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

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Does eq. of continuity hold in vacuum too?

When a streamlined flow of water flows down through an ordinary tap, it's cross-sectional area decreases according to eq. of continuity due to atmospheric pressure. If the same apparatus were to be ...
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1answer
45 views

How the flow is distributed when the water flow from one river/drain to multiple rivers/drains?

Assuming that water ( total amount $Q$) flows down from one river/drain, into multiple rivers/drains, under the action of gravity, as shown below: How the flow ($Q$) will be divided among different ...
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0answers
14 views

Should tunnel calibration factor be less than 1?

Regarding an experiment in which air is blown past a small-scale object (i.e. a cylinder) in a wind tunnel, should the tunnel calibration factor be less than 1? I couldn't find anything about this ...
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0answers
21 views

Hydraulic conductivity and flow rate

I have several sources that have the following equation relating the change of volume in a cell to the hydraulic conductivity (permeability coefficient) $L$ and pressure differential $\Delta P$: $$ \...
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1answer
37 views

How do I find a stream function given a volumetric flow rate?

How do I find a stream function given a volumetric flow rate? The flow only occurs in one direction, between 2 plates, and I have no knowledge of velocity. I know that volumetric flow rate = ...
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3answers
972 views

When passed, why does my car 'rock' on the highway when I'm stopped, but not when I'm moving?

I am the blue car in this scenario. If I am stopped on the highway and am passed by a car going fast (about 65 mph), I feel my car rock in the left/right direction. I think I understand why this ...
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0answers
65 views

Flow in a cylindrical pipe

A cylindrical pipe is, at the left of section A, divided by a plane passing through its axis. The upper half is supplied with water at a velocity $V_1$, the lower half is supplied with water at a ...
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10 views

Separation bubble in flow through a pipe bend

I understand that the separation bubble (length L) will grow with Re, as inertial forces on the fluid elements cause an adverse pressure gradient in proximity of the inner wall just downstream of the ...
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0answers
54 views

Origin of spin and direction in the magnus effect

If you solve the Bernoulli equation: $$p=p_0-\rho_0{v^2 \over 2}$$ using a complex flow potential for a flow around a cylinder: $$W(z)=v_0 z + {v_0 R^2 \over z} - {\Gamma \over 2 \pi } \ln(z)$$ you ...
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41 views

How to restict air flow without reducing pressure

I have a large volume of lightly pressurized air say 10000 cubic feet at 1 psi above atmospheric pressure. I want to move it to another area through a duct which is 20 in by 20 in. Airflow will be ...
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15 views

Is there a relationship between maximum flow rate of a fluid through perforations in a cavity and the flow rate of the fluid in the cavity itself?

I have a scenario where water is flowing horizontally through a (rectangular) cavity. The underside of the cavity has a set of perforations that look something like: and I need to determine the ...
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1answer
936 views

Why are mass flow rates found using Venturi meter and pitot tube different?

Regarding an experiment to find the mass flow rate of a fluid (air) using a venturi meter and a pitot tube: What could be the cause of a variance in results obtained using the 2 instruments mentioned? ...
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19 views

Several suction pumps connected to same air flow source in parallel, is this set up unequal?

I have some sensors with built in vacuum pumps that are open to the room exhaust. I have a single sample source (a compressed air tank, connected to a T fitting and I side stream sample from one of ...
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0answers
190 views

Calculating mass flow rate, force of thrust produced compressed air discharge

This one's a bit of a doozy, so please feel free to comment on any one single part or parts to this physics problem. The setup is simple--I have a container (an empty bottle) which I fill with a ...
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0answers
51 views

Venturi “Turn Down” [closed]

I'm sorry if this isn't the right forum for this question, but physics is the only stackexchange which had many results for Venturi. I'm trying to measure the flow of air through a 16mm hose/pipe ...
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1answer
19 views

Is there reduced water supply due to reduction in pipeline diameter?

I have a 3" water pipeline length 80'coming in from municipal supply, say pipe A, to my water meter. After the water meter, a 2.5" pipeline goes 160' to my underground water tank, say pipe B. Water ...
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1answer
69 views

What is actually the characteristic length in fluid dynamics description?

