What is Fluid mechanics: Definition and 757 Discussions

Fluid mechanics is the branch of physics concerned with the mechanics of fluids (liquids, gases, and plasmas) and the forces on them.:3
It has applications in a wide range of disciplines, including mechanical, civil, chemical and biomedical engineering, geophysics, oceanography, meteorology, astrophysics, and biology.
It can be divided into fluid statics, the study of fluids at rest; and fluid dynamics, the study of the effect of forces on fluid motion.:3
It is a branch of continuum mechanics, a subject which models matter without using the information that it is made out of atoms; that is, it models matter from a macroscopic viewpoint rather than from microscopic. Fluid mechanics, especially fluid dynamics, is an active field of research, typically mathematically complex. Many problems are partly or wholly unsolved and are best addressed by numerical methods, typically using computers. A modern discipline, called computational fluid dynamics (CFD), is devoted to this approach. Particle image velocimetry, an experimental method for visualizing and analyzing fluid flow, also takes advantage of the highly visual nature of fluid flow.

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  1. M

    How Do You Calculate Shear Stress in a Flowing Fluid?

    Homework Statement Water at 20 degrees C flows in a 0.8cm diameter pipe with a velocity distribution of u(r) = 5[1-r2/(16x10-6)]m/s. Calculate the shear stress on (a) pipe wall (b) at a radius where r = 0.2 cm (c) at centerline of pipe Homework Equations Shear stress = viscosity x du/dr...
  2. W

    Fluid Mechanics: Tilted Axes and Weight of Gate

    Homework Statement AB is homogeneous with mass of 180 kg, goes 1.2m in the page and is hinged at A and resting on aa smooth bottom at B. All fluids at 20 C. Find height of water that will result on 0 force at B Homework Equations M_s = \int\int_s \ (\vec{r} \times \hat{n} )PdA...
  3. G

    Not enjoying thermo, will I enjoy fluid mechanics?

    I'm pondering courses for the autumn and I'm at a bit of a crossroad. Doing an intro thermodynamics class right now which involves all the stuff I don't really enjoy - measurements, looking stuff up in tables, memorization, etc. Very non-theoretical. It feels like an AP chemistry class...
  4. I

    Why Is My Fluid Mechanics Solution Incorrect?

    Homework Statement Task number 2. The problem is that my solution is wrong but the lecturer didnt want to explain what is wrong, she insists on doing it by myself. But to be honest I'm not really good at it and I just need someone either explain it or solve or at least check it and tell me...
  5. R

    Fluid Mechanics: Fluid in a Tube

    Homework Statement The problem depicts a tube shaped like a "U". The arms of the tube are 0.3m in height and the horizontal part of the tube is 0.6m long. The left arm of the tube is open while the right arm of the tube is closed. The problem states that the liquid in the tube is of density...
  6. B

    Fluid Mechanics and perpendicular force

    I was just wondering why a body immersed in a fluid at rest experiences a perpendicular force on its surface? Why can't there be a component of force in parallel direction to the surface ? I read somewhere that this would cause the fluid to flow parallel to the surface but i don't quite...
  7. 5

    How can I find the mass of the object being held up by the water?

    Hi, I was wondering if anyone would be able to help me with this problem:Homework Statement I have a mass, that is being held in the air by several downwards pointing jets of water. I know the diameter of the nozzles from which the jets are flowing, and the flow (Q) from each jet, which is the...
  8. N

    Fluid Mechanics: Incompressible flow and pressure

    Most liquids can be assumed 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 density ρ, p=c_s^2 \rho we see that the pressure in constant as well. Now, say that I look at a...
  9. N

    Fluid Mechanics (Time derivatives)

    Hi Guys. I hope some of you are able to help me out. This is NOT a homework. I have to explain the difference between the three different rate of change (time derivatives) of a property (such as mass, momentum, internal energy, etc) in a continuum? 1 )The partial time derivative 2)...
  10. S

    Conceptual questions regarding fluid mechanics

    Homework Statement I have some conceptual question in the fluid mechanics topics which has been bugging me for quite some time now. 1) When wax is rubbed on cloth why does the cloth become waterproof 2) A weightless baloon is filled with water. What will be the apparent weight when...
  11. N

    Stream function/velocity potential in fluid mechanics

    Hi! When you are calculating ##\psi## or ##\phi## from the horizontal or vertical velocity components of a fluid's velocity, you end up with a constant ##C## carried along with the function. In my class, the professor just said something about them being arbitrary (I think..) and set them to...
  12. P

    [Fluid Mechanics] How is the pressure at 2 different heights the same?

