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

    Is this a valid way to calculate capillary force / pressure?

    When figuring out the capillary pressure on a liquid in a tube of a certain cross-section, the typical approach is to consider the Young-Laplace pressure and the curvature etc. I was looking through some of my old notes and I had an equation for the capillary force: fc = γ cosθ dS/dx where γ...
  2. Adesh

    I Why volume is conserved but not the surface area?

    A water drop of radius ##10^{-2}## m is broken into 1000 equal droplets. Calculate the gain in surface energy. Surface Tension of water is ##0.075 ~N/m##. So, for the solution of the above problem we need to know how much surface area (combining all 1000 droplets) have increased from the...
  3. Tymofei

    Pressure Differential in Fluid Dynamics: Why More on the '+s' Side?

    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...
  4. Adesh

    How does a pressure distribution keep the fluid from moving?

    Let’s say we have a unit volume of some fluid in a column on the Earth surface. Let ##\mathbf F## be the gravitational force that acts on the unit volume of the fluid. Consider a small volume element ##\Delta \tau## in the fluid and let’s assume it to be a cuboid with dimensions ##\Delta x##...
  5. A

    Calculation Involving Thermodynamics, Gravitation and Fluid mechanics

    I figured out stokes law equation but I am unable to proceed further
  6. A

    Bernoulli's equation from an elemental fixed streamtube control volume

    Elemental fixed streamtube control volume from Professor White’s textbook “Fuid Mechanics”: I was unable to develop the intermediate steps for the following approximations: (continuity equation according to the book ) Where and (Momentum equation according to the book) In...
  7. Adesh

    Oscillation of a boat in still water (Metacenter and Center of Mass)

    Let’s say we have a boat whose longitudinal axis is the y-axis (which goes into the screen in the figure below) standing upright in a still water . ##S## is the Center of Mass of the boat and ##C## is the Center of Mass of the displaced water.On ##S## lies the force ##\mathbf W##...
  8. S

    Fluid Mechanics: Fluid Transfer Between Two Reservoirs at Different Heights

    A reservoir supply tunnel transfers water from a high level storage reservoir via a 200mm diameter pipe to a lower intermediate reservoir. The total height difference between the free surfaces of each reservoir is 76 m. The pipe is 700 m long and the coefficient of friction, Cf is 0.009. The...
  9. Adesh

    Why the existence of the potential function ##U## is not sufficient?

    In Sommerfeld’s Lectures on Theoretical Physics, Vol II, Chapter 2, Section 6, Page 43 we derive an expression for the equilibrium of liquids as $$ grad ~p = \mathbf F$$ Where ##p## is the pressure and ##F## is the exertnal force. Then he writes, [ The equation above ]includes a very remarkable...
  10. C

    Fluid mechanics problem: Hydrostatic forces acting on a gate

  11. Geith

    (Fluid mechanics) How to find the flow rate of a gas from a vessel

    I am working on a project where I have to calculate various results relating to the motion of a water bottle rocket being launched. I am currently stuck on trying to find how long the thrust period of the rocket is. The model for the rocket is as follows: It is a 2L (0.002m3 bottle filled with...
  12. A

    Finding the Reaction Scheme for Photocatalytic Oxidation of Phenol

    I researched the solar collectors implemented in practice for water detoxification and I found out that the preferred design is the Compound Parabolic Concentrator. Knowing that I have no information regarding radiation beyond what's taught generally in heat transfer courses in chemical...
  13. Adesh

    Classical I need some self-contained introductory books on Fluid Mechanics

    By Fluid Mechanics I mean the mechanics of fluids, both at rest and in motion. I'm unable to find introductory books on Fluid Mechanics which contains everything in itself, for example I downloaded Fundamentals of Fluid Mechanics by Munson, Young, Okiishi, Huebsch and I don't know why but I...
  14. A

    What Equation Is This? (Fluid Mechanics)

    Can someone please tell me what is the name of below formula? ##H = z + \frac{v^2}{2g} + \frac{p}{γ}##
  15. D

    Fluid mechanics — Question about this vector diagram

  16. KingOfDirewolves

    Intro Physics Which Fluid Mechanics Textbook is Best for High School Students?

    Can anyone suggest me a Fluid Mechanics textbook? I am currently in High School in my Junior Year. I am looking for a entry-level textbook so I will be able to solve I.E. Irodov's Hydrodynamics section. (My Mathematics is quite strong)
  17. CheesyPeeps

    Force on side of tank filled with liquid of variable specific weight

    Homework Statement: An open tank with a rectangular side 1 m wide and 4 m high is filled with a liquid of variable specific weight, γ, with γ = 50 + 2y (N/m3), where y is measured vertically downward from the free surface. Find the magnitude of the force on the side of the tank. Homework...
  18. D

    Best way to learn fluid mechanics while in high school

    Hi, I am a high school student doing a project on fluid dynamics and need to understand the relevant maths so that I can understand how to apply the mathematics of fluid flow (particularly air flow around a cylinder). I have a basic calculus understanding and need to understand the navier...
  19. T

    Fluid Mechanics: Wooden plank floating in water at an angle

  20. S

    Understanding Streaklines: Uses & Differences

    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. .
  21. K

    Engineering Fluid Mechanics Problem: Water Forces on a Parabolic Gate

  22. jahan123

    Fluid Mechanics Challenging Problem

    Homework Statement: how far from the mercury surface must a horizontal line be drawn in a 2 meter square gate whose one side is at the fluid surface so that the hydrostatic forces in the two newly formed surfaces are equal Homework Equations: 1) F = yAh where y= specific weight A is the cross...
  23. M

    What is the relationship between pipe diameter and frictional loss?

