What is Fluid dynamics: Definition and 631 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. N

    Pressure Drop Across a Change in Diameter

    Greetings, I have very little experience with fluid dynamics and I was wondering how I can calculate a pressure drop across an abrupt change in diameter of the piping used for water. Any help is appreciated! Thanks!
  2. S

    Modeling of two-phase flows in electric and magnetic fields

    Hi, Can anyone direct me to some literature that describes the numerical solution of full Maxwell's equations and Navier-Stokes equations for two-phase/multi-phase flows in coupled electric and magnetic fields. Thanks!
  3. N

    Threshhold compressible flow Ma = 0.3

    Hi guys, I'm trying to delve into compressible flow and in the various textbooks I'm reading I've found two school of thoughts when it comes to how to calculate the threshold (or error compared to incompressible flow) of 'M' when to consider a flow compressible. In Fundamentals of Aerdnyamics...
  4. mertcan

    Computational Fluid Dynamics: Dissipation Function Density Based Solver

    ((((As a correction dissipation function in picture should have square of divergence of U)))) Hi, first of all I am aware that we have to discretize the non linear navier stokes equations to reach the almost exact solution, and pressure based or density based algorithms are deployed for that...
  5. O

    Compute Fluid drag, Swim Physics

    Hello, I'm trying to create a simulation of swimming "Animats" (artificial animal). However, I'm only an high school student, so I don't know how to deal with fluid drag and fluid dynamics. In this link you could find a short animation I made describing the swim motion my animat is going to...
  6. Kevin

    Pressure Gradient for Nitrous Flow

    Hello everyone, I am currently working on an undergraduate club team for the Intercollegiate Rocket Engineering Competition. I am attempting to do a calculation to determine the pressure needed in a vessel leading to another pressurized combustion chamber to achieve a desired mass flow rate...
  7. F

    What causes pressure and is it isotropic in a moving fluid?

    I'm studying fluid dynamics and we just had a lecture about the momentum equation. We started the lecture by talking about pressure in terms of molecules moving across a hypothetical surface element and carrying their momentum with them (in both directions). There are 2 things confusing me about...
  8. I

    Bernoulli's Equation, Find gauge pressure at 2nd point

    Homework Statement At a certain point in a pipeline, the velocity is 1 m/s and the gauge pressure is 3 x 105 N/m2. Find the gauge pressure at a second point in the line 20 m lower than the first if the cross-section at the second point is one half that at the first. The liquid in the pipe is...
  9. H

    Laminar and turbulent flow on dripping blood

    Can laminar and turbulent flow be used to explain dripping blood? Be it blood dripping from a weapon/ impacting on an uneven surface?
  10. J

    A Anamolous Aerodynamic behaviour of small spheres?

    This refers to the behaviour of cricket balls. Every cricketer in the world believes that a cricket ball "swings" more when the atmospheric conditions are cool and damp (as in the UK) as opposed to hot and dry (as in Australia). I have watched a bit of baseball and I have never heard...
  11. U

    Fortran Fortran for Computational Fluid Dynamics Problems

    Dear, Everyone I am a new member here, nice to meet you.. First, I want to introduce my self, I am a master student of physics and I am studying CFD right now. It's a new topic for me and I will also do my research about simulation of fluid dynamics related to CFD. Actually, I got this topic...
  12. S

    Business major.... fluid dynamics question....

    Homework Statement I have a syringe filled with water. This syringe is a cylinder with a length of 3 inches (L), diameter of 1.5 inches (D). Attached to the syringe is a constant force spring, which pushes the plunger into the syringe with a force of 2 pounds (F). Ignore the friction between...
  13. K

    Calculate the rate of potential energy loss of water in a pipe

    Homework Statement Question: what rate does the water lose gravitational potential energy? Data: I have a pipe that water is flowing through and the pipe has 2 sections. In section 1: - the pipe is 11.9m above section 2 so, h = 11.9m - the velocity of water is $$v_1 = 0.3240ms^{-1}$$...
  14. L

    Finding the density inside a tank as air escapes

    Homework Statement A tank of constant volume V contains air at an initial density pi. Air is discharged isothermally from the tank at a constant volumetric rate of Q (with SI units of m^3/s). Assuming that the discharged air has the same density as that of the air in the tank, find an...
  15. thepikminman

    Fluid Mechanics - Why? How? Why?

