Fluid dynamics Definition and 641 Threads

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. M

    Which type of kite is better for low wind conditions: LEI or foil?

    just wanted to say hi first as this is my first post. I will explain the story... There is an ongowing debate within the Kitesurfing world regarding the aerodynamics of LEI (leading edge inflateable) kites and Foil (like RAM aim parachutes) kites. LEI Kites: They have large inflateable...
  2. J

    Higgs Field and Fluid Dynamics

    Can fluid dynamics be applied to a particle moving through a Higgs field? Like is there a wake, or even a slipstream in which a trailing particle might be affected less by the Higgs field or not at all?
  3. A

    How High Should Aquarium Drains Be to Prevent Sand from Being Sucked Out?

    Homework Statement A tank at sea level with fresh water measuring 36"x19"x30" contains a one inch bed of sand. The sand particles are .21 mm in size and have a specific density of 2.6. The water in the tank recirculates at a rate of 1,000 gph. There is a one inch return at the surface of...
  4. S

    Intro Fluid Dynamics homework question

    How much force is necessary to lift a ring, diameter 20mm, made of fine wire, and placed on the surface of water at 20 degrees celsius? All the equations from the chapter: Shearing stress = F/A = Viscosity*(velocity parallel/h) Kinematic Viscosity = viscosity/density Change in pressure =...
  5. S

    How high can water rise in a stream when a hand is placed in it?

    "If you put your arm in a stream flowing at U metres per second, how far can water rise up it?" Not really sure if what I'm doing is right. Presumably it depends on the angle of your arm in the water. If we let the speed of the water at your arm be V, we get, by Bernoulli, taking the height...
  6. L

    Fluid Dynamics (flow rate, Re,)

    Homework Statement An average person has about 5 litres of blood in their body. The heart circulates all this blood around the body in only about 1 minute. Find the time averaged volumetric flow rate Q of the aorta, which is a pipe of inner diameter 2.2 cm. Find the time and space...
  7. R

    Fluid Dynamics Question: A glass tube areas, pressure, determine height.

    http://home.cc.umanitoba.ca/~loly/102-dec_word.pdf The above is a link to the problem - Question #3. Homework Statement A glass tube has several different cross-sectional areas with the values indicated in the figure. A piston at the left end of the tube exerts pressure so that the mercury...
  8. D

    Bernoulli's Equation & Fluid Dynamics LAB

    Before I describe the problem, I would like to apologize for my lack of comprehension of this subject. It is the first semester of Physics, but the end, and has become quite complicated. Homework Statement There is a 2.0 L soda bottle used, with a hole a certain height (hhole) from the...
  9. U

    Help solving the Rayleigh Problem in fluid dynamics please

    Homework Statement Consider the Rayleigh problem, but allow the plate velocity to be a function of time, V(t). By differentiation show that the shear stress, tau = du/dy*absolute viscosity, obeys the same diffusion equation that the velocity does. Suppose that the plate is moved in such a way...
  10. F

    Can Galactic Fluid Dynamics Be Analyzed More Analytically Using Fluid Equations?

    Hey guys, I have the following (non-homework) problem: I am simulating a collection of normally distributed non-interacting stars falling into a much larger galactic potential from some radial distance and some initial velocity and watching them slosh around in this potential. Currently i...
  11. M

    How Does Viscosity Affect the Velocity of Coaxial Tubes in Fluid Dynamics?

    We have a combination of two very long coaxial tubes with radii R and 2R. The tubes are placed vertically, the space between the tubes is filled with a heavy fluid of viscosity. The outer tube glides stationary down under the action of gravity, the inner tube is at rest. Both tube ends are open...
  12. M

    Fluid Dynamics: Flame front in a channel

    A flame front accelerates exponentially in a channel of width 2R with non-slip boundary conditions at the walls. Flame acceleration creates pressure gradient -deltaP/density=exp(sigma*t) (x-direction) directed parallel to the channel walls. Assuming a plane-parallel flow, find velocity...
  13. D

    How Does Fluid Dynamics Apply in a Rotating Sphere?

