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Question: <p>Poiseuille's Law relies on the fact that velocity is not constant throughout a cross-section of the pipe (it is zero at the boundary due to the no-slip condition and maximum in the center). By Bernoulli's Law, this means that pressure is maximum at the boundary and minimum at the center. But in the book ... | https://physics.stackexchange.com/questions/67398/why-is-pressure-gradient-assumed-to-be-constant-with-respect-to-radius-in-the-de |
Question: <p>I was trying to understand the derivation of the boundary layer equations at p.145 of <a href="http://www.unimasr.net/ums/upload/files/2012/Sep/UniMasr.com_919e27ecea47b46d74dd7e268097b653.pdf" rel="nofollow">http://www.unimasr.net/ums/upload/files/2012/Sep/UniMasr.com_919e27ecea47b46d74dd7e268097b653.pdf<... | https://physics.stackexchange.com/questions/74853/boundary-layer-equation |
Question: <p>I'm trying to understand the Blasius boundary layer solution, but I'm having some difficulties. Using wikipedia, I wonder how they get the first formula: <a href="http://en.wikipedia.org/wiki/Blasius_boundary_layer" rel="nofollow">http://en.wikipedia.org/wiki/Blasius_boundary_layer</a>. $$\frac{U^2}{L}\app... | https://physics.stackexchange.com/questions/74906/blasius-boundary-layer-solutions |
Question: <p>I have been studying fluid mechanics and currently I was trying to understand Euler's equation for fluid flow. For that purpose, I was following <a href="http://www.av8n.com/physics/euler-flow.htm" rel="nofollow">this</a> webpage.</p>
<p>My problem is in understanding Eq.(12). The author states that that ... | https://physics.stackexchange.com/questions/76127/non-uniform-field-pressure-on-fluid |
Question: <p>While reading on <a href="http://en.wikipedia.org/wiki/Froude_number" rel="noreferrer">Wikipedia</a>, I read the following</p>
<blockquote>
<p><em>The Froude number is defined as:</em></p>
<p>$$\mathrm{Fr} = \frac{v}{c}$$</p>
<p><em>where $v$ is a characteristic velocity, and $c$ is a characte... | https://physics.stackexchange.com/questions/75585/what-does-the-froude-number-represent |
Question: <p>I have a fluid line which passes high density fluid at $60 \text{psi}$. At the end there is a valve. I have a $30 \text{psi}$ dynamic pressure drop in the line valve itself creates a back pressure of $10 \text{psi}$. How do I reduce my pressure drop without changing tube parameters?</p>
Answer: <p>I could... | https://physics.stackexchange.com/questions/76019/how-to-reduce-pressure-drop-in-a-5-16-ss-tube |
Question: <p>I'm doing a project (dissertation) on the mathematics of Aerofoil Theory. I wonder if I could get some advice on a possible structure. I'm new to fluid dynamics, so it's quite hard to know where to start. </p>
<p>So far I've looked at different types of flows; streamlines and velocity potentials. I've als... | https://physics.stackexchange.com/questions/76765/aerofoil-theory-project |
Question: <p>When making cacao (the non-instant type), one usually mixes the powder with a small amount of milk or water before mixing this slurry into the rest of the milk/water. Some manufacturers of slurry feeding systems for biogas plants claim the same principle for their product: One mixes the solid feedstock int... | https://physics.stackexchange.com/questions/80023/why-is-a-solid-easier-to-suspend-in-a-thick-slurry-than-in-a-liquid |
Question: <p>Air compresses (change in volume) and it creates pressure. It's the internal energy (momentum of each molecules) creates that pressure. But in liquids as it can't be compressed (may be by .3% if I am sure about water) it can't be pressurised, right? This is only possible by an external force on water itsel... | https://physics.stackexchange.com/questions/81156/energy-of-liquid-and-gas-at-same-pressure-is-different |
Question: <p>Suppose there are two tanks(airtight) fully filled with water.one is kept on top of a ten storey building and one on top of a twenty storeyed one.They are NOT interconnected.Will there be a pressure difference?</p>
Answer: <p>Forget the airtight part. That just confuses the issue by making you deal with t... | https://physics.stackexchange.com/questions/82132/pressure-difference-in-water-tanks-at-different-heights |
Question: <p>Where does the motivation come from? $\tau$ is the shear stress, $u$ is the velocity and $\mu$ is the shear viscosity. </p>
<p>EDIT: Since I wrote the question on phone I wasn't clear enough about what I was actually wondering about (see comments below); thus let me clarify. </p>
<p>I was simply wonderin... | https://physics.stackexchange.com/questions/88897/what-is-the-motivation-behind-tau-mu-frac-mathrmdu-mathrmdy-for-new |
Question: <p>Suppose that a fluid is flowing parallel to and over a flat plate. Obviously, a boundary layer develops in which the velocity ranges from 0 to 99% of the upstream velocity U. Could somebody please show me how the streamlines would look in this boundary layer? What do they typically look like in boundary... | https://physics.stackexchange.com/questions/90456/streamlines-in-boundary-layer |
