What is Fluid mechanics: Definition and 755 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. T

    Fluid Mechanics question (shear stress)

    The problem and solutions is here http://img206.imageshack.us/img206/6093/problem1rm4.th.png Isn't the shear stress for both the inner and outer negative? When i take the derivative i get negative. The derivative is basically ln ( 1/x) since the rest are just constants. Edit: I meant that...
  2. A

    One question about stream function in fluid mechanics

    Hi... Suppose we consider a circular cylinder moving with constant velocity U in x-direction in a two-dimensional unbounded, irrotional, incompressible, inviscid fluid. If the motion of the fluid is completely resulted from the motion of the body, we know the velocity field of fluid can be...
  3. A

    One question about stream function in fluid mechanics

    Hi... Suppose we consider a circular cylinder moving with constant velocity U in x-direction in a two-dimensional unbounded, irrotional, incompressible, inviscid fluid. If the motion of the fluid is completely resulted from the motion of the body, we know the velocity field of fluid can be...
  4. J

    Fluid Mechanics - U-tube and mercury

    A U-shaped tube, open to the air on both ends, contains mercury. Water is poured into the left arm until the water column is 20.0 cm deep. How far upward from its initial position does the mercury in the right arm rise? So far, this is my work: Using pressure = density(water) x g x...
  5. A

    Solving a Tricky Fluid Mechanics Problem

    Hi. i am trying to brush up on my fluid mechanics for when i do it next year at uni. do any of you guys have any idea how to solve the follow question? 'A suction pump moves water from a reservoir to a holding tank. The system is designed in such a way that the suction pump is inclined...
  6. H

    Scaling in fluid mechanics and other physical discipline

    Hi all! I always come across "scaling" in various subjects. Like in Fluid mechanics, I am confused about why there is a need to choose some characteristic scales and non-dimensionalize the differential equation? I am confused about this...can anyone expain me the rationale behind this...
  7. P

    Solving Fluid Mechanics Question: Forces on Plane Areas

    Ok I have a question that I am stuck on which is about forces on plane areas. I can do the questions ok where the water acts aboce the gate but in this case the water acts below it if you get what i mean. Can someone please give an explanation of the approach to this question and how you do it...
  8. L

    Question concerning Fluid Mechanics.

    Is their a easy formula to find out how strong a pump needs to be based upon the number of elbows in a piping system. I am working on some heat transfers of the piping system, but now I need to know about the pump, and I have no knowledge of fluid mechanics to use to answer find this formula...
  9. P

    Fluid mechanics faucet problem

    a stream of water in steady flow from a kitchen faucet. at the faucet the diameter of the stream is .96cm teh stream fill a 125cm^3 conaienr in 16.3s find teh diamiter if the stream 13cm below he opening if the faucet i know that A1V1 = A2V2 = constant so pi *.49^2 *V1= pi r^2 *V2 how do i get...
  10. A

    Navier-stokes equation (fluid mechanics)

    i'm revising for my exams, and i didn't go to many of my fluids lectures, now I'm well confused. in the navier-stokes equation for viscous fluid flow, there is a term: v(del squared)u where v is the kinematic viscosity and u is the velocity field of the fluid. at this point in my notes, the...
  11. B

    How Do You Model Water Draining from a Spherical Tank Over Time?

    Fluid Mechanics - Draining sphere - I need Help! I just found this forum and it seems like a wealth of knowledge; wish I had found it sooner. Looking for some help and if anyone can, it will be appreciated more than you'll ever know. Here's the problem: A spherical tank of diameter D is...
  12. G

    What is the shape of a rotating mercury surface in an astronomical telescope?

