What is Fluid flow: Definition and 213 Discussions

In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation.
Fluid dynamics offers a systematic structure—which underlies these practical disciplines—that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves the calculation of various properties of the fluid, such as flow velocity, pressure, density, and temperature, as functions of space and time.
Before the twentieth century, hydrodynamics was synonymous with fluid dynamics. This is still reflected in names of some fluid dynamics topics, like magnetohydrodynamics and hydrodynamic stability, both of which can also be applied to gases.

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  1. j3dwards

    Fluid flow/pressure in a pipe going uphill

    Homework Statement Water is flowing along a pipe. Points B and C in the pipe are at the same height but point A is at a higher elevation.The pipe has the same cross-sectional area at points A and B but is wider at point C. Rank in order from largest to smallest, the pressures at the three...
  2. M

    MHB Exploring Streamlines and Cutoff Points of a Fluid Flow

    Hey! :o The velocity field $u=ax^2, v=bxy$ ($a, b=\text{ constant }$) represents a flow field of an incompressible fluid. Construct the streamlines and find the cutoff points of the flow ($\overrightarrow{u}=(u,v)=0$). From the fact the fluid is incompressible we have that $$div u=0...
  3. V

    Using Laminar Flow to measure Thermal Conductivity

    So, there's a project I'm working on (no, it's not school related), where I'm trying to figure out how to measure thermal conductivity of a material using laminar flow. The idea is to integrate this into a larger system, and it's a measurement I'd like to take in the process. I know the...
  4. A

    The velocity profile for viscous and non-viscous fluids

    I want to know if the velocity profile is uniform for viscous fluids or not ?
  5. 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...
  6. M

    Simulation error messages solidworks - invalid goals

    I am running a simulation on a flat plate heat exchanger and the solver is coming up with some error messages. The first says that a vortex crosses the pressure opening and the second says that my heat transfer rate goals are invalid. How can I get the heat transfer goals to be valid as I need...
  7. R

    Flow Rate in Horizontal Rectangular Channel: Solve Now

    Homework Statement In a horizontal rectangular open channel 20 m wide the water depth is 9 m. When a smooth hump 1.5 m high is introduced in the channel floor, a drop of 1 m is produced in the water surface. What is the flow rate, neglecting energy losses? It is proposed to place a pier at the...
  8. C

    What force makes fluid flow faster in a smaller pipe?

    Thinking of individual fluid particles, my guess is that the "force" is simply particles backing up somewhat at the constriction point and contributing a higher proportion of collisions on particles ahead of them in a direction down the pipe. As the average movement of the particles is directed...
  9. H

    Why is Resistance in Fluid Flow inversely related to r^4 rather than just r^2?

    So Volume Flow Rate (Q) = (P2-P1)/R where R is the total resistance of the system. R is directly proportional to Length and inversely proportional to surface area, and the inherent resistance (viscosity) of the fluid. But R =nL/r^4. r^4 rather than r^2. So there has to be another factor...
  10. E

    Lubrication Theory: Fluid Flow and Integration

    Basically, I'm modelling the flow of a "coating" process -- a fluid flow between a flat moving plane and a stationary cylinder, 2D, cartesian coordinates. Subscript 0 is the at the minimum height b/w the plane and the cylinder, and subscript c is at the point at which the flow leaves the moving...
  11. 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...
  12. K

    Fluid flow out of pressurized vessel

    I have a non-rigid vessel holding a fluid with a tube for fluid flow out. It is initially at equilibrium pressure with the atmosphere. (Think a water bladder for a camelback hydration system) A pressure is then applied to the bag to cause fluid to flow out the tube. Is there a way to relate the...
  13. J

    Fluid flow through positive pressure gradient

    I am a student of 11th standard and being introduced to Bernoulli's principle made me wonder , how does flow takes place in positive pressure gradient (i.e. from low pressure region to high pressure region), in a diffuser or a diverging part of a venturi meter , since we know that flow always...
  14. Z

    Why incompressible fluid flow is advantageous in numerical computation

    Hi, When we want to solve the Navier-Stokes equations coupled with the conservation of mass for incompressible fluids using the primitive-variable approach, we have to face to the problem that the equation for the continuity equation does not contain the pressure which leads to spurious...
  15. M

    Calculate fluid flow in pipeline

    Homework Statement The pump in the system below has an efficiency of 75%. The atmospheric pressure is 101 kPa and the vapor pressure is 2.3 kPa (in absolute units). Assume kinematic viscosity is 0.96x10-6 m2/s. Neglect minor losses. a) Calculate the velocity through the main pipe and of...
  16. D

    Fluid Flow out of a Liquor Bottle

    I was working on a project for which I was considering letting a liquid flow out of a bottle rather than pump it out, but I know that the flow rate changes as the height of the fluid within the container changes, which is an issue. I then remembered that bartenders count time to measure their...
  17. M

