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. surfwavesfreak

    A What are the boundary conditions for rotational flow?

    Hello everyone, The boundary condition : P=0, z=ζ is very common when studying irrotational flows. When cast with the Bernoulli equation, it gives rise to the famous dynamic boundary conditionn, which is much more convenient : ∂tφ+½(∇φ)2+gζ=0, z=ζ But what happens if the motion is rotational ...
  2. surfwavesfreak

    Bonjour - french physical PhD student

    Hello every body, I am very excited to be now part of your community. Me in a few words : I am french PhD student, working in the field of physical oceanography for 2 years now., more specifically on the wonderful topic of ocean surface waves. I am particularly interested in asking you some...
  3. A

    Automotive Cengel's Fluid Mechanics: Fundamentals and Applications (Book & CD-ROM)

    Is anyone here use Cengel's Fluid Mechanics: Fundamentals and Applications (Book & CD-ROM)? I've heard the CD-ROM contain CFD code for Fluent Flowlab. The question is, I just want to know if the Fluent Flowlab (beside the code) is include in the CD-ROM.
  4. MexChemE

    Modeling ideal gas flow using Bernoulli's equation

    Hello, PF! I'm currently brushing up my fluid mechanics and came across some questions while studying the compressible flow of an ideal gas using Bernoulli's equation. First, consider incompressible flow in the following system Neglecting any changes in elevation, the Bernoulli equation for...
  5. S

    Fluid in rotating tube with different initial levels

    Homework Statement Homework Equations Fluid in rotation The Attempt at a Solution This exercise is quite different from the classic one of fluidi in rotation. Before rotation starts the height in one branch is bigger than in the other, so I do not really know how to approach the problem...
  6. H

    Why Are Multiple Pressure-Velocity Coupling Algorithms Used in ANSYS Fluent?

    In Fluent, there are several 'pressure-velocity coupling' algorithms. Why are these necessary when, in many fluid mechanics textbooks, it is proposed that for incompressible fluids, an equation for Pressure can be found by taking the divergence of the Navier-Stokes equation, and inverting using...
  7. akhan90

    Calculating the equation for a float in a rotameter

    I'm trying to design a rotameter, a flowmeter consisting of a float in a tube of increasing area (like a cone). I know the equations equating drag with gravity, but I'm more interested in the equation of the float's velocity over time, just as steady state flow begins (so x(0)=0) Because the...
  8. M

    Some questions on pressure drops and head loss in pipe flow

    I would like to ask you that why pressure drop is constant through pipe? How can we know that dP/dx=constant? Thank you.
  9. A

    Does the height of the water column on top of this pump matter?

    We are using the following pump to measure the strain on a special tube. http://www.instechlabs.com/Support/manuals/HABP.pdf This special tube is connected on each side to another tube that is connected to one of the two connectors on the pump. (The two connectors of the pump were put parallel...
  10. Qais Hassan

    Confused about Reynolds Number- Fluid Mechanics

    Hi, I am working on the laminar flow and during my calculation at the outlet of my nozzle my Re was even greater than 120,000 however my other calculations seemed legit to me. And someone told me that I am calculating the Reynolds number of an open channel and for that flow can remain in laminar...
  11. W

    Similarity in fluid mechanics

    Homework Statement i know that the ratio of length of prototype divided by the length of model would yield Lr But , some book gave that length of model divided by length of prototype also= Lr ?Homework EquationsThe Attempt at a Solution Which is correct ?
  12. smosikas

    Solve Fluid Mechanics Homework: Q, m, t, P

    Homework Statement A hot oil(specific gravity = 0.7) flows through a pipe of 4 cm internal diameter, at a velocity of 0.2 m/s. Determine:i) The volumetric flow rate of the oil discharged from the pipe. ii) The mass flow rate of the oil discharged from the pipe. iii) If the pipe discharges the...
  13. J

    Fluid Mechanics-Bernoulli and Energy Equations

    Homework Statement A well-fitting piston with 4 small holes in a sealed water-filled cylinder,shown in Fig is pushed to the right at a constant speed of 4 mm /s while the pressure in the right compartment remains constant at 50 kPa gage. Disregarding the frictional effects,determine the force...
  14. T

    I Calculate Minor Losses due to Flow Geometry Alone

    Hi does anyone know a way to calculate the Minor losses related just to flow Geometry isolated from Major frictional losses, all the k tables I can find combine the frictional losses with the geometry losses eg see below blurb from but I was hoping to obtain a first principles formula that...
  15. E

    Calculating pump head required

    Homework Statement I need to calculate the pump head required for a fluid transfer system. The pump is located 3m above a storage vessel vented to atmosphere (1 bar) with a total pipe length of 5m to pump suction. The pump discharge is connected to a pressurised vessel at 2 bar absolute with...
  16. E

    Dimensional Analysis:Relating Particle Diam, Viscosity, & Weight

    Homework Statement It is found the terminal velocity ut of a spherical particle in a fluid depends upon the diameter d of particle, the dynamic viscosity μ of fluid and the buoyancy weight W of the particle [given by the difference in density between the particle and the fluid (∆ρ) ×...
  17. F

