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

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Head loss and discharge in a pipe system [on hold]

Two reservoirs, whose surface levels differ by 30m, are connected by a pipe O.6m in diam and 3000m long. The pipeline crosses a ridge whose summit is 9m above the level of and 300m distant ...
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2answers
15 views

Vorticity and circulation in potential flow

There is a plenty of situations where the vorticity $\vec{\omega} = \nabla \times \vec{u}$ is zero all over the system (i.e. potential flow) and yet the circulation $\Gamma$ is nonzero (e.g. ...
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47 views

When is a flow a shear flow?

Let us say I have a velocity profile of a flow: $$\vec u= \begin{pmatrix} v_x \\ v_y \\ v_z \end{pmatrix}$$ Under what circumstances would this be called a shear flow? And can we say anything for an ...
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2answers
39 views

Bernoulli equations when different fluids and volumetric flow rates are involved

I have doubts on the use of Bernoulli equation when multiple volumetric flow rates are involved. Consider for istance the device in picture. Water flows in the main tube, while in the tank below ...
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41 views

Calculation of Drag coefficient for infinite cylinder

I would like to calculate the drag coefficient for an infinite cylinder for various Reynolds numbers. I'm using $C_D=\large{\frac F{\frac 12Av^2\rho}}$ My question is how do I calculate force ? ...
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1answer
21 views

Bubbles in Hot Tub Jets

Ever since I was a child I have noticed a strange phenomenon in hot tub/jacuzzi jets, if you partially cover them, the water will still flow but the bubbles stop. No matter what hot tub I'm at, I can ...
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42 views

Wind Flow Simuation Equation

I have a data that contains pressure measurements in difference locations. Now i want to do wind flow simulation based on the pressure difference between these places. The problem is i want to do this ...
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39 views

Gradient identity for streamlines

I am studying a 2D flow and I have a resource telling me that the following holds true for streamlines in general. Let $f$ be the density of the flow, and suppose there exists a unique streamline ...
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1answer
79 views

A fan is connected to a pipe, what happens to the airflow after the pressure drop?

Overview I am trying to find out what happens to the air flow within a pipe if a fan cannot generate the required pressure to overcome the friction within the pipe. After much research I am aware ...
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1answer
75 views

Is the flow of a viscous fluid in free space under no pressure gradient always laminar?

Consider a (Newtonian) incompressible viscous fluid in three spatial dimensions, whose velocity field $\mathbb{v}=\mathbb{v}(x,y,z,t)$ moves according to the Navier-Stokes equations $$\tag{1}\label{...
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2answers
78 views

What is the velocity in the Navier-Stokes equation?

I have been looking at the Navier-Stokes equation, and can't seem to find anywhere a clear description of what velocity it represents. From what I have read it could be any of the following: The '...
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1answer
49 views

Why does laminar flow turn turbulent(*) in external fluid flow and why doesn't a fully developed laminar flow turn turbulent in flow through pipes?

(*:with increase in distance from the leading edge.) I would appreciate if you give detailed explanation for the first question and then apply the same logic to answer the second.
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Modelling a flow due to an oscillating hemisphere?

Say I have a long cylinder filled with air, closed at one end and open at the other. Now say I place a compressible hemisphere at the closed end and make it oscillate (compression and expansion of the ...
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3answers
63 views

Flame shape and size(length) depending on gravity

How would the shape and size of a flame(from a simple candle for example) depends on the gravity? Suppose all the relevant information is known, like candle dimensions and its chemical composition, ...
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6answers
94 views

Can I recirculate water from an open reservoir to the bottom of a bigger, closed one, without a pump?

A fountain head pumps water out of the main tank into a 'pond' reservoir. Can the water recirculate back into the main tank without the help of another pump? I'm sorry if this a dumb question. I'm ...
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39 views

How to make an equal flow rate in 4 glass tubes with different inner diameters?

I would like to ask a question regarding a flow rate project I've been working on that required pneumatic software to solve. Unfortunately, I don't have the software, and I don't know how to control ...
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25 views

Air pressure equalisation

I'm programming a physics simulation and have the air pressure impact the movement of rigid bodies in the system. I know how to (approximately, both for simplicity and performance) specify bodies' ...
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1answer
43 views

Cooling power of CO2 being released from a gas bottle

I need help in calculating how much a constant flow of CO2, being released into a small pipeline from a pressurised gas bottle, cools down the pipeline (in watts), to figure out if I'd need to heat up ...
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3answers
54 views

Tank draining derivation: is it correct to use Bernoulli and continuity equations?

I'm confused about a classical exercise on tank draining, which asks to find the time requested for empty the tank. I'll put here the derivation I found on textbook and on the web, which I'm not ok ...
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32 views

How is zonal flow defined and computed?

The transition to turbulence in pipe flow was recently observed to be in the same universality class as directed percolation. This was done by reinterpreting the turbulence and laminar flow in terms ...
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2answers
73 views

Can air be considered incompressible as long flow velocities are less than 100 m/s (Ma = 0.3)?