    Homework Statement A tank containing water with a small nozzle at the bottom right where the water flows out. Homework Equations Bernoulli's equation: p_1+\frac{1}{2}\rho v^2_1+\rho g h_1=p_2+\frac{1}{2}\rho v^2_2+\rho g h_2 3. Assumptions (1) Quasi-steady flow (2)...
  13. A

    Best fluid mechanics texts for math majors

    Hey all. I am an undergraduate math major in my third year who is planning to do a reading course in fluid mechanics next term. I have taken courses in rigorous advanced calculus, real and complex analysis, topology, and intro ODE and PDE. I would be taking a differential geometry course, which...
  14. C

    Fluid Mechanics Piston Problem

    Homework Statement A hydraulic car lift has a reservoir of fluid connected to two cylindrical fluid filled pipes. The pipe directly below the car has a diameter of 1.8 m. the pipe o which the plunger acts has a diameter of 0.045m. the plunger is depressed a distance of 1.5m. How much does the...
  15. S

    Exploring Mars with Inflatable Balloons: Fluid Mechanics Question Help

    Fluid Mechanics Question! Help needed :( Homework Statement It has been proposed that we could explore Mars with inflatable balloons. the density of the Martian atmosphere is 0.0154kg/m^3 (ignore that this varies with temperature). Suppose we make the balloons out of a thin tough plastic...
  16. W

    Fluid mechanics, Draining a cylindrical tank, some help

    For the problem attached, I solved it and found the answer for part b : 80.21 s How to get sure or know if the answer is right or not. Thanks
  17. W

    Fluid mechanics, help in finding the dancy friction factor

    How to find the dancy friction factor by using the colebrook white equation (not using the moody chart) ; to calculate the 1/√f = -2LOG[(e/d)/3.71 + 2.51/(Re*√f)] help please
  18. Saitama

    Fluid Mechanics problem - cylinder over a orifice

    Homework Statement The horizontal bottom of a wide vessel with an ideal fluid has a round orifice of radius ##R_1## over which a round closed cylinder is mounted, whose radius ##R_2>R_1##. The clearance between the cylinder and the bottom of vessel is very small, the fluid density is ##\rho##...
  19. S

    Using Fluid mechanics to rate power output of an engine.

    I trying to come up with a way to measure the power output of an engine using a water pump, And I wanted some one to go over my math and check for flaws in my thoughts. My idea is to measure the flow rate and the pressure of the output of the water pump. Using this math to solve for power...
  20. M

    Fluid mechanics navier stokes flow around geometry

    hey pf! i am studying fluid mechanics and was wondering if any of you are familiar with a flow around some geometry? for example, perhaps a 2-D fluid flowing around a circle? if so please reply, as i am wondering how to model the navier-stokes equations. i'll be happy to post the equations...
  21. N

    Simple vector-decomposition (fluid mechanics)

    Homework Statement I am reading an introductory book on fluid mechanics (freely available on the WWW) and I came across this on page 10: I don't understand the underlined part. We have a force-vector πx, which we decompose to find the overlap with some surface element dS. Shouldn't the force...
  22. M

    Fluid mechanics study navier stokes

    hey pf! i am studying fluid mechanics and we are reviewing navier/stokes equations. we have gone over a few problems, but i could definitely use practice on more. do you all have any suggestions that include solutions, not just answers, so if I am stuck i can see how to solve? problems...
  23. P

    Basic Question about Force for Fluid Mechanics

    Homework Statement The block of ice (temperature 0°C) shown in Figure P9.57 is drawn over a level surface lubricated by a layer of water 0.10 mm thick. Determine the magnitude of the force needed to pull the block with a constant speed of 0.50 m/s. At 0°C, the viscosity of water has the...
  24. O

    How Does Viscosity Affect Flow Rate According to the Hagen-Poiseuille Equation?