    Been looking through my notes for a basis to start this question but can't seem to find a starting basis due to poor handouts (or more likely bad note taking by me) Heres the question A cocnave astronomical telescop mirror may be made by rotating a circular tank of mercury. Find an...
  13. Clausius2

    Experimental Fluid Mechanics Videos Series

    Hi everyone, Maybe this resource is new for someone. It's a collection of videos made in the 60's by the very best experimentalist scientists of the best universities of the United States. There you may watch how Taylor gives you a lesson in Low Reynolds Flow, how Lighthill gives a lesson in...
  14. N

    Fluid Mechanics - Highest Possible Water Can go in a Straw

    I need to figure out the highest possible height that water can be sucked up into a straw on Earth. You have unlimited water. So far I've figured out that when you suck, you create a vacuum that allows the water to rise up due to the atmospheric pressure and the force is creates pushing down...
  15. A

    Fluid mechanics: Some elementary concepts

    In this thread, I will explore some elementary concepts in fluid mechanics, starting with the distinction between a particle description and a field description (Lagrangian vs. Eulerian formalism). I will continue by distinguishing between the concepts of particle trajectories, streamlines...
  16. V

    Why is the Mercury Displacement Different in the Left Arm of the Tube?

    There is a question that I have been stumped on for a while now. it is as follows: "The left arm of a tube has a corss sectional area A1 of 10.0cm^2 and the right arm has a cross sectional area of A2 = 5.00cm^2. 100g water are poured into the right arm. b) givent he density of...
  17. V

    Fluid Mechanics: Worked Out Problem, Check Work?

    Hi, I have two problems that I'm having difficulty with, and I don't think that my answers are correct. Problem: A swimming pool measures 5.0m long x 4.0m wide x 3.0m deep. Compute the force exerted by the water against a) the bottom; b) either end. (Hint: Calculate the force on a...
  18. P

    Fluid Mechanics of a weather balloon

    Here are a couple problems I would like to check and a couple I'm not sure how to do: 1.3)A 650kg weather balloon is designed to lift a 4600kg package. What volume should the balloon have after being inflated with helium at 0C and 1 atm pressure to lift the total load? Density of helium =...
  19. V

    Fluid Mechanics: Hydraulic Lift

    Hi, I have here a problem that I've been working on, and am not sure if I've gone about it correctly. The method I chose seems too simple, and I was wondering if someone could go over the answer that I've found, and let me know if I'm doing this right.The problem: The piston of a hydraulic...
  20. P

    Calculating Water Vapor Pressure at 160 F: Understanding Fluid Mechanics

    When a fluid flows through a sharp bend, low pressure may develop in localized regions of the bend. Estimate the minimum vapor absolute pressure in psi that can develop without causing cavitation if the fluid is water at 160 F. How does one calculate the vapor pressure of water when given a...
  21. R

    Mass conservation in fluid mechanics

    Part of the mechanics course I'm taking this semester are also fluids, but the material our teacher gave us to this topic is very poor (but unfortunately I haven't found a better source). The problem is that there are many "magic formulas", which come just out of nowhere - without any...
  22. A

    Calculating Fluid Eflux: The Impact of a Cylindrical Tank on a Platform

    A cylindrical tank of diameter 90 cm rests on top of a platform 6m high. Initially the tank is filled with water to a depth of 3m. A plug whose are is 3 cm^2 is removed from the orifice on the side of the tank at the bottom. 1) at what speed will water strike the ground? 11) how long...
  23. B

    Recommend a fluid mechanics book

    As part of my chemical engineering degree I have to do a module called fluid flow. Turns out I'm pretty bad at it. I'm trying to find a book which covers as much of the module as possible, with plenty of worked examples. The syllabus: Introductory concepts of fluids, units & dimensions...
  24. B

    Fluid mechanics friction factor formula

    hopefully this will be my last question... My textbook says friction factor = 64/reynold's number for laminar flow. But it doesn't say how this equation is derived. does anyone know where this equation comes from? is it an approximation (i.e. will be more accurate for certain Re's and...
  25. B

    Is There a Y-Component of Velocity in Fully Developed Pipe Flow?