  24. Navier-Stokes Equations - Numberphile

    Navier-Stokes Equations - Numberphile

    Tom Crawford (sporting a Navier-Stokes tattoo) talks about the famed equations - subject of a $1m Millennium Prize.
    • Swamp Thing
    • Media item
    • cfd fluid mechanics
    • Comments: 0
    • Category: Classical Mechanics
  25. tjholi

    Derivation of the Emptying Time for a buoyant box to drain

    Problem Statement: I am having trouble deriving the expression from the initial equations. (Calculate the emptying time considering Volume conservation) Relevant Equations: Q=A*sqrt(b(H-h(t)) And we have dh/dt =Q/S (conservation equation) and we have to obtain h/H = 1-(1-t/te)^2 with te=...
  26. V

    Basic fluid mechanics questions about an oceanography paper

    Problem Statement: There is no precise problem statement since it's an homework to be done independently, but I will try my best to explain it concisely (I also apologize for my mistakes in English) : I want to reproduce the simulation of the model presented in the pdf file attached to this...
  27. K

    Fully Developed Flow: Laminar vs Turbulent

    Does the definition of fully developed flow is different for laminar and turbulent? I understand the fact that the entrance length are different in laminar and turbulent flows, but I believe the definition of fully hydrodynamically developed flow means that the velocity profile (hence momentum)...
  28. M

    Fluid Mechanics problem: Oil pressure calculations in pipe flow

    Problem Statement: An oil with density 900 kg/m3 and viscosity 0.18 Ns/m2 flows through a circular pipe which inclines upwards at 40° to the horizontal. The length of the pipe is 10 m and the diameter is 6 cm. The fluid pressure at the lower end of the pipe is 350 kPa and the pressure at the...
  29. Clout

    Fluid mechanics - pump in a horizontal pipe connecting two pipes

    So when the velocity of v1 and v2 is 0 (because the tanks are much bigger), the bernoulli equation to dh is dh = (dp-dpl)/(rho*g) with dp = Phyd / V = 1000W / 0.01m³/s = 10^5 Pa and rho = 1000 kg/m³ So I am getting first without the pressure loss on the orifice dh = 10^5 Pa / (1000 kg/m³ *...
  30. E

    Show that a tilted free liquid surface undergoes shear stress

    i really can't understand the answer of this question, is the question 1.3 in fluid mechanics by Frank ,M White For the triangular element in Fig P1.3, show that a tilted free liquid surface, in contact with an atmosphere at pressure pa, must undergo shear stress and hence begin to flow. i...
  31. M

    Fluid Mechanics: Momentum Equation- When to include p_atm in equation?

    So if we define point 1 at the entrance and point 2 at the exit, then we can write out Bernoulli's equation along a horizontal streamline as such: p_1 + \frac{1}{2}\rho v_{1}^2 = p_2 + \frac{1}{2}\rho v_{2}^2 = p_{atm} One question is: won't there be p_atm also contributing to the static...
  32. M

    Fluid Mechanics: Momentum Equation Propeller Question

    For this question, this is my working. The main issue is I cannot figure out where the factor of \frac{1}{2} comes from. So I consider a control volume right around the propeller (in the frame of reference of the propeller) and I apply R(-->) Force = Change in Momentum Flux F = \dot{m_{o}}...
  33. M

    Fluid Mechanics: Head Loss Question (Conceptual)

    I am not really worried about the numbers, but more about the simple concepts with head loss in these pipe flow questions. I want to confirm that head loss just means the change in static head, right? I have been advised that for a problem like this, it is nothing more than the conservation of...
  34. WhiteWolf98

    Fluid Mechanics: Flow rate required to achieve a constant height

    Some thoughts that I've had on the question are saying the volume flow rate (##Q##) in, must equal the volume flow rate out. If that's the case, then: ##Q_{in} = Q_{out}## ##A_1V_1=A_2V_2## But... no areas have been given. And height doesn't enter this equation at all. Then I thought it...
  35. A

    Fluid Mechanics, Particle Size, Bouyouncy Force

    1. What should be the size of object/Particle (sphere) so that it should remain suspended (neither it should sink nor it should float)? container dimensions 30*25*25, density of fluid 0.9g/cm3 , density of particle 0.86g/cm3 , particle is coated with aluminium having density of 2.07g/cm3.(if...
  36. J