    Homework Statement see the pic attached Homework Equations Newton's law of viscosity The Attempt at a Solution okay, i knew that , since the viscosity of the fuid in the second tube is low, it flows easily than the other, but i don't know which exact euation connects visocsity...
  25. N

    Simple Fluid mechanics problem

    Homework Statement A uniform wooden stick of density d is completely immersed in water of density D (D>d). One end of the stick is free to rotate about a hinge which is attached to the wall of the container. In equilibrium the stick the stick makes an angle θ then tanθ is- (a)0 (b)d/D...
  26. G

    Fluid Mechanics - Linear momentum Analysis

    Homework Statement Water is flowing into and discharging from a U-shaped pipe section as shown. At flange (1), 30 kg/s of water flows into the section with the total absolute pressure of 200 kPa. At flange (2), the absolute pressure is 150 kPa. At location (3), 8 kg/s of water discharges...
  27. N

    Just a thought experiment on fluid mechanics.

    I am thinking that... if a tank of water which contains a small wooden block is kept in an elevator which is accelerating upwards from rest, will the block get more dipped or remains constant position with respect to water??
  28. N

    Geometries of potential theory (fluid mechanics)

    Hello! My book (fluid mechanics by White) doesn't explain the formulas it uses for finding geometric information about a potential field. For instance, sometimes if a stream-function is kept constant it, will form a figure like the one in this picture...
  29. K

    Top Book Recommendations for Studying Fluid Mechanics: Landau vs. Alternatives

    Can anyone recommend me a book on Fluid Mechanics? I've been recommended Landau's book on Fluid Mechanics, but I haven't learned Statistical Mechanics which is required in his book.
  30. N

    Fluid Mechanics: Friction of a moving surface

    Hey! So for Newtonian fluids, the shear-stress is given by \tau = \mu \frac{du}{dy} Now, let's assume you have water flowing horizontally in laminar steady state motion, where its surface is also moving. Above it is air. So if we disregard the friction from air, the shear-stress will become...
  31. S

    Introductory Fluid Mechanics book.

    Could someone recommend me a good Introductory Fluid Mechanics book? It's only an introductory course so it doesn't have to be too comprehensive at all. Thanks.
  32. N

    Steady state in fluid mechanics

    Hey! When a stream is steady-state, you can cancel the acceleration term in navier-stokes equation, right? so: \rho \vec{a} = 0 = - \nabla P + \rho \vec{g} + \mu \nabla ^2 \vec{V} But there are many terms in the total acceleration which are not dependant on time! The acceleration term in...
  33. B

    Engineering Researchers in fluid mechanics: engineers , Physicists ?

    Researchers in fluid mechanics: "engineers", "Physicists" ? Dear all, I was reading the book "Turbulent flows" of S. Pope and I went to his website at Cornell and started to see his work. In case you do not know him, I can tell you that his work is 100% applied mathematics and fluid physics...
  34. T

    Fluid mechanics and circular flow

    Dear all I am having a problem on circular flow of fluid. On all books I have read they say \frac{dp}{dr}=\rhov^{2}/r Which make sense by using infinitesimal square volume and take the force exert. But if I use a circular infinitesimal volume (which is usually the case for circular...
  35. P

    Momentum for a control volume (Fluid Mechanics)

    Homework Statement http://i988.photobucket.com/albums/af10/postop/equationsmomentum_zpse8c8d44a.png Homework Equations The Attempt at a Solution Can somebody explain to me in the two equations above what is the "u" and what is the "v"? In the question, it says that the water at...
  36. Z

    How Do You Calculate Airflow and Pressure Changes in a Duct System?

    fluid mechanics question help!? Homework Statement Air flows through a horizontal duct of dimensions 300 x 300 mm with a velocity of 15 m/s. At position (1) in the duct a water gauge (water manometer) registers a hieght of 215mm. The duct bends downwards and reduces in size to 240 x 240 mm...
  37. W

    Discover the Proof for the Dynamic Viscosity Formula in Fluid Mechanics

    What is the prove for this formula, or in another way the provement of the dynamic viscosity multiplied by the shear strain will get us the shear stress,
  38. Z

    Fluid Mechanics shear stress, conceptual question

    Homework Statement Consider a fluid between two plates. One on the bottom which is stationary, and one at the top which is moving at constant velocity V. The plates are separated by distance h. Does shear stress change as you move further from the moving plate? Homework Equations the...
  39. B

