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

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460 views

Fuel tank draining [closed]

A cylindrical fuel tank is being drained from the bottom as in this picture : Conservation of flow rate : $v_A = \frac{S_B}{S_A}v_B = \alpha v_B$ Assuming that $z_B = 0$, Bernoulli's theorem ...
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1answer
149 views

Isothermal compressibility

How does one get from the thermodynamics definition : $$ \chi_T = -\frac{1}{V} \left(\frac{\partial V}{\partial p}\right)_T$$ to the fluid dynamics definition : $$ \chi_T = \frac{1}{\rho} ...
3
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1answer
188 views

Inexplicable Results in a Vacuum Experiment

We've been doing the following experiment in our Physics Lab course and are coming up with some strange results which we're at a loss to explain. The purpose of the experiment is to determine the ...
2
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2answers
147 views

Will the box move if I blow air inside it?

Suppose that I have a box in space and it is filled with air in it. I keep a fan at one end and blew the air to other end. The air will hit the box with some velocity, so it should move. I know that ...
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2answers
403 views

Is it easier to simulate compressible flow than incompressible flow?

If I want to simulate an incompressible flow, I need to solve pressure p by a Poisson equation (which is hard to solve numerically). But if it is a compressible flow, the pressure equation can be an ...
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2answers
901 views

Platform diving: How deep does one go into the water?

I am a platform diver. I am trying to figure out how deep in the water I go depending on which platform I dive from. The platforms are 1m, 3m, 5m, 7.5m and 10m above the water surface. By ignoring ...
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0answers
55 views

Dissipation depending on viscosity - where am I wrong?

Accodring to this answer to an older question of mine, dissipation in a fluid in W/kg is proportional to U³/L (U characteristic speed, L Length). I was wondering why this is independent of viscosity, ...
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0answers
80 views

Definition of Irreducible Tensor Parts in an Exercise

I am addressing exercise 23.9 on http://www.pma.caltech.edu/Courses/ph136/yr2011/1023.1.K.pdf. The exercise says that a fluid flowing through spacetime $\vec u(\mathcal P)$ can have its gradient ...
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1answer
830 views

Why is the dynamic pressure not a vector quantity? [duplicate]

I understand that static pressure is a scalar quantity as it acts equally in all directions, then by the same reasoning dynamic pressure should be a vector quantity as it only can be measured by ...
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1answer
118 views

Hydrostatic pressure is equal everywhere, however, the answer I'm getting is incorrect [closed]

Question: A hydraulic car lift has a pump piston with radius 0.015 m and a resultant piston with radius 0.120 m. The combined weight of the car and the plunger is 2500 N. Assume that the ...
14
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1answer
720 views

Does anyone know the mechanism behind this double helix cloud formation?

This looks like m=2 swirling instability mode of the axisymmetric jet, but how could an axisymmetric jet form up in the sky like that?
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45 views

Covariant Fluid Flow approach

I am doing Cosmological perturbation. Currently reading a paper by Bruni et al. In that it is mentioned that they are using covariant fluid flow approach to cosmology. Can any body give me a rough ...
0
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1answer
131 views

How does a piezoelectric drop generator work?

In a piezoelectric drop generator used for generating a single droplet which is 0.5 mm in diameter, there is a piezo-actuated brass diaphragm to generate droplets (for example here or here). What is ...
0
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1answer
259 views

Is the physics of $j = \rho v$ questionable? What are the consequences? [closed]

In electrodynamics you have the quantity $\mathbf{j}$, which represents density of current per surface area. It is often said that $\mathbf{j} = \rho\mathbf{v}$, for geometric reasons. When I make ...
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0answers
48 views

hydrodynamic entrance length [developing flow]. Non-native speaker needs some help [closed]

I am currently writing my thesis in English as an non-native speaker. From time to time, I struggle quite a bit with the correct expression of the sentences. Could you have a look on the highlighted ...
2
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1answer
261 views

Langevin equations in translational and rotational direction

I want to describe the following system. A bead is connected with a tether. There is a force $\vec{F}_{up}=F_{up}\hat{y}$ that acts on the bead. The tether acts with a force on the bead, this force ...
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0answers
82 views

How to make liquid marbles at home?

