What is Fluid dynamics: Definition and 631 Discussions
In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation.
Fluid dynamics offers a systematic structure—which underlies these practical disciplines—that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves the calculation of various properties of the fluid, such as flow velocity, pressure, density, and temperature, as functions of space and time.
Before the twentieth century, hydrodynamics was synonymous with fluid dynamics. This is still reflected in names of some fluid dynamics topics, like magnetohydrodynamics and hydrodynamic stability, both of which can also be applied to gases.
In classical and continuum mechanics if we want to find equation of motion of the body we draw force diagram and apply Newton's 2nd law.
In continuum mechanics, equation of motion actually refers to a special point of the body known as center of mass (COM) which can be proven by definition of...
Work - energy principle states that work done by net force acting on the body equals change in kinetic energy of the body. We are talking about continuum mechanics. This principle is usually introduced in mechanics of solid bodies. For us to describe the motion of the body, it is enough to know...
Work - Energy principle states that work of resultant force or sum of work of all forces acting on some system equals change in kinetic energy of the system.
For inviscid fluid flowing in a pipe such theorem can be used to derive Bernoulli's equation because as fluid flows it is subjected to...
If I have fluid with area 10 and velocity 10, if the velocity increases to 20 the area will become 5. But if we switch to a reference frame moving at velocity 1 opposite this motion, then it would be 10 and 11 to 5 and 21, violating the continuity equation. What is wrong?
I am trying to calculate the flow rate of O2 from a known volume 25 in^3. The cylinder will fill up to a maximum pressure of 140 psi in 11.26 seconds. Any help to determine the flow rate will be appreciated. Do I use Bernoulli equation to find the flow rate?
Hi guys,
I've been doing some light reading on hydraulic jumps.
For example:
So I've been through the basics, super critical to sub ciritcal etc:
https://en.wikipedia.org/wiki/Hydraulic_jump
So far I understand that the jump occurs at the two points either side of the critical depth, like we...
When fluid is placed between two parallel plates such that one plate is moving and other is stationary, fluid will start flowing. Between plate and the fluid there is viscous friction given by equation: $$ F = -\eta A \frac {dv} {dy} $$
where $ \eta $ is fluid viscosity, $A$ is area of a plate...
I have a empty bottle and immersed it into the water, where the pressure inside the bottle is equal to air pressure. If I want to make a hole on the bottle, how big is the hole to prevent the water leak into the bottle at different depth?
what kind of parameter is involve in this phenomena? can...
Consider a manometer as shown above with different widths W and w.
If we take a mass (red) that is frictionless and does not allow water to leak of mass M, then I would like to calculate the height of water H in the narrow tube of width w. I arrive at a non sensical answer of H = 0 in one...
Hello all, I am trying to understand how a force at the opposite wall from water entering a pressurized air (atmospheric pressure) tank, and for this discussion it is rigid, with no relief valve to displace the compressed air can be deduced. I have created a simple illustration and believe this...
(a) Write down an expression for the velocity field corresponding to uniform
rotation. Find the vorticity corresponding to this flow.
(b) Consider a small perturbation u' to the state of uniform rotation with angular
velocity Ω, which has the form of a plane harmonic wave
u'= A exp i(k·x−ω t) +...
Greetings,
I am about to start experimenting with misnamed rocket stoves and rocket mass heaters. I say misnamed because I think the velocities are too slow to be rocket science. (Why would I experiment with these? Because I have cement, perlite, and reinforcement materials at hand and I just...
Does anyone know of any good papers/lectures/textbooks/etc that discuss the physical and mathematical principles that explain the structure and motion of clouds? Thanks.
The attachment below describes a tank, hollow pipe and two flexible (balloon like) bags forming one body of weight W_tank.
My two questions are what are the downward forces acting on the submerged body in both cases.
Hello,
The question will probably be related to mechanical engineering / chemical engineering / aeronautics. I come from the field of optics and have no background at all on fluid dynamics.
