Proving Grounds in the Marshall Islands as part of Operation Hardtrack. In some recently remastered footage of the Wahoo ...
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Why do curved flows accelerate?

So I’m a bit of a fluid dynamics nerd, but for a while now this has been bothering me. We know that wings produce lift in part because of the flow accelerating over the top of the curved wing, and as ...
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Why turbulent boundary layer is much thicker than laminar one?

boundary layer thickness is a function of molecular diffusion or vorticity diffusion within boundary layer along the plate. more vorticity diffusion(more spread out) give us thicker boundary layer but ...
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Why does rainwater form equidistant waves on an inclined road? [duplicate]

It was raining down on this hairpin road, while I took this image. There was some very interesting waves forming with more or less equal spacing between each other. Also, if you could walk along the ...
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Effect of Reynolds number on shear stress (skin friction drag)?

in this chart: we see that as Reynolds number increase, skin friction decreases for both layers (laminar and turbulent). now if we assume that increase in reynolds number is due to the increase in ...
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Conditions of Bernoulli's equation: Do they matter?

Bernoulli's equation: $P+\frac{1}{2}\rho v^2+\rho gh=\text{constant}$ There are some conditions to use Bernoulli's equation. But often we neglect them. The fluid must be incompressible. But we use ...
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Velocity of a floating object underwater

I tried to find an equation for the speed and acceleration of an object floating from a certain depth of water to the top. But the equation always gives an imaginary solution in the case of floating ...
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Will a contained fluid and a fixed, perfectly consistent source of disturbance eventually settle into a pattern, or will it be chaotic?

Imagine you have a large room, which is completely sealed, and a cordless fan in the corner that constantly blows at a low speed. Disregarding effects like heat transfer from outside, minute physical ...
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Venturi Meter and Pascal's principle

When trying to understand how the venturimeter works, I got stucked with the following affirmation: Then, we have the equation $P_1 = P_2 + \rho g d$ Where $d$ is the distance between the two points,...
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Is Joukowsky Transformation still for airfoils?

The only example I can find for airfoil using Joukowsky Transformation is the 1912 Gottingen aircraft. I assume it's not used anymore ? What is the most recent math model / formula used nowadays ? ...
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The Venturi meter [closed]

The Venturi meter is a gauge to measure the flow speed of a fluid in a pipe. A manometer tube is also attached to it. At point 1, velocity of fluid is given by, In this gauge, why and how manometer ...
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Is the drag coefficient the same thing as damping coefficient? Can I find the drag coefficient using the data of a damping oscillating sphere?

I am currently working on a lab experiment to find a relationship between the diameter of a sphere and its drag coefficient. I will be using a spring-mass system that oscillates vertically and then ...
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Can a boat move by using an onboard fan to blow its sail?

Consider a boat with one sail and a fan fixed on the boat's deck. The fan is blowing air into the sail. If the fan is strong enough, will the boat move?
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Finding the drag coefficient of an object from damped simple harmonic motion (spring-mass system)

I am currently working on an experiment to determine the relationship between the diameter of a sphere and its coefficient of drag. I will be using a spring-mass system that oscillates vertically and ...
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How can air turbulence be less powerful than the wind shear that produced it?

The vortices from a plane's wingtips can rotate at a speed of 220 mph or ~300 feet per second. But I read that the air turbulence intensity resulting from these vortices can reach up to 85 feet per ...
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Compressible Navier-Stokes Equations and Millennium Problems

The 4th Clay Institute Millennium Problem is about the existence and smoothness of the Navier-Stokes Equations. The definition of the problem is limited to the incompressible fluid equation. What ...
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What forces act on a droplets hanging from surfaces?

What are the different forces acting on a hanging water droplet (tension of the droplet itself, surface adhesive forces, meniscus formation, etc)? What is the direction of each force, and how does ...
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G-mode wave in Stratified Fluid layers

I am currently studying on how internal gravity waves propagate within stratified disks of fluid (function of $y$ as shown in the picture). I am referring to the source written by Jim Pringle and ...
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Is damping rate of a pendulum dependent on the number density of the gas?

Robert Boyle in 1660 conducted experiments where he pumped air out of a vessel with a swinging pendulum. He discovered that the damping rate of the pendulum is independent of the number density of the ...
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What does it mean to have delta-correlated process physically?

I am reading about Langevin dynamics, and I see the following equation: $$\frac{dx}{dt} = -\frac{1}{\xi} \frac{\partial U}{\partial x} + g(t)$$ Then, they claim that the average $$\langle g(t) \rangle ...
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How do we use $Δh=v(Δp)$ in pumps assuming $ΔT=0$ while the temperature can increase for the fluid such as in rankine cycle?

In incompressible fluids. for liquids & Constant-temperature processes, as in pumps (ΔT=0) then Δh=v(Δp) . but for a pump in rankine cycle it will increase the temperature so how will we use Δ h=...
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Coriolis force at small scale

I would premit that I am not an expert (just an enthusiast) and my mathematical background is limited. That said I am trying to figure it out if the effect of coriolis force of big system (our planet ...
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Why isn't Navier-Stokes existence and smoothness obvious? [duplicate]

If I have understood the problem correctly (and I do not exclude the possibility of having misunderstood it), the problem of the existence, uniqueness and smoothness of solutions to the Navier-Stokes ...
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Can ellipsoid aircraft reach high speeds [closed]

Imagining an ellipsoid aircraft/spacecraft something like Could something like this reach high speeds? Assuming those nacelles hold some high tech ramjets or something equally powerful. I noticed ...
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How can mass diffuse out of a lagrangian control volume when it always tracks the same mass?