    Exploring Pressure Energy in Incompressible Fluid Flow

    Homework Statement Consider a tube of uniform cross section, let one end (a) of the tube is at height h1 and other end (b) is at height h2, where h2>h. Now an incompressible fluid passing through the tube the workdone to pass the liquid at end (a) P1V1 and workdone to pass the liquid at end...
  18. C

    Minor head loss for turbulent vs. laminar fluid flow

    Hi, I need clarification on the difference in head loss for turbulent flow and laminar flow. I understand how the head loss due to friction is different for the two regimes. For friction head loss, the friction factor is 64/Re for laminar flow, and a more complex formula for turbulent flow. I...
  19. F

    Hurricane Fluid flow, torque, cross product

    Homework Statement In 1993 the radius of Hurricane Emily was about 350 km. The wind speed near the center ("eye") of the hurricane, whose radius was about 30 km, reached about 200 km/h. As air swirled in from the rim of the hurricane toward the eye, its angular momentum remained roughly...
  20. D

    Fluid Flow and Projectile Motion

    Homework Statement Water travels through a pipe with a radius of 1 inch at a speed of 2 m/s. There is a nozzle at the end of the pipe with a radius of 1/4 inch. The pipe is horizontal and 2m above the ground. How far does the water travel in the air before hitting the ground? r1 = 1 in. r2...
  21. S

    Fluid flow around a sphere, what's the net force?

    Homework Statement A sphere of radius ##a## is submerged in a fluid which is flowing in the z-hat direction. There is some associated viscosity in the fluid which will exert a force on the sphere. Use symmetry to argue that the net force will be in the z-direction. Show that it will have the...
  22. G

    How Do You Determine Pipeline Pressure with a Faulty Manometer?

    Homework Statement You are given an open-ended mercury manometer and asked to determine the pressure in a pipeline that supplies feed gas to a reactor. However, when you connect the manometer to the pipeline, you notice that the calibration markings in the leg that connects to the...
  23. D

    Can you 'increase pressure' by restricting fluid flow?

    I just read this, from a site dedicated to popularizing science: " ...think of air as being like water. If you have a garden hose and put your thumb over the end, the pressure increases and water sprays out. Same thing with air. Except the increased pressure is under a plane's wings and...
  24. C

    Viscous fluid flow in a manufacturing process

    In work that I've been doing, we've come across an interesting problem. In a manufacturing process, a highly viscous, non-Newtonian fluid goes down a vertical chute and then gets pushed horizontally out the bottom by some rotating screws. Sometimes, the fluid gets pushed out the bottom, but...
  25. F

    Fluid flow - pressure v volume?

    This a practical problem for the design of a system which uses a water driven hydraulic motor. Assume a 100 gallon tank is filled with water, constantly filled further pressurized by a pump to 500psi Assume a hydraulic powered motor which operates with intake required at 200psi...
  26. F

    Controlling fluid Flow under pressure?

    this is not a homework problem, its a practical problem for a system I'm working on, but its looks pretty much like a homework problem so posting here. Homework Statement Assume a 100 gallon tank is filled with water, constantly filled and pressurized by a pump to 1000psi Assume a hydraulic...
  27. zhangwfjh

    On representation of expansion in fluid flow

    In Helmholtz original thesis On integrals of the hydrodynamical equations, which express vortex-motion, he mentioned in the first section that the change undergone by an arbitrary infinitesimal volume of water under the time dt is composed of three different motions. One of them is an expansion...
  28. D

    Pressure, energy density, and power of a fluid flow

    I've read that you can view static pressure of a fluid as energy density, which makes sense to me. I've also seen that the power of a fluid flow can be calculated by multiplying the pressure by the volumetric flow rate. However, doesn't a flow also have kinetic energy? How can you calculate the...
  29. R

    Fluid Flow Problem-Viscous Flow

    I am working on a fluid mechanics problem modeling something I've come into contact with at work. I have an open to atmosphere reservoir of a fluid with properties as follows SG=1.48 Viscosity= 47000 Cp Height of fluid column, 3 inches or so. i.e. Neglible I then have a pressure...
  30. B

    How can the probability of a particle entering a fluid flow be modeled

    Ok so maybe this will take some work to wrap your heads around. Maybe not. I sure know that I have had some real doozies of headaches working with this and visualizing it. Rather than look at particle capture in a gold sluice as a CFD problem I have been trying to visualize it as a statistcal...
  31. T

    Why does fluid flow faster in a narrow tube?

    Fluid flows faster in a narrow tube which results in low pressure and high pressure in a large tube?
  32. T

    Fluid flow through a pipe - Conservation of mass and/or momentum?