    Rotation of a Submerged Disc

    1. A 20-lbf disc with diameter 18" and thickness of 3" is held static while completely submerged in water. Upon release of a lock, the disc experiences a torque from a torsional spring that causes rotation about its center of mass along the x/y axis (think coin toss, not wheel). If the spring is...
  37. LordGfcd

    A fluid mechanics problem -- Shape of a falling water drop

    Homework Statement A drop of water fall towards the ground with initial mass [m][/0] and radius [r][/0] (assume the initial shape of that water drop is sphere). the air resistance is F=½.ρ.A.[v][/2].C (C is the drag coefficent, A is the area that the air contact with the water drop and ρ is the...
  38. Roy S Ramirez

    How can I predict the flow rate for a real life water hose?

    Hello! I hope you are all doing well! I've been always intrigued by fluid mechanics and decided to try out a quick experiment with my water faucet. After using some equations I found online [1] [2], I plugged a hose to the faucet and let the water run. I filled a 1 quart bowl and recorded the...
  39. Alexanddros81

    I want to understand this equation - Fluid Mechanics

    Hi all! I have started reading Fluid Mechanics at my own pace (no university study) and really I would like to grasp the ideas behind it. So I have Fluid Mechanics by Cengel - 4th edition. At page 45 the coefficient of compressibility or bulk modulus of elasticity (κ) is introduced. ##κ =...
  40. WhiteWolf98

    Fluid Mechanics: Determining Elevation in a Piezometric Tube

    Homework Statement [/B] Homework Equations ##P=\rho gh## The Attempt at a Solution So this is the first time I'm doing fluid mechanics, and I'm trying my best to understand it. This was the first question, and truth to be told, I'm not very confident. I know what gauge pressure is: the...
  41. Z

    Exploring the Maths/Physics/Chemistry of a N2O Cylinder's Height

    Hello, I am trying to understand the maths/physics/chemistry behind this situation. Here is the scenario. I have 8 grams of pressurized N2O in a cylinder at 60 bar/ 900 psi. If the temperature stays constant (let's say 50-70°C, or at a temperature where the N2O can stay as pressurized as...
  42. A

    I Can the volume of a control volume change with time?

    Can an expanding balloon be considered a control volume?
  43. A

    How Do Biomimetic Sensors Work?

    Hi all, Ameya here from the University Of Twente Netherlands pursuing masters in electrical Engineering. Currently doing my thesis. My topic involves developing a biomimetic sensor.
  44. T

    Normal Stress Balance at a Fluid-fluid Interface

    I am trying to determine a normal stress balance at an axisymmetric and dynamic fluid-fluid interface, ##z(r,t)##. For a static, free surface, this simplifies to the Young-Laplace equation: $$ \Delta p=\rho gz-\sigma2H=\rho gz-\frac{\sigma}{r}\frac{\partial}{\partial r}\left(r\frac{\partial...
  45. CptXray

    Flow Around a Cylinder with Linear Vortex and Points of Stagnation

    Homework Statement Find the flow around a cylinder with radius ##a## generated by linear vortex ##\Gamma## in point ##z=b##. Find points of stagnation. Also ##b>a## Homework Equations Complex potential of vortex: $$\omega_{vortex} = \frac{\Gamma}{2\pi i}\ln{z}$$ Milne-Thomson circle theorem...
  46. M

    What does the word 'Jet' mean in fluid mechanics?

    What does it mean the word 'Jet' in fluid mechanics, special when it depends on the free surface?!
  47. T

    Energy equation for fluid mechanics

    Homework Statement Water is supplied at 4.50 m3/s and 415 kPa (abs) to a hydraulic turbine through a 1.0-m inside diameter inlet pipe as indicated in the figure. The turbine discharge pipe has a 1.2-m inside diameter. The static pressure at section (2), 3 m below the turbine inlet, is 25 cm Hg...
  48. stockzahn

    I Exploring Reynolds Vortices: Fact or Fiction?

    Dear all, recently I read in a belletristic book about Reynolds Vortices. In the fictitious story the author writes about special (Reynolds) vortices generated in the whitewater, which can be passed in only one direction by objects of a "critical" density, which then will be kept in the vortex...
  49. J

    Hovercraft Lift: Measuring Clearance Height & Lift Force

    << Mentor Note -- thread moved from the technical forums so no Template is shown >> Hello, I built a hovercraft not long ago for an experiment. What I did was applying more power to the motor and looking at how high the hovercraft could go. However, the formula that I was planning to use, uses...
  50. F

    Pressure inside the zeppelin for it to float

    Homework Statement A zeppelin of an ellipsoid shape (a=32m, b=c=a/3) iz filled with hydrogen. Pressure of the surrounding air is 100 000 Pa. Temperature of air and hydrogen is 20°C. The mass of an empty (not filled with hydrogen) zeppelin is 10 000 kg. What does the pressure of hydrogen inside...
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