I am trying to understand how mass conservation in fluid flow works and how it relates to lagrangian and eulerian control volumes. The way I understand eulerian control volumes is that they are ...
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If three vortices with circulations of $\Gamma_1$, $\Gamma_2$, $\Gamma_3$ respectively merge, what is the circulation of the final vortex?

Assuming an ideal fluid (ie no viscosity) would it be: $\Gamma_{final} = \Gamma_1 + \Gamma_2 + \Gamma_3$ ? What would happen if the fluid is not ideal?
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What's the relation between temperature and scale factor for arbitrary EoS $-1 < w \le 1$?

I'm considering standard FLRW cosmology for a simple perfect fluid of pressure $p = w \, \rho$, with $-1 < w \le 1$. In the special case of $w =\frac{1}{3}$ (radiation), the temperature is $T \...
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Drag force on an object in a rotating fluid

A hollow cylinder filled with a Newtonian fluid starts at rest and is then rotated about an axis through its center. To the top and bottom surfaces, an object is attached. Case 1: The cylinder is ...
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Is a vacuum viscosity to entropy density relation 'hidden' in Ted Jacobson's thermodynamic formulation of Einstein field equations?

Ted Jacobson showed Einstein's equations can be obtained by applying thermodynamic laws to so-called Rindler horizons. In this paper Eling details Jacobson's thermodynamic derivation and then, by ...
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Why does the transverse Alfven mode not undergo wave steepening and hence resulting in shock waves?

Initial Question: I am currently working through the second edition of Introduction to Plasma Physics by Donald A. Gurnett & A. Bhattacharjee In section 8.3.8 on page 304, they state that: .. on ...
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Wave drag at high altitudes is high or low?

Density decreases with increasing altitude. Consequently, Reynolds number decreases and boundary layer thickness increases, so friction drag and pressure drag increase. What about wave drag? Does wave ...
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Is the van der Waals fluid viscous?

The van der Waals equation of states is well known: $$\tag{1} p(\rho) = \frac{a \rho}{1 - b \rho} - c\rho^2. $$ What is the energy-momentum tensor of this gas, considered as a fluid? Is it the simple ...
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Liquid velocity after a filter

Consider a water piping system of constant flowrate and diameter. The water passes through a filter and experiences a pressure drop (https://www.orangeresearch.com/why-differential-pressure-gauges.php)...
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Will adding an electric outboard to my sailboat provide the desired benefit of added propulsion when under sail? [duplicate]

I am considering adding an engine mount to the transom of one of my catamaran's hulls so I can move the electric outboard that is on my tender and get added propulsion when trying to sail to windward (...
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Why liquid in a duct flows when there is a pressure difference?

Liquid flows in a pipe when a pressure difference is applied on the ends. But can a liquid flow even if there is no pressure difference? Like in case the liquid (ideal) is flowing with uniform ...
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The relation between shockwave thickness and shockwave strength

What is the relation between shockwave thickness and shockwave strength? I mean with increasing altitude and increase shockwave thickness, shock become stronger or weaker? Defining strength of a ...
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Why are vortices stable?

Vortices persist over time, but change their shape. I am used to a structure that persists being “stable” as in it is robust against small perturbations. How can one define stability of a Vortex? For ...
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What is the upper speed limit for wind powered Blackbird?

Background Imagine you have wind powered car "Blackbird". The objective is simple make the fastest wind powered car. So I was watching Veritasium and learned that "Blackbird" can ...
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Resolution of some coupled Stokes equations

Let $B$ a solid ball of center $a \in \mathbb{R}^3$ and radius $R$. Consider the following stokeslest equation in the whole space, where $u_1$ denotes the speed of the fluid of viscosity $\mu$ and $...
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Book recommendation for hydrodynamics of bubbles, drops, and particles

I am wondering if someone could please recommend to me some references on the topic of hydrodynamics of bubbles, drops, and particles, preferably in the context of complex and bio fluids. I am ...
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Does increased air temperature cause increased maximum height of a jump by a person straight up into the air?

Assuming constant pressure, when the air is hotter, on a hot day, it will have less density and therefore cause a smaller fluid upthrust but also exert less air resistance. So, on a hot day, other ...
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Possible for Magnus effect to overcome rotational phenomena?

I’ve noticed that when a moving, rotating disk is in contact with a surface, it curves the opposite way it is spinning (eg, a puck on a table moving forward and rotating clockwise would curve left). ...
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Winds on gas giant planets: Would they increase if closer to their star?

The planets Saturn, Uranus, and Neptune are all primarily heated by their internal radiated heat, not by the Sun. Each of them have rotational periods shorter than that of Earth despite their much ...
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Why fluid pressure force is perpendicular to surface

I am informed that the pressure is due to the collision of particles on the surface.If so on the surface of water in a glass, the air particles could collide to water surface in many different ...
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Blackbird debate: Case when speed of car smaller than speed of downwind

I am puzzling my head around the Veritasium famous video right now: https://www.youtube.com/watch?v=yCsgoLc_fzI Also the Physics Olympiad problem Part B1 https://www.aapt.org/physicsteam/2019/upload/...

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