    Hi, I've been studying fluid mechanics for my mech. engineering degree for the past few months. Unlike my other subjects (mechanical analysis, thermodynamics, automated systems, mechanical vibrations), I can't seem to grasp the problem-solving technique. The annoying thing is, I find the...
  16. S

    What does FL represent in the drag coefficient equation?

    So I did a project about a year ago and I can't remember one of the things I wrote in this equation. The equation apparently I got it from NASA's website. https://www.grc.nasa.gov/www/k-12/airplane/dragco.html This is my equation CD = FL/ (0.5 * Air viscosity * V^2 * Area) = 0.4These are the...
  17. I

    How to express velocity gradient in cylindrical coordinates?

    Homework Statement The vlasov equation is (from !Introduction to Plasma Physics and Controlled Fusion! by Francis Chen): $$\frac{d}{dt}f + \vec{v} \cdot \nabla f + \vec{a} \cdot \nabla_v f = 0$$ Where $$\nabla_v$$ is the del operator in velocity space. I've read that $$\nabla_v =...
  18. P

    Fluid Dynamics -- a spherical particle immersed in water

    Homework Statement Consider a spherical particle immersed in water. It will experience random collisions with the surrounding water molecules. Suppose there are such water molecules around the particle. Half (n/2) of the water molecules will push the particle to the right and the other half to...
  19. B

    Velocity in microchannel with temporal temperature variation

    a microchannel of length 2L and width h in the thermal cycling region. the temperature profile ...(1) the cyclic temperature profile leads to a time dependent density ...(2) using the mass conservation equation i.e. ...(3) and momentum balance equation i.e. ...(4) we have to find the exact...
  20. A

    What is happening in this fluid dynamics problem and how can we approach it?

    Homework Statement Problem: https://imgur.com/a/ppDy6 Calculate the fluid speed at a certain point Given fluid and sound speed before the point Length of the conduct 2. Useful Equations: Uniformly accelerated motion(my solution) I have been studying this problem it for some time, have...
  21. G

    Fluid dynamics: simulation of an oil system

    Good day folks! I am working on the simulation of an engine, and in particular the oil system makes my head ache. I already finished the calculations for viscosity and temperature, but now I'm stuck on coming up with formulas for pressure and flow rates. With what should I start? For...
  22. M

    What are the best resources for studying astrophysical fluid dynamics?

    i am an aerospace engineer and have good knowledge in fluid and gas dynamics and i want to study astrophysical fluid dynamics , should i study intro to astronomy and astrophysics ? and what are best books in astrophysical fluid dynamics ?
  23. T

    I No Slip condition in an Inviscid Fluid

    In an Inviscid fluid would the no slip condition exist? If it didn't would it follow that the free stream velocity would exist at the wall ?. If this was the case would surface roughness still present an orthogonal area upon which the kinetic energy of the fluid would interact causing a...
  24. R

    Engineering Research in Fluid Mechanics for MS

    Hi Everyone, I am currently doing undergraduate program in mechanical engineering. I want to pursue masters after my B.Tech in the field of fluid mechanics and aerospace engineering.I want to know about the prospects of this field in the future research. Thanks in advance, Ritwik Kulkarni
  25. R

    What are the future research opportunities in impinging jets and related fields?

    Hi All, I am Ritwik from India and I am very interested in the area of fluid mechanics.Currently pursing B.Tech in Mechanical Engg. in IIT. I am currently doing my project in impinging jets. I want to explore and want to continue in the field for research in the graduate programmes. I want to...
  26. ramzerimar

    Courses Is CFD fluid mechanics + computer science?

