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

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66 views

finding equation of a water droplet

I have a water droplet which is falling down through its gravity. I've supposed that my droplet is an ellipsoid and I want to find the equation that represents this ellipsoid in XYZ coordinate system. ...
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0answers
15 views

For thermal mass flow measurement technologies is it necessary to measure gas pressure to determine volumetric flow rate?

Mass flow readings from thermal mass flow measurement technologies often provide output readings in volumetric units (e.g. standard liters per minute). Mathematically I can derive the volumetric flow ...
2
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1answer
42 views

Effect of gravity on large tower with reduced air pressure

Suppose I built a 5km high building. The pressure of the air at the top would be around 50% compared to the pressure at the ground (I assume that the exact values don't matter in my case). Now ...
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5answers
44 views

Particles passing through a surface

Today is the day I ask silly questions : The book says the particles passing through the surface $dS$ are the ones contained in the cylinder of volume $dS.v.dt.cos(\theta)$ but I really don't see ...
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0answers
17 views

Hot wire anemometry and gas species

Hot wire anemometry is a technology that measures mass flow of a gas stream in the neighborhood of a heated wire. The sensitivity of a flow sensor using this technology is usually specified for a ...
3
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1answer
46 views

Bernoulli's equation for flow between cylinders

Let's consider the situation bellow noting that the water cylinders aren't equal and there will be water flowing to the right (As indicated by the arrow) Taking Bernoulli's equation at the tip of ...
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1answer
66 views

How does the divergence theorem justify the integral interpretation of the continuity equation?

I vaguely understand the continuity equation (at least its integral interpretation), but I don't really understand the differential interpretation of the continuity equation. I'm having trouble ...
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0answers
32 views

In terms of scale, where does the concept of Reynold's number cease to have meaning?

The Reynolds number is classically described in terms of pipe geometries but its use has also been usefully extended to other more complex surface geometries to predict transitional flow behavior. But ...
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2answers
57 views

Dynamic water pressure from flow and diameter

I've to test some fire hydrants and need to get the dynamic pressure. For that I know I can use a Pitot tube but... I don't have. After Googling a lot, I found two formulas allowing to compute the ...
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0answers
23 views

Equation of acoustic pressure in moving fluid: derivation

I'm looking for a detailed derivation of the equation of acoustic pressure with harmonic time dependence (of type $p(t,{\bf r}) = \psi({\bf r})e^{i\omega t}$) in moving fluid and under assumptions ...
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0answers
15 views

If a nozzle that converges from an inside diameter of 5cm to 3.5cm carries a gas at a VFR of 0.10 m^3/s, what is the change in average velocity? [closed]

If a circular nozzle that converges from an inside diameter of 5 cm to 3.5 cm carries a gas at a volume flow rate of $0.10 m^3/s$, what is the change in average velocity of the gas? (A nozzle being a ...
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0answers
20 views

flow through an orifice [closed]

The surface area of a first orifice with 2 mm diameter is 3 mm$^2$. The surface area of a second orifice is 5 times bigger from the surface area of the first orifice (15 mm$^2$). How much would be ...
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3answers
56 views

Propellers and the Speed of sound

I was reading this website that described a novel wind turbine technology and it has this quote: In the mid-20th century, open propeller-driven planes with piston engines reached performance ...
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0answers
14 views

What is “full clutching flow” in fluid-dynamics with regards venturi design?

As the title says, what is "full clutching flow" in fluid-dynamics with regards venturi design? I came across this reference a few times and can not find any further info on it, I'm currently ...
2
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0answers
69 views

Steady-state adiabatic nozzle, unknown exit velocity & temperature [closed]

The question is 2.10 taken from: Introductory Chemical Engineering Thermodynamics, 2E by Elliot,Lira Air at 30ºC and 2MPa flows ata steady state in a horizontal pipeline with a velocity of 25m/s. ...
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0answers
41 views

Static,total and velocity pressure at a point

I have a past exam question that I am stuck on. $200$m$^3/s$ of air is entering a shaft of $5m$ diameter, the density is $1.18$kg/m$^3$, and I have shock loss of factor $X=.5$ I want static, ...
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1answer
47 views