In many fluid-dynamics models and quantities (Reynolds number, Strouhal number... generally various turbulent flow descriptions) there is a parameter (usually $L$ or $\ell$) descripted as ...
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29 views

Extension of the advection diffusion equation with diffusion perpendicular to the flow

Assume you model particle flow in fluid in a cylinder by an advection-diffusion equation, thus taking into account both diffusion and bulk flow. What would happen to the model if you would, at some ...
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1answer
32 views

Does groundwater flow depend on the geometry of the aquifer?

I consider two cases of a confined aquifer and want to calculate the pressure / hydraulic head in a quasi 1d case. These two cases are shown in my drawing. I assume homogenious, isotropic darcy flow, ...
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1answer
40 views

Karhunen-Loeve transform of a repeating process

This question is inspired by measurements of an unsteady flow. I have some doubts about interpretation of principal component transform using Karhunen-Loeve theorem. I have (centered $\equiv$ zero ...
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1answer
39 views

Why does liquid flow along the mug [duplicate]

I have been wondering why situation described in the picture below happens Why does the water/milk or any liquid poured from the mug/bottle flow along the surface of the vessel instead of leaving it ...
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1answer
132 views

What shape is a vortex?

When I see a whirlpool form around the drain in my tub, or see a hurricane on the radar, to my naked eye it looks pretty much circular from above. Is it a perfect circle? An ellipse? If not, ...
2
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1answer
954 views

Why does the Nusselt Number for a Constant Surface Temperature, Thermally Fully Developed Circular Pipe Converge To a Constant of 3.66?

I have flow in a pipe with a constant surface temperature boundary condition. The velocity profile is fully developed and the temperature profile is also fully developed. In my textbook, it says that ...
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1answer
46 views

What is the property which flows as described by the stress energy tensor in GR?

I found the following definitions: The stress–energy tensor (sometimes stress–energy–momentum tensor or energy–momentum tensor) is a tensor quantity in physics that describes the density and flux of ...
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42 views

How to determine which one is dominant shear rate vs. flow rate

I have a question for the image below. Now we have a pump connecting to a votator for transferring some slurry. The pump yields a flow rate Q, and the votator yields a shear rate 𝛾. I wanna ...
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1answer
84 views

Intuitive explanation for subsonic Fanno flow

In most situations in physics, the effect of kinetic friction is to reduce the macroscopic kinetic energy of a system and convert it into heat, thereby increasing its temperature. but in the case of ...
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1answer
196 views

Whirlwind/tornado/dust devil in the middle of nowhere

I live in area which have many properties similar to desert. Many times when I drive by I see a whirlwind/tornado/dust devil of sand or other garbage parts. I would like to ask how this was normally ...
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4answers
473 views

Does steady flow imply laminar?

Most secondary school textbooks, in their chapter about fluid dynamics, seem to suggest that "steady flow" and "laminar flow" are synonyms. Though I never received any fluid mechanics course when I ...
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19 views

Fluid flow in porous medium with moving boundary

Everyone, I would like to numerically model axisymmetric fluid flow in a porous medium with a moving boundary, where the fluid pressure is specified on the boundary, whose radius increases with time. ...
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0answers
46 views

Force of Leaky Bucket over time

Indie Lab Procedure: I attached a cylindrical can to a force sensor. On the bottom of the can I drilled holes of various diameters. I then added a volume of water while collecting data from the force ...
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0answers
11 views

Reactor opening and total time to reach a specific temperature

Let's say I have a reactor (we assume that its shape can be approximated by a horizontal cylinder) in which there is air at the temperature of 1000K and at pressure of 1.5 bar. Now, I want to open it ...
0
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1answer
351 views

Calculating flow rate of a syringe

I wanted to know how would I go about calculating the flow rate of a syringe with a metal tip that is dispensing water using a pressurized air. I have had a look on internet about this and on this ...
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38 views

Fluid Dynamics - How does air behave out a window?