    Homework Statement The Attempt at a Solution So first I found the density of the air coming in and going out. Next I used conservation of momentum with two forces caused by the pressures at the entrance and the exit of the nozzle. I end up getting 1004 which is not the same as...
  33. D

    Question about fluid flow and pressure in pipes

    Does a pipe have to be completely filled with a fluid to measure its pressure? For instance if I have a small diameter pipe that diverges to a bigger pipe. The small pipe will be completely filled with water, but will the bigger pipe be? If the bigger pipe is only half full of flowing water...
  34. A

    FLuid Flow through a Divergent Section

    Hi, Can Someone Elaborate the fluid(water) Characteristics Such as Velocity n pressure When it passes through a divergent Part. Actually The Fluid is pumped Out from A 0.5HP Centrifugal Pump and then made to pass through a Divergent Part.
  35. E

    Solving for the Constants in Fluid Flow through a Pipe

    Hi, I'm looking at the solution to a question on fluid flow through a rigid pipe. Original equation: \mu u = 0.25r^{2} dp/dx + Aln(r) + B After applying boundary conditions: \mu u = 0.25dp/dx (r^{2} - a^{2}) I don't understand how the constants have been solved for. Below is as far as I get...
  36. E

    What causes an increase in boundary layer thickness in fluid flow?

    hi all,i have recently started studying a subject heat transfer,in which i learned that there are two types boundary layers.one is velocity boundary and other is temperature boundary layer..now my question is that..boundary layer thickness increases in flow direction,what is the physical...
  37. tomwilliam2

    Incompressible vs constant density fluid flow

    This may sound like a basic question, but it's just to get it clear: When describing fluid flows, does the term "incompressible" mean exactly the same thing as "constant density"? I was under the impression that if a fluid cannot be compressed, then its density must remain constant for any...
  38. L

    Calculating Fluid Flow through a Simple Heat Exchanger: Step-by-Step Guide

    Hi guys this is my first ever homework post on here so be nice please :D. 1. I have attached an attempt on paint to give you a very rough idea of the very simple heat exchanger. The pipes are cooled by the air and it is a good few metres above the ground. For simplicities sakes let's say, for...
  39. T

    Solving Two Layer Fluid Flow with Different Viscosities and Equal Densities

    Following this example, http://www.creatis.insa-lyon.fr/~dsarrut/bib/others/phys/www.jwave.vt.edu/crcd/batra/lectures/esmmse5984/node53.html I know you can solve for v by integrating the equations along with boundary conditions. How would you solve a problem where you have another...
  40. T

    How Can Pressure and Diameter Determine Fluid Velocity in a Pipe?

    A little help. I want to calculate the volumetric flow rate (SCFM (standard cubic feet per minute) of a pipe knowing the pressure inside the pipe as well as the diameter of the pipe. I know Where v is velocity and A cross sectional area. However, I need help finding out my...
  41. A

    (Fluid Flow) Differential momentum balance problem

    Attached pdf contains the problem, and my progress in working it. My question is, I'm not really sure how to proceed. Anyone care to push me in the right direction?
  42. A

    Fluid flow problem with the momentum balance equation

    All problem info, and my work is done in the attached pdf. Basically, I'm not sure that I have done it correctly.
  43. R

    Applied laws of gravity and fluid flow

    A cylinder, open at both ends, laying flat level is to be filled with a substance that will harden as cement.One end has a 90 elbow attached at one end in order to fill cylinder.The cylinder is 25 ft long and 1 ft in diameter.Will gravity alone take the fluid to the very end of the cylinder...
  44. J

    Fluid Flow Questions: Gas Flow Direction

    I have a question. All things being equal as far as flow and pressure goes...where would the gas preferentially flow in the drawing I made. To T1 or T2. Is there equation someone can point me to that will show this. Thanks.
  45. I

    Why is current constant in a series connection? AND fluid flow in pipe

    My physics book explains that this is because of the conservation of charge and the fact that charge doesn't accumulate at a certain point. Can someone please explain this in detail, especially the part where it says that charge can't accumulate. Another question which i think is similar is...
  46. O

    Fluid Flow Analysis of Howitzer Recoil Mechanism

    I'm looking to do a fluid flow analysis on the recoil mechanism of a howitzer. The analysis will involve simulating oil flowing through some complex orifice profiles. There will be 2 fluids (oil & nitrogen) in different parts of the recoil mechanism. The results I would like from the...
  47. P

    Fluid flow rate lab- with analysis

    Homework Statement Problem statement: We are measuring the flow rates of liquids of different viscosities through holes of varying sizes. We ultimately want to observe the relationship between the viscosity and the flow rate, and also between the diameter and the flow rate. Variables...
  48. T

    Inviscid fluid flow past a square cylinder.

    The flow of an inviscid incompressible fluid around a circular cylinder is commonly studied in fluid dynamics courses. There's a wikipedia article about it here: http://en.wikipedia.org/wiki/Potential_flow_around_a_circular_cylinder. However, what about a square cylinder? There seem to be...
  49. U

    Designing a gravity-driven fluid flow system

    Basically, I'm designing a simple method in which a small reservoir of water is connected to a narrow pipe and the rate of flow of water changes with changing height of the reservoir. Now, the water coming out of the narrow pipe is fed into a microchannel. The resistance is given, by the...
  50. M

    Fluid flow rate and friction problem

    Hello, I'm new here - so apologies in advance if this is in the wrong place, also I haven't done physics for a few years prior to the course I just started - and I've never tried to write out formula in computer text, so apologies in advance again if everything I write is completely wrong...
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