Effect of Reynolds number on wake region

For a flow over a smooth sphere, does the wake region increases with increase in Reynolds number? And if so, then why?
5
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1answer
85 views

Titanic Question

I was reading this question: Was Titanic's captain's decision correct? @oakad commented about a Russian vessel keeping itself afloat by going in reverse, using hydrodynamic pressure to keep ...
0
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1answer
31 views

Interaction of ocean waves and currents

I was on a small island recently near high tide. As the tide started to go out, a tidal pond emptied into the ocean through a narrow channel with a strong outgoing current. There was also wind on ...
2
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1answer
294 views

Calculate flow rate of air through a pressurized hole

I was wondering about this: If there is a pressurized container, like a tank of compressed air at some pressure that is greater than the ambient air pressure, and this tank of air has a hole in it, ...
3
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2answers
31 views

air flow with line fans

I must vent air through an 8 inch duct from one area to another using an 8 inch line fan. One goal is to vent the maximum amount of air possible through the duct. Is there any different between ...
2
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2answers
51 views

Fluid flow at mach 1

fluid-dynamics is not my preferred discipline, yet I have been landed with this problem and just seeking some clarification. I have a nozzle at the end of a tube, with 8 holes in it, and we are going ...
2
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1answer
34 views

Erosion effect from Coriolis force in a South-to-North water channel?

Imagine we could build a channel (like those cool ones in some countries) but very, very long, parallel to a meridian (ie South-North direction).. The channel would contain water, which would ...
0
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1answer
45 views

Flow rate is calculated only using the parallel component of the velocity vector

Flow rate is calculated using only the parallel component of the velocity vector to the area vector. Why is this? How can I mathematically prove this? Namely, how do I prove any perpendicular ...
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4answers
931 views

Calculate water flow rate through orifice

I'm not very good with fluid physics, and need some help. Imagine the following setup with water contained in-front of a wall with an opening on the bottom: How do I calculate the water flow $Q$?. ...
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2answers
73 views

Intuitive explanation of Poiseuille's law — why $r^4$?

According to Poiseuille's law, the effective resistance of a tube is inversely proportional to the fourth power of its radius (as given by the following equation). $$R = \frac{ 8 \eta \Delta x}{\pi ...
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1answer
132 views

Calculation of pressure from flow rate of water

Anybody kindly help me to find how to calculate pressure in bar from flow rate. I have a pipe and from that I am transferring water at a constant flow rate of 5ml/min. At this flow rate, with a 0.5 cm ...
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42 views

st. venant shallow water equations for pipe flow

As far as I know from the fluid dynamics class, St. Venant equations (the shallow water equations) are derived by depth-integrating the Navier-Stokes equations. This depth-integrating is done with the ...
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2answers
114 views

Fluid dynamics - Water level in a container

An open container is being filled with water from the top at a constant volumetric flow rate $300 \frac{cm^3}{s} $. At the same time, water is leaving the container trough a circular whole at the ...
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0answers
17 views

Rapids in a River

Can I expect to have bigger or smaller rapids in a river that has a water level that is higher than average? I am not sure which way this would go. With the lower water, one is closer to the rocks, ...
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0answers
35 views

Speed of Water in a River

Does a river flow faster the higher the water level - or does it go at exactly the same speed? I was recently tubing in a river and the water seemed to be going faster with the water level being ...
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1answer
45 views

Flow of water in a lake [closed]

You are 10 miles upstream from a dam. A 50 sq ft gate 30 feet above the lower water level is opened and water starts to flow from the dam. How long is it until your boat starts moving towards the ...
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1answer
55 views

How does one calculate calculate buoyancy with gases?

I have hot air flowing vertically down a circular duct into the ambient cold air. I'm trying to find the power $P$ that resists the flow. I know the: Volumetric flow rate $Q$ $[m^3/s]$ Flow speed ...
3
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1answer
150 views

What is the math/physics behind maximizing tinker's damage?