I'm trying to calculate the dependence of pressure on distance, i.e. P(x) in a gas flow problem: I...
Typical box fan+air filter setups use axial consumer-grade fans designed for providing maximum air flow at low power consumption. These fans do not provide sufficient air flow at the high static pressure requirements typical of air filters. The air filters DIYers use are high Merv(e.g Merv 13)...
v1- velocity of water at the top of the barrel
v2- velocity of water at the the pipe (bottom of cylinder)
p + (⍴ *(v1)^2)/2 + ⍴gh=p + (⍴ *(v2)^2)/2 + ⍴gh
atmosferic pressure cancels out
(⍴ *(v1)^2)/2 + ⍴gh = (⍴ *(v2)^2)/2 + ⍴gh
density doesn't affect the result(cause its in every term)...
The problem states:
Two parallel plates separated by distance h, the plate at the top moves with velocity V, while the one at the bottom remains stationary.
My initial approach was:
I considered, ##du/dy = V/h## and for the shear stress ##\tau = \mu \frac{\partial u}{\partial y}##
For...
in class we derived the following relationship:
$$\frac{1}{V}\frac{dV}{dt}= \nabla \cdot \vec{v}$$
This was derived though the analysis of linear deformation for a fluid-volume, where:
$$dV = dV_x +dV_y + dV_z$$
I understood the derived relation as: 1/V * (derivative wrt time) = div (velocity)...
What is best theoretical shape of undertray for maximum downforce , maybe wing shape or venturi shape?
classic "venturi shape" with diffuser
"wing shape"
Earlier today I realized that, when a strong gust of wind would blow through my area, it would pick up leaves off the ground and typically blow them in circular patterns, and typically the leaves would go in at least several complete circles before coming to rest back down on the ground. Why is...
So, it's a long way to the solution, but I'm finding it difficult to find a starting point. I'm going to say that as a first step, I should find what the value of the stream function ##\psi## is, at the surface. In order to do this, I need to use the following equation:
##F=\phi+i\psi##
If I...
Let's start with a horizontal tube with a constant diameter. I'm not sure if it's important, but let's assume it's frictionless. I will have some fluid flowing in this tube and if it's important, we can make the fluid incompressible, inviscid, irrotational, etc.
To create a flow in the tube...
I hope you guys don't mind a bizarre question from a novice. I've learned just enough about fluid dynamics to be dangerous.
Assume that we have a straight, rigid tube with a constant inner diameter. It's not long, let's say it's around a foot (in case that matters). We cut a chunk out of the...
hi guys
I'm really struggling to get the expression for average speed in turbulent flow
The book explains absolutely nothing about how the integration is carried out, in addition to the fact that the logarithmic term becomes undefined when r = R what I did was carry out the integration up to...
I have a problem with plumbing in the bathroom at my condo (quite old) that I am living. The plumbing inside the walls of my bathroom make this whistle noise always and it goes away when I flush the toilet. And then it comes back again after sometime. Do you know what could be happening here?
I am a layman with very little experience in math and physics and recently I became curious about how to analyze dampened oscillations occurring in fluid mediums, such as those following a disturbance in a pool of water. What sort of math and physics is required to understand this phenomenon and...
I have few conceptual doubts in fluid mechanics. Here is the one I will ask first.
I want to understand the force direction acting on the solid liq interface during fluid flow, Let's say a fluid is flowing in a pipe. Now the fluid applies a shear stress at the walls of pipe in the direction of...
With the assumptions of Inviscid flow, no pressure gradient and no body force terms in 1-D Navier Stokes becomes 1-D nonlinear convection equation;
And if we assume velocity of wave propagation is constant value c, equation becomes 1-D linear convection equation;
This is online derivation and...
Here i added a page from my fluid dynamics book where it shows particle model for deriving the equation. My question is why pressure is more at stream side aka 'positive "s" direction'.I would expected more pressure on the other side because for example when you trying to push a rigid object or...
