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. Feodalherren

    Fluid Mechanics: Rotating cylinder viscometer

    Homework Statement Homework Equations τ = μ (du/dy) The Attempt at a Solution For part B) dM = τr dA τ = μ (rΩ/Δr) ∫ (μrΩr2πr / Δr)dr = μR4πΩ / 2Δr pretty sure that's correct. I'm confused for part A though. I want to set it up as dM = τR dA = τR (2πRdL) and τ = μ (RΩ/L)...
  2. B

    Fluid Mechanics: velocity u for circular pipe

    Homework Statement For low-speed(laminar) , steady flow through a circular pipe, the velocity u varies with radius and takes what form? Please see this link for picture of the pipe...
  3. Feodalherren

    Fluid Mechanics: Cone-Plate viscometer

    Homework Statement Homework Equations Fluid Mechanics τ =μ (du/dy) The Attempt at a Solution I got far enough to write down dM = μ (Ωr/tanθ) dA from just substitutions, easy enough. I get confused when I'm solving for the differential surface area. I somehow need the dA for a cone. For...
  4. C

    How to Determine Pi Groups for Fluid Flow Through an Orifice

    Homework Statement a) A orifice, diameter d (m), in the walls of a tank discharges water under a head, h (m), subjected to gravitational acceleration, g (m/s2). If the fluid has density, ρ (kg/m3)and viscosity, μ (Ns/m2), show that the quantity of fluid Q (m3/s) flowing out of the tank may...
  5. 462chevelle

    Can Taking Fluid Mechanics Without Completing All Prerequisites Work?

    I was wondering if I could get you guys advice on something. My school only offers fluid mechanics every other Fall. This spring I'm taking physics 1, calc 2, and chem 2. In the fall I'll for sure be taking physics 2, and calc 3, I could take rigid body mechanics and experimental techniques, but...
  6. Y

    Fluid mechanics question--slip boundary condition for gas?

    In solving the Navier Stokes equation, the typical boundary condition imposed on the tangential velocity at a solid surface is that of no-slip. However, it is known that for gaseous flow there always exists a non-zero velocity near the wall, especially at relatively big Knudsen number. Is there...
  7. I

    Does the shape of a car produce lift or downforce?

    I have a few questions related to downforce in cars. Please forgive any fundamental misunderstanding of aerodynamics. Does the shape of a car, say a Volkswagen Golf, driving on a road produce lift or downforce? Is the Coanda Effect at play there? How does the height of the car above the ground...
  8. A

    Fluid mechanics and pipe flow questions

    < Mentor Note -- thread moved to HH from the technical engineering forums, so no HH Template is shown > Pics are attached, my concerns are with question 4 and 5. For q4 -which way is flow? How do we know? -the working then goes on to say that energy loss is compensated by increasing in...
  9. AdityaDev

    Understanding Buoyant Force: Exploring FBD and Equations in Accelerating Vessels

    If I have an object of mass m tied to the lower surface of a vessel having a liquid and the vessel accelerates upwards... From FBD of object, Buoyant force acts upwards, mg down, pseudo force downwards (frame of reference is vessel) T down. Here's the doubt. Why is F(buoyant force) = Vp(g+a)...
  10. Hemmer

    Intuition about Stokes flow beween solid walls

    Hi there, I have a question about incompressible Stokes flow in a channel between solid walls (with no-slip boundary conditions at ##y = 0, L_y##). It is my intuition that, if the flow direction is ##x## (periodic), and the direction normal to the walls is ##y##, then there cannot be a net...
  11. K

    A basic fluid mechanics concept that's puzzled me for years

    And it seems like it's so straightforward for everyone else, which is incredibly frustrating. It's about the relationship between pressure and flow rate of a fluid moving in a pipe or closed system. Often what I've heard is, they have an inverse relationship...but then there are cases where...
  12. R

