Tagged Questions

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Can one model a spiral galaxy with a similar manifold to one for a whirlpool?

My question is more of a phenomenological question than literal, since the forces involved are very different. When one looks at the distortions (or wrinkles or whatever you wish to call them) in the ...
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What is the relationship between the angular speed and the diameter of the eye of a water vortex?

In a water vortex formed in a plastic bottle, what is the relationship between the angular speed of the water and the diameter of the hole in the cap? I would have expected that according to the ...
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How to determine the pressure of the moving water at the bottom of a vertical pipe [on hold]

Water is flowing upwards in a vertical pipe with an inside diameter of 0.06 m at a velocity of 0.0152 m/s. The length of the pipe is 0.5 m. What is the pressure at the bottom of the pipe? Density of ...
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The shape of water column flowing from tops [on hold]

My question is what are the useful to study about the shape of water column flowing from tops?
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Estimate the maximum distance of water spatter

There is a faucet dripping water from height $H$ onto a smooth, horizontal ceramic surface, and I need to give a upper bound of the maximum distance between the water spatter and the point directly ...
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flow through an orifice [on hold]

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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Isn't it impossible to make a theoretical model to describe the behavior and the statistics of a turbulent flow? [on hold]

Why mathematicians are interested to smooth solutions of Navier Stokes equations? For the three-dimensional system of equations, and given some initial conditions, mathematicians have not yet proved ...
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If a body is floating in a static fluid, then the volume of the displaced fluid equal to the volume of the inmerse part of the object (proof)

Suppose an arbitrary body is floating in a static fluid, either totally or partially immersed in it, then the volume of the displaced fluid equal to the volume of the immersed fraction of the object. ...
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How to design windy area - what variables?

When you're walking around malls or parking structures, or a building corner, you'll sometimes notice areas with consistent windiness. I was wondering what positions, angles, wind direction, ...
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When I dissolve sugar in my cup of tea/coffee, does it become a liquid or gas, or neither? [migrated]

When I dissolve sugar in my cup of tea/coffee, does the sugar go from being a solid to being a liquid or a gas, or neither? Related: What keeps the sugar suspended in the tea?
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Calculate surface pressure due to forced vibrating plate using wavenumber space [on hold]

My problem lies in the field of acoustics. I have a given complex velocity distribution. The velocity is the velocity in the normal direction to a rectengular simply supported vibrating plate. I now ...
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Is a causal relationship implied by Newton's 2nd Law? [on hold]

Throughout my time learning physics I have been imbued with the notion that forces cause accelerations, period. Accelerations don't cause forces, and they aren't merely correlated phenomena. By ...
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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 ...
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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 ...
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Flushing Volume [closed]

Say you have a 'long' tube : a tube where the length is at least 100 times its diameter. And this tube is initially filled with fluid 'A'. At one end of the tube, fluid 'B' is introduced in such a ...
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How fast would a bullet travel through liquid air?

According to Wikipedia, a bullet from a .22 Long Rifle travels at a speed of 320 m/s and the density of liquid air is 870 kg/m3. What equation would calculate the speed of a bullet fired into liquid ...
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Velocity of a fluid in presence of sphere [closed]

Consider the following problem: A rigid sphere of radius $a$ is placed in a stream of fluid whose velocity in the undisturbed state is $V$. Determine the velocity of fluid at any point of the ...
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Notation regarding the continuity equation for conservation of mass [migrated]

I have the following equation for the net mass flow out of a control volume through a surface $S$ - $$\int \int_S p \overrightarrow{V} \cdot \overrightarrow{d}S$$ (Actually there should be an ellipse ...
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Movement of a cylinder filled with water

Not long ago I was pretty bored at a dinner and I started playing with a water bottle that was not empty: I've been quite interested in its behavior when putted on its side and pushed: the bottle of ...
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At what speed would you die upon impact with water?

If we hit the water at great speeds, we die. This is because the water has no time to "move out of the way" and acts as a "solid" surface. At what falling speed can we consider the water as a ...
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Is it possible to limit water flow this way and how is this effect called?

I needed to propose a mechanism to store water and keep water flow at the same level with 100% passive equipment. Here's what I came up with. If you turn a water reservoir upside down and put in ...
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Can we measure the depth of water by scattering water?

Suppose we release an object and make it fall on the surface of water, then the scatter of water is recorded, Taking some observations, can we calculate the depth of the water by analyzing the ...
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What are the principles behind foam formation?