Question: <p>I have a bottle of vodka that has a load of gold flakes suspended in it. It has been sat still for over 24 hours and the flakes are all still suspended within the liquid: they have not risen to the surface or sunk to the bottom. Any ideas as to the physics behind this? </p>
Answer: <p>The viscosity of wat... | https://physics.stackexchange.com/questions/91243/festive-physics-gold-flake-vodka |
Question: <p>I want to get the density of a fluid going through a pipe. I can measure the flow and pressure with a flowmeter and the temperature using a thermometer. With this information, I want to calculate (or approximate) the instantaneous density of the fluid passing through my instruments.</p>
<p>How would I g... | https://physics.stackexchange.com/questions/92554/approximating-density-from-pressure-and-flow |
Question: <p>I have a cylinder full of water with diameter $D$ with a round opening on the bottom with diameter $d$. The water is friction-free and incompressible. Now I need a relationship for the efflux speed $v$ with which water exits the cylinder and I shouldn't use the approximation $d \ll D$, but formulate a gene... | https://physics.stackexchange.com/questions/94217/efflux-speed-of-ideal-fluid-dependent-on-diameter |
Question: <p>On small private aircraft the engine is placed at the front of the fuselage, or on the wings
E.g. Stationair, Otter </p>
<p>On combat aircraft the engine/s is placed at the end of the fuselage
E.g. Raptor, Typhoon </p>
<p>On larger aircraft constructed to carry cargo/passengers the engines are placed on... | https://physics.stackexchange.com/questions/32532/can-ship-boat-propellers-be-placed-with-adequate-protection-alongside-the-fuse |
Question: <p>There would be heat diffusion, of course, but heat diffusion occurs even without the exchange of fluid parcels between each environment.</p>
<p>We do know that cold air tends to be denser than warm air, and that pressure differences drive the exchange of fluid parcels. But let's assume that there is no pr... | https://physics.stackexchange.com/questions/43236/if-there-is-significant-temperature-difference-between-indoor-air-and-outdoor-ai |
Question: <p>Some fellow flutists and I are pretending to be experts at fluid dynamics and reading <a href="https://ccrma.stanford.edu/~pdelac/research/MyPublishedPapers/Thesis.pdf" rel="nofollow">Patricio Cuadra's thesis</a> on the topic:</p>
<p>On page 17, it says:</p>
<blockquote>
<p>The central speed of the jet... | https://physics.stackexchange.com/questions/43355/why-does-central-jet-velocity-of-a-flute-air-stream-not-include-aperture-size |
Question: <p>I apologize if this is too basic of a question for this forum, but when having arm-chair discussions about the fluid dynamics of flute playing, a friend has said:</p>
<blockquote>
<p>The lip-hole area together with the lung pressure is the cause of the pressure built in the mouth.</p>
<p>When measu... | https://physics.stackexchange.com/questions/43364/when-playing-the-flute-does-lip-hole-aperture-size-affect-air-pressure-in-the-m |
Question: <p>The Navier-Stokes fluid dynamics equations, said that, as Sir William Thomson (or Lord Kelvin) predicted:</p>
<ol>
<li><p>When two smoke-rings are moving in the same direction, with the same speed, one behind the other, the 'leading' ring will slow down and enlarge, while the 'following' one will get smal... | https://physics.stackexchange.com/questions/46506/how-can-these-fluid-dynamical-smoke-ring-phenomena-be-explained |
Question: <p>Very 'applied' question, but I have nowhere else to turn, so I'm asking the physics experts here: I have a carport whose ceiling is made of very lightweight paneling. I've had several times now that those panels have fallen down, without an evident reason. So I'm wondering: the wind (because of the placeme... | https://physics.stackexchange.com/questions/47925/could-the-bernoulli-effect-be-causing-my-ceiling-to-come-down |
Question: <p>The <a href="http://en.wikipedia.org/wiki/Darcy%E2%80%93Weisbach_equation" rel="nofollow">Darcy-Weissbach</a> friction factor for laminar flow would be $\frac{64}{Re}$</p>
<p>Now, having a shear thinning (non-newtonian) fluid where the viscosity is not constant how do I arrive at $Re$?<br>
To know an appa... | https://physics.stackexchange.com/questions/48587/how-to-calculate-the-darcy-weissbach-friction-factor-for-shear-thinning-laminar |
Question: <p>I was told that the total integral of the stress over the surface of a swimmer (i.e. the total force exerted by the swimmer on the fluid) always vanishes, because there are no external forces applied on it. That seems fair by Newton’s third Law.</p>
<p>But, how does it take into account the effects of the... | https://physics.stackexchange.com/questions/52187/swimming-and-forces |
Question: <p>Suppose I have a rod that has a density of $X <1$. If I were to submerge that rod in water (density 1), I would expect $X$ of the rod to be below water and $1-X$ of it to be above water (simple buoyancy).</p>