    Air Jet Fluid Mechanics Experiment

    Hi all, Recently did a lab experiment where we had a nozzle pointing vertically upwards at a flat plate normal to the direction of the flow of air. The plate had a spring gauge on it so that the force of the air on the plate could be measured. The plate was moved to various distances above the...
  13. S

    Fluid mechanics- High Reynolds number flows over bodies

    A 40 km/hr wind is blowing parallel to a storage facility , as shown in the figure. estimate the normal force on a 0.5-m high, 1-m long window if the front door is left open. assume the windspeed along the outside of thewindow is 1.2 U. Air density is 1.22 kg/m^3. There's a picture that...
  14. J

    Fluid Mechanics Viscous Dissipation

    I am trying to find an expression for viscous dissipation for burger's vortex Velocity field which only has velocity component in the V theta direction. I'm confused as to which equation for viscosity dissipation is correct. I am seeing a lot of different things tau:S, tau:delV..which one is...
  15. A

    [Conceptual Question] Fluid Mechanics Analysis of Pipe Flow

    Homework Statement As shown in the figure, if the pipe net work is shifted bodily by 10m vertically up the tank, and all the other conditions remain the same as the previous figure. Will the volume flow rate change? Or I rephrase it as, in the calculation of elevation head of pipe flow, is the...
  16. A

    Slip Length: u - u_wall = β ∂u/∂n

    Wondering if someone could link me to a derivation of this formula? It's on the Wikipedia page for the no-slip condition. u - u_wall = β ∂u/∂n β = slip length n = coordinate normal to the wall
  17. A

    MATLAB MATLAB code for Computational Fluid Mechanics

    Hello guys, I'm writing to get some help on an exercise I've been thinking but I can't get to solve. I have to write the code for the Example 8.5 of the book White, Fluid Mechanics. Here is the problem and the solution I have to obtain. It is about one duct that has three sections in which I...
  18. K

    Approximating Windshield Shape of a Car: Velocity at Points A & B

    Homework Statement [/B] The shape of a car windshield is approximated in the figure below; its length is 2.0 ft and height is 1.5 ft. Obtain an equation of the windshield shape r as a function of θ, r(θ), in the polar coordinate system shown in the picture. When the car moves at 55 mph...
  19. W

    Investing in Stock Markets: Fat Tails, Persistence, Multifractals & Turbulence

    Does anyone here know much about these topics? I understand they surround the absence of normally distrubted returns, excessive kurtosis. Fat tails somehow disprove the EMH? Can anyone explain this argument? I've been advised that there are links to turbulence in fluid dynamics, joined by the...
  20. PrincessIceFall

    How to perform a metacentric height lab experiment

    I need help in understanding how to conduct this experiment. I found this lab report online but it is confusing https://www.google.ae/#q=metacentric+height+experiment http://site.iugaza.edu.ps/mymousa/files/Experiment-2hydraulics-lab-.pdf I am finding it difficult to visualize the...
  21. Kushwoho44

    Fluid Mechanics: Dimensionless Groups Question, explain an outlier

    Homework Statement Hi guys, I need to explain the outlier point here, which has been shaded in the excel spread sheet when comparing the two dimensionless groups, The dimenionsless group, drag-coefficient is given by Drag/(density*V^2*D^2) and dimensionelss group, spin parameter, is given by...
  22. M

    Science-Based Fluid Mechanics Recomendation

    Lately I have found an interest in fluid mechanics and found Landau's Fluid Mechanics text. Despite know it wasn't introductory, I decided to give it a try before deciding I need something before it. Is there a science-like (as in not engineering) fluid mechanics textbooks that would help...
  23. S

    Mechanical engineering and fluid mechanics, thermodynamics

    I'm curious as to roughly how many mechanical engineering graduates have found jobs where they utilise the knowledge they gained in fluid mechanics, thermodynamics and heat transfer as part of their university degrees. Reason I'm curious is because, from my class, I'm not actively aware of...
  24. J