Some months ago I was reading a bunch of papers about the dynamics of liquid marbles. I was wondering if any of you have worked with them and know how to make them. I bought graphite and tried to ...
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2answers
66 views

Resources for droplets investigation

I am interested in investigating droplets mechanics. I have read some documents and journal papers related to some aspects of (water) droplets e.g. surface tension, collision with flat surfaces or ...
0
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1answer
429 views

Orifice Jet Flow experiment

I am writing up a report on Orifice jet flow experiment in which I am required to find coefficient of flow velocity, $C_v$, and the Coefficient of discharge, $C_d$. There are couple of things that I ...
3
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2answers
73 views

Adding a tracer to the surface of a water droplet

I have a 2 mm water droplet generated by a syringe and falling down. I am using two perpendicular cameras to capture simultaneous frames from it. I need to track the droplet during the time and ...
0
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1answer
179 views

Lubrication Theory

Basically, I'm modelling the flow of a "coating" process -- a fluid flow between a flat moving plane and a stationary cylinder, 2D, cartesian coordinates. Subscript 0 is the at the minimum height b/w ...
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0answers
31 views

Flow in the strip $0 < x < \pi/2$, $y > 0$ [closed]

Could anyone please explain how to show that a complex valued function represents a flow? For example, how does one show that $\Phi(z) = \sec^2 z$, where $z = x + iy$ with $x, y \in \mathbb{R}$, ...
2
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1answer
234 views

Fluid flow through an orifice

Forgive me for my ignorance. What would be the method to determine the pressure a non compressible fluid creates when forced though an orifice? Keep in mind this orifice does not have a constant ...
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0answers
74 views

Modeling a collision phenomenon [closed]

I have a single water droplet (d~3 mm) which collides with a solid particle (d~2 mm) with a relative velocity around 10 m/s. After collision, particle rips the droplet and goes through it. Therefore, ...
12
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3answers
2k views

How to prevent water droplets becoming larger on the tip of a nozzle?

I use an ordinary syringe to generate a single water droplet. However, it is not usually able to make a droplet smaller than 1 mm (because of surface tension forces, inner diameter of needle, etc.) ...
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1answer
102 views

Qualitative idea of viscosity [duplicate]

Suppose we are considering some fluid. As I currently understand, viscosity exists because of the following: supposing we draw one infinitesimal surface on the fluid, then the fluid parcels on either ...
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2answers
3k views

Why would the lack of air in a mine in an asteroid prevent you from flooding it?

In Isaac Asimov's I, Robot novel, two scientists stationed in an asteroid where mining activities are performed say "We could flood the mines, if this weren't an airless asteroid" when considering ...
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1answer
617 views

Why to write the Navier-Stokes equation with dimensionless quantities?

The Navier-Stokes equation is $$\rho \dfrac{D\mathbf{u}}{Dt} = -\nabla p+(\lambda+\mu)\nabla(\nabla\cdot\mathbf{u})+\mu\nabla^2\mathbf{u}$$ Then if the flow is incomprresible, and the fluid is ...
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1answer
253 views

Vorticity versus Viscosity

For a work project I need to revive my aerodynamics knowledge again. Can somebody help me with the distinction between vorticity and viscosity. If a flow vorticity is not equal to zero, the flow is ...
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2answers
714 views

Do wind turbines convert the kinetic energy of air?

It is often said that wind turbines convert the kinetic energy of the wind into electricity. But in respect to horizontal wind turbines with airfoil shaped blades this is imho not the case. Wind ...
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1answer
26 views

Can the nonlinear hydrodynamic forces be neglected when a capsized ship is righting? [duplicate]

Can the nonlinear hydrodynamic forces be neglected when a capsized ship is righting? Thank you for answering my question.
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3answers
202 views

Solving flow equations with less information

Suppose we consider the flow of a fluid through a channel, considered to happen in a plane. We want to consider the region $D = [0,L]\times [-a,a]\subset \mathbb{R}^2$ representing the piece of the ...
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2answers
85 views

What is the speed at which hydraulics take place

Consider a long pipe filled with some newtonian liquid, with piston at both the ends. You push the piston at end A, and observe it at the other end B. How much time does it take for piston at B to ...
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2answers
364 views

Does gravity change the pressure of a column of water when the column is tilted from horizontal to vertical?

