The quantitative study of how fluids (gases and liquids) move.

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What is the relationship between Q-Factor and viscosity for a Newtonian fluid based damper?

I am working with a rotary damper (paddle hanging off a shaft attached to the bottom of a rotary table and into a vat of fluid). I know the viscosity of the current Newtonian fluid, I know the flow is ...
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23 views

Amount of fluid that moves along a path

Let suppose that $\vec{F}$ is the velocity vector field of of a fluid in space, and $\vec{s}$ is a straight path of arbitrary length. Let's suppose that $\vec{F}$ and $\vec{s}$ are parallels and point ...
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51 views

How laminar or turbulent is air?

Consider an outdoors scenario, with good weather and no sensible air currents at the floor level. How turbulent or laminar is the air surrounding this environment?
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105 views

Relationship Between Stream Function and Velocity Potential

My understanding is that a velocity potential is a scalar function whose gradient yields the x and y components of a flow's velocity vector. Velocity potential can be graphed, where lines of ...
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80 views

Landau & Lifshitz - Euler's equation for one-dimensional flow

One page 5 in Landau & Lifshitz Fluid Mechanics (2nd edition), the authors pose the following problem: Write down the equations for one-dimensional motion of an ideal fluid in terms > of the ...
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55 views

Euler equation with single state variables

I want to simulate a flow using the Euler equations. For this reason I'm wondering if there's a modified version of the Euler equations. At the moment my formula looks like this: $$ ...
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127 views

Fluid Mechanics with calculus on manifolds

Fluid Mechanics is a branch of physics that uses a lot of vector calculus in $\mathbb{R}^3$ to describe phenomena mathematically. Calculus on manifolds, however, is the straightforward generalization ...
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24 views

Energy required to transport fluid through tube

We have a tube (rigid or compliant) filled with a fluid (Newtonian or non-Newtonian). We apply a pressure drop and mobilize the fluid. What is the amount of energy required to transport a certain ...
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61 views

Need help simulating a fan

I'm trying to write some code to approximately simulate a number fans in an arbitrarily shaped room. I'm not real strong in physics, and could use some help. If it helps I'm not interested in fine ...
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235 views

Differential or integral form of the conservation equations?

Is there a 'rule' for when it is best to use either the differential or integral form of the continuity and momentum equations in calculations?
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135 views

What is the physical application of Navier-Stokes existence and smoothness?

Recently, mathematician Mukhtarbay Otelbaev published a paper Existence of a strong solution of the Navier-Stokes equations, in which he claim that he solved one of the Millennium Problems: Existence ...
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What is the minimum pressure of a medium for which a sound wave can exist?

At what pressure will be particles in a medium be unable to form a sound wave when disturbed? How can this pressure be described mathematically? My guess is that this would correspond to the point at ...
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23 views

What is $l_i$ in The wetted perimeter

The wetted perimeter can be defined mathematically as $$P=\sum_{i=0}^{\infty} l_i$$ what is this means that $l_i$ is the length of each surface in contact with the aqueous body? the length of each ...
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48 views

What kinds of reactions happen when bubbling air through water?

Mostly I have seen air bubbling used to remove impurities in the water itself, like exemplified in this course packet. This is called "Sparging," but I have yet to learn much about transfer between ...
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4answers
144 views

Force of an impact on water

Today, at the Brazilian news, I heard that a men fell from a cruise into the sea, from a height of 50m, and decided to see if he could have survived. I took his weight for being 80kg. I did ...
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2answers
261 views

How do I calculate the Reynolds number in multiphase flows?

I am modeling a gas flowing through a liquid. How do I calculate the Reynolds number in multiphase flows? And, at what Reynolds number should I consider the flow to be turbulent? The problem is of a ...
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70 views

Are Mach Diamonds radially symmetrical?

Videos like this show a form that suggests a radial symmetry in the gas jet. The same is reinforced by schematic illustrations. But other images, like this, look like there is a twisting structure ...
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126 views

How is a vacuum formed and measured by this pneumatics attachment?

Please excuse me if this question is misplaced and also for my narrow understanding of physics. Firstly, I'm asking simply because the robot I've now been set to work with uses an air pneumatics ...
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1answer
201 views

Excluded Volume Calculation in Van der Waals Equation

When accounting for the excluded volume for in the Van der Waals equation, it is assumed that the molecules are hard spheres and are of diameter. If we consider a cube of volume V, then we can say ...
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45 views

Integration of Forchheimer equation for unsteady-state permeability determination

I would like to know the steps for the integration of Equation 17 in Section 6.2.1.2 of American Petroleum Institute Recommended Practices 40 for Core Analysis to yield: ...
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2answers
125 views

Self Stirring Boiling Liquid

A couple of weeks ago, a friend and I were brewing a new batch of beer. We boil our wort in a turkey fryer. Pretty standard setup for beginners. Anyway, our wort was getting pretty close to boiling ...
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1answer
36 views

Deborah Number for harmonic excitation

I think I do not understand well the concept of Deborah number. It is presented in the sources available to me as the ratio between the relaxation time of a fluid and a characteristic time scale of ...
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0answers
47 views

Fluid Dynamics Tsunami

I have been given a energy head (pressure) in meters for a given tsunami on land. My question is if the tsunami hits a wall 1 meter by 1 meter, is it possible to calculate the height it will reach. ...
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145 views

Head losses on parallel pipes

I've been studying Fluid Mechanics recently and on the book Fundamentals of Fluid Mechanics 7e, Munson et al. on page 456, the book states Another common multiple pipe system contains pipes in ...
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338 views

What will happen if we put balloon in water tank in space

Imagine this. You have some object (let say barrel) and fill it with water. The water remains rather calm so it doesnt' spills out. Then we take a balloon filled with air and push it in that tank. ...
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53 views

What is is a molecular/microscopic explanation for why a balloon rises in water?