<p>But here's the catch. Suppose I attach one corner of the rod to a frictionless hinge, suspe... | https://physics.stackexchange.com/questions/51275/how-does-a-hinge-affect-the-amount-of-a-submerged-material |
Question: <p>We know that the lower atmosphere has high pressure and as we go up, the pressure decreases, if it's so then why doesn't all gases fly up into the upper atmosphere from the lower following <a href="http://en.wikipedia.org/wiki/Bernoulli%27s_principle" rel="nofollow">Bernoulli's theorem</a>? I do expect tha... | https://physics.stackexchange.com/questions/55820/query-about-bernoullis-principle |
Question: <p>How do I make a ripple effect in a bowl of water. I have tried throwing small pebble sin but it just splashes and sinks. I have read that I need to make the water a thicker liquid ie add glycerine, will this work and why? </p>
Answer: <p>Making water ripples in the bowel of water by throwing a pebble in... | https://physics.stackexchange.com/questions/56032/water-how-do-you-make-ripples |
Question: <p>Is it possible to have a membrane that will not let a liquid through it at normal pressures due to gravity, but pass that liquid when substantially pressurised?</p>
<p>For instance, a few inches of water (say 0.1psi) would be blocked, but 100psi would pass through. </p>
Answer: <p>Such membranes do exist... | https://physics.stackexchange.com/questions/56046/membrane-that-allows-liquid-to-pass-only-when-forced-under-pressure |
Question: <p>Consider the following:</p>
<pre><code> /‾‾ Valve --- Watering hose
Pump --- Pressure regulator ------ Valve --- Watering hose
\__ Valve --- Watering hose
</code></pre>
<p>A pump generating an arbitrary pressure and a pressure regulator
to curb... | https://physics.stackexchange.com/questions/55954/flow-in-parallel-paths-after-pressure-regulator |
Question: <p>In order to prove the Bernoulli’s principle ($\frac{p}{\rho} + \frac{1}{2}u^2+\phi = constant$ ), I have to use the <a href="http://en.wikipedia.org/wiki/Euler_equations_%28fluid_dynamics%29" rel="nofollow">Euler equation</a>: $\frac{Du}{Dt} = -\frac{1}{\rho}\nabla p + g$.</p>
<p>I know how to prove it, b... | https://physics.stackexchange.com/questions/56116/what-does-euler-equation-mean |
Question: <p>I am trying to understand <strong>the Bernoulli's theorem:</strong></p>
<ul>
<li><strong>$\frac{p}{\rho}+\frac{1}{2}u^2+\phi$ is a constant along a streamline</strong></li>
</ul>
<p>I got that:</p>
<p>$\frac{\partial u}{\partial t}$ + ($\nabla \times u)\times u$ = $-\nabla(\frac{p}{\rho}+\frac{1}{2}u^2+... | https://physics.stackexchange.com/questions/56323/bernoullis-theorem-fracp-rho-frac12u2-phi-is-constant-along-a-st |
Question: <p>Using all cylindrical coordinates, pipe with z-axis vertically upward and radius of $r = G(z)$, flow is incompressible, inviscid and steady, Using appropriate boundary conditions I want to find the wall pressure.Flow is axis symmetric and irrotational, and of the form $(a(r,z), 0, c(r,z))$ in cylindrical c... | https://physics.stackexchange.com/questions/57254/wall-pressure-of-a-fluid-flow-in-a-pipe-of-variable-radius |
Question: <p>Is it possible to calculate the force exerted on a bound, infected red blood cell under various shear stresses? The strength of an adhesive interaction is normally measured by SPR or AFM, however using microfluidics, you can increase the shear stress until the cell dislodges, therefore, can you use this da... | https://physics.stackexchange.com/questions/59304/blood-fluidics-can-you-determine-the-force-exerted-on-a-bound-red-blood-cell-u |
Question: <p>I'm in the business of purifying used cooking oil. Normally, I heat the oil up and let it settle for a couple of days. Water and solids settle to the bottom and cleaner oil remains on top. I'm trying to accelerate this process. </p>
<p>So, the idea is to take a vertical tank 5ft diameter, about 10ft tall ... | https://physics.stackexchange.com/questions/59629/spinning-liquid-to-create-a-centrifuge-effect |
Question: <p>I remember in the high school physics, my teacher told us that the design of the plane wing is because we want the air above the wing flowing faster than the air flowing below so the pressure above and below will be different so the net force is pointing upright. I am thinking if it is possible to explain ... | https://physics.stackexchange.com/questions/59977/how-to-explain-the-upright-force-for-the-plane |
Question: <p>I’m trying to convince my boss that the mixers we are using are too much. I’m trying to prove that we are over-mixing our product. Our product is ink…just your basic ink found in your printer at home. We mix in a 23 inch diameter 50 gallon vessel using a 2.75 inch diameter axial flow impeller going at 1050... | https://physics.stackexchange.com/questions/62786/what-is-a-good-reynolds-number-for-this-process |
