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. A

    Cauchy's equation in terms of material acceleration

    Does anyone know which formula is used or how to arrive at the righthand side of the equation below, which is the dot product of del and rho*a 2nd order tensor(V V). . represents dot product and X a vector quantity This problem is in connection with transforming cauchy's equation in terms of...
  2. L

    Fluid Mechanics: Pressure in Fluids

    Homework Statement The gauge pressure at the inlet of a horizontal venturi meter is 40kPa. The vacuum at the throat is 38 mm mercury. If a differential U-tube manometer containing mercury is the U-tube and the oil in the connecting tubes is connected to the venturi, what will the difference in...
  3. P

    Fluid Mechanics: Weight vs Pressure

    Homework Statement A thin uniform circular tube is kept in a vertical plane. Equal volumes of (The liquids subtend a right angle at the centre) two non miscible liquids whose densities are a and b respectively fill half of the tube as shown. (The diagram depicts a>b) In equilibrium the radius...
  4. ltkach2015

    Steady Flow-Does That Mean ALL Properties of Flow are Steady?

    QUESTION: In general: when a flow is considered steady does that mean all properties of the flow are steady? Or: can a flow have steady and unsteady properties?
  5. dodonaomik

    Px in horizontal direction (about fluid mechanics)

    1. Plot Px in horizontal direction about three quarters of cylndrical surface ABCD Px: horizontal force in unit length 2. formula: P=ρgh3. my question: ①Why does Px point at the right? ③What does the blank mean? Because ABCD is only 3/4 of a circle...
  6. A

    Physical Interpretation of velocity potential

    What is physical interpretation of velocity potential? Is a conservative quantity, i.e, line integral of velocity potential around a closed loop is zero>
  7. T

    I Confusion Over Hydraulic Gradient, L parameter

    I've come across two different approaches to quantifying what l is in the equation for hydraulic gradient Δh/L. In this first picture L is the parallel distance along the datum across the reference plane But in this second picture L is the length along the pipe Why are the two L's...
  8. T

    Is Drag Coefficient Constant for same shape, different size?

    I've read that drag coefficient depends on the shape of the object but I am confused as to what shape means. Does it mean geometric shape or is area included in that? Say I have one sphere of radius r and keep fluid velocity, density, and viscosity constant and find its drag coefficient. Would...
  9. 0

    Consequences of Choosing Incorrect Variables in BuckinghamPi

    This question arose as I was studying mathematical modeling in fluid mechanics. It was posted to math.stackexchange, but there a was a lack of response, probably due to the applied nature of the problem. One form of the Buckingham Pi Theorem says that for nn variables with kk dimensions, the...
  10. R

    Resultant force on pipe (Fluid Mechanics)

    Homework Statement Posted in picture below Homework Equations Bernoulli's Equation P/pg + v1^2/2g + z1 = P/pg + v2^2/pg + z2 The Attempt at a Solution Posted in picture below Wasn't sure if what I did was correct...still practising the topic itself
  11. E

    How Does Tube Diameter Affect Reynolds Number in Gravity-Driven Laminar Flow?

    < Mentor Note -- please remember to use the Homework Help Template when posting schoolwork questions > Consider the fully developed laminar flow due to gravity of water in a vertical circular tube. Assume atmospheric pressure at inlet and outlet. Show that the relationship between diameter and...
  12. Sheezey

    Fluid Mechanics: Calculating Force Required

    Homework Statement Gate AB in Fig. P2.62 is 15 ft long and 8 ft wide into the paper and is hinged at B with a stop at A. The water is at 20°C. The gate is 1-in-thick steel, SG =7.85. Compute the water level h for which the gate will start to fail. Homework Equations F = δhcgA Ycp =...
  13. A

    Rotating sprinkler head and torque

    Hi, can anyone tell me where this "shaft torque" is coming? What is causing this torque? Screenshot is from Fundamentals of Fluid Mechanics by Munsun. http://postimg.org/image/3zilpmzbv/ Thank you.
  14. A

    Power required to rotate a disc in a fluid

    Homework Statement This is an optional question given to Fluid mechanic students to work on for leisure. P = power ρ = fluid density, rho ω= angular velocity omega μ= dynamic viscosity, mu D= diameter Homework Equations Show the that the power required to rotate the disc is given by...
  15. L

    Change in pressure of a gas inside a tube

    Homework Statement A U-shaped tube of uniform section "S" has one extreme closed and the other one open to the atmosphere. The tube contains mercury (M) in the central part, a gas (G) to the left that exerts a pressure "p" and a column of water (W) of height h_w to the right. Then, a mass "m"...
  16. I

    Water and saline fluid mechanics

    Hey Guys, i have a system that I'm pumping with water/ saline. as illustrated below. At the inflow i hooked up a pressure gage to my pump and read 120mmHg (closed system), and at the outflow I am reading 400ml/min ( I did this by disconnecting the system and timed filling a beaker). I'm trying...
  17. A

    Compressible fluid other than air.

    Hello Is there any fluid other than air which is compressible. http://www.scienceinfusion.com/air-the-fluid/
  18. L

    Viscoelasticity of Steel: Is it Right?

