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. B

    Advantages/disadvantages of penalty formulation for incompressible fluid flow

    Advantages/disadvantages of "penalty formulation" for incompressible fluid flow Hi everyone: I'm interested in getting into some fluid flow modeling (e.g., advection-diffusion). I'm a newbie, so sorry in advance for any silly questions. Today I came across the "penalty formulation" and...
  2. D

    Fluid flow and momentum equation. Do I have the right equation?

    http://img89.imageshack.us/img89/3914/unled23g.png F1x+F3x = density x Q(Vx2 – Vx1) F1x = -Rx F3x= (pressure 1 x area 1) + (Pressure 2 x area 2) (Cos B) F1y+F3y = density x Q(Vy2 – Vy1) F1y = -Ry F3y = (Pressure 2 + Area 2)(Cos B) So is it: Rx= (pressure 1 x area 1) + (Pressure 2 x area 2) (Cos...
  3. D

    Fluid flow and momentum equation. Do I have the right equation?

    http://img89.imageshack.us/img89/3914/unled23g.png Uploaded with ImageShack.us F1x+F3x = density x Q(Vx2 – Vx1) F1x = -Rx F3x= (pressure 1 x area 1) + (Pressure 2 x area 2) (Cos B) F1y+F3y = density x Q(Vy2 – Vy1) F1y = -Ry F3y = (Pressure 2 + Area 2)(Cos B) So is it: Rx= (pressure 1 x area...
  4. J

    Solve Fluid Flow Problem: Find Water Rise in Cylindrical Bucket

    Homework Statement A cylindrical bucket, open at the top, is 30.0 cm high and 14.0 cm in diameter. A circular hole with a cross-sectional area 1.72 cm^2 is cut in the center of the bottom of the bucket. Water flows into the bucket from a tube above it at the rate of 2.00×10^−4 m^3/s ...the...
  5. J

    Continuum Mechanics: Check if fluid flow is real

    Homework Statement see attachment. Homework Equations Navier Stokes continuity equation: The Attempt at a Solution So what I tried to do was to use the above equation to see if it equals zero. del(rho)/del(t)=del(xyz-t)/del(t) =-1 then to make the deriving easier...
  6. R

    Why Does Bernoulli's Equation Not Apply to Unsteady Flows?

    Hi 1. I was wondering why Bernoulli’s equation does not work for unsteady flows (where there is acceleration). If there was a horizontal pipe initially at steady flow, if the pressure at one end suddenly increases to cause a constant acceleration for the entire fluid body in the pipe (say...
  7. R

    Calculating Pressure Drop and Hole Size in a Pipe

    Hello everyone, I got a question that has been bugging me for quite a while and i can't seem to find the answer for it, and here it is... If we have a pipe let's say 20" in diameter, with a flow rate of 1 m^3/sec at a pressure of 10 psi, and we get a pressure drop of 9 psi, is it possible...
  8. J

    Fluid Flow: Water Pipe with Vertical Pipes

    Homework Statement Consider a water pipe that tapers down from a diameter dA= 5.0 cm at end A to a diameter dB = 2.5 cm at end B. At each end a vertical pipe that is open to the air at the top is attached to the pipe as shown in the Figure. (Not to scale, the pipes are much taller than shown.)...
  9. M

    Optimizing Fluid Flow into Tanks: Pressure, Diameter, and Length Considerations

    Hi, I got a puzzling question. In a scenario where I have a pipe connected to an empty atmospheric tank and the flow is from the pipe into the tank. Pressure at the pipe inlet is 500kPag and the pipe diameter and length is 6" and 5m respectively. There are no fittings in between. I...
  10. S

    Designing a Cap to Stop Fluid Flow from an Underwater Pipe

    "Capping" fluid flow from pipe If there is a 4.1cm diameter pipe located ~10m underwater, with water (negligible volume and mass flow rates - the water is only really trickling out) flowing out of it at 2 bar (so 1 bar difference in water and ambient pressure), does anyone have any rough ideas...
  11. J

    Forces on a clyinder in a steady fluid flow

    For my project been given the task of finding the fluid flow round a cylinder. My task for the weekend is to find the forces in work here. All of our work is numerical so no analytical solutions will really help although they might help push me in the right direction. As such we have the...
  12. H

