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

learn more… | top users | synonyms (1)

2
votes
1answer
152 views

The original thorium reactor?

With lunar thorium being common, and heavier than iron or nickel, does earth's core have the the occasional nuclear reaction?
1
vote
1answer
50 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 ...
1
vote
1answer
85 views

Computing the force generated by a sail on a boat

This is a follow up question to the question I asked yesterday: Problem understanding basic sail mechanics I am focusing purely on the Newtonian aspect of motion and I am computing this as ...
0
votes
1answer
48 views

How to determine pressure at the bottom of a reservoir? [on hold]

I am trying to solve a problem of fluid dynamics. This is not a school assignment or anything like that, just a small project for myself. Suppose we know: 1. h and L 2. v0 approximated at 0 since the ...
0
votes
0answers
22 views

air column in mercury

When we put an infinitely long tube in mercury beaker the mercury colum rises to a height. But there can be various cases involved like the tube is just below the mercury level , or it is at a depth d ...
2
votes
1answer
181 views

Thought experiment about fluid mechanics (reductio ad absurdum)

In an interview a philosopher said: "Suppose I cut the handle off your coffee mug leaving two holes. Would the coffee flow out of one hole faster than the other? If we tried to figure this out by ...
0
votes
0answers
23 views

How to calculate the linear and angular dampening of a solid moving in a liquid? [on hold]

I am currently making a 2D physics simulation and I have to calculate the linear and angular dampening of a composite body (represented by a force vector field). I already calculate the linear and ...
3
votes
2answers
29 views

Water level of ice in cup [duplicate]

Since ice is less dense than water, it floats on it, we all know this. Now suppose, if ice is floating in a glass cup, when the ice melts there should be some change at water level in the glass cup. ...
1
vote
2answers
52 views

What's the physics origin and meaning of $\delta_{ij}-k_ik_j/k^2$

The projection tensor $P_{ij}\equiv\delta_{ij}-k_ik_j/k^2$ happens frequently in fluid mechanics or field theory. What's the physics origin of this structure and what's the meaning?
0
votes
2answers
49 views

Liquid placed in a rotating cylinder

The Question A closed vertical cylinder is filled with an incompressible liquid of mass m completely. The cylinder is now sealed from all sides and rotated about ...
2
votes
1answer
48 views

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 ...
2
votes
2answers
980 views

How much water must flow trough canal to maintain a constant water deep?

In order to maintain a constant water deep in canal, how much water must flow trought the pipe ? As shown on picture, canal have a rectangular shape. I don't know if canal length have an influence. ...
3
votes
1answer
65 views

Does water maintain equal level in connected vessels?

Consider a system as illustrated below: There are two 55 gallon barrels used to store water coming down the gutter. These barrels are connected together on the bottom to maintain equal water level ...
1
vote
4answers
234 views

Pressure in fluid mechanics of incompressible liquid

Most liquids can be approximated to be incompressible, since the Mach-number is much smaller than 1. That means that the density variations are negligible and from the relation between pressure p and ...
1
vote
1answer
216 views

Calculating water flow as function of the height of water above the inlet pipe [on hold]

The Source of Water is Pond where the water level do change randomly. A pipeline of 200mm pipe diameter run for around 2500 m. The Height difference between the level of the inlet pipe and the level ...
1
vote
1answer
98 views

Can I use Runge-Kutta to solve these equations?

Edit: I'm going to give some more background and derivation to show how I got to these equations. I am basically following the derivation that is found in the appendix of the following paper: ...
1
vote
0answers
83 views

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 ...
2
votes
1answer
53 views

Predicting balls's movement in well due to fluid flow

I am a total newbie in fluid dynamics. In one of my experiments/open project, my experiment setup is as below: a small ball sits in a circular well (has mass density a bit heavier than water), with ...
2
votes
1answer
56 views

Is placing a heater in the coldest part of a room the most efficient place to put it?

I've noticed that stores blow hot air in a "sheet" by doors and windows, which is "where cold air enters". I assume they do this because it saves money and/or keeps the store a uniform temperature. ...
4
votes
3answers
604 views

How much heat from a fire actually warms your home?

A fire in a hearth disperses heat to, I guess, three places: the bricks of the chimney out the hearth (where the person tending the fire is standing) out the chimney, above the house How would you ...
5
votes
4answers
185 views

Particles scattering on fluids: breakdown of the effective continuum description

When does the macroscopic continuum description of a medium like a fluid break down? Say I'm interested in a scattering process of some particles with momentum $p$ and energy $E$ off a fluid of ...
4
votes
1answer
320 views

Considerations and questions for a DIY heat pipe; how to choose a working fluid?

I plan to build a DIY heat pipe! For more info on what a heat pipe is, see Wikipedia. I would like to use it to cool a desktop graphics card I have. I am having trouble deciding how to choose the ...
5
votes
1answer
792 views

What is the roaring in a roaring fire?

I was just starting a barbecue fire by blowing on the smouldering coals when I realised I had no idea what the sound was actually caused by. I can make the sound by blowing at almost any flame I can ...
0
votes
1answer
565 views

Pressure loss in a syringe

I'm currently working on a problem which is really giving me some issues. The problem concerns the force required to expel water from a syringe. We have a 20 ml syringe (which is $2\times10^{-5}$ ...
5
votes
1answer
91 views

How to estimate the time spending along the fluid flow

I have a 2d flow field with a singular point $$\dot x=y-px^2\\\dot y=-x-qy^3$$ where $p,q$ are small parameters. How do I compute the cost time of a particle from $(x_0,y_0)$ to ambient of the ...
0
votes
1answer
25 views

Making water spin a wheel [closed]

Let's say that I have a wheel with 8 symmetric arranged rectangular plates of area $A$ and the water, with density $\rho$, in the river it moves with $v\: \mathrm{m/s}$. How do I calculate the ...
1
vote
0answers
48 views

Non-Darcy Flow : Forchheimer plotting method

Recalling Darcy's equation for gas flow, assuming ($z\mu_g$) = Constant $$\tag{1} q_{g,sc}=\frac{kA}{L}\left(\frac{T_{sc}}{Tp_{sc}}\right)\left(\frac{1}{2z\mu_g}\right)(p_1^2-p_2^2)$$ For ...
1
vote
1answer
27 views

How do you work out the energy requirement for a submerged pump?