    Bernoulli's equation - fluid mechanics question

    1. A sphere 1 ft in diameter is moving horizontally at a depth of 12 ft below a water surface where the water temperature is 50F. Vmax = 1.5Vo, where Vo is the free stream velocity and occurs at the maximum sphere width. At what speed in still water will cavitation first occur? Given: speed...
  25. P

    Pipe Flow Rate: Guarantee Constant Volumetric Flow

    I have a pipe with regular diameter connected to a tap, the water comes from public supply, I assume that public supply can vary on pressure and flow rate. How can I guarantee that I allways get the same volumetric flow rate at the end of the pipe? Will a pressure reducer be sufficient? Thank you!
  26. E

    Shear stress on a tire from a puddle of water

    Homework Statement A car is moving at 65 mph and hits a puddle of water 1 inch deep. What is the shear stress on the tire from the puddle of water if the radius of the tire is 16 inches. r = 16 inches u = 65 mph y = 1 inch mu = viscosity = 2.344*10^-5 lbf*s/ft^2 Homework Equations angular...
  27. B

    Theoretical Fluid Mechanics - Ideal Fluid Flow

    Homework Statement Write down the complex potential for a source of strength m located at z=ih and a source of strength m located at z=-ih. Show that the real axis is a streamline in the resulting flow field, and so deduce that the complex potential for the two sources is also the complex...
  28. M

    Struggle learning fluid mechanics

    Hi I just started on my fourth year of a masters degree in mechanical engineering, and I got this fluid mechanics course that is nothing like anything I have had before. This course is based on finding expressions using Stokes equations. Combining and deriving momentum, continuity and energy...
  29. U

    Eulerian vs Lagrangian approach in fluid mechanics (wave example)

    Hi All, Recently we've been working on the distinction between the Eulerian and Lagrangian approaches in Fluid mechanics. I understand the simpler examples like a running stream of hot water etc. However one example is really tripping me up. So what's confusing me is that in analyzing...
  30. T

    Fluid mechanics self-studying book

    I am a mechanical engineering undergrad and i am currently trying to study fluid mechanics but the books i tried are not sufficient enough in my opinion. I read the first three chapters of Fluid Mechanics : Fundamentals and applications by Cengel and Cimbala, and Fundamentals of Fluid Mechanics...
  31. S

    Fluid mechanics modeling question

    Physics Forum: Can someone show me how to model, mathematically, what happens if you place a drink box with a straw sticking out of it, in a vacuum chamber and apply a vacuum?
  32. E

    Engineering - fluid mechanics

    I have a question about fluid mechanics. I know it's not completely physics, but in the end, it involves physics: Suppose you are computing the blood flow in an artery segment with length 3 cm and diameter 3 mm. The artery has a constant cross section and its positioned horizontally in your...
  33. R

    Areas Of Reasearch in Fluid Mechanics & Mechanical Design

    Hello! My friend and i are interested in doing a project.My area of interest in Fluid mechanics and my friend's is mechanical design can you guys help us out by providing some topics of research which encircles both these areas.
  34. TheTank

    Fluid mechanics -- fluid in a container moving down an incline

    I have added a picture of the problem with an attempt for a solution. Please let me know if its right or wrong, and what I have done wrong if its wrong..
  35. F

    Fluid mechanics: books and other learning resources

    Hello everyone! I'm a civil engineering (bachelor) student, and I was fascinated by the "hydraulics" course. unfortunately, my study plan doesn't include other courses on the matter for at least one year. Thus, I am looking for some easy books to begin with, to study it a bit on my own...
  36. N

    "Violation of Bell's inequality in fluid mechanics"

    I thought it might be interesting to point out this article: Title: Violation of Bell's inequality in fluid mechanics Authors: Robert Brady and Ross Anderson (Cambridge) Abstract:
  37. M