    I Divergence of the Navier-Stokes Equation

    The Navier-Stokes equation is: (DUj/Dt) = v [(∂2Ui/∂xj∂xi) + (∂2Uj/∂xi∂xi)] – 1/ρ (∇p) where D/Dt is the material (substantial) derivative, v is the kinematic viscosity and ∇p is the modified pressure gradient (taking into account gravity and pressure). Note that the velocity field is...
  18. M

    Fluid mechanics - Pascal's principle

    Homework Statement Mercury is poured into a U-tube as shown in Figure a. The left arm of the tube has cross-sectional area A1 of 9.4 cm2, and the right arm has a cross-sectional area A2 of 4.50 cm2. One hundred grams of water are then poured into the right arm as shown in Figure b. (b) Given...
  19. M

    Forces appearing on the pipe when a fluid flows in it

    Hi, I study linear momentum. But I cannot understand enough that how can forces appear on a pipe when fluid flows in the pipe? Fluid have a momentum as m*v how can forces appear on the pipe. I cannot demonstrate the situation in my mind. How can I find a demonstration or a free body diagram for...
  20. M

    Fluid mechanics civil engineering

    As shown in the attached image, a tank has an inclined wall at an angle of 450 to the horizontal. On this wall, there is a 1m square door that is hinged at A and has a simple latch at B. The distance between A and the free surface of sea water measured along the inclined wall is 2 m. (Specific...
  21. M

    Non-slip condition for inviscid fluids

    Hi, I would like to ask that whether or not ## non-slip condition## is valid for inviscid fluids. We know that inviscid fluids there is no friciton. If there is no friction in the inner surface of pipe (I do not name its technical name) so it seems that there cannot be the non-slip condition...
  22. M

    B A simple differentiation and partial differentiation

    Hi, in the above why is the left-hand side simple differentiation, i.e V is only function of t but in the right it is function of t, x, y, and z. It is very strange that one side is different than the other. Would you like to explain it? Thank you.
  23. Alfreds9

    Water evaporation, temperature, wind and heat capacity?

    Hi, I'd like to know how I'd put together, either elegantly or at least in physical terms, that surely water evaporation in a large pool of V volume and S surface is influenced by wind (increased by it as opposed to having side barriers), temperature (increased by direct sunlight as opposed to...
  24. Villa

    In fluid mechanics what does pressure energy mean?

    In Bernoulli equation we use pressure energy... Pressure* volume gives the unit of energy... But what does this mean... If someone says it is potential energy per unit volume, then what does datum head refers to?... Please help... Can't go ahead without having thorough knowledge about this..
  25. P

    High electric field / droplet levitation

    Dear All, I know this may sound a bit of a broad approach for a question but I would like to know what equipment I would need to create a very high electric field in order to levitate a non-highly conductive droplet (from water to water + salts but not metallic, in the milli-microscale). I will...
  26. Max KL

    What is the needed flow rate of the impeller with this info?

    Hi everyone! As an experiment I am trying to calculate building my own PWC similar to a jetski assuming it is for sea level use. I really appreciate all detailed answers as I want to understand. The impeller will be installed under rear of craft, engine is mounted on top. Given Information...
  27. T

    Working Out Shaft Torque in a Stirred Tank with a Cylindrical Shape

    Here is some background to the problem (in a stirred tank): "With yield stress non-Newtonian (viscoplastic) fluids, it is possible to generate an agitated volume around the impeller, defined as a cavern, surrounded by a stagnant region where the shear stress is insufficient to overcome the...
  28. Mingsliced

    Fluid Mechanics - Head Loss Due to Friction

    Homework Statement This is simply a sanity check concerning the system described and attached. My concerns are detailed within my attempts at the solution. Any guidance will be greatly appreciated! The diagram attached represents a process for which a pump and associated pipe work require to...
  29. S

    Fluid Flow Equations With Real Values

    Hi, all I am working on a project that involves analyzing fluid flow behavior in oil & gas pipelines. I am interested in calculating and plotting the velocity profile, and also(pressure distribution, temp distribution) Having studies fluid mechanics last year I am aware of the EOS for fluid...
  30. C

    [Fluid mechanics] Navier-Stokes and Hagen-Poiseuille

    Can the Hagen-Poiseuille equation be used for a vertical flow in the water tab or any flow that has circular cross-sections with varying diameters? If not, how can the Navier-Stokes equations or any other equations be used to describe a viscous incompressible free-falling vertical jet?
  31. C

    Blasius Solution for Boundary Layer

    Is the Blasius solution valid for internal flow in an underdeveloped pipe? Can the function for the boundary layer thickness be used to calculate when the boundary layers will meet in the center of the pipe? I don't see how it could be valid since the assumption in its derivation is that...
  32. C

    Water flow through a perforated plate

    Hi, I'm seeking the formula to calculate how water moves from one tank into another through a perforated plate driven by waterlevel compensation. I found the calculation for the discharge of water through submerged orifices, but I think the calculation does not include that holes, one above the...
  33. C