    Fluid Flow between parallel infinite plates

    Hello I am trying to understand some fluid mechanics I have two parallel infinite plates with fluid between the plates and some fluid above the plates. The fluid above the plates has a free surface exposed to the atmosphere. And we can neglect body forces. The fluid flow (steady and...
  13. R

    Solve Fluid Flow Pump System: Volume Flowrate & Power

    I am currently doing revision for an upcoming exam and can't work out how this particular question is solved. Attached is an image of the system. Homework Statement A pump draws water from a large tank and delivers it to atmosphere through a 50 mm diameter nozzle at a level 10 m above the free...
  14. M

    Toricelli's principle and fluid flow

    Hello to all, I've been reading an article about modeling in which there is Toricelli's principle stated: rate of fluid flow through a hole in a tank is proportional to square root of its height. That is easy to understand and to derive this using Bernoulli formula. I have derived this to a...
  15. D

    How can the density, area, and velocity be related in a cyclic fluid flow?

    [PLAIN]http://img811.imageshack.us/img811/4882/stumped.png So from the above question I presume that the relation (Density)x(Area1)x(Velocity1)=(Density)x(Area2)x(Velocity2), cannot be applied due to the flow being unsteady and thus the control volume changing with time. I've read up about...
  16. T

    Fluid Flow Continuity in Control Volume Analysis for Shallow Channels

    Ey guys, girls Trying to work out what I've attached below Now i can get the right part of my expersion to match however the left I am not 100% sure how to change d/dt from control volume analysis to delta(h)/delta(t) I think I am more stuck with the maths here than anything, not the...
  17. J

    Software for modeling fluid flow?

    Hey everyone, This is my first-ever post on a forum, so my apologies if this is the wrong section or if this topic has been covered... Anyways, I'm trying to design an optimized propeller/generator that will be in a closed pipe, but I have no idea what kind of software to use as I've never...
  18. V

    Deriving equation for ideal fluid flow problem (~bernoulli equation)

    Could anyone offer some feedback? I'm reasonably sure I got the gist of it, but I'm not sure how neat a solution it is (i.e. nothing relevant missing, or irrelevancies included). It's a past paper question so I haven't tried to tidy it up. Homework Statement Homework Equations...
  19. R

    Valve, Gas fluid flow question

    Hi all, I am new here and need your help. After sudden opening of a ball valve with cross section area of 10 mm come to an blow up (explosion) of the 2" pipe. (before opening) Up stream the valve was the gas pressure 190 bar during downstream the pressure was 0 bar, however it was air inside...
  20. J

    Valve, fluid flow question

    Hi all, Right, this may be a bit hard to explain but I'll do my best. Hopefully attached is a sketch of the situation. The water flows from the tank into the "rigid container" through valve (1). This tank is then heated until the water reaches boiling at which point the thermostatic valve...
  21. C

    Finding fluid flow with Numerical Method

    Homework Statement For fluid flow in pipes, friction is described by a dimensionless number, the Fanning friction factor (f). The Fanning friction factor is dependent on a number of parameters related to the size of the pipe and the fluid, which all can be represented by another dimensionless...
  22. V

    Fluid flow problem- pressure vs momentum

    I am having a tank at the bottom of which a pump suction line is connected.. there is another parralel line to that bottom line which is open to atmosphere. Please note that this second pipe is connected to the bottom pipe; not to the tank... there is only flow inlet to the tank...
  23. J

    Next set of PDE, which presents fluid flow

    Hallo, I must solve next set of PDE, which presents fluid flow. dP/dx=d/dx(mi*dv/dx)+d/dy(mi*dv/dy) dP/dy=d/dx(mi*du/dx)+d/dy(mi*du/dy) where mi=const with BC: v=v at x=0 u=u at y=0 Can you give me some hint? thanks j.
  24. F

    How to Calculate Orifice Size for Fluid Flow Dispensing?

    hello all, i need to calculate the size of an orifice that will pass a certain volume of a viscous fluid per time of say 10 seconds pressure and viscosity are the variable values. the application is in the design of a valve for dispensing accurate amounts of a liquid of a given...
  25. P

    Does the small size of a hole affect fluid flow rate?

    I would like to calculate the rate at which fluid(oil) is transferred from one chamber to the other. Note the orifices is in the range of 0.0030 to 0.0760 in I'm wondering if the very small size of this hole requires any special consideration. http://myimgs.net/images/oyfi.jpg I realize...
  26. A

    Can Non-Newtonian Fluid Velocity Profiles be Calculated and Drawn?