Question: <p>In 2-d, one ripple would mean the velocity of water particles move out radially forming a circular wavefront. The Navier Stokes equations say the divergence of velocity has to be zero, but this circular radiation pattern has nonzero divergence. What am I missing here, since water ripples clearly exist?</p>... | https://physics.stackexchange.com/questions/64038/water-ripples-and-nonzero-divergence |
Question: <p>At room temperature....</p>
<p>How long will the sugar stay suspended once dissolved ?</p>
<p>What governs the rate of settling ? </p>
<p>What part does Brownian motion play ?</p>
<p><em>Sugar might be a bad example...please substitute as needed.</em></p>
Answer: <p>Anything dissolved is kept "suspend... | https://physics.stackexchange.com/questions/5562/what-keeps-the-sugar-suspended-in-the-tea |
Question: <p>How do I go about finding the pressure exerted on a rectangular surface in a free flowing air stream?</p>
<p>I wouldn't imagine that this is directly related to the airspeed / surface area, but have no idea where to start. Is there even an equation, or does one need to do some kind of FEA?</p>
<p>For ins... | https://physics.stackexchange.com/questions/5850/pressure-vs-wind-speed-on-a-rectangular-surface |
Question: <p>I am trying to model a system in which cubes of about 2 cm in size are floating in a circular water thank of about 30 cm in diameter. The cubes move around under the influence of the fluid flow induced by four inlets that point toward the center of the tank, and are located at the positions $0$, $\pi/2$, $... | https://physics.stackexchange.com/questions/6098/reynolds-number-turbulence-regime-and-drag-force |
Question: <p>I want to compute the viscosity of argon at different temperatures. What is <a href="http://en.wikipedia.org/wiki/Viscosity#Gases" rel="nofollow">Sutherland's constant</a> of argon?</p>
Answer: <p>I meanwhile found the constant by intensive googling (for example in <a href="http://www.cse.scitech.ac.uk/ce... | https://physics.stackexchange.com/questions/9995/sutherlands-constant-of-argon |
Question: <p>There is a <a href="http://io9.com/5811236/this-is-the-coolest-science-experiment-youll-see-all-week" rel="noreferrer">video</a> of an experiment from University of Mexico using corn syrup (highly viscous) and water. They are "mixed together" in a container by turning a crank but when the crank is turned i... | https://physics.stackexchange.com/questions/11065/entropy-decrease-using-stokes-flow |
Question: <p>I having trouble with this formula (asked first in math.Se, I didn't know the existence of physics.se)</p>
<p><span class="math-container">$$
Z_1(t) = Z_e+(\sqrt{Z_1-Z_e}-\frac{2S_0}{S_1}\sqrt{2g\left(1+\frac{S_1}{S_2}\right)}.t^2
$$</span></p>
<p>where <span class="math-container">$Z_1(t)$</span> and <s... | https://physics.stackexchange.com/questions/10778/communicating-vessels-formula |
Question: <p>Say I have a cylindrical container of some volume $V$, that I fill with water or some other fluid with dynamic viscosity $\mu$. Here, the bottom of the container is milled such that some fraction, $p$, of its surface area, $A$, is removed to allow passage of fluid. One could, for example, drill pores unt... | https://physics.stackexchange.com/questions/13242/pressing-a-fluid-through-leaks |
Question: <p>Suppose I have a flow of hot air around a cold and unevenly shaped object with holes and tunnels (think about it as a bed packed with some objects). I would like to know the Reynolds number of this flow and its convective heat transfer coefficient. The definition of the Reynolds number contains a "characte... | https://physics.stackexchange.com/questions/13321/can-i-measure-the-reynolds-number-or-the-heat-transfer-coefficient |
Question: <p>Is it possible for a liquid to exist in a high quality vacuume? For example, a few Torr.</p>
<p>If so what are the methods for doing this?</p>
Answer: <p>It's absolutely possible to have stable liquids at low pressures. It all depends on the equilibrium phase diagram of the liquid in question.</p>
<p>Lo... | https://physics.stackexchange.com/questions/14722/behaviour-of-liquid-in-vaccume |
Question: <p>Let's say I initially have an open, empty, soda can. I then turn it over and lower it into a bowl of water, and then release it. Obviously water rises to some level in the cup and then there is air at the top of the can, which was initially the bottom.</p>
<p>Are there only three forces on the can once it... | https://physics.stackexchange.com/questions/16147/clarification-of-equilibrium-expression-for-upside-down-can-in-water |
Question: <p>Okay... this is a bit desperate...</p>
<p>I am reverse engineering an excel program that is used for calculating outputs for a pressure vessel used for industrial process fluid heating.</p>
<p>There is a part in the excel sheet where a pressure drop is being calculated. But there are too many unit conver... | https://physics.stackexchange.com/questions/16403/what-formulae-for-calculating-fluid-pressure-change-involves-these-parameters |
Question: <p>There's an old puzzle (but the physical it is):</p>