    Heya , sorry but could someone check what I've done is right ? The remainder of the question relies on these answers :S Homework Statement We consider a homogeneous fluid in a sphere of radius r0 = 1 in the limit of kinematic viscosity v = 0 which is rotating uniformly about its axis...
  14. G

    Fluid Dynamics, Calculating viscosity using damping coeffiecient

    Homework Statement Hello, I am doing a project which requires damping and have decided to use some viscous damping. It is simply on a hacksaw blade with a weight on the end. Therefore, other than just trial and error I would like to calculate the range of viscosities that may be useful for...
  15. B

    Fluid Dynamics Question(not too difficult)

    Homework Statement The spout heights for a container are 10 cm, 20cm, 30cm, and 40cm. The water level is maintained at a 45 cm height by an outside supply. Which water steam has the greatest range relative to the base of the container. --- I know that the one at 20cm is the greatest range...
  16. S

    Fluid Dynamics: Find the Pipe Radius at Height Increase

    Homework Statement Water is flowing through a pipe of radius 4 cm with a speed of 15 m/s The pipe increases 3 M in height with no change in pressure or speed. What is the radius of the pipe in cm at this new height?Homework Equations P1+1/2\rhoV12+\rhogY1=P2+1/2\rhoV22+\rhogY2 The rho's are not...
  17. B

    Fluid Dynamics: Using Bernoulli's equation and Volume Flow Rate

    Homework Statement Water flowing out of a 15.0mm -diameter faucet fills a 1.50 L bottle in 5.00s. At what distance below the faucet has the water stream narrowed to 10 mm in diameter? Homework Equations Bernoulli's equation: P_1+pgh+1/2pv^2=constant Q(volume flow rate)=vA Continuity...
  18. R

    What is the length of the can above the water level?

    Hi everyone, I hope you can help me out with this question as my exam is tomorow. Homework Statement A 355 mL soda can with diameter=6.2 cm has a mass of 20g. If it is half full with water, and it is floating upright on water, what length of the can is abover the water level...
  19. P

    Continuity Between Statistical Mechanics and Fluid Dynamics

    Imagine a jet of fluid (perhaps air) impinging on a flat plate. It could be said that the jet has a slightly higher mean velocity in the direction normal to the flat surface (we'll arbitrarily call this X). From a classical thermodynamic point of view it could be said that the gas has a higher...
  20. Run Haridan

    FLUID DYNAMICS AND BEHAVIOUR OF REAL FLUID help

    FLUID DYNAMICS AND BEHAVIOUR OF REAL FLUID help! Homework Statement a jet of fluid issues from a 50mm diameter nozzle on the end of 100mm diameter horizontal pipe. A pressure gauge just upstream of the nozzle measures a pressure of 150 kPa. Determine the discharge of (a) an ideal fluid...
  21. V

    Looking for a comprehensive fluid dynamics textbook?

    could anybody suggest me a book on fluid mechanics which provide strong basics as well as detailed knowledge thanks
  22. F

    How Does Airspeed Affect Pressure Calculations in Aircraft Fluid Dynamics?

    I have 2 questions. Homework Statement 1)An aircraft is flying at sea level at a speed of 280km/h. Calculate the static pressure and total pressure at the stagnation point. From a standard atmosphere table, for sea level altitude, pressure is 101325 Pa. Density of air is 1.2250 kg/m3. 2)...
  23. A

    Fluid Dynamics Homework: Solving for Water Speed and Range in a Container

    Homework Statement A container has spouts 10 cm, 20 cm, 30 cm, and 40 cm. The water level is maintained at a 45 cm height by an outside supply. (a) what is the speed of the water out of each hole? (b) which water stream has the greatest range relative to the base of the container...
  24. M

    Which Equations Solve Fluid Dynamics in a Pressurized Container?