    Dear Colleagues, i sent your esteem a message through the physics forum, i don't know if it reached you or not, this is my first time to join a forum :-( any way i will try to summarize my problem: 1- i need to calculate and draw the velocity profile for a Non-Newtonian fluid 2-fluid is...
  27. J

    (Biomedical Engin.) Fluid flow through a semi-porous membrane (COMSOL)

    Hi all - I have a problem that I'm probably going to model in COMSOL and would love to hear some ideas on how to get the proper BCs. Attached is the picture from Truskey. Essentially, the problem consists of removing waste (water) from the membrane tube at a rate of ~ 1 mL/min with a pressure...
  28. L

    Fluid flow question using bernoulli's and continuity equations

    Homework Statement The pressure in a section of horizontal pipe with a diameter of 2.0 cm is 140 kPa. Water flows through the pipe at 2.80 L/s. Assume laminar nonviscous flow. If the pressure at a certain point is to be reduced to 102 kPa by constricting a section of the pipe, what should...
  29. B

    Comsol-Pressure drop fluid flow in rectangular channel problem

    Dear all, I am trying to solve a simple model with Comsol to find the pressure drop in a rectangular channel W=5mm, h=0.6mm, L=10mm. When i try to set the inlet velocity to 0.5m/s the solver shows the error message "Maximum number of Newton iterations reached". The solver works fine if i set...
  30. F

    Proving Fluid Flow Velocity & Vorticity Equation

    Homework Statement For a fluid flow of velocity u and vorticity w=∆ x u, show that: (u. ∆ )u=-u x w + ∆(1/2|u|²) Sorry the triangles should be the other way up! Homework Equations ∆(u.v)=(u.∆)v + (v.∆)u +u x (∆ x v) + v x (∆ x u ) The Attempt at a Solution I need to...
  31. Saladsamurai

    Calculate DN for 25 m/s Fire Hose Flow

    Doing some review here: Homework Statement A fire hose has an inner diameter of 5 inches and water is flowing at 600 gal/min. The flow exits through a nozzle contraction with diameter dn. For steady flow, what should dn be in inches in order for the exit velocity to be 25 m/s. My...
  32. P

    Fluid Flow; Bernoulli's Equation

    Homework Statement Using the data of Example 10-11, calculate the average speed of blood flow in the major arteries of the body, which have a total cross-sectional area of about 2.0cm2 Homework Equations well... Actually, I don't know how to solve this problem. The Example 10-11...
  33. H

    Have they solved this fluid flow problem right?

    This is a problem about fluid flow in ducts the fluid has viscosity and it is laminar flow. Please look at the problem and sollution here: http://img156.imageshack.us/i/80737443.png/ They have said that the head loss equals the elevation change. But if you use bernoulis equation with the...
  34. L

    Fluid Flow (Water Jets Combine)

    Homework Statement Two water jets collide and form one homogeneous jet as described below: Jet 1, with v=4 m/s, enters directly upwards through a pipe of diameter .10m into a connector pipe. Jet 2, with v= 6 m/s, enters from the left in a pipe of .12m diameter which is perpendicular to Jet...
  35. O

    Can Changing Hole Diameters Result in Equal Volume Flow Rate in a Pipe?

    Here's my situation: I have a long pipe with n amount of openings along the top, that have an equal distance apart. At one end of the pipe a constant pressure is applied by a pump, and the pipe has a constant diameter all the way to downstream. I’m trying to find a mass flow rate by changing...
  36. H

    Fluid flow between parallel plates

    Homework Statement The velocity distribution for laminar flow between parallel plates is given by u/umax = 1-(2y/h)2 where h is the distance separating the plates and the origin is placed midway between the plates. Consider flow of water at 15 0C with maximum speed of umax=0.05 m/s and h=5 mm...
  37. J

    Finding Outlet Diameter for Compressible Fluid Flow

    hii , i know the inlet conditions i.e. dia 2mm , pressure = 100 bar, density= 0.001176 m3/kg, mass flow rate remains constant= 0.09017 m/s , for same mass flow rate for pressure drop 80 bar(i.e. pressure at outlet is 20 bar) for COMPRESSIBLE FLUID what will be the outlet dia? take fluid carbon...
  38. H

