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.

View More On Wikipedia.org
  1. VincentIsoz78

    I Static sphere with gravitating fluid

    Hi The rotating bucket problem with a fluid is well known as a homework. For the fun i wanted to adapt it to the case of a massive non-rotating sphere surrounded by a fluid. However i don't know if the calculations i made are correct or don't make sense at all (even if the result lead to an...
  2. Tallus Bryne

    MATLAB MATLAB: Fluid Flow - Curl of a Vector Field

    I am working with some data which represents the fluid position and velocity for each point of measurement as an x, y, u, and v matrix (from particle image velocimetry). I have done things like circulation, and discretizing the line integral involved was no problem. I am stuck when trying to...
  3. mishima

    B Fluid Flow Deflection Bending Ahead of Airfoil?

    Hi, I am a high school teacher in need of some help explaining fluid flow. I don't have much experience with fluids at a college level. We were reviewing lift (Bernoulli's velocity/pressure relation, deflection of air downwards, etc) and I showed them: this online simulation. One student asked...
  4. mahdis

    Fluid flow rates in straight vs coiled tubes

    If you have 2 pipes of the same cross sectional area, same volume of fluid, and same length, the only difference is one pipe is coiled several times over a cylindrical object theoretically shortening the length of the pipe, while the other is a straight pipe. Will the flow rate be same in both...
  5. S

    A Conservation Laws from Continuity Equations in Fluid Flow

    Consider a fluid flow with density ##\rho=\rho(t,x)## and velocity vector ##v=v(t,x)##. Assume it satisfies the continuity equation $$ \partial_t \rho + \nabla \cdot (\rho v) = 0. $$ We now that, by Reynolds Transport Theorem (RTT), this implies that the total mass is conserved $$...
  6. huangdaiyu

    A Steady state confined flow field: Is it cyclic?

    For a fluid that is confined to a finite region with no sources and sinks, are the only options for the flow field a) static, and b) cyclic? The example I have in mind is Rayleigh convection in a shallow dish heated from below, where convection cells are formed beyond a certain temperature...
  7. A

    I Fluid flow through a pin-hole of x diameter in a closed container

    Greetings, I've come across lots of exercises regarding Bernoulli's equation. However, never seen one where the top of the vessel is closed, and fluid flow exists via gas (air) going in. Has this problem been studied in the past? Assume a cylindrical vessel filled to the maximum with a D-sized...
  8. samy4408

    I About Bernoulli's equation for fluid flow

    Hello, I am currently studiying Bernoulli's equation and I have trubble understanding something , say we have a horizontal hose (no change in altitude of pressure ) Bernoulli's equation state that an ideal fluid can flow thought the hose with the same velocity , does an ideal fluid need a...
  9. P

    Bernoulli equation / fluid flow / finding height

    Hi, everyone! Doing some fluid flow/Bernoulli tasks. Ok, so the task is: «A hose with a radius of 0,035m is connected to a nozzle, which reduces the radius of the hose to 0,018m (2). The hose carries (qv) 0,0075 m3/sec and the totalpressure (3) in the wide section (1) is 211 kPA. The density of...
  10. O

    I Fluid force from a fluid flow vs. from a fluid jet

    In fluid flow (such as wind), the force exerted on a perpendicular surface is derived from kinetic energy and is ρAv^2/2. But in problems involving a jet of fluid that strikes a plate, the force is derived from momentum and is explained to be ρAv^2, lacking the 1/2 factor. Can someone please...
  11. Anachronist

    B Beam of air: Extending the range of a fan

    If one Googles for "laminar flow nozzle", one finds many interesting tutorials on creating a nozzle for a laminar water jet; a stream of water that remains coherent over a long distance without breaking up. These typically consist of a large-diameter tube with regions inside (like sponges and...
  12. F

    Fluid flow inside a cylindrical tank

    Hi, I´m quite lost and would appreciate guidance I have solved for 2 tubes using Bernoulli´s equation before, but now how does it change? Is it really going to rise water level inside? Why?
  13. Dario56

    I Work - Energy Principle Application to Fluid Flow

    In classical and continuum mechanics if we want to find equation of motion of the body we draw force diagram and apply Newton's 2nd law. In continuum mechanics, equation of motion actually refers to a special point of the body known as center of mass (COM) which can be proven by definition of...
  14. Dario56