<p>Lumberjack chop wood and float it down the river. He noticed an interesting feature: in the spring, when the water is comming, timber is nailed to the shore. In the hot summer, when the water lowers, timber, by contrast, floats exactly in the middle o... | https://physics.stackexchange.com/questions/16696/timber-floating-in-the-river |
Question: <p>An incompressible inviscid fluid is rotating under gravity g with constant angular
velocity $\Omega$ about the z-axis, which is vertical, so that $u = (−\Omega y, \Omega x, 0)$ relative
to fixed Cartesian axes. We wish to find the surfaces of constant pressure, and
hence surface of a uniformly rotating bucket... | https://physics.stackexchange.com/questions/19880/rotating-fluid-under-gravity-fluid-dynamics-question |
Question: <p>We all have noticed that changing the temperature of the water in the shower is not instantaneous, rather the result is felt when the water that was in the tap works its way up to the showerhead. However, changing the pressure does feel instantaneous. I wonder at what speed the change in pressure propagate... | https://physics.stackexchange.com/questions/21184/speed-of-a-dynamic-hydraulic-system |
Question: <blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="https://physics.stackexchange.com/questions/3244/vortex-in-liquid-collects-particles-in-center">Vortex in liquid collects particles in center</a> </p>
</blockquote>
<p>Sorry for my bad English. :-) Hello !</p>
<p>Here is my question :
... | https://physics.stackexchange.com/questions/21041/why-tea-dust-in-a-cup-of-tea-seems-to-concentrate-in-the-bottom-center |
Question: <p>Consider a yield-stress liquid in gravity. I assume that the buyouncy of a small gas-bubble will not be enough to overcome the yield stress (so the liquid doesn't behave liquid), thus leaving the bubble trapped. Is this so in theory, or is there a flaw in my thinking?</p>
<p>Sme argue that there are no yi... | https://physics.stackexchange.com/questions/29153/is-it-possible-to-calcualte-the-yield-stress-of-a-fluid-by-measuring-the-smalles |
Question: <p>My understanding of Kolmogorov scales doesn't really go beyond this poem:</p>
<blockquote>
<p>Big whirls have little whirls that feed on their velocity,<br>
and little whirls have lesser whirls and so on to viscosity.</p>
</blockquote>
<p>The smallest scale according to wikipedia* would be
$\eta = (\... | https://physics.stackexchange.com/questions/30125/how-do-kolmogorov-scales-work-in-shear-thinning-fluis |
Question: <p>I have a bottle filled with a fluid A, and a tube of volume $V_0$ filled with a fluid B leading away from it.
When I now start pumping fluid A out of the bottle, I am interested in the concentration $c(V)$ of fluid A in fluid B at the end of the tube after the volume $V$ exited the tube.</p>
<p>In my seco... | https://physics.stackexchange.com/questions/30907/concentration-of-fluid-pumped-through-a-tube |
Question: <p>Suppose you have a simple setting: a thin (scale of hundreds of nanometer to single digit micrometer) but in relation to that very wide (up to millimeters) box with an input and an output hole in it.</p>
<p>Given how thin the space is, would a fluid even go in there and fill out the box? How long would i... | https://physics.stackexchange.com/questions/427610/behaviour-of-fluids-in-thin-spaces |
Question: <p>In some of the literature I read that blood can be considered as Newtonian fluid when a larger vesses with high shear stress is considered... How is the shear stress calculated for aorta and how do they claim that shear stress is more for larger vessel when compared to the smaller ones . What is the relati... | https://physics.stackexchange.com/questions/428813/blood-as-newtonian-fluid |
Question: <p>What justifies this assumption on the free surface of the sea, taken from Faltinson's book (page 15), for a potential flow?</p>
<blockquote>
<p>A fluid particle on the free-surface is assumed to stay on the free-surface</p>
</blockquote>
Answer: | https://physics.stackexchange.com/questions/445776/justification-of-an-assumption-in-fluid-mechanics-free-surface |
Question: <p>From Franz Durst's <em>Fluid Mechanics: An Introduction to the Theory of Fluid Flows:</em></p>
<blockquote>
<p>When a fluid element reacts to pressure changes by adjusting its volume and consequently its density, the fluid is called compressible. When no volume or
density changes occur with pressure o... | https://physics.stackexchange.com/questions/449903/is-gas-flow-always-compressible |
Question: <p>Bernuolli says that in a pipe when speed <strong>increases</strong> pressure also <strong>decreases</strong> and that happen when pipe become <strong>narrower</strong>. </p>
<ol>
<li>So,if a fluid <strong>accelerate</strong> (increases speed) due to pressure difference in a pipe tha... | https://physics.stackexchange.com/questions/461861/does-pressure-decreases-in-accelerating-fluids |
Question: <p>[Edit: earlier version was even more messy]
I just watched a video of a jellyfish caught in a diver's 'air ring' - a torus blown for the sake of watching it rise. The jellyfish gets drawn into the torus and spun like a top as the bubble rises.