We know that while pouring water in a glass, there is close to no foam, but if pouring beer, there is much foam (unless pouring "slowly"). So, can the most prominent factors that contribute to foam ...
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Definition of pressure in Bernoulli's principle

I have a difficulty to understand Bernoulli's Principle which states increased fluid speed decreases the pressure. But in a wind tunnel when we measure the pressure with a pitot tube, both the ...
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Electrohydrodynamics: How will electric potential develop in a fluid when potential is applied from ends

Lets say, I have a fluid in a rectangular enclosure (2D). I apply electric potential $U=U_1$ at left boundary and $U_2$ at right boundary. In the lower and upper boundaries, the potential varies ...
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Orientation of large water drops break-up

I have observed that if you pour small globs of water from a considerable height (let's say more than 20 meters), the globs will break up. This is not surprising at all since the amount of water ...
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What is the difference between a vortex ring and a circular line vortex?

Can someone explain the difference between a vortex ring and a circular line vortex? Or are they the same?
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Flow from the bottle

I made some calculations about flow from the bottle, but problems occured when the experimental data came back. Need to refine calculations, but problems occur when trying to link the angle to the ...
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How a fan moves air? [duplicate]

How does a fan moves air towards you (I mean in 1 direction). Also propeller and fan have different shapes, does it mean they work different?
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U.S. Standard Atmosphere

My textbook states that "Ideally, we would like to have measurements of pressure versus altitude over the specific range for the specific conditions (temperature, reference pressure) for which the ...
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What is going on in front of and behind a fan?

Why is it that when you drop paper behind a fan, it drops, and is not blown/sucked into the fan, whereas if you drop paper in front of a fan, it is blown away?
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Basic understanding of stress tensors in a fluid

So, after having spent the last 9 hours attempting to understand the basic tenets of stress tensors in fluids, I can honestly say that I think I know less now than when I began. My questions are ...
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Basic understanding of stress tensors in a fluid [duplicate]

So, after having spent the last 9 hours attempting to understand the basic tenets of stress tensors in fluids, I can honestly say that I think I know less now than when I began. My questions are ...
30 views

Feeling the Breeze

This question is based on an odd phenomenon I noticed last week. Since then, I've been collecting more data to try to get an accurate picture of the facts. Each morning, I go to my bus stop. It's on ...
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How do I enforce the no-slip boundary condition in time dependent incompressible pipe flow?

This is a technical problem which must have been solved already. It won't be in beginners textbooks but there should be a solution somewhere. I welcome reading suggestions. Maybe someone with ...
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Derivation of the equation of motion of a viscous fluid by Landau & Lifshitz

I am trying to follow Landau and Lifshitz, from the Volume 6 (Fluid Mechanics) of the Course of Theoretical Physics, on their derivation of the momentum equation for a newtonian viscous fluid, but I ...
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Why Are Normal Shock Waves Unstable in a Converging Channel?

While learning about shock waves in an introductory Gas Dynamics course, it was revealed that normal shocks are unstable if formed in a converging channel. Even if the local conditions ostensibly ...
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Woodstove coppertubing heat exchanger [closed]

I am trying to use the excess temperature of my wood stove's stack to heat a copper tube heat exchanger with water running through it. The water is piped through my concrete floor for radiant floor ...
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Given a fluid element whose circulation was determined counter-clockwise, how can I calculate the Vorticity of the element? The circulation is $$\Gamma = (\frac{\partial u_2}{\partial ... 1answer 44 views Weight held by jet stream of water Consider a bucket of weight W, held in air by a jet stream of water from the ground (moving vertically upwards) at height h. The water is fired from the ground at the rate of \mu (units ... 1answer 60 views Why do we need the material derivative? I'm studying fluid mechanics, and I got the impression that the material derivative is nothing more than "differentiating along a path" and so I got confused on why do we need it. Basically, let ... 1answer 55 views Relationship between Connection and Material Derivative Suppose D\subset \Bbb R^3 contains a fluid and that f : D\times \mathbb{R}\to \mathbb{R} is a time dependent function defined on the fluid region. In that case, the material derivative is defined ... 1answer 26 views How to find the required inlet velocity/pressure to achieve 0.5 m/s in one part of the underground tunnel? [closed] I have this problem here related with tunnel and ventilation. As you can see at the picture below, it is a top view of the tunnel. The tunnel has an inlet and an outlet. The air flows from the inlet ... 1answer 38 views Why do we use time-dependent regions in this derivation? I'm studying fluid mechanics and I have the following doubt: on the book, the author first deduces the differential form of the equation of balance of momentum. First he argues that if the fluid is ... 2answers 43 views Bulk Modulus, How are these formulas equivalent? Bulk Modulus is defined as$$ B = \frac{VdP}{-dV}$$Where V is volume and P is pressure. It is also defined as,$$ B = \frac{\rho dP}{d\rho} Where $\rho$ is density. Question: How are these ...
I've been studying fluid mechanics and I have some doubts on the mathematical model of a fluid. First we let $D\subset \mathbb{R}^3$ be a region in three-space filled with a fluid. This region has as ...