My first post here!
I have calculated everything i need, except the thickness of the second layer dZ*, therefore i can't solve V3/V2=(R2ˇ2)/(R3ˇ2)
Trying for days now, i would appreciate any help.
I know that taking the scalar product of the harmonic (Laplacian) friction term with ##\underline u## is
$$\underline u \cdot [\nabla \cdot(A\nabla \underline u)] = \nabla \cdot (\underline u A \nabla \underline u) - A (\nabla \underline u )^2 $$
where ##\underline u = (u,v)## and ##A## is a...
Hi PF!
I'm running a two-phase simulation, which takes a long time to run. The simulation is simply a partially filled tank being drained in zero gravity, and the tank is a little smaller than a mailbox (~ 160 X 40 X 40 mm). Before running the simulation I would like to know if my mesh is...
Hi sorry about the way I've posted I'm new to this site. Anyway basically I've been set this question which should be attached to this post, I have attempted to do this question but I'm having trouble in forming an equation in the first place. I'm unsure where to start, I understand I need to...
Hello, i have a problem that look's easy to solve but really is not.
It involves a rotating paddle wheel submerged in water and i want to know the force exerted on the wheels and the torque required to rotate it. I have made a simple drawing to illustrate the problem below. I want to use the...
I'm studying fluid and propulsion mechanics by myself.
I stumbled upon this website from MIT: http://web.mit.edu/16.unified/www/SPRING/propulsion/UnifiedPropulsion2/UnifiedPropulsion2.htm#fallingblock
It states that "Newton’s second law for a control volume of fixed mass" is $$\sum...
Hi,
I am trying to find out Force on a rigid body when it is completely inside a fluid with density p, i.e. the body is completely drowned in the liquid and then another liquid is pushed into the container with different density 'r' (such than r > p).
Thanks.
My background is in fluid dynamics. Controlling high velocity fluids via atmospheric and offset dynamics.
I have put some evidences together, for discussing a new working principle theory. These simple experiments, along with known experiments found on YouTube, come to be a very interesting...
My approach was that I consider the pressure of cross section A first
Pa= P + dgh
Now by writting Bernoulli's Equation between the cross-section A and the opening :
$$ Pa + 2dgh + 2dV^2/2 = Pb + 2dV'^2/2$$
Where Pb is the pressure of the opening which is equal to the atmospheric pressure...
Almost 90% of all humanity lives in the Northern hemisphere. Due to colonization, expansion, growth, war, water sources, etc. we have amassed our populations in specific areas around the Northern hemisphere. We continue to build at an unprecedented rate. Our buildings are growing wider, taller...
Summary: I have been looking around and trying to understand what the physical use is for a streaklines. While we are at it, maybe we can discuss how they differentiate from pathlines, streamlines and timelines as well as discussing their uses. Thanks for your feedback in advance.
.
The first part of the problem I just used Stevin's law:
$$p_{atm}=P+ρg(h_1-h_2)=> h_2=(P-p_{atm}+ρgh_1)/(ρg) =>h_2=0.94m$$
Is this right? I considered ##ρ=10^3 {kg/m^3}##
About the second part... how can I be sure that ##h_1## remains unchanged? If it is unchanged, then can I use Bernoulli's...
Friendly argument at work (both non physics majors) with what tube would fill up faster with a flow rate (siphon like) that remains the same through two different diameter tubes. The dialysate jug is open to atm pressure. One tube is about .5 inches in diameter and the other is .25. We were...
My name is Martin Scholtz and I am a postdoc researcher at the Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic.
I'm working mainly in the area of gravitational physics, but I am interested in different topics as well, see tags...
There are many fluid dynamics applications such as pipe flows, jet flows, boundary layers where we ignore any sound waves present in the system. I don't understand this though, because all sound waves are caused by pressure disturbances so why can we ignore these pressure disturbances when we...