I want to know how fast, in rpm, the jellyfish is spinning at a... | https://physics.stackexchange.com/questions/490190/divers-air-torus-rising-from-10m-underwater-edited |
Question: <p>(Theoretically) suppose you had a material that only allowed water through one way but not the other.</p>
<p>Then you have a box of water and then put this material at the halfway point dividing the box in two. Eventually one side of the box would have less water than the other?</p>
Answer: | https://physics.stackexchange.com/questions/498348/can-you-create-a-pressure-differential-with-a-material-that-only-allows-flow-in |
Question: <p>I've been struggling with this concept for a very long time. I know about boundary layers in a very informal sense, such as in boundary layer separations at the trailing edge of airfoils and other objects immersed in flowing fluid. I also know about the boundary layer development in a pipe, as a plug flow ... | https://physics.stackexchange.com/questions/504467/what-is-a-boundary-layer-exactly |
Question: <p>The classical derivation of the Pitot tube equation assumes that the fluid is in a steady flow to use the Bernoulli equation version for steady flows. But in practice, does Pitot tube can be used also for unsteady flows? </p>
Answer: <p>Certainly. Unsteady flows (i.e., where the flow velocity changes with... | https://physics.stackexchange.com/questions/512675/can-pitot-tubes-be-used-for-unsteady-flows |
Question: <p>I was studying something related to fluid mechanics and then I found that <span class="math-container">$\nabla^2 \Phi = 0$</span> where <span class="math-container">$\Phi$</span> is the fluid velocity potential (<span class="math-container">$\vec{V}=\nabla \Phi$</span>). So I was wondering what does it mea... | https://physics.stackexchange.com/questions/523906/what-does-the-laplacian-of-a-fluid-velocity-potential-mean |
Question: <p>If we have an object submerged in water with a density greater than it then it will sink while objects with less density will float. This is found in many scientific articles and videos.. but why?</p>
<p>Particularly speaking, How do we understand this in a molecular picture? If we think of it using a free... | https://physics.stackexchange.com/questions/595362/molecular-explanation-of-floating-and-sinking |
Question: <p>Given a cylinder of fluid that is rotating the surface is of a parabolic shape. From what I can tell when deriving this the shape of the bottom of the cylinder should not influence the shape of the surface (as long as it is bellow the fluid surface). Is this true in practice?
Consider a parabolic bottom ve... | https://physics.stackexchange.com/questions/604116/does-the-bottom-of-a-rotating-cylinder-influence-the-shape-of-the-fluid-surface |
Question: <p>I'm trying to derive the fully compressible Euler-Momentum equation for the given Lagrangian.</p>
<p>We wish to derive <span class="math-container">$$\rho\frac{D\boldsymbol{u}}{Dt} + \nabla P + \rho\nabla\phi = 0 $$</span> from the Lagrangian <span class="math-container">$$ \mathcal{L} = \rho \left( \frac... | https://physics.stackexchange.com/questions/616297/derive-the-momentum-equation-from-a-lagrangian-fluid-dynamics |
Question: <p>I've noticed some people pouring coffee from a mokka pot alternates between two cups instead of directly filling one after the other. The reason argued is related to the beverage homogeneity, as the initial vapor will go through totally fresh coffee, in opposition to the very last drops. Neglecting the pos... | https://physics.stackexchange.com/questions/620048/mokka-pot-coffee-homogeneity |
Question: <p>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 velocity through a horizontal pipe, the pressure along the horizontal direction remains same.</p>
<p>Please expla... | https://physics.stackexchange.com/questions/650028/why-liquid-in-a-duct-flows-when-there-is-a-pressure-difference |
Question: <p>I'm trying to obtain <a href="http://en.wikipedia.org/wiki/Euler_equations_%28fluid_dynamics%29" rel="nofollow">Euler equation</a> for a perfect fluid in laminar or stationary flow. A particle fluid is submitted at volume forces and surface force. The fist, in my case, is giving only by gravity and the sec... | https://physics.stackexchange.com/questions/45648/euler-equation-of-fluid-dynamics |
Question: <p>I recently went to a dam and when I saw the water coming out of its gates with huge pressure. The water instantly got converted to cloudy fog and there was fog all around. Why and how this water gets converted to fog? Does pressure has to do something with this?</p>
Answer: <p>Sudden decrease in pressure ... | https://physics.stackexchange.com/questions/343249/water-coming-out-of-dam-gates |
Question: <p>Yesterday I answered <a href="https://physics.stackexchange.com/questions/208353/force-applied-to-a-90-degree-elbow-by-hydraulic-flow/208362#208362">this question</a>, using analysis of forces <a href="http://www-mdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/fprops/cvanalysis/node49.html"... | https://physics.stackexchange.com/questions/208430/centripetal-forces-acting-on-fluid-flow-in-a-bent-pipe |
Question: <p>If we have a fluid element that is subjected to:</p>
<ul>
<li>Translation</li>
<li>Rotation</li>
<li>Extensional strain (dilatation)</li>
<li>Shear strain</li>
</ul>
<p>As in this picture starting from time <span class="math-container">$t$</span>
<a href="https://i.sstatic.net/eIXgz.png" rel="nofollow nore... | https://physics.stackexchange.com/questions/210072/angular-velocity-of-a-fluid-element |
Question: <p><a href="https://i.sstatic.net/FztW0.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/FztW0.jpg" alt="enter image description here"></a></p>