I often smoke out a window, and I know that if you're driving a car, the passing air will affect the pressure inside and "suck" out the smoke for instance. But what if you're in a window pane? I have ...
2
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1answer
46 views

Self similarity for slowpokes

I am struggling with the concept of self similarity. If I google search, I either find examples that don't explain all too much or detailed explanations that go waaaaay over my head. I've found a ...
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3answers
986 views

Laminar vs Turbulent flow separataion

(Left is a laminar separation, Right is a turbulent separation) I have been having a bit of trouble understanding this concept. How come the laminar separation involves a much larger wake than the ...
4
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1answer
117 views

Stationary waves on a laminar liquid flow near collision with a surface [duplicate]

Look at the picture below I know about plateau rayleigh instability. And my opinion is that the reason of this phenomena is plateau rayleigh instability. But there's a question, in the picture ...
2
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1answer
47 views

Friction in a fluid

when an object is moving in a fluid(air for example), the air will resist the object's movement: molecules of the air will collide with the surface of the object (no slip condition) and then we will ...
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1answer
183 views

Finding diffeomorphism given vector fields [closed]

Given a vector field how do you find the associated diffeomorphisms? Say I am given a vector field in Minkowski space $$\xi = x \frac{\partial}{\partial t} + t \frac{\partial}{\partial x}.$$ How do ...
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1answer
79 views

flow rate in split bottleneck

water flows from top to bottom. first there are two pipes, one with 10 LPM max flow rate and another with 20 LPM max flow rate. they both go to another pipe, which is 20 LPM max flow rate. the total ...
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1answer
81 views

How viscosity and velocity relate in a pipe?

Assume we have a pipe that there is a fluid stream in it. By increasing the velocity of the fluid the resistance will increase either (because of the viscosity I think). My question is how are these ...
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1answer
39 views

Can a compressible fluid flowing , change its speed in the absence of a pressure gradient?

I've heard that in a high velocity nozzle, any random 'fluid particle' experiences an increase in kinetic energy at the cost of internal energy and pressure energy.And I do understand that for any ...
0
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1answer
33 views

What is the difference between hydraulic radius and geometrical radius in a cylindrical pore?

What is the difference between hydraulic radius and geometrical radius in a cylindrical pore? I was going through the 'stacks' present in an thermoacoustic refrigerators there I came across the ...
4
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1answer
530 views

How does a hollow-point bullet move smoothly through the air, presenting a 'cup-shaped' nose instead of an actual sharp-point to the fluid?

Hollow-point rounds move smoothly through the air when presenting a 'hollow cup-shape' instead of a traditional 'sharp point' to the fluid air. Does this mean the air trapped, and at some assumed ...
4
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2answers
563 views

Why does the vortex form in the von Karman Vortex Street?

Why does the vortex form in the von Karman Vortex Street? So far I have this for the reasoning: 'It occurs when a fluid flows around a cylindrical object. The pressure on a fluid particle rises to ...
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1answer
63 views

Streamlines and ideal / real fluids

I was going through some basic description of streamlines in which I noticed that streamlines in an Ideal fluid where shown "equidistant" from each other at a place . whereas in the real fluid ...
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1answer
131 views

Streamlines and line of flow of fluid particles

I am very confused with this thing can someone clarify these problems given below-- 1 //Do or can the streamlines of a fluid particle show the position of the particle at a time( using the streamlines)...
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59 views

Drag Force on a cylinder with its long axis aligned with the flow

yesterday I started looking into equations that link a cylinders diameter $r$ and length $L$ to the force experienced in a highly viscous medium ($Re<<1$). I found the onseen-approximation but ...
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2answers
363 views

Does water follow the path of least resistance

I am having hard time proving this either right or wrong. Let's take for example a river, does the water flowing down follow the least resistant path?
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44 views

Angular momentum transfer in a bottle vortex

A colleague and I were discussing the following fluid mechanics experiment, which most people have probably tried in their kitchen: take a bottle full of water (a 2-litre transparent soda pop bottle ...
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156 views

SU(2) critical point and volume dependence

I am doing multi-dimensional plots of $\beta_j$ for SU(2) for infinite volume to understand the flow behavior and I was wondering, before I go too much further, if anyone knew off the top of their ...