I need to settle an argument. I think gravity causes a column of water to exert greater pressure against the walls of a pipe in which it is contained as it is tilted from horizontal to vertical. In ...
0
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1answer
115 views

Sum of static and dynamic pressure in a tube constant?

The sum of static pressure and dynamic pressure is said to be constant along a streamline. Except for energy conservation reasons I don't understand why that is. Static pressure is proportional to ...
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2answers
79 views

Potential energy of Hydroelectric plant before the dam was built

So the energy potential of a Hydroelectric dam is the difference between the head and base. Before the dam was built where does all that energy go? I can understand that for a long valley that is ...
2
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3answers
170 views

How do the flow equations relate to the actual situation?

This question might seem silly but I'll try to make it clear. It's a question (I think) about partial differential equations systems in general, but since currently I'm studying fluid mechanics I'll ...
3
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1answer
2k views

Why do vapour cones form around jet fighters?

Apparently this phenomenon has nothing to do with jets breaking the sound barrier and has something to do with the Prandtl-Glauert singularity as described on Wikipedia. But, the Wikipedia article ...
4
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1answer
306 views

Intuitive meaning of a special case of the Bernoulli equation

In the Bernoulli equation, if $h$ equals zero, it reduces to $$P_1+\frac12\rho v_1^2 = P_2+\frac12\rho v_2^2$$ The equation does not have an intuitive meaning other than the fact that it is a bare ...
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4answers
361 views

Mathematical Reasoning for Fluid Pressure as a Scalar

This question from a while ago and answers/comments to this question from earlier today both make heavy mention of the fact that fluid pressure is a scalar. Although this information was surprising ...
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2answers
784 views

Direction of pressure in fluids

ok so my friend told me that in a container, the pressure exerted by the walls on the liquid in the container act in the upward direction.Is he correct ? so what I am imagining is a cylindrical ...
2
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1answer
603 views

Difference between a “source dipole” and a “force dipole”

I know quite well what a dipole is and in general what multipole moments are (in the context of, for instance, electrodynamics). What I find myself confused by is something called a "force dipole" in ...
8
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3answers
428 views

finding equation of a water droplet

I have a water droplet which is falling down through its gravity. I've supposed that my droplet is an ellipsoid and I want to find the equation that represents this ellipsoid in XYZ coordinate system. ...
0
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1answer
94 views

Kinetic energy of fluids in Venturi Injector

Since the cross sectional area is smaller in the middle the water flows faster and experiences a smaller hydrostatic pressure. Additional mass is sucked in from the middle tube and gets accelerated ...
0
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1answer
68 views

Which moves faster in a time $t$: $A$ or $B$? [closed]

Suppose we have two objects, $A$ and $B$, both made of the same substance. They also have the same shape (e.g. two spheres), but $A$ is larger and therefore more massive than $B$. Both $A$ and $B$ ...
3
votes
1answer
372 views

I would like to know what variables to consider when I experiment with pouring from bottles and the “glug” effect?

I am a middle school science teacher and want to model a science fair project for my students. Specifically I want to investigate using a vent in the top of the handle of a gallon milk jug to ...
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0answers
51 views

Can we take transport equation of imaginary quantity?

In the RANS equation we approximate the nonlinear fluctuating terms to eddy viscosity times strain rate. Then by using turbulence models like Spalart-Allmaras etc, we take the transport equation of ...
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0answers
704 views

How to calculate the centerline velocity inside a pipe?

Well, I was reading about fluid-solid/structure interaction models for make a simulation in COMSOL, and in few papers about it [1] I find an expression about the centerline velocity. I understand the ...
2
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2answers
109 views

How stable are Benard Cells when the thermal gradient begins decreasing?

I've found lots of information on the formation of Benard Cells and convection currents but very little information about what happens to the self-organized structures when the energy gradient being ...
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1answer
103 views

Does this type of equation for an airfoil exist?

In a common airfoil, such as a plane's wing, diminished pressure over the top of the wing and increased pressure under the wing, generally speaking, will cause the wing to lift. Now, a man standing ...