<p>This very beautiful picture shows a jet of fuel in the combustion chamber of a diesel engine. Does anydody could explain me what is the physical rea... | https://physics.stackexchange.com/questions/244864/why-jets-entrain-mass |
Question: <p>I am trying to make a high pressure water jet using DIY hand pump which pushes water into a sealed vessel with non-return valve at the inlet. I am planning to do it by first closing the valve to the nozzle until i pump in enough water into the vessel so that pressure is created.then after open the nozzle v... | https://physics.stackexchange.com/questions/249734/i-want-to-increase-pressure-of-water-in-a-closed-vessel |
Question: <p>I have a basic question about efficiency of pumping. </p>
<p>If I have a well of 100 meters depth, but water filled till top, and I want to circulate the water. What will be most energy efficient. A) Pumping the water to 100 meters head and then discharging the water at top of that well but below water ... | https://physics.stackexchange.com/questions/249742/efficient-way-to-move-water-pumping-vs-circulation |
Question: <p>I have a mock exam problem that deals with fluid forces acting at different angles. Here are the scans:
<a href="https://i.sstatic.net/PE9AW.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/PE9AW.png" alt="enter image description here"></a>
<a href="https://i.sstatic.net/vAu0n.png" rel="nofol... | https://physics.stackexchange.com/questions/249805/how-does-a-fluid-force-behave-at-different-angles |
Question: <p>Recently, I found out about /r/InfrastructurePorn, and I found a particularly interesting photo of the Gouwe Aqueduct in Gouda, NE: </p>
<p><a href="https://i.sstatic.net/HG7Wi.jpg" rel="noreferrer"><img src="https://i.sstatic.net/HG7Wi.jpg" alt="enter image description here"></a></p>
<p>It seems like th... | https://physics.stackexchange.com/questions/250104/how-much-load-does-an-aqueduct-support |
Question: <p><a href="https://i.sstatic.net/Eptst.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Eptst.jpg" alt="enter image description here"></a></p>
<p>This picture shows a fuel ejector of a diesel engine that propels ships.</p>
<p>When the fuel line pressure exceeds 380 bars, the tension of the sp... | https://physics.stackexchange.com/questions/251934/a-question-about-droplets-formation |
Question: <p>Consider two identical pipes where two identical air flows take place. The pipes are "obstructed" by two filters made of the same fabric, one flat, the other pleated as shown in the following picture.</p>
<p><a href="https://i.sstatic.net/u7WKp.png" rel="nofollow noreferrer"><img src="https://i.sstatic.ne... | https://physics.stackexchange.com/questions/254754/pressure-drop-through-a-flat-vs-pleated-filter |
Question: <p>I am trying to learn how hydrofoil works. A big part of it is Bernoulli's principles.</p>
<p>I found this <a href="http://web.mit.edu/2.972/www/reports/hydrofoil/hydrofoil.html" rel="nofollow noreferrer">article</a> on MIT website.</p>
<p>There are two explanation for how it works:</p>
<ol>
<li>The cons... | https://physics.stackexchange.com/questions/258858/why-is-the-velocity-of-fluid-on-top-a-hydrofoil-higher-than-that-on-the-bottom |
Question: <p>I was filling a rubber pool for my baby using a hose. But I noticed that if I put the hose outlet directly with the floor there is an attractive force!
This is strange, because the hose is throwing water, and by action/reaction it should experiment a repulsive force upward (...I noticed this repulsive forc... | https://physics.stackexchange.com/questions/262495/attractive-force-between-hose-and-floor-when-a-pool-is-filled |
Question: <p>Hydraulic ram (<a href="https://en.wikipedia.org/wiki/Hydraulic_ram" rel="nofollow noreferrer">wikipedia</a>)(<a href="https://www.youtube.com/results?search_query=ram%20pump" rel="nofollow noreferrer">youtube</a>) uses the water hammer (<a href="https://en.wikipedia.org/wiki/Water_hammer" rel="nofollow no... | https://physics.stackexchange.com/questions/264398/how-does-an-hydraulic-ram-pump-work |
Question: <p>I have built a simple inline chamber for my irrigation system. I have made it so I can add powdered fertilizer to the chamber which will then be pumped through the system to the drip feed sprinklers. What I need to know now is how many liters of water must enter the chamber to replace the original contents... | https://physics.stackexchange.com/questions/272878/how-much-input-fluid-is-needed-to-fully-replace-the-contents-of-my-inline-chambe |
Question: <p><img src="https://i.sstatic.net/GnUeT.jpg" alt="enter image description here"></p>
<p>There's this fountain where I work. I haven't really studied fluid dynamics, so my question is about how it works. </p>
<p>The way the fountain is designed, is that there is one long big pipe that runs down the middle o... | https://physics.stackexchange.com/questions/299136/question-about-a-fountain |
Question: <p>Let's say we have a closed chamber filled with incompressible liquid and there are two area's(smaller(a) and larger(A)) where we can apply force or keep objects.We keep an object of weight W on larger area.Due to this,pressure at every point in a liquid will increase by W/A ,according to pascal's law.The s... | https://physics.stackexchange.com/questions/302454/why-the-excess-pressures-are-equated-in-hydraulic-press |
Question: <p>so I have been working on this problem :</p>
<ol>
<li>Diameter1 at wide end: 8cm || V1 = 1.56m/s</li>
<li>Diameter2 at narrow end: 3cm || V2 = 11.094m/s</li>
</ol>
<p><strong><em>Find the manometer reading</em></strong></p>
<p><a href="https://i.sstatic.net/ZKpT0.jpg" rel="nofollow noreferrer"><im... | https://physics.stackexchange.com/questions/305140/manometer-reading-from-fluid-dynamics |
