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

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Fluid Virtual Mass

In this paper of Lighthill, the author studies the motion of a fish in a constant flow field $U$, modelling the movement of the fish as a deforming, rotationally symmetric, rigid surface in an ...
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Dyson Air Blade as a propulsion system?

I've read from many sources that Dyson Air Multipliers are more efficient and quieter than normal fans. Now, with the proof of concept, is it possible to use its principles as a propulsion system for, ...
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25 views

st. venant shallow water equations for pipe flow

As far as I know from the fluid dynamics class, St. Venant equations (the shallow water equations) are derived by depth-integrating the Navier-Stokes equations. This depth-integrating is done with the ...
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44 views

Is a non-Newtonian gas possible?

I was wondering if it was possible to have a Non-Newtonian Gas. I was planning a science fair experiment to try to create one if its possible.
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64 views

Which temperature to evaluate fluid properties in pipe?

I am always confused about which temperature to evaluate fluid properties at. Let's say I have a helical pipe and I know the inlet temperature, outlet temperature, and surface temperature and the ...
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195 views

(How) Does A Vortex Speed Drainage?

When a sink drains it forms a vortex. Does that vortex speeds drainage. If yes, how does the vortex speed drainage? The only relevant thing I could find was an expensive article and a science fair ...
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84 views

Problem understanding basic sail mechanics

I am trying to understand the physics behind a single sailed boat. I have read the following questions Sailing against the wind. Is this a fair model? What exactly is the 'lift' of a ...
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67 views

Irrotational fluid

Often, when threating some problem of fluid dynamics I have read that people make the approximation of irrotational fluid, i.e. the velocity field is assumed irrotational: $$ \nabla \times \vec{v}=0 ...
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66 views

Euler Equations, Sod shock tube & conservation

Conservation of momentum? I am considering the Euler equations in conservative form and solving the Sod shock tube problem I have written a Godunov finite volume type solver. It solves for density ρ, ...
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79 views

Fluid dynamics - Water level in a container

An open container is being filled with water from the top at a constant volumetric flow rate $300 \frac{cm^3}{s} $. At the same time, water is leaving the container trough a circular whole at the ...
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26 views

Water Droplet Saturation Phenomenon

What is the term used to describe the behaviour of (for example) a water droplet in free fall when it has reached a certain speed and then the force on the droplet causes the larger droplet to ...
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57 views

What is a superfluid in field theoretic terms?

I'm wondering how one precisely defines a superfluid in terms of the effective field theory description. In Nicolis's paper http://arxiv.org/abs/1108.2513 there seems to be an extremely simple ...
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47 views

Calculate Euler equations of fluid dynamics without division?

I'm working on the calculation of the Euler equations with the finite volume method. Unfortunately I'm not allowed to do a division. So I'm wondering if there's a form which does not need a division. ...
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161 views

Sailing against the wind. Is this a fair model?

I was ruminating the explanations about how boats can sail against the wind (or "into the wind"), and wondered if one could devise a simple mechanical model without hydrodynamics involved. Imagine a ...
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443 views

About turbulence modeling

I have some questions about this paper: Lagrangian/Hamiltonian formalism for description of Navier-Stokes fluids. R. J. Becker. Phys. Rev. Lett. 58 no. 14 (1987), pp. 1419-1422. After reading ...
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52 views

How do adhesive and cohesive forces affect surface tension? [closed]

Surface tension appears at the interface of two immiscible fluids if the cohesive force of attraction is more than adhesive force. What will be the physical effect if the adhesive force is more than ...
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33 views

Could heavy-lift ships be used as oil tankers to stop oil spills? [closed]

Years ago, I was watching a science programme about some law of physics that prevents liquid from spilling if it was a container underwater. I recall that it was proposed as a safe way to transfer ...
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255 views

Compressilibility and the form of Newton's second law in fluid mechanics

In deriving Euler's equations for fluid mechanics, in particular $$f=\rho \partial_t v +\rho v\cdot \nabla v$$ for some body force $f$ (e.g Landau & Lifschitz 2.3) one assumes the continuity ...
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60 views

What force does a tall building exert on air?

I once heard that a tall building, let's say 10 stories, actually causes wind to blow by virtue of simply existing. It also was said that is why metropolitan downtown areas tend to be windy. What are ...
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8 views

To estimate the energy of heterogenous vortex for emulsion?

I remember seeing in some fluid dynamics course an equation which relates the energy of a nonhomogenous vortex to the frequency. The fluid is here blood (emulsion). How can you estimate the energy ...
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130 views

Can Smoothed-Particle Hydrodynamics (SPH) be used to simulate porous media flow and deformation?

I am trying to use Smoothed-Particle Hydrodynamics (SPH) to study fluid flow in and around porous media. The aim is to observe how it causes erosion and failure. For this, from my understanding, there ...
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33 views

Capillary action column height in a tube fitted inside another tube?

I was thinking about how would capillary action change in a tube (classic example) and in a tube fitted inside another tube (considering water as the liquid involved). Height of liquid column: ...
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141 views

Why will two bubbles floating on water surface attract each other?

Two identical bubbles floating on water surface will form clumps, according to the "cheerio effect". But what's the detail about the force? It's necessary to calculate the shape of water surface, in ...
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51 views

Torque required to turn the inside of a drum (Honey extractor) [closed]

I need to mount a motor with a variable speed drive(VSD) onto a honey extractor but need to know how much torque I need to start the extractor to start turning. The diameter is 700mm and the max ...
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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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264 views

Conserved quantities and total derivatives?

I am having a bit of a crisis in understanding of the physical meanings of total derivatives. When a quantity $\rho$ (be it a vector or a scalar) is said to be conserved, then (mathematically) ...
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62 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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Distribution of temperature in a plume of a jet

The exaust gases of a plume of a missile have a distribution in temperature and in density vs. distance from the nozzle. Using a CFD software it is quite simple to get such distribution. Is there some ...
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299 views

Is supercritical CO$_2$ a newtonian fluid?

Is supercritical CO$_2$ a newtonian fluid? I can't seem to find any articles describing the stress-strain relationship for carbon-dioxide in a supercritical state (high temperature/pressure ...
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27 views

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

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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52 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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120 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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50 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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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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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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107 views

Looking for the name of a physical phenomenon in fluids' mechanics

I have not even an idea about how I would search for that on Google, that is why I'm trying my chance here. As electrical engineer I have no clue about fluid mechanics. We all now that when water is ...
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121 views

How does a ducted fan suck in air?

I am thinking of a simple ducted fan with a single set of rotating blades, no stator vanes behind. If the effect of the fan is to raise the pressure of the air, how is there flow into the fan against ...
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58 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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104 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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22 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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What is the Coandă effect? How is it defined, and what causes it?

Can anybody explain to me the Coandă effect well? I am finding that many definitions and explanations conflict. I am particularly confused about the following points regarding the Coandă effect: ...
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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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156 views

Ducted or open fluid flow, which is best for aerodynamics and lift [closed]

I'm designing a copter and trying to decide if the propellers should be ducted or open axial flow. I've read some theory on ducted and open air flow but I can't find any where that compares the two. I ...
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308 views

Can we make an environment where the density of air equals the density of water?

Also, in case an environment with equal density of air and water can be made: Will it be possible for a human to breathe in that environment?
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39 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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94 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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235 views

What is the aperture in the hydraulic analogy of Ohm's law

Note: My question is duplicate of Why doesn't water come out of tap/faucet at high pressure when I turn it on?. None of the answers given there explains how the continuity equation fits properly. ...