# Tagged Questions

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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### 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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### What is atmospheric stratification?

In the context of atmospheric stability, what are the meanings of stable or unstable stratification? What is stratification?
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### 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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### 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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### 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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### 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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### 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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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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### 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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### Must flow be supersonic for disturbances not to affect upstream?

I'm studying oil production and found a fact that puzzled me. It states that fluid flow downstream of the wellhead must be supercritical in order not to disturb the flow upstream of it. From PetroWiki:...
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### 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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### 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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### 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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### 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 ...
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### 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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### 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 ...