    Viscoelasticity is a property of a material that exibits both viscous and elastic properties.. When under load,within elastic limit,steel offers resistance to deformation (viscous) and regains shape after removal of load..So is it right to say steel is VISCOELASTIC in elastic limit?
  19. L

    Turbulent Viscosity: Definition & Effects on Flow

    whats turbulent viscocity?How it different from viscocity?Also i read that viscocity is fluid property.So has flow condition like laminar or turbulent has any effect on viscocity?
  20. Brian T

    At what distance does a seaplane's boundary layer transition to turbulence?

    Homework Statement A seaplane flies at 100 mph through air at 45 *F. At what distance from the leading edge of the underside of the fuselage does the boundary layer transition to turbulence? Homework Equations Re = pvL/u Re is Reynolds number p (rho) is the density V is the characteristic...
  21. J

    Calculate velocity in fluid mechanics question

    Homework Statement Water is flowing upwards through a vertical pipe. When a manometer is attached to the pipe in the manner shown in the diagram, the manometer fluid (mercury) is displaced by 10 cm as illustrated. Ignore friction in the pipe. (i) Express the pressure at point (1a) in terms of...
  22. M

    Fluid mechanics - Find the ratio

    Hello! A two-dimensional beam of thickness S and velocity c (evenly distributed at the thickness) falls in stationary plate and get separated. Calculate the ratio of thicknesses S1/S2 as a function of the angle φ. (see attachment)In my notes there is this solution: Continuity equation: Let...
  23. O

    Fluid Mechanics: Constant Pressure and Incompressible flow

    Assuming a flow can be idealised as incompressible, then can you use the constant pressure assumption ? I just want to get my understanding clear. My problem is the following.Consider a fluid element with volume ##V## and a fixed number of molecules. If the flow is incompressible, then the...
  24. MexChemE

    Transport phenomena -- Direction of shear stress

    Greetings, PF! I have some questions regarding the problem I attached below. It is some sort of Couette flow variation. It's not homework, I'm just learning the basics of TP on my own. I fully solved the problem with the Navier-Stokes and continuity equations, using some assumptions in order to...
  25. P

    How can I accurately measure the density and volume of microdroplets in oil?

    I need to measure the density of aqueous microdroplets in oil. My first idea was to obtain a set volume of the droplet-in-oil mixture and weigh it to obtain the density, weigh the same volume of oil without droplets, then estimate the volume of the droplets so I can work out their density...
  26. A

    When is the rate of change of momentum equals zero ?

    When is the rate of change of momentum equals zero ?
  27. J

    What Are the Best Fluid Mechanics Textbooks for Self-Study?

    Hello! My name is Josh Currently going into third year physics. My university does not offer a single course involving fluids except the most basic intro to bernoulli's equation. So, I thought I would make it my own project for the summer to learn some fundamentals. I was wondering if anyone...
  28. J

    Question about Fluid Mechanics, pumping

    Homework Statement The water in the bottom tank (position 1) is pumped into!the!roof tank (position 2) through a long pipe (containing two elbows a and b separated by 1 meter) which discharges freely at a height 50 cm above the liquid surface in the upper tank. To fill up the upper water tank...
  29. S

    Velocity of Fluid flow due to gravity

    I am designing a system for an engineering project at school. It's essentially a clock to be powered by water turning a mechanical system of gears (not generating electricity). Imagine a rectangular basin full of water placed at some height above the ground. There is a hole in the bottom...
  30. B

    Manometer with non linear height change.

    I am trying to establish a mathematical relationship between heights h1 and h2 (please refer to figure attached) for a manometer whose RHS channel is the shape of a triangle (defined by a base length and the angle theta). I want to be able to calculate the heights h1 and h2 for a given change to...
  31. Feodalherren

    Fluid Mechanics: viscous flow in pipes

    Homework Statement Homework Equations ρ=789, μ=.0012 The Attempt at a Solution From the energy equation we get hf=0.9 We know that hf=f(L/D)(V^2)/(2g) [sorry don't know how to use latex after they removed the bar on the right] Now I can substitute V for Q, but I'm stuck with f and Q as...
  32. A

    Exploring Advective Acceleration in Fluid Mechanics

    I am just starting on this subject and I am trying to get a feeling for the concepts. One thing that confuses me a lot is the idea of an advective acceleration. We have that the rate of change of the velocity in a fluid is given by the material time derivative: Dv/Dt = ∂v/∂t + (v⋅∇)v Now in...
  33. R

    Atmospheric humidity for water production.

    *Suggestions for Water Production for California.* California is still in the midst of a huge drought: Annie Sneed Science 03.23.15 7:00 am California’s About to Run Out of Water. We Have to Act Now. http://www.wired.com/2015/03/californias-run-water-act-now/ There appear to be however...
  34. S

    Nozzle problem between subsonic and supersonic speed & nozzle area

    Hi all, I have really a confusion between subsonic and supersonic speed evolution when the area decrease or increase I have a problem to understand why in supersonic regime the velocity evolution in a nozzle is adverse of the subsonic regime? for example in subsonic regime, when the area...
  35. AdityaDev

    How does the melting of ice affect the oil-water interface in a fluid system?

