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

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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 ...
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1answer
180 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 ...
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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. ...
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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?
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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 ...
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1answer
47 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 ...
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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 ...
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1answer
97 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: ...
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3answers
602 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 ...
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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. ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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. ...
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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 ...
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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 ...
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4answers
93 views

Can the weight of a bird be measured, considering air friction? [duplicate]

Assume that a bird of mass 1.5 kg is held in a box at height 500m and this setup is placed on a weighing machine. Now, the bird starts to hover in the box pushing the air downwards, and is at a ...
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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 ...
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1answer
65 views

How high will the Ball Jump? [closed]

A small ball of density $\rho$ is immersed in a liquid of density $\sigma$, ($\sigma>\rho$) to the depth $h$ and released. How can we find the height above surface of the liquid up to which the ...
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22 views

Value of Pressure Gradient in a static Fluid [closed]

How can we prove that the value of Pressure Gradient in the horizontal direction represented by $\frac{\partial p}{\partial z}=-dg$ ; { $z$ direction is vertically upwards and $d$ is the density of ...
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1answer
32 views

Viscosity and Flow

I have a system with a fairly viscous fluid, 70,000 cP. The flow is induced by applying pressure to a plunger via compressed air. The error in viscosity for this material is +- 15% which can be ...
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8 views

Argument for stability of journal bearing via inertial and viscous forces?

As I understand a journal bearing, a rotor is levitated by hydraulic forces from the lubricant. While these are lots of studies on this subject, I can't manage to find a paper that coherently breaks ...
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1answer
24 views

Does gravity affect water permeability?

Suppose I have an approximately rectangular prism composed entirely of folded paper. If I place 600lbs on top of these rectangular sheets of paper, the paper should compress. How does this affect ...
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1answer
13 views

Conservation Equations forming a Determinate Set

I was reading "molecular gas dynamics" by Bird and came across the the statement that For conservation equations to form a determinate set shear stress and heat flux must be expressed in terms of ...
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1answer
65 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 ...
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1answer
41 views

Where can I get fluidics components?

Many years ago people were interested in developing fluidic circuits, i.e. circuits that are analogous to electric ones but that use fluids rather than electricity. It used to be possible to buy ...
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17 views

Would a solid inside of a parcel moving due to buoyancy be affected by Bernoulli's Principle?

If a parcel (or column) of hot air were rising due to buoyancy and an extremely light solid were to be inside of this parcel (rising with it), would Bernoulli's effect cause the solid to stay inside ...
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2answers
34 views

height of dam to allow certain flow rate

You observe water at rest behind an irrigation dam. The water is 1.5m above the bottom of a gate that, when lifted, allows water to flow under the gate. Determine the height h from the bottom of the ...
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26 views

Books on experimental methods, fluid mechanics related

I need some good books on experimental methods, requirements are: Fluid mechanics related; Thermal, multi-phase etc. topics should be covered; Traditional methods are good, but it would be greater ...
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3answers
3k views

Emptying a bottle faster by swirl

A moment ago, I was emptying bottles filled with water (2 liters) that are on the terrace of my house. As I did so I remembered something I saw on TV a some time ago (I don't remember when or where or ...
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21 views

Bernoulli and ideal flows

The question states that there is a permanent source of liquid at the bottom of a given reservoir and I need to find the maximum elevation of the liquid surface given two cases: $1.$ a straight narrow ...
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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 ...
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1answer
51 views

Does angular momentum of our planetary spin explain the natural 'log e' explanation (the spiral pattern) of my fossil gastropod collection? [closed]

If so, where is the momentum conserved? Any shell may shatter if from a recent land or sea shell. Is a fossil the same way, just waiting for decompression?
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1answer
37 views

Do de Laval nozzles have to be asymmetric?

All pictures of de Laval nozzles I've seen have an hourglass shape where the convergent section is shorter than the divergent section. Is this necessary to attain supersonic exhaust velocities, or ...
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1answer
25 views

Enstrophy and energy spectral density of vorticity

I'm processing some flow field data obtained by PIV for a turbulent jet with the intention of using the energy spectral density (ESD) function to say something about the processes going on. I'm ...
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1answer
32 views

Sum of velocity fields

In hydrodynamics the for a non-viscous flow the velocity (and density) fields are given by the continuity and Euler equations: $$\rho\frac{\partial \vec{v}}{\partial ...
4
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1answer
37 views

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 ...
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0answers
50 views

References on De Broglie-Bohm pilot wave theory

Are there any good books related to the not much popular De Broglie-Bohm pilot wave theory and its application in hydrodynamics, walking droplets concepts?
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2answers
47 views

What really is “inertial force”?

In Fluid Mechanics we often see the term inertial force when discussing Reynolds number. The problem is, I didn't really get what's this inertial force. Basically, the notion of inertia I have is that ...
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32 views

Home experiment with airfoils and Reynold's number

I want to do an experiment about lowering the Reynolds number of an airfoil moving through air. I want to figure out how to lower the turbulence around an airfoil. So my two hypotheses to lower the ...
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2answers
45 views

Create air stream from heat

We know that heating the air inside a bounded box raises its pressure. And if there is a hole in the box, then air flows out until the pressure inside and outside balances. So in this case we would ...
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2answers
54 views

How can we show that pressure is exerted sideways too?

We can show that pressure upward and downward in a fluid is caused by weight of fluid column or volume. A simple derivation of this: ...
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2answers
52 views

How come milk pours smoothly from a bag?

I have seen the commercial about the new beer can where it is vented by puncturing a whole on the can (air behind water). If you just pour normally with normal cans it will get bottle necked and the ...
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11 views

Kármán Line Definition from “Aeronautical Flight” (Mass, Area, and Lift)

This question asks something very similar, and the single following answer says, in part, that the balance is achieved when: $$ \frac{2m}{\rho(r) A C_L r} = 1 $$ [...] I note that the mass ...
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22 views

Maximum velocity in a viscous fluid

Situation: A viscous fluid is flowing through a tube, and the rate of ejection is x $m^3s^{-1}$ Finding the velocity of the ejected fluid would be simple enough, by dividing the rate of ejection by ...