    Solve UROV Fluid Mechanics Homework: Max Vel, Time, Distance, Drag Force

    Homework Statement Im working with a UROV and I have a technical scenario that I am supposed to solve. It seems pretty easy but i keep getting ridiculous answers. Assuming a max thrust of 5 N for 1 motor/propeller, for the forward direction only, use the above information to determine the Max...
  34. prashant singh

    What is the Best Book for Fluid Mechanics from Beginning to Advanced Level?

    which is better fluid mechanics book , frank white or munson from complete beginning to the advanced level.
  35. C

    Fluid Mechanics Videos: Resource for Video Lectures

    Hello, does anyone know a good resource for video lectures on the subject of fluid mechanics?
  36. jdawg

    Fluid Mechanics: Cart and tank of water

    Homework Statement A cart has a tank of water on it which has a nozzle. Water jets out from the nozzle onto a turn vane oriented at theta = 30° which deflects the flow upward. The cart is held stationary by a rope as shown in the image below. Find the force in the rope if the velocity of the...
  37. jdawg

    Fluid Mechanics Velocity at Outlet

    Homework Statement Water flows through a 1.5 [in] diameter pipe. In a 1.5 [ft] section of the pipe water is injected through the porous walls into the pipe at a velocity of 3 [in/s]. What is the average velocity at the exit if the inlet velocity is 6 [ft/s]? Homework EquationsThe Attempt at a...
  38. M

    Calculating Pipe Diameter for Desired Pressure in Inclined Fluid Flow

    The question: There is a 650m long tube on a 1 degree incline. At one end of the tube is a pump that alone has a volumetric flow rate of 750 g/min. The fluid in question is water and its a PVC pipe. What diameter does this tube need to be in order to have 25 psi on the top end of the tube...
  39. jdawg

    Fluid Mechanics Gate Problem

    Homework Statement A rectangular plate AB is 1.8 [m] wide and 2.0 [m] long. As shown below the plate is used to keep water (blue region) confined to the region. Find the weight of the gate necessary to keep the water enclosed. Assume the hinge at A is frictionless. Homework EquationsThe...
  40. leafjerky

    Finding the weight of water lost from cloud [Fluid Mechanics]

    Homework Statement The rain cloud has an approximate volume of 6.50 mile3and an average height, top to bottom, of 350 ft.1 mile = 5280 ft. If a cylindrical container 6 ft in diameter collects 2 in. of water after the rain falls out of the cloud, estimate the total weight of rain that fell from...
  41. leafjerky

    Bulk modulus given, find change in P [Fluid Mechanics]

    Homework Statement If the bulk modulus for water at 70∘F is 319 kip/in^2, determine the change in pressure required to reduce its volume by 0.3%. Homework Equations E = dP/(dV/V) E - Bulk Modulus dP - change in pressure dV - change in volume V - volume The Attempt at a Solution Well I just...
  42. A

    Why Does the Shape of a Container Not Affect Fluid Pressure Calculations?

    for static fluids we have studied that p=patm +density*g*depth. and this equation is derived from Newton's laws,but in fbd why didn't we consider the force exerted by curved surface area of container,it doesn't cancel out when containers are in frustrum shape.and the vertical components add up...
  43. Raul Trejo

    Fluid Dynamics-Drag Force Problem.

    Homework Statement Consider the flow of a fluid with viscosity μ through a circular pipe. The velocity profile in the pipe is given as U(r)=Umax(1-rn/Rn), where Umax is the maximum flow velocity which occurs at the center line; r is the radial distance from the centerline; and U(r) is the flow...
  44. Ian Limjap

    Fluid Mechanics: Tank problems.

    Homework Statement In the attached file. Homework Equations P1/rhoe+v1^2/2+gh1=P2/rhoe+v2^2/2+gh2 The Attempt at a Solution I do not know how to begin it; however, I think part(iii) is the same as part (iv)[/B]
  45. E

    Torque of rotating coaxial cylinders with gas between them.

    I was going through a worked example in book "Concepts in Thermal Physics" by S.J. Blundell and K.M.Blundell. The example talks about measuring viscosity of a gas between two coaxial cylinders. Homework Statement Two vertical coaxial cylinders. Outer cylinders is rotated by a motor at constant...
  46. D

    Askew Pitot tube, airplane velocity measurement

    Homework Statement A horizontal Pitot tube (with one end open for airflow and another closed) is accidentally installed into an airplane askew, so that the tube is not horizontal. Instead the closed tube end is higher (in the y-direction of a xy-plane) than the inlet end. How does this affect...
  47. P

    Fluid mechanics - impact of jet question

    Consider a case- Force excerted on a stationary flat plate held normal to the jet. The Jet strikes on plate (see fig.) Which is smooth hence the exit velococity of jet = entering velocity of jet. According to theory. The fore is applied on plate due to change in momentum of jet. But my doubt...
  48. L

    Fluid Mechanics- inviscid fluid pressure in a pipe

    Homework Statement Water flows through a circular pipe with a 180° horizontal elbow and exits to the atmosphere through a nozzle as shown in Fig. Q3. The diameter of the pipe is 300 mm and the diameter of the nozzle exit is 160 mm. The density of water is 999 kg/m3 . The mass flow rate of...
  49. 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...
  50. 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...
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