    Homework Statement A cube of ice is floating in water such that some part of the ice is submerged. Oil is poured on the water.( so water on the bottom, oil on top and ice in between). When the ice melts completely, the level of oil-water interface ______(rises/falls) and the top level of oil...
  36. L

    What is the resultant force exerted by the sides of the glass on the water?

    Homework Statement A glass full of water has a bottom of area 20 cm 2 , top of area 20 cm 2 , height 20 cm and volume half a litre. (a) Find the force exerted by the water on the bottom. (b) Considering the equilibrium of the water, find the resultant force exerted by the sides of the glass on...
  37. L

    Classical I need a fluid mechanics textbook

    Hello, everyone, please forgive me for my poor English. I'm a sophomore, major in Astronomy. I've finished Hassani's book(Mathematical Physics). And I've learned Real variable function and functional analysis （I do not know what exact name of this course） I'd like to buy a textbook with...
  38. M

    How Does Bulk Modulus Affect Water Compression in a Tank?

    Hey all, I am having trouble getting to the answer of the attached file below. It would be appreciated if anyone had some tips on getting to the answer.
  39. B

    Molecular Modeling of Fluid Mechanics

    As I've been reading up on fluid mechanics recently, I've discovered several different molecular models which attempt to explain heterogeneous fluid flow from a molecular level. Classical fluid mechanics assumes that hard body approximation- that atoms are hard spheres knocking into each other...
  40. P

    Can liquids be treated as rigid bodies for moment of inertia

    Consider a partially filled bottle of water. When it's tipped over and rotating about its pivot point where its edge touches the ground, it has an angular acceleration. Assuming the liquid is not viscous at all, so flows perfectly, at a given instant can it be considered to have a moment of...
  41. Wyn

    Other Intr. Fluid Mech. for Physicists and Mathematicians by Pert

    Any thoughts on this book? I'm interested in a fluid mech book for physicists, this one looks good but I can't find any reviews on it. You can suggest other books as well, as long as they have available new editions.
  42. A

    I want to know the explanation of this problem

    Homework Statement By How much does the pressure in a cylinderical jet of water 4mm in diameter exceed the pressure of the surrounding atmosphere if the surface tension of water is 0.0718 N/M? Homework EquationsThe Attempt at a Solution ΔP= σ/r=0.0718/2*10^-3 , This is the answer I have but I...
  43. A

    Pressure and normal stress in fluid mechanics

    Hi, everyone. I am learning fluid mechanics. One book says that for a infinitesimal fluid cell, surface force includes 1) the pressure, which is imposed by the outside fluids surrounding the concerned fluid cell 2) the shear and normal stress, which result in shear deformation and volume...
  44. I

    How can I displace the maximum amount of water in a bucket?

    The scenario involves dropping something into a bucket of water. I'm trying to do an experiment where I have to figure out a relationship between the amount of water that leaves the bucket and a certain variable of the object that is dropped. I'm wondering what could maximize the water that...
  45. Feodalherren

    Newtonian fluid mechanics: Navier-Stokes equation

    Homework Statement Homework Equations Navier-Stokes The Attempt at a Solution Not really trying to solve a problem, trying to understand what is going on in my textbook. So look at the stuff in red first. I see where all that is coming from, it's clear to me. However, the stuff in green...
  46. C

    Compressible Flow, Pressure and Mass Flowrate

    I am doing a lab report and it is to do with compressible flow through rotameters. An upstream and downstream rotameter to measure flow rate with a needle valve between the two. The needle valve acts as a fixed orifice in one part of the experiment. Then the inlet pressure is altered. Plotting...
  47. D

    Fluid mechanics: intuition about the 'convective' term

    Hi, I am doing an introductory course on fluid mechanics, and I'd like some intuition (that's why I'm posting on the engineering forums and not on the math forums, even if I'm studying for a degree in math) about the concept of the total derivative and, particularly, its convective component...
  48. Feodalherren

    Fluid Mechanics: Hydrostatic Pressure on a gate with hinges

    Homework Statement Homework Equations Fluid Mechanics The Attempt at a Solution Lets start with the easy part: The pressure of the air is constant so the pressure will act as if it's a concentrated force on the center of gravity of the gate. F = PA = (10,000Pa)(.3)(.6)=1800N The moment...
  49. Feodalherren

    Fluid Mechanics: Manometry - Fluid through a pipe

    Homework Statement Homework Equations Hydrostatic equation The Attempt at a Solution Call length from 2 to the Hg "h". Yhg = specific weight of Hg, from book = 846lbf/ft^3 Yw= water = 62.4 lbf / ft^3 Then P2 = P1 + Yw(5sin45 + h + .5) - Yhg(.5) - Yw(h) Then P2 - P1 = simplify and plug in...
  50. K

    Calculating the force air has on an object

    I am trying to calculate the force that compressed air has on a cylinder. These cylinders are pushed in a production line for transportation using air. I would like to calculate the force such air puts on the cylinder. I have the velocity of the air, the área of the cylinder. Will using the...
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