    Fluid Mechanics: Pressure Question

    Homework Statement A tyre pressure gauge indicates 20 N/cm2 for a tire at 34°C after a fast motorway run. Assuming that the volume of the air in the tyre is constant, atmospheric pressure is 760 mmHg and the air gas constant is 0.287 kJ/kg.K: i) Estimate the indicated pressure when the tyre...
  38. P

    Fluid Mechanics Venturi meter/manometer

    Homework Statement Question: http://i.imgur.com/aoXUDP1.png Homework Equations Q=v1A1=v2A2 Bernoullis Equation P=P0 + ρgh The Attempt at a Solution I have got an answer of 3.55*10^-3 m^3 /s. The answer i have been told is 1.29 x 10-3 m3s-1. I am not sure if i am wrong or the answer...
  39. Q

    Fluid Mechanics and hydraulic lever

    Homework Statement In a hydraulic lever consisting of two ideal fluid lined cylinder/pistons with a fluid filled line coupling the two cylinders, the output force is 100 times the input force. For 1 Joule of work done on the input side, the work done on the output side is (in J):Homework...
  40. X

    Fluid mechanics sinking barrel

    Homework Statement Suppose a cylindrical barrel falls off a ship and sinks to the bottom of the sea at a depth of 1.61 km. Assume that the seawater is incompressible, so that its density at the bottom of the sea is the same at the surface :1020 kg/m^3 If the pressure inside the barrel is...
  41. X

    How Do You Calculate Net Inward Force on a Submerged Barrel?

    Help with fluid mechanics!? Suppose a cylindrical barrel falls off a ship and sinks to the bottom of the sea at a depth of 1.61 km. Assume that the seawater is incompressible, so that its density at the bottom of the sea is the same at the surface :1020 kg/m^3 If the pressure inside the...
  42. W

    Radial and tangential velocities for Inviscid flow (fluid mechanics)

    After I have an expression for the stream-function in a problem, I can differentiate to get the tangential and radial velocities because I need those to solve the problem. But I don't understand when the tangential velocity will be 0 and when the radial is 0. Can some on explain?
  43. R

    Air Flow through cooling tower- fluid mechanics problem

    Hey everyone! I am working on improving natural draft counter flow cooling tower efficiency as my final year B.E. project. I came across a research paper that said that at transverse cross section of the tower, above drift eliminators, the air velocity decreases from the periphery to the...
  44. T

    What is the Relationship Between Pressure and Height in Fluid Mechanics?

    The correct answer to this problem is h2 = h1 but I don't get it. According to what I understand, F=p/A So for the Tube on the left: F1 = P/A = (\rho*g*h1)/A1 For tube on the right: F1 = P/A = (\rho*g*h1)/3*A1 I get h2=3h1 (i know if you think about it this does not make sense...
  45. N

    Finding stream functions for a cylinder [fluid mechanics]

    Homework Statement Hi The stream function for a cylinder with radius a in a uniform crosswind is given by (https://en.wikipedia.org/wiki/Potential_flow_around_a_circular_cylinder#Stream_function) \psi = Ur \sin(1-a^2/r^2) How does one show this formally?
  46. T

    Basics of Fluid Mechanics and Pressure

    Hello I am having difficulty in comprehending the basics of fluid mechanics . I have few questions which I would like to put one at a time , so as not to create any confusion . In the following attachment , a container with a liquid rests on a surface .I would like to understand what are...
  47. P

    Fluid Mechanics and Venturi meter

    Homework Statement A Venturi meter is constructed with an inlet diameterof 100 mm and a throat diameter of 40 mm. The meter must be calibrated prior to leaving the factory. The meter is installed in a 100 mm diameter water main with a...
  48. N

    Fluid Mechanics and order of magnitude calculation

    Hi In my lecture notes we making some calculations and all terms \mathcal O(M^3) are to be thrown away. Here M is the Mach number. Now, there is the expression (u denotes the velocity): uu\partial_t \rho \approx \rho_0 uu\nabla u which in my notes are thrown away because they claim it is...
  49. 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...
  50. 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...
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