    I'm having fluid dynamics classes right now and I'm enjoying it very much (much more than my solid mechanics classes, by the way). Also, I do like programming and computer science, and CFD looks like a very interesting field. I'm developing a real interest for it. One question for those who are...
  27. W

    Reynolds Transport Theorem Derivation Sign Enquiry

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  28. B

    TFD (topological fluid dynamics) matricial form

    Homework Statement Using the matricial form of TFD (discret Fourier Transform) calculated : X=Fd(x) for x=(1,0,2j,1-j)^T from K^4 Homework Equations X=wx The Attempt at a Solution I know the "x" matrix and the "w" matrix but i don't know how to find the "ω" variable from the "w" matrix...
  29. T

    Melted cheese-like flow -- What is it called and its cause?

    There are some plastics I am using that when melted, pull apart in a stringy way. My best comparison is like melted cheese in a sandwich. I want to know more about this, but other than looking up 'polymer rheology', I'm not sure what I should call this type of flow. I want to know what causes...
  30. J

    Directional Grooves on the Interior of Pipes

    Hey everyone! My name is Jing and I am participating in a one month summer program called SHAD where 800 high school students across Canada come together to try and solve some of the world's most multi-dimensional problems. One of the aspects of this program is the Entrepreneurial Project, where...
  31. Gotbread

    Using a centrifuge to extract heavy water (help with the calculations please)

    Hello everyone! I have seen several DIY projects which successfully gathered heavy water from normal water. For example Cody from codys lab used electrolysis to "enrich" the water. This however is a messy process. So i became curious, if this can be done easier by centrifugation. Based on...
  32. F

    Surface Runoff - Explained and Debated

    Homework Statement In my book , i was told that when the drainage of surface is high then the surface runoff will be low . However , i don't think it's correct . Homework EquationsThe Attempt at a Solution Definiton : Runoff can be described as the part of the water cycle that flows over...
  33. K

    Fluid Dynamics: Dimensional Analysis and important forces

    I am stuck on the questions, 5.3.10 and 5.3.11 which are part of a chapter on dimensional analysis in fluid mechanics by Streeter. Question 5.3.10 (see also the attachment): It asks me for the given fluid dynamic problems, where is the inertial force not important. It lists several fluid...
  34. TheRumpus

    Does air flowing through a tube cause a pressure change?

    I have been involved in a fairly furious debate about a fluid dynamics experiment regarding the pressure of air passing through a tube attached to a moving car. It is similar in concept to the issue of whether or not an opening in an aeroplane fuselage would suck people out, where the opening...
  35. M

    Viscosity and temperature, density is changing....

    Homework Statement Hi, I am doing physics lab on finding coefficient viscosity of fluids and how it changes by temperature by dropping a marble into fluids, finding terminal velocity, then using stoke's law to find viscosity. (using density of fluid, sphere, sphere diameter etc). The equation...
  36. A

    Fluid Dynamics - Water Storage Tank

    Hi All, Looking for some help (any is greatly appreciated). I've been tasked with the below, and am unable to find a worked example to cross check my work against. If anyone with a greater knowledge than me could have a look at the below and advise if I'm right the right track. Thanks 1...
  37. X

    How does a pressure/temperature difference cause a force?

    Hello. I am inquiring about how a pressure difference between a hot room (roughly room temperature) and a cold room (roughly the temperature of a standard refrigerator) can cause a force inside the cold room when exposed to its hotter counterpart. More specifically, I would like to apply this...
  38. LiamB

    Fluid Flow rate and fluid dynamics

    Homework Statement More a report question but unsure where to put it. Take a 5mL syringe and a 10mL syringe (both filled to 5mL) with the plungers removed. Time how long it take to full drain each syringe Make a statement regarding your results. Homework Equations Fluid flow rate = volume /...
  39. Ahmad Esber

    B Is it possible to harvest energy from fluid buoyancy?