If we consider a balloon full of air submerged in water then we all know that it will rise rapidly. I am having trouble understanding this at the level of individual molecules of air and water. What ...
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36 views

Fluid mechanics - rotating Bucket - euler fluid - symmetries

Rotating Bucket, gravity, euler fluid. E.g faber ch 2 or landau, if we start from the full 3 d equations in cylindrical coördinaties, we have symmetry over the azimuthal angle, but why is there ...
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61 views

Uses of the Reynolds number

I have seen a lot of places talking about the Reynolds number and how it is calculated, but I have never seen an equation that actually made use of this number to calculate lift, drag, or other ...
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1answer
83 views

Entropy is constant. How to express this equation in terms of pressure and density?

In hydrodynamics of an ideal, non-compressive flow we use 5 variables: pressure $p$, density $\rho$ and velocity field $\mathbf{v}$. So we need 5 equations. Landau's "Hydrodynamics" states that the ...
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1answer
71 views

Vorticity - Paradox

I am having trouble grasping the concept of vorticity. Above is a picture of fluid element under deformation (rotational). Say we ignore the vertical motion, which is $\frac {\partial {v}}{\partial ...
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1answer
117 views

Feynman's derivation of Bernoulli (part of it)

OK, so what's up with the $\Delta M$ here? I don't get it. In fact, my textbook doesn't even put it in. I don't think it is a type-o because he continues on with the explanation. If anything I got ...
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2answers
57 views

How does the viscosity (besides density) of a fluid affects sinking

If water, air of whatever fluid had a different viscosity, but the same density, would things fall/sink differently?
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1answer
100 views

Explicit form of the entropy production in hydrodynamics

I'm trying to understand how hydrodynamics arise from a precise, mathematical formulation of thermodynamics, learning mostly from Landau's "Hydrodynamics". So Landau starts from formulating the ...
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2answers
76 views

Can we 'see' the Kolmogorv microscale

My understanding of Kolmogorov Microscale is that in a turbulent fluid, smaller eddies tend to be similiar to larger eddies - until you arrive at the microscale. My understanding (that may be wrong) ...
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73 views

Are there any substances that allow sound to travel better then air? [closed]

The question is the same as the one I put in the title but here it is in more words. I was wondering if there were any substances that allowed sound to travel more efficiently. For example water is ...
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1answer
108 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 ...
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87 views

What is “hydrostatic uplift pressure”?

I was reading Wikipedia about the St. Francis Dam and came across this sentence. Water that collected in the drainage pipes under the dam to relieve the hydrostatic uplift pressure was carried ...
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50 views

Does the lift created by a wing change when the slats are deployed?

This is a conceptual question as much as an empirical one, but the question is: Does the lift of a wing change when the slats (or any other leading edge device) are deployed? I am stipulating that the ...
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2answers
88 views

Pressure $p$ in the Bernoulli equation

I know the Bernoulli equation that states that the energy along a streamline is constant: $$ \frac{v^{2}}{2}+gh+\frac{p}{\rho}=C $$ However I can't seem to figure out what exactly $p$ is in this ...
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70 views

Movement of compressed air inside a rolling tire?

Does it stay still wrt the axis? Does it rotate along with the tire? Is it drawn away from the center of rotation?
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207 views

Why do turbine engines work?

I know roughly how a turbine engine (let's say a gas turbine producing no jet thrust) is supposed to work: The compressor forces fresh air into a combustion chamber, where it reacts with fuel to ...
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2answers
85 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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110 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 ...
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2answers
67 views

What would cause a spinning fluid to stop spinning?

I once saw a demonstration where an electric current caused a drop of mercury to spin. The drop contained bits of iron, which could be seen flowing around in a circular pattern. As soon as the ...
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2answers
80 views

Deriving Bernoulli's equation via conservation of E

So I'm not OK with how some people derive this equation. These people consider a pipe whose endings have cross-sectional areas and heights which are different. They then use the conservation of ...
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1answer
66 views

Measuring flow rate of gases

Flow rates of liquids could be easily measured with a stopwatch and a known volume container. But gases, if entrapped in a container will create a back pressure, and may lead to decreased flow. I ...
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1answer
123 views

Why is the pressure on top of a slab of water greater than the pressure on the bottom?

In the image below, my book seems to be saying that if you have a cup of water in complete equilibrium, then if you have a small cube of water inside the cup given by $dm=ρAdy$ there is a downward ...
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42 views

Liquid pressure equalization (fluid-dynamics)

Will filling a gas tank fill quicker with a 2 inch inlet flowing straight down into it or with the inlet starting at the bottom filling it from bottom to top. With pressure being equal will the fill ...
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1answer
69 views

Wavy stream of liquid

When pouring a liquid into a glass some streams have a wavy shape, like the one in the following photo: (Couldn't find a better picture, sorry.) What causes the stream to be of such a shape?
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131 views

Determine the maximum capillary rise

The problem I have is this: A capillary tube is immersed vertically in water. Knowing that water starts to evaporate below 2kPa, determine the maximum capillary rise and tube diameter. Assume the ...