Multiple sources state that steady air flow (in open systems) can be considered incompressible at velocities less than 100 m/s (Ma = 0.3). Example: Deborah A. Kaminski, Michael K. Jensen, "...
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1answer
63 views

Power generation with a long, horizontal pipe, using atmospheric pressure differences

Straight to the point. If I float a pipe starting from a point in the ocean that has the atmospheric pressure of 101 kPa (Call it Point A) all the way to another geographic position on the ocean with ...
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1answer
40 views

When does $ S\cdot v=\mathrm{cost}$ hold?

In fluids dynamics what are the limitations for the use of the volume flow rate conservation law? $$ S\cdot v=\mathrm{cost}$$ Does it still hold when there are external forces acting on the system, e....
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59 views

Is flow energy the same as work?

Studying thermodynamics I face this following text from Cengel's book. Throttling valves are usually small devices, and the flow through them may be assumed to be adiabatic (q = 0) since there is ...
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1answer
73 views

Why is turbulence caused?

In high Reynolds numbers we have turbulent flow. This is because the inertial forces are much greater than the viscous forces. I understand inertial forces to be actually the fictional forces due to ...
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1answer
43 views

Why does increasing heat conductivity decrease Nusselt number?

Normally we expect that when heat conductivity(k) increases heat transfer is also increases. But for fluids increasing k decreases Nusselt number. My senses tell that using high conductive fluid cause ...
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60 views

Do you need to increase pressure to pump a fluid from a large pipe through a small pipe?

The application of this question is towards clogged arteries and blood flow. I am wondering why people with clogged arteries have high blood pressure if a smaller artery (assuming it is smooth and ...
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24 views

Are the blades of a propeller necessarily in the shape of wings or would flat blades work?

I think I have seen that airplane propellers are airfoils -- but I am not sure that flat blades would not work and if they do, how much more efficient are airfoils?
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1answer
25 views

A mathematical question on an Ultrasonic flow meter (Time of flight)

I'm trying gain a better understanding of expressions used to derive a formula to calculate the flow velocity Here are the following expressions: $$t_d= \frac{L}{(v+ucosĪø)}$$ $$t_u= \frac{L}{(v-...
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1answer
61 views

How long time before all the water in a lake has been replaced? [closed]

Studying hydrology, and in that context we've seen some information about lakes and the times it takes for the water to renew completely in them. This got me interested in finding out how this is ...
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1answer
27 views

Liquid Flow In A Vertical Tube

A cylindrical vertical tube has uniform cross section $A_1$, and length $l$. It is open at both ends. Water enters from the top with a constant velocity $v_1$, and allowed to flow out from the bottom. ...
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1answer
60 views

When does the shock occurred?

I'm between this 2 conditions that when does the shock occurred over an airfoil. When the speed of point of an airfoil reach to sonic velocity of environment. When the speed of point of an airfoil ...
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8 views

Why is a controlled shear test compared to the natural flow?

Looking for the areas where contolled shear stress (CSS, where force is fixed while rate of deformation is measured) and controlled stress rate (CSR, where conversely the force is measured while ...
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2answers
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How to quantify the spreadness of beam of air molecules as they escape from a capillary to a vacuum?

Consider a tube from an oxygen cylinder attached into a vacuum chamber. When the cylinder is opened, the molecules escape out into vacuum chamber. What makes the molecules spread out when they escape ...
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56 views

Energy of electrons in wire

The Drude Model helped me quite a lot to visualize how current could flow in a circuit. However, there is still a point that I cannot grasp in the explanation given by some people when they talk about ...
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34 views

Calculating optimal heat dissipation/air-flow out-of/into an enclosure - hole size vs number of holes

I am not sure if this is the right place to ask, but I figured it would be a physics question. Essentially I have an enclosure that I will be using to house the components to build a computer. I am ...
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1answer
29 views

Can a piston-like displacement be miscible?

I have a question regarding miscibility and piston-displacement of fluids. My question is as follows: I am given that a fluid is displaced miscible. At the same time, I am also given that the ...
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43 views

Flow Rate in a tube with zero roughness [closed]

Assume the following setup. Given the Diameter of the pipe, difference in elevation (z1 - z2), pipe length, what would be the theoretical way of determining the flow rate (Q) within tube? Assume ...
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84 views

How to calculate velocity of air through a pipe? [closed]

I was wondering if there is any equation that helps to calculate air velocity through a pipe? I cannot find anything although I did find that velocity of air (not in a pipe) can be found by: Is there ...
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Temperature of throttled flow

In a pipe with a throat, closed off to the left, I'm pouring in $\dot{n}$ atoms per second from the left. These atoms combine and do a chemical reaction, which releases energy. To the right, past the ...
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1answer
43 views

relationship between electrical resistance and Hagen Poiseuille's law

For the electrical resistance of a conductor, we have $$R = \rho \frac{l}{A}$$ Noting the structural similarity between the Hagen-Poiseuille law and Ohm's law, we can define a similar quantity for ...
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43 views

Isentropic flow through nozzle

I've a question concerning the use of the Bernoulli principle. Let's say I have a pipe filled with air at atmospheric pressure, with a constricting section ala the figure below. The volume before the ...
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2answers
44 views

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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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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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
51 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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1answer
38 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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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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2answers
85 views

When I open a window to air out the room, how does the smell disperse?

Let's say I'm in a room with some kind of noxious stink, possibly of flatulent nature. The quickest way to right the world that comes to mind is to open a window. When I open a window, how do the ...
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68 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 ...