I was wondering if you were to place a pump in a submerged container and then were to open a hatch allowing water to flood the previously vacant cavity how much energy would be required to discharge ...
0
votes
0answers
42 views

Boundary conditions of stream function

I have to do an problem about solving numerically the flow that goes under an airfoil. The airfoil has a flap deployed downwards and I need to solve the mesh that it's under the airfoil. I have drawn ...
1
vote
0answers
11 views

How do we force a turbulent fluid to keep the input energy rate equal to energy dissipation rate?

If I want to do a DNS (direct numerical simulation) for turbulent fluid, and I know $\nu$, how can I add an external force so that the input energy rate is equal to the energy dissipation rate? If ...
1
vote
1answer
33 views

Pressure coefficient on fluid mechanics

I have to solve numerically a fluid mechanics problem. I have an airfoil with a flap deployed downwards, under the airfoil I have set a mesh with some nodes. I have already computed stream function ...
7
votes
4answers
3k views

Polar vs non-polar fluid

In the book "Vectors, Tensors, and the Basic Equations of Fluid Mechanics" by Rutherford Aris I read the following: If the fluid is such that the torques within it arise only as the moments of ...
6
votes
4answers
2k views

Effect of water pressure on sinking objects

As I understand, water pressure increases as we go towards bottom of the ocean. So if an object* is thrown into water and it starts sinking with some speed, does the sinking object's acceleration ...
6
votes
1answer
123 views

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 ...
3
votes
1answer
241 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 ...
0
votes
0answers
14 views

Direction, closeness and range of streamlines in a flow domain with solid boundary and free surface?

I have a flow-field with solid boundaries and a free surface, I have plotted the streamlines, however I am not sure whether my graph is correct. In fact, I drew the streamlines by taking a range of ...
3
votes
0answers
82 views

Why (and how) do foods stick to a pan?

We all (sooner or later) have noticed that foods relatively high in protein (especially those low in fat) are very prone to sticking to a pan, or in general to any non-specially-coated metal surface. ...
3
votes
4answers
536 views

How is wind created?

I know that 'blowing air is called wind', but what I don't know is, how is wind created? And I don't want the answer from Google Search. I want to know more about wind at the atomic or molecular ...
23
votes
3answers
4k views

Is this really a golden ratio spiral?

In this blog post, I found this picture: Tehre are other similar photos: and Does the water really form golden ratio spiral in such cases? Or is the photo just a provocative example, without ...
0
votes
2answers
572 views

Difference resultant aerodynamics force on an airfoil and a flat plate

From basic airfoil theory the following free body diagram can be determined for a two dimensional asymmetric airfoil: Here the direction of the resultant force is governed by the geometry of the ...
2
votes
1answer
95 views

Rayleigh-Taylor Instability dependence on acceleration direction

I'm trying to bolster my understanding of the Rayleigh-Taylor instability, and I've gotten stuck on the point of which fluid (more or less dense) is being accelerated into the other. Cases of uniform ...
2
votes
1answer
81 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 ...
0
votes
2answers
48 views

Force needed to push a syringe plunger: does one add force associated with downstream back-pressure to frictional plunger force?

I am trying to figure out how much force $F$ is needed to push a syringe plunger. The plunger needs to overcome the friction force $F_1$ and (a much smaller) inertia force $F_2=ma$, giving the total ...
2
votes
2answers
9k views

Does pressure drop across pipe affect flow rate?

Let's say there is a main pipe containing $100\: \mathrm{m^3/hr}$ a fluid of density $750\: \mathrm{kg/m^3}$ and it's gonna be branched into 2 pipes (Pipe A and Pipe B) of the same diameter. If Pipe A ...
-3
votes
1answer
39 views

Jets of equal height from a pipe

Lets say I have a pump that delivers some flow and pressure to a horizontal pipe with holes at different location. Let's say L=0.5 m, 1m, 2m etc... The question is: What should the diameters of these ...
2
votes
2answers
94 views

Flow velocity out of a pipe

For a compressible homoentropic gas is the flow velocity out of the pipe the same as the velocity into the pipe?
0
votes
0answers
58 views

How to compute volume flow rate of water being sucked up in a straw?

If I know the pressure on one side of the straw (atmospheric) and the pressure inside the mouth, can I compute the volume flow rate? This is first disregarding the transient rise and fall and only ...
3
votes
1answer
66 views

How do simple bird waterers work?

I made a simple bird waterer made from two 1.25L PET bottles. Let's call these two bottles the reservoir and the tray. Setup The tray is a bottle with the top cut off to leave only the bottom ...
1
vote
1answer
45 views

Liquid film in a narrow slit

If a thin sheet of some material in which a slit is cut is immersed in a liquid and removed, a liquid film (bridge) stays in the slit. Is it possible to calculate the shape of the film if the ...
5
votes
1answer
179 views

Fluids in thermodynamic equlibrium

I am reading about the Euler equations of fluid dynamics from Leveque's Numerical Methods for Conservation Laws (Amazon link). After introducing the mass, momentum and energy equations, some ...