    I am trying to solve for the temperature/pressure profiles of a small closed-end (one side) tube inside a pressurized container kept at constant temp./pressure. For now, I am assuming that vacuum conditions exist within the tube. I am not sure, however, which equations I should be using...
  25. L

    Fluid Dynamics, Buoyancy problem

    Homework Statement How many cubic metres of helium are required to lift a balloon with a 400 kg payload to 8000 m? Assume balloon maintains constant volume, and density of the air decreases with altitude z according to the expression \rhoair = \rho^e^-z/8000, where z is in metres and po =...
  26. I

    Verifying Fluid Dynamics Equation

    [b]1. Verify that vj∂jvi=∂i(1/2*v2)-εijkvjωk,where ωk=εklm∂lvm Homework Equations The Attempt at a Solution I am confused on how to proceed with this problem up to this point I have decomposed ωk into Curl(v). Which leaves vj X Curl(v). Decomposing this leaves vm∇ivm-vl∇lvi. I am...
  27. G

    Optimizing Water Flow in a Vertical Pipe: Calculating Pressure and Speed

    Through a pipe 15.0cm in diameter, water is pumped from the Colorado River up to Grand Canyon Village, located on the rim of the canyon. The river is at an elevation of 564m, and the village is at an elevation of 2096m (a) What is the minimum pressure at which the water must be pumped if it is...
  28. U

    Fluid Dynamics Studies: Path to an Undergraduate Degree

    Hello all, I'm interested in studying fluid dynamics as a profession but I'm uncertain as to what course of study I should pursue as an undergraduate. I've been thinking about taking my BA in mathematics and physics but due to the seemingly heavy computational nature of much of the work being...
  29. G

    How Fast Does Water Exit a Hole in a Tank?

    Heh...this question actually looks as simple as hell (and it probably is)...but there always seems to be one variable missing: A large storage tank, open at the top and filled with water, develops a small hole in its side at a point 16.0m below the water level. if the rate of flow from the...
  30. B

    Fluid Dynamics, Linearization Question

    Homework Statement Consider an ideal fluid large enough to experience its own gravitational attraction. If the fluid is initially at hydrostatic equilibrium with density \rho_{0} (r) and pressure p_{0}(r) , it can develop small amplitude pressure waves which may be analyzed as follows...
  31. N

    Fluid Dynamics: Determining Velocity Coefficients

    Homework Statement I have an incompressible, irrotational fluid with velocity v in the form: v_x = c_xx x + c_xy y + c_xz z v_y = c_yx x + c_yy y + c_yz z v_z = c_zx x + c_zy y + c_zz z The coefficients c_xx, c_xy, etc. are constants. How can I determine how many independent coefficients I...
  32. B

    Fluid Dynamics Question about streamlines help?

    Fluid Dynamics Question about streamlines...help!? If the velocity field, v, of a fluid depends on x and y, v(x,y) and we know there exists some function psi(x,y) such that vx= partial w.r.t (y) of psi vy = -(partial w.r.t (x) of psi) show that the curves psi(x,y) = constant, are...
  33. F

    How Do You Calculate Flow Rate and Water Level Change in a Tank with a Hole?

    Homework Statement a 4mm hole is 1m below the surface of 2m diameter water tank. a.what is the volume flow rate through the hole in L/min? b.what is the rate in mm/min at which the water level in the tank will drop if the water is not replenished...
  34. I

    Intro to Fluid Dynamics: Top Book Recommendations from a Physics Perspective

    can someone suggest a good introductory book on fluid dynamics from a physics pov?
  35. B

    Is it possible to increase fluid pressure by blowing air through a straw?

    Hello everyone, this actually happens to be my first post on PF. So, this question is a rather basic one, however the conversion between theoretical and experimental is not going so well. So, here is the initial question/dilemma: Is it possible to blow across the top of a straw so fast that...
  36. D

    How Does a Siphon Work with Different Liquid Heights and Pressures?