    Fluid Flow in a Pipe: G-Greater, L-Less, E-Equal

    Homework Statement Use the picture as a guide. P is the pressure in the pipe, and vi is the speed of a non-viscous incompressible fluid at locations i = 1,2,3,4,5.(For each statement select G-Greater than, L-Less than, or E-Equal to). A) P1 is ... P4 B) v1 is ... 2v3 C) P4 is ... P5...
  39. E

    Bernoulli's fluid flow in a tube [desperate]

    It is 2 days before final exam and I don't even know how to solve this. I am so screwed.Homework Statement http://img201.imageshack.us/img201/9822/picture1ap8.png (The answers written above are supposed to be the correct answers.)Homework Equations P + (1/2)pv2 + pgh = constantThe Attempt at a...
  40. V

    Fluid Flow: Pressure vs Gravity Explained

    recently i was asked one question in an interview! How fluids flow? i mean whether it is because of pressure difference or any other reason. one more thing! could anyone explain me what is actually the pressure of a fluid and what is the gravitational force exerted on fluid(i.e weight, as i...
  41. R

    Can a U-tube with a moving piston maintain continuity in fluid flow?

    Please consider a U-tube filled with an incompressible fluid as in the attached figure. Piston P divides the fluid in two segments. When P moves, the fluid particles on immediate vicinity of either face (points marked 1 and 2) will have same velocity. Does this mean, they may considered to be...
  42. A

    Vector Field Describing Fluid Flow in a Torus

    Homework Statement Write a vector field equation which describes fluid flowing around a pipe of radius r whose axis is a circle of radius R in the (x,y)-plane. Homework Equations x2+y2=r2 Equation of a torus? The Attempt at a Solution What I've gathered from the question: the pipe...
  43. E

    Boundary conditions for fluid flow

    What are the general boundary conditions for nonviscous, incompressible fluid flow? I am trying to find the velocity of fluid at the surface of a sphere with the incident fluid having uniform velocity. I am surprised to find in the solution that the radial velocity at the surface does not...
  44. V

    How Does Fluid Flow in Nozzles Impact Jet Engine Noise?

    Hi I am trying to reduce the noise from jet thrust in the Turbofan/Turbojet Engine. 1.what type of flow, the hot gases (from the turbine) behaves before existing the Nozzle in the Turbofan/Turbojet Engine? 2.Explain the Flow properties and it's behaviour in the Nozzle Ryan
  45. S

    Fluid flow out of a tank design

    Hi Everyone, First time posting here...pretty cool forum. Anyway, here is what I am looking at in nonspecific terms. I need to design a tank (non-specific aluminum material that is holding water at room temperature) that is approximately 2.5 feet (must be round) in diameter and 1.5 feet...
  46. Loren Booda

    Exploring Faster Fluid Flow with Obstacles: A New Perspective

    I believe I heard somewhat of the following thesis on TV: Take a constant and homogeneous fluid flow, introduce an obstacle, and you can find at least one path connecting original endpoints that is quicker than without the obstacle. Might this be so?
  47. S

    Calculating Oil Flow Speed: Density 850 kgm^3, Pipe Diameter 8 cm

    Homework Statement oil w/ density of 850 kgm^3 goes through a pipe diameter 8 cm at a rate of 9.5 liters / s. what is the speed of the oil? Homework Equations v_1 = (dv/dt)/a_1 = (9.5*10^-3)/(pi(.04)^2) = 1.9 m/s The Attempt at a Solution i have the solution because this...
  48. G

    Fluid flow question through hose

    Here's a silly question. If I'm comparing two different sizes of hose, using the same flow rate in gpm, how do I calculate the pressure drops through each for comparison? I'm considering using hoses with interior diameter .438 and .688, each with a length of 5 inches.
  49. N

    Clarification on fluid flow

    Hi, I'm just looking for some clarification on some flow concepts which I'm having a bit of trouble getting my head fully around :S any help on this would be greatly appreciated! thanks. Basically, I understand the theory and derivations of Bernoulli's equation, the continuity principle and the...
  50. S

    Is Del . V = 0 a valid assumption for steady flow of water through a pipe?

    a perfect and incompressible fluid flowing in circular path about a center. the flow is two-dimensional and steady. I need to find differential relation between the pressure and the tangential velocity and the radial distance.?? I couldn't find which eqn i can use for this problem. I first...
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