    Shear Stress and Fluid Mechanics

    Homework Statement It's a relatively simple problem I'm sure, but I'm a bit confused on how exactly to go about it: There are three parallel plates with water (viscosity of 0.8807 cp @ 30°C) between plates 1 and 2 (plate order of 1 on bottom, 2 in middle, 3 on top), and toluene (viscosity...
  40. R

    Calculating Pressure Change in a Manometer Due to Removal of Air Bubble

    Homework Statement a manometer consisting of tube that is 1.25 cm inner diameter . on one side , the manometer leg contains mercury,10cc of an oil(S.G.=1.4)and 3 cc of air as a bubble in oil . the other leg contains only mercury . both legs are open to atmosphere and static . An accident...
  41. B

    Fluid mechanics problem, need explanation please

    Hi please check the highlighted question in the attachment and the solution and see the problem, i need help please. I have two questions about it: 1- why didn't we take the plug as a vertical wall and thus the force would be integral of pressure x area? 2-WHERE DID THE FORCE DUE TO...
  42. B

    Simple Fluid mechanics question, Need Help

    I've been solving fluid mechanics problems and i encountered two problems that made no sense to me. Both problems that ask about the force done by water on a VERTICAL wall under the level of water. One problem was solved by taking the integral of the gauge pressure and multiplying it by the...
  43. N

    Lagrange-Young equation in Fluid Mechanics

    Young-Laplace equation in Fluid Mechanics EDIT: I meant the Young-Laplace equation, of course, not the Young-Lagrange.. sorry! Heya! According to said equation, ΔP*area = γ*circumference, for an interface of spherical fluid-element. Can I pls get some explanations? 1) Why is...
  44. A

    Fluid mechanics book recommendation for new grad

    Hey all, I'm a Math major (most of my coursework was in PDEs) and just got accepted into Grad school (yay) for Mechanical Engineering. I need to be very familiar with fluid mechanics and have about 5 months to do so. Trouble is, the last fluid mechanics course I took was about 3-4 years ago...
  45. W

    Fluid Mechanics Newtons law of viscosity

    Homework Statement having problems differentiating Homework Equations Tw ( wall shear stress)= -U(viscosity)*du/dr been given u as 2V(1-(r/r)^2) The Attempt at a Solution i substituted u in and got d/dr (2V(1-(r/r)^2) i tried to multiply out the minus sign and 2V and got...
  46. V

    How Can Two Stones and a Stopwatch Help Measure the Width of a Lake?

    Homework Statement The question asked is: Two students are given 2 stones and a waterproof stopwatch, along with swimwear. Using this material they are then required to estimate the distance across a lake. This question could obviously be answered using fairly simple process, however, it is...
  47. liometopum

    Fluid mechanics, source-sink question

    In fluid mechanics, the velocity of the liquid going in or out (source-sink) of a hole in a two dimensional model is Q/(2 pi r). http://farside.ph.utexas.edu/teaching/336L/Fluidhtml/node63.html What is the velocity in three dimensions? Is it Q/(4 pi r^2) ?
  48. M

    Fluid Mechanics - Resistance to fluid motion using Chezy's formula

    Homework Statement The quantity of water delivered through a buried pipe line that is 2 000 m long and has an inside diameter of 200 mm has over the years steadily decreased to 80 % of its original flow. This is due to encrustation inside the pipe. It was then decided to have the pipe...
  49. H

    How Do Impulse and Reaction Turbines Utilize Fluid Mechanics Principles?

    Hi all:I have a question regarding the fluid mechanics of turbine, both impulse and reaction turbines. I have searched many sites , including my fluid mechanic textbook, and yet I still don't quite understand the physics behind a turbine.Impulse turbine is a bit easier to understand as I can...
  50. D

    Laplace equation in rectengualar channel (Fluid mechanics)

    Homework Statement Estimate the speed a potential flow in gravity field would have in direction y in rectangle channel with depth h [/iteh] and length l . The fluid is incompressible and on the surface z = 0 we have boundary condition \dfrac{\partial^2 \phi}{t^2} + g\dfrac{\partial...
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