    Siphon with a liquid of density P and negligible viscosity. With the bottom of the tube in the contained at point A d + h1 from point B at the top of the siphon, and the bottom of the tube extracting the liquid at point C d + h1 + h2 from the top of the siphon and h2 away from point a. (All...
  37. D

    Pax Scientific's Fluid Dynamics

    I was wondering if there was anyone on here who could explain more about this company's technology. (www.paxscientific.com) They're an R&D company that is specializing in designing fans and mixers that create a vortex that allows the fluid to flow more efficiently from point a to point b. I...
  38. Astronuc

    CFD - Computational Fluid Dynamics

    There are a few threads in this forum about CFD, but I thought I'd establish one for a general discussion of CFD methods and applications and tie it in with others as appropriate. In the December '07 issue of Aerospace America in the Aerospace Sciences section is a short article on the recent...
  39. T

    Question on Fluid Dynamics book

    Hi All, Does anyone here can advise me which of the following Fluid Dynamics is good for Beginner? Title: An Introduction to Fluid Dynamics: Principles of Analysis and Design Author: Stanley Middleman ISBN: 0471182095 Publisher: Wiley Title: Fluid Dynamics: Theoretical and...
  40. M

    Archived How Does Bernoulli's Equation Determine Flow and Pressure in a Tank System?

    Water flows steadily from an open tank as in the figure below. The elevation of point 1 is 10.0m, and the elevation of points 2 and 3 is 2.00m. The cross-sectional area at point 2 is 0.0480m^2; at point 3 it is 0.0160m^2. The area of the tank is very large compared with the cross-sectional area...
  41. M

    Fluid Dynamics: Cylindrical Bucket, Water Flow & Height Increase

    A cylindrical bucket, open at the top has height 30.0cm and diameter 10.0cm. A circular hole with a cross-sectional area 1.35cm^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 2.20×10−4 m^3/s How high will the water in the...
  42. N

    Fluid Dynamics standard reference

    Hi. What's a standard reference for physicsts concerning the topic of fluid dynamics or computational FD.
  43. P

    Fluid dynamics vs Electrodynamics

    If you could only do one which one would you choose? And why?
  44. B

    Computational Fluid Dynamics - Introduction

    Hi, hope this is the right area for this. I'm currently doing preliminary research for my computer science dissertation. I'm thinking of doing something in CFD...either representing the effects of wind on fur, or simulating a river flowing. Most CFD 'googles' have resulted in me finding...
  45. S

    What Forces Are Involved in the Navier-Stokes Equations?

    Hey guys a few questions. Question1) Descrive the forces that make up the NSE(Navier-Stokes Equations). Which forces generate motion and which alter motion. I have answered this 1st question, I got: pressure gradient force - generates coriolis force - alters frictional forces: wind...
  46. S

    Fluid Dynamics: Answering Pressure in a Full Tank

    I understand the concept of this question, I think, but I don't know how to go about getting an answer. A tank is completely full of water with no air. A valve at the bottom is opened, while one on top remains closed. What is the lowest pressure that the tank will reach. From valve to valve...
  47. D

    Classic buoyancy demo discussion on fluid dynamics

    Hello, I was attending a physics discussion on fluid dynamics (fairly basics concepts) and the classic buoyancy demo came up. (A test tube is inverted and allowed to be filled with enough water to float with the volume of air trapped in the tube, the test tube is inside a larger bottle which...
  48. J

    Fluid Dynamics (finite difference or finite volume)

    Homework Statement I'm trying to create a program which models fluids using the finite difference methodHomework Equations This is what I'm looking for:)The Attempt at a Solution I'm hoping someone can point me in the right direction. I guess at first I'll just simulate incompressible fluids...
  49. F

    Fluid Dynamics: Pressure / Opening a hatch underwater

    Let's say that you're deep under the surface of the water in a submarine type thing. There is a hatch on the top. Let's say that the absolute pressure on the top of the hatch was calculated to be 2 atm. Inside the vessel, the pressure is only 1 atm. Someone is inside the vessel and...
  50. Q

    Fluid Dynamics Forces: Steady, Pressure-Driven Flow Between Parallel Plates

    I would really appreciate any help with this problem. I'm pretty stuck. Homework Statement An incompressible viscous fluid occupies the region between two parallel plates. The lower plate is stationary and the upper plate moves with a velocity u. Find the velocity of a steady...
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