    So I've noticed my little sister's helium balloons floating at the ceiling. Made me wonder if someone could create a device that could harvest energy from this buoyancy. What if I tied a very long rope to a huge balloon filled with helium, and rolled the other end of the rope to a gear attached...
  40. P

    Friction between cart and a surface covered with a liquid?

    << Thread moved from the technical forums so no Homework Help Template is shown >> Hello, I'm attempting an experiment where I take a cart and slide it down a ramp. Each time, I will coat the ramp with a different liquid. I want to compare the effects of the dry ramp, a ramp with water poured...
  41. F

    Flow thru a channel constriction

    Homework Statement When a part of the channel is constricted , why will the Emin = Eo ? Homework EquationsThe Attempt at a Solution I just have the figure showing in case 1 and case 2, Emin = Eo without any explanation ... Can someone explain about it ? I tried to search many online resource ...
  42. YURIIMkZERO

    Comsol Help -- How to Enable Rotating?

    Hi, I'm a newbie at Comsol and want ask for guide how to fill something with fluid and make sphere rotate. My goal in creating system where one sphere contains second. Second sphere rotates on its axis. Volume between is filled with fluid. I understand how to create spheres, but couldn't...
  43. D

    Energy conservation for a Newtonian fluid?

    Homework Statement ρ= density, vi = i-th velocity component, gi=i-th component of gravity vector, p=pressure, μ= viscosity, D/Dt = material derivative Homework Equations Continuity equation: div v = 0 The Attempt at a Solution
  44. Will1119

    Velocity of a Cart accelerated by a Jet stream

    This is a problem for a fluid dynamics class I'm in. My current approach is to use a conservation of mass approach and say that the d/dt(momentum in the cart) = momentum into the cart. This leads to (u is speed of the cart, V is volume J is jet velocity, A is cross sectional area of the jet)...
  45. MOHAMMAD UMAIR

    PBL Velocity Profile: Sinusoidal Variation w/ Height

    Why does the planetary boundary layer velocity profile shows a sinusoidal variation with height? Reference: Fig:14.10 Page 576 Fluid Mechanics - Kundu and Cohen 2nd edition
  46. S

    Assumption of local thermodynamic equilibrium in a fluid

    Moving fluids are generally in a state of non-equilibrium. However, in fluid dynamics, people generally assume a state of local thermodynamic equilibrium and argue that in such a condition, equilibrium thermodynamic concepts such as pressure, temperature, entropy, internal energy etc. can be...
  47. G

    Calculating Flow from Tank to Vessel w/ Power

    I am trying to calculate the flow in a system from an underground tank up through a pump into a vessel. But cannot find or derive a formula that yields a good result, I don't think I can use the same head calculations as Velocity will have changed. 1. Homework Statement ρ = 1000 kg m–3 μ =...
  48. S

    Conceptual Issue Dealing With Atmospheric Pressure

    Homework Statement A 1m^3 steel cube is to be floated on mercury (specific gravity=13.6). On each side of the cube there is a 5mm clearance. Assume that the container is open to atmospheric pressure at 100kPA. Find the mass of the mercury. Homework Equations P=F/A The Attempt at a Solution I...
  49. D

    Would the velocity of a fluid increase right after exiting a pipe into open air?

    If you have an non-viscous incompressible fluid flowing in a pipe whose static pressure is higher than atmospheric pressure, then after exits the pipe will the dynamic pressure increase? The static pressure of the fluid right after exiting should decrease because it should be equal to the...
  50. S

    What is the speed of air flow in a pipe driven by compressed air for 12 minutes?

    Homework Statement A tank with a 25.5 litre capacity contains air compressed into 355 atmospheres used to drive a torpedo by expansion into an engine via a pipe of diameter 0.08cm. A mechanism ensures that the gas flows to the engine at a constant rate and any cooling of the air during...
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