    Let's say we have a horizontal pipe with steady, incompressible, two dimensional flow. There is friction at the top and bottom of the pipe which causes viscous effects. The flow is fully developed. The velocity profile is parabolic. Obviously there is an x-component (u) of velocity...
  26. B

    Fluid Mechanics -continuity equation

    Fluid Mechanics --continuity equation This is for a 300 level fluid mechanics class. "Consider the y-component of the velocity (v) at any cross-section in the entrance region. For simplicity, take the lower half of the pipe; the content of the flow field is going to be symmetric with respect...
  27. J

    Conceptual fluid mechanics question

    Suppose we have a tube whose cross-sectional area narrows from A_1 to A_2. We attach this to a tank which supplies fluid a constant flow rate Q. Assuming the fluid is nonviscous, we can apply Bernoulli's equation to the narrow and wide ends to calculate the pressure drop \Delta p = p_1 - p_2...
  28. M

    Fluid Mechanics Q: Find Vol. Flow Rate & Head Loss at C

    Ok guys, here's a q from a past exam and I am not sure how to tackle it. At point C, there is a leak and flow rate is given in L/s. I am also given the friction factor. I also know the diameter of the pipe. The question asks for the vol. flow rate into the bottom tank. And then the head...
  29. Cyrus

    Exploring Fluid Mechanics: Understanding a Second Order Tensor Quantity

    Hello, Please help me out here as I self study fluid mechanics. I ran into what they are calling a second order tensor quantity, which seems to be fancy words for a 3x3 matrix of sigmas and rhos, for shear and normal stress. They have a picture of a cube, with all the positive stresses...
  30. Cyrus

    Introduction to Fluid Mechanics

    Hey guys, I haven't taken thermodynamics yet, I have only taken it in general chemistry, which amounts to pretty much nothing. But I've heard from many friends that Fluid mechanics is a very tough course, so I am trying to teach it to myself before I have to take it next year. I've only...
  31. H

    Primitive variables in Fluid Mechanics

    Hello! I know that the primitive variables in fluid mechanics are velocity and pressure. But why? I don't see how "primitive" these variables are...What does it mean by a "primitive variable"? Is that all other variables in a fluid flow can be derived from velocity and pressure? Is there any...
  32. S

    Best Book for Fluid Mechanics & Thermodynamics

    Hi all! I'm an undergraduate student. I'm going to consolidate my what I've learned in fluid mechanics and thermodynamics. I would like to pick up a nice book and read through it from the beginning.(learning from the very basic) So, I would like to know what books you would recommend?
  33. Clausius2

    Crane paper #410 and learning Fluid Mechanics

    First question I want to arise is: what is Crane paper #410?. As far as I have looked for it in the web, it seems to be something like a Handbook for those engineers which are involved in fluid flow calculation in professional enterprises. It has lots of tables and formulation (which surely...
  34. A

    Fluid Mechanics - Torque at hinge of closed vessel

    The closed vessel contains water with an air pressure of 10 psi at the water surface. One side of the vessel contains a spout closed by a 6-inch diameter circular gate hinged along one side. Horizontal axis of the hinge is located 10 ft below the water surface. Determine the minimum torque that...
  35. A

    Fluid Mechanics - Pressure - U-Tube Manometer

    A piston having a cross-sectional area of 0.07 m^2 is located in a cylinder containing water as shown in the figure. An open u-tube manometer is connected to the cylinder as shown. For h1=60 mm and h=100 mm, what is the value of the applied force, P, acting on the piston? The weight of the...
  36. R

    Fluid Mechanics: Questions on 2D Flows

    Dear Friends, I'm studying the 2D flows, and I have any questions. In a square, there's a grid of flow in horizontal an vertical linear flow. The flow that entry the square must be the same that exits form it. \frac {\partial \Psi_e}{\partial x} -\frac {\partial \Psi_O}{\partial...
  37. R

    What is the Geometric Balance of an Object in a Fluid Flow?

    Dear Friends, I have a problem on fluid mechanics that I can't solve. The question is one boat that has great velocity. In front of it, it's created a wave because of the boat. Now, imagine that this boat has greater and greater velocity. The angle of the wave in the front, at great...
  38. E

    Fluid Mechanics Help: Find Balloon Radius & Pipe Flow Rate

    A spherical helium-filled balloon is used to lift a load of 5905 N (in addition to the weight of the helium). Suppose the density of the air is 1.24 kg/m3. Find the minumum necessary radius for the balloon. A 24.8 liter container is initially evacuated, and then 5.7 grams of water is placed...
  39. cepheid

    Is Incompressibility a Prerequisite for Steady Flow in Fluid Mechanics?