Question: <p>(Hopefully this question isn't too elementary for this StackExchange.)</p>
<p>Given a micro-organism we'll define as two "cells" (which are the
atomic things in this model):</p>
<ol>
<li>A "main" larger cell: <code>O</code></li>
<li>A "tail" smaller cell: <code>o</code></li>
</ol>
<p>The <code>o</code> ... | https://physics.stackexchange.com/questions/313395/simplest-model-of-simplest-organism-swimming-in-fluid |
Question: <p>There is a large amount of expository material out there about the self similar solution to the Sedov Blast wave problem, and I am interested in obtaining the analytical expression so I can code it up and compare it to my numerical results.</p>
<p>From Chapter 17 of Shu's "The Physics of Astrophysics ... | https://physics.stackexchange.com/questions/601690/expressions-for-analytical-solutions-of-the-sedov-blast-wave-problem |
Question: <p>Is the pressure of an incompressible fluid discontinuous or continuous across an aperture? E.g. inside the fire hose water is at high pressure, outside of it it's at 1atm, but what does the transition look like at the aperture of the nozzle?</p>
<p>Since water is only <em>mostly</em> incompressible I'm sur... | https://physics.stackexchange.com/questions/607513/is-the-pressure-of-an-incompressible-fluid-discontinuous-or-continuous-across-an |
Question: <p>I'm learning hydrodynamics by googling stuff so forgive me if the question is super simple.</p>
<p>Imagine that I'm holding a cup of water, which I proceed to drop in a bucket laying next to my feet. The water will splash, and after some movement it will spread across the bottom of the bucket forming a thi... | https://physics.stackexchange.com/questions/608793/is-dropping-water-from-a-cup-in-a-dry-bucket-an-incompressible-flow |
Question: <p>There are already many answers to the general question of why birds or planes can fly. But my question is more specific: I would like to understand the relative importance of the viscosity. The air has a very low viscosity, so I am wondering whether it really makes a difference that the viscosity is non-ze... | https://physics.stackexchange.com/questions/610126/would-birds-be-able-to-fly-if-the-air-had-no-viscosity |
Question: <p>In the book of Batchelor, <em>Introduction to Fluid Mechanics</em>, at page 71 the author defines the fluid/material elements as a volume that contains the same fluid particles all the time. In other words, the fluid elements defined by the fluid particles that they contain.</p>
<blockquote>
<p>Nevertheles... | https://physics.stackexchange.com/questions/610408/if-a-fluid-element-defined-by-the-fluid-particle-it-contains-it-becomes-useless |
Question: <p>I have a 4' hose that is closed at one end and connected to a Airdata Test Set (precise control of pressure) and a high accuracy pressure monitor on the other end with a T and valve. The valve allows the Airdata Test Set connection to be closed off resulting in a hose connected to the pressure monitor and... | https://physics.stackexchange.com/questions/2158/why-does-measured-pressure-change-over-time-in-closed-hose-with-temperature-grad |
Question: <p>A barrel/drum with a diameter of 60cm is rotating at 20RPM to get a good mixing of the fluid contained (type thick oil). </p>
<p>At what RPM should a barrel of 30cm rotate to get the same mixing efficiency with the same fluid? To get the same peripheral velocity, the RPM should be 40RPM, but will this giv... | https://physics.stackexchange.com/questions/4038/mixing-of-fluid-in-a-rotating-barrel |
Question: <p>I have a use case where I want to produce fog (an aerosol) using an industrial grade high-volume fog generator and then I would like to direct the resulting fog to different locations i.e. small boxes in the same room. This way, I can have concentrated fog where I need and keep rest of the room space clear... | https://physics.stackexchange.com/questions/577913/how-to-pump-liquid-aerosol |
Question: <p>My textbook says that the volume of liquids is assumed to be such under atmospheric pressure. What if the atmospheric pressure is reduced? Will the liquid stop exerting pressure according to Pascal's law? Will there be an intrinsic force that the liquid will exert?</p>
Answer: <p>If you pull a vacuum on a... | https://physics.stackexchange.com/questions/566883/how-do-fluids-behave-in-a-vacuum |
Question: <p>The torus-shaped rotating space station, familiar from science fiction, is a way to produce artificial gravity in space. Would the fluid dynamics of gas in a rotating torus cause a person standing inside to notice any airflow?</p>
<p>It's noted (for example <a href="https://physics.stackexchange.com/quest... | https://physics.stackexchange.com/questions/309124/how-would-air-flow-inside-a-toroidal-space-station |
Question: <p>In most simple terms, Bernoulli's principle dictates that</p>
<ul>
<li>a fluid or gas moving in one direction exposes less pressure in orthogonal directions.</li>
<li>the sum of the pressures, in the direction of movement and otherwise, is equal the pressure as measured in rest.</li>
</ul>
<p>Essentially, ... | https://physics.stackexchange.com/questions/588481/bernoullis-principle-in-a-closed-loop |
Question: <p>In the hydrostatic case with no viscosity, we can write the gradient of the pressure inside a container of water within the gravitational field as
<span class="math-container">$$ \nabla P = g \rho$$</span></p>
<p>Moving close to a wall vertical wall, We encounter a normal force which should reduce our pres... | https://physics.stackexchange.com/questions/595136/evaluating-the-gradient-of-pressure-at-the-boundary-of-container |
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