Tinker is a hero in the popular game Dota 2. He has a spell called 'March of the Machines' that creates a stampede of little robots in a rectangular area. The robots do damage on impact of an enemy ...
3
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1answer
145 views

Torque on a rotational cylinder in viscous fluid

I've been stuck on what I'm pretty sure is a simple part of a larger question. It's a cylinder (radius a) spinning in a viscous fluid. It's rotating at rate $\Omega$ .During this question we get that ...
6
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2answers
94 views

What makes laminar cascade break?

Near my house there is a mall that have a cascade, which has a pratically constant flow, and doesn't seem to have perturbations (at least near the edge where water falls), between its two levels. ...
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1answer
117 views

Bernoulli's principle

In steady flow, the air that flows faster causes a lower pressure, the lower pressure causes it to move faster, or exactly both at the same time? Also how is it that we're talking about the pressure ...
0
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1answer
110 views

Determining fluid flow velocity from experimental volumetric flow rate data

I would be very grateful if someone helps me with my issue. I have a pump pumping water into a tube. My goal is to find velocity of the fluid flow in another tube that will be connected to the first ...
0
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2answers
81 views

Wind bouncing off surfaces

What are the physics of wind (or any gas flow really) bouncing off surfaces? If a wind hits a wall directly (in a 90 degree angle) does any of it bounce back? Are there any similarities with, say, ...
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0answers
56 views

An equivalent for the Bernoulli equation for viscous liquids

I was wondering whether there is any equation for viscous liquids (probably derived from energy and mass conservation principles) relating the pressure, rate of volume flow, area of cross section and ...
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2answers
59 views

principle in a water Faucet [duplicate]

If you try to block with your finger the flow of the water out of the faucet or a water hose, the water's speed increases. But while you're blocking the water flow out of the faucet by turning the ...
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2answers
140 views

Integrating the divergence of a velocity field (Fluid Mechanics)

I'm looking more for verification of my answer as I'm not 100% sure how valid my integration is here: If I have a 2-D incompressible fluid velocity field given by ...
2
votes
1answer
78 views

Why does (potential) fluid flow bend around a solid surface in the flow?

Potential flow obeys Laplace's equation with certain boundary conditions (i.e. no fluid penetrates the solid body in flow, and far away from the body, the flow is uniform with a given velocity and ...
1
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1answer
45 views

Minimum amount of fluid to experience turbulence?

Turbulence is a challenge to model and simulate: "When I meet God, I am going to ask him two questions: Why relativity? And why turbulence? I really believe he will have an answer for the ...
2
votes
1answer
58 views

Darcy Flow in porous material - consider porosity in cross-section area?

According to Darcy's Law, the volumetric flow rate Q of a fluid occuring due to a pressure difference $\Delta p$ over a distance L and through a cross-sectional area A of a porous medium (volume V) ...
2
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1answer
96 views

Continuity and Blood Flow

Consider a tube with two different diameters (one section wider than the other). Because what comes in must go out (conservation of mass), the flow rate in the wider section must be the same as the ...
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0answers
24 views

Explicit solutions to simple one-dimensional fluid flow problems? [duplicate]

In order to test and verify numerical simulation results, I'm looking for explicit (or approximate) solutions to simple fluid flow problems to recalculate (like e.g. the pressure development during ...
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3answers
2k views

Why does water gulp out of a water bottle with a narrow opening instead of a steady flow?

For example, take a water bottle. Fill it with water and then turn it upside down. Instead of flowing steadily downward, it gulps down in parts. Why?
3
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1answer
71 views

Mathematically impossible for a vortex line to have loose ends?

Could someone show the math behind it? Source : "A vortex is a bunch of air circulating around itself. The axis around which the air is rotating is called a vortex line. It is mathematically ...
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3answers
146 views

Does the equation of continuity hold for turbulent flows?

My textbook mainly deals with laminar flows. The book derives the equation of continuity, which states that the cross-sectional area times the velocity of a flow is always constant. But nowhere in the ...