    In fluid mechanics, one hears the term steady, incompressible flow. Steady flow refers to the fact that the overall flow pattern (the flow lines, which indicate the paths of individual particles within the fluid) do not change with time. Incompressible flow refers to the fact that the fluid...
  40. J

    Fluid Mechanics: Solving 8 Min Water Flow Problem

    This is the last problem with fluid mechanics and I have no clue about this one... any ideas? Water flows through a horizontal pipe and is delivered into the atmosphere at a speed of v1=15.9 m/s. The diameters of the left and right sections of the pipe are 8.5 cm and 2.5 cm, respectively. (a)...
  41. J

    Fluid Mechanics of water and oil

    Here's the question: Water and then oil are poured into a U-shaped tube, open at both ends, and do not mix. They come to equilibrium as shown in the figure below, where y oil = 26.9 cm and y water=18.6 cm. What is the density of the oil? (Take the density of water as 1000 kg/m3.) I know that...
  42. T

    Fluid Mechanics - Pipe Flow

    Hi there, I'm struggling with a question that I've been given regarding the force on a bend in a pipe, and I wondered if any of you guys could help me out with a few clues. The question is as follows: A contracting pipe bend turns water through 135° (In a horizontal plane) before discharging...
  43. K

    Just some simple fluid mechanics questions

    bernoulli's principle says.. total pressure = static pressure + dynamic pressure + pressure from height, right? but how come I hear that an increase in velocity is a decrease in pressure? if you increase velocity as the 'v' part in dynamic pressure won't the entire pressure increase as well...
  44. D

    Fluid Mechanics - Equations of motion circular flows

    Departing from the Navier-Stokes equations for an incompressible flow (with \rho and \mu=\rho \nu constant): \frac{Du_i}{Dt}=\frac{\partial u_i}{\partial t}+u_j \frac{\partial u_i}{\partial x_j} = -\frac{1}{\rho} \frac{\partial p}{\partial x_i} +\nu \frac{\partial^2 u_i}{\partial x_j^2}...
  45. A

    Fluid Mechanics and Bernoulli's principle

    A pump and its horizontal intake pipe are located 12 m beneath the surface of a reservoir. The speed of te water in the intake pipe causes the pressure there to decrease, in accord with Bernoulli's principle. Assuming nonviscous flow, what is the maximum speed with which water can flow through...
  46. H

    Fluid Mechanics: Calculating Radii of Spherical Ball & Cavity

    I'm doing some practice problems because I have a final tomorrow. I ran across this problem and I haven't seen an equation or example like it in our textbook. If you could give me a little direction I'd appreciate it I probably won't have one like it on the test but I'd still like to figure it...
  47. C

    Fluid Mechanics - Pressure measurements

    I'm having difficulty with one problem and was hoping someone could help me out. Here's the problem: Mercury is poured into a U-tube as in Figure P14.18a. The left arm of the tube has a cross-sectional area A1 of 107.0 cm2, and the right arm has a cross-sectional area A2 of 4.10 cm2. One...
  48. T

    Calculating Fluid Displacement in a Multi-Fluid System

    i seem to be stuck on a problem which involves fluids of 2 different densities, and an object floating in/on them. A block of wood is floating in a jar of water. oil is then poured onto the water. how can i calculate the mass of "the fluid displaced" when it is composed of 2 different fluids...
  49. F

    Fluid mechanics force balance question

    Please see the attached image to see what I'm talking about. I understand how the forces (in terms of the pressures and areas) are equated, but then it says 'for small delta x' and from there on I'm confused. It's something to do with differentiation, but I don't get it. Can someone...
  50. S

    Fluid Mechanics Density problems

    Is this correct? A 6-kg piece of metal displaces 1 liter of water when submerged. What is its density? Density = mass/volume 1 liter of water = 1000 cm3 = 1 kg Ans: 6 kg / 1000 cm3 = .006 cm3 How would this one work out? When a 2.0-kg object is...
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