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

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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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0answers
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 ...
2
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1answer
46 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
38 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 ...
0
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1answer
367 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 ...
4
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3answers
94 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?
2
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0answers
49 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: $$ ...
8
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0answers
90 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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0answers
23 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 ...
2
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1answer
131 views

Sum of forces with liquid in rotation

It's not homework (I'm teacher). I would like to compute sum of forces on this study : The shape is symmetrical like that I'm sure the center of gravity is in the center of the shape. I compute ...
29
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3answers
2k views

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 ...
-1
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1answer
105 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 ...
0
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1answer
111 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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56 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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2answers
80 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 ...
5
votes
1answer
115 views

Sound Propagation using Finite-Difference Time-Domain (FDTD) considering wind effects

I am trying to plot the propagation of sound from a fixed source in a 2D environment using Finite-Difference Time-Domain (FDTD) Method taking into account the effects of the wind velocity. I came ...
2
votes
1answer
98 views

Calculating Length Scales from Passive Scalar Field

I have a set of PLIF images of a passive scalar advected in a turbulent flow. I'm wondering if it's possible to estimate the integral length-scale based on the images of the passive scalar, and if ...
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0answers
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 ...
3
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1answer
889 views

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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0answers
41 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 ...
0
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1answer
85 views

How to calculate fluid(oil / hydrocarbon) loss under pressure

I'm trying to calculate the amount of fluid that would flow through an area dependant on the amount of pressure that there is. I'd also like to know the rate at which it would flow. Essentially I ...
4
votes
1answer
135 views

Pipe in a flowing river problem

I'm working on a certain problem in fluid mechanics, which isn't really my strongest area. The problem is as follows: Curved pipe is partially submerged in a flowing river so that one end is pointing ...
0
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2answers
68 views

Finding power with Drag Force equation

The mass of the car is 1500 kg. The shape of the body is such that its aerodynamic drag coefficient is $C_D=0.330$ and the frontal area is $2.50 m^2$. Assuming that the drag force is proportional to ...
3
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1answer
146 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 ...
3
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1answer
302 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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0answers
33 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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1answer
115 views

What makes an abstract physical system describable by a “fluid” equations of motion?

We can describe (some of) the dynamics of many systems using fluid mechanics. Of course these include classical fluids like water, more exotic fluids like photon gases and the universe as a whole and ...
1
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1answer
35 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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2answers
224 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. ...
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votes
3answers
2k views

Reynolds number and inertial force

The Reynolds number is defined as the ratio of ´inertial´ forces to viscous forces. $$ Re = \frac{\text{Inertial Forces}}{\text{Viscous Forces}}$$ Now, viscous forces make sense to me. They are ...
3
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1answer
35 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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2answers
7k views

Relation between pressure, velocity and area

In a nozzle, the exit velocity increases as per continuity equation $Av=const$ as given by Bernoulli equation (incompressible fluid). Pressure is inversely proportional to velocity, so we have lower ...
6
votes
1answer
231 views

How to calculate strength of wind speed in a von Karman vortex?

I am working on a project involving Von Karman vortices coming off of a mountain. I was able to calculate the shedding frequency (thanks to tpg2114 in a prior question), but now find it necessary to ...
11
votes
2answers
15k views

What exactly is the difference between advection and convection?

After reading Wikipedia articles on advection and convection, I still cannot determine whether there is a consensus on a difference between these two terms. Sometimes, the term convection seems to ...
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2answers
6k views

Convective and Diffusive terms in Navier Stokes Equations

My question has 2 parts: I just followed the derivation of Navier Stokes (for Control Volume CFD analysis) and was able to understand most parts. However, the book I use (by Versteeg) does not ...
0
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1answer
67 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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0answers
41 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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2answers
321 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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3answers
289 views

A simple logical problem regarding pressure and force

Suppose a 2 meter long pipe, with area of cross section is $1 m^2$. The pipe is vertically placed, with the bottom end closed. Inside the pipe, at the closed bottom end, there is $1 m^3$ of air, ...
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2answers
51 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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0answers
27 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 ...
2
votes
1answer
67 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 ...
2
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1answer
63 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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2answers
44 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?
13
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4answers
573 views

Why does string not wick down?

I regularly drink tea at work and I often reuse the tea bags (yes I know I'm a cheapskate). Yesterday afternoon I used a tea bag once and kept it in the cup in case I wanted another cup before I ...
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2answers
1k views

How to estimate the Kolmogorov length scale

My understanding of Kolmogorov scales doesn't really go beyond this poem: Big whirls have little whirls that feed on their velocity, and little whirls have lesser whirls and so on to viscosity. ...
0
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2answers
59 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 ...
1
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2answers
48 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 ...
0
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1answer
51 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 ...
4
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3answers
346 views

Addes mass forces: can a force depend on acceleration?

My friend and I had a little discussion about added mass forces. I always interpreted $F=ma$ as a cause-effect relationship, so I find rather uneasy to accept that the cause can instantaneously ...