    I Work - Energy Principle Application to Fluid Flow

    Work - energy principle states that work done by net force acting on the body equals change in kinetic energy of the body. We are talking about continuum mechanics. This principle is usually introduced in mechanics of solid bodies. For us to describe the motion of the body, it is enough to know...
  15. N

    Fluid flow rate calculation

    I am trying to calculate the flow rate of O2 from a known volume 25 in^3. The cylinder will fill up to a maximum pressure of 140 psi in 11.26 seconds. Any help to determine the flow rate will be appreciated. Do I use Bernoulli equation to find the flow rate?
  16. ergospherical

    A Fluid Flow Symmetry: Showing $\pi_b G^b$ is Constant

    I don't know where to start with this problem. If ##\pi_a = (\mu + TS) u_a## then show that \begin{align*} u^a \nabla_{a} (\pi_b G^b) = 0 \end{align*}where the field ##G^a## is a symmetry generator. [##S## is entropy/baryon, ##T## is temperature, ##u_a## is a one-form field corresponding to a...
  17. M

    What are the key parameters affecting heat transfer in thin tubes?

    Hi, I am trying to understand how I can estimate the time it takes for a fluid at room temperature flowing through a thin capillary glass tube (2 mm ID) connected to an oven to reach the equilibrium temperature (oven temperature). Assuming the oven is preheated and the tube inside the oven is...
  18. S

    Is ideal fluid flow around an airfoil the Lambert W function?

    NOTE: By "ideal", I mean incompressible & inviscid (the forum doesn't allow a long enough title). I was looking at this Wikipedia article, and the graph of this function struck me as looking exactly like ideal fluid flow around an object. https://en.wikipedia.org/wiki/Lambert_W_function...
  19. R

    Fluid flow and characteristics in a vacuum (Cryophorus)

    trying to calculate the mass flow of Water vapour that is produced within a vacuum of 30 inhg when the water temp is 40 degrees. How is velocity calculated in this scenario. Also what boundary layer does the water vapour have.
  20. T

    Fluid flow around a wind turbine blade -- help please

    I have to estimate the Reynolds number of the fluid flowing around a blade but I only have one detail: the length of the blade is 0.66m. I have no idea how to do it and I got to submit the assignment in a week, I am desperate for help here.
  21. Rahulx084

    Some questions about Friction in fluid flow

    I have few conceptual doubts in fluid mechanics. Here is the one I will ask first. I want to understand the force direction acting on the solid liq interface during fluid flow, Let's say a fluid is flowing in a pipe. Now the fluid applies a shear stress at the walls of pipe in the direction of...
  22. R

    Flow of a Non Viscous Fluid Through this Nozzle

    My first post here! I have calculated everything i need, except the thickness of the second layer dZ*, therefore i can't solve V3/V2=(R2ˇ2)/(R3ˇ2) Trying for days now, i would appreciate any help.
  23. brotherbobby

    Water flowing out of a tank through a hole

    I assume the water to start flowing from rest at position 1, hence ##v_1 = 0##. Applying the continuity equation, ##A_1 v_1 = A_2 v_2##, we find the (wrong) result that the velocity at position 2 is ##v_2 = 0## also! (We assume that ##A_2## is small but finite) Hence, to answer the question...
  24. ramadhankd

    Can We Design a Tube to Resist Fluid Flow?

    Hello everyone, I want to ask something. Can we design a tube that can completely resist the flow of a fluid? Maybe using either viscosity or surface tension approach? Thanks
  25. maistral

    2D advection-dispersion velocity component for fluid flow in a pipe

    Pardon if the answers to my questions are obvious, because as usual I am trying to decipher everything on my own (as the material has not been taught to us quite well; then again it's graduate school). I just need someone to reassure me that I am understanding this correctly. Say for example I...
  26. T

    Calculating Fluid Flow: Help with Q, A1, A2, Delta h, g & C

    Hello all I was hooping someone could help shed some light on the following:- I have the equation shown below: This equation relates to flow rates of fluids. I know:- Q = flow rate A1 & A2 = Area Delta h = Difference in Head Loss g = Gravity But what does C relate to or even mean? Can...
  27. B

    I Analytical Open Channel Rectangular Fluid Flow

    Hi All, I'm looking for an analytical solution to the open channel rectangular fluid flow profile. The flow is bounded by three walls but the top is open to atmosphere. Assume steady state flow that is parallel and incompressible.I've already found information involving a rectangular flow...
  28. A

    Velocity gradient decomposition of a fluid flow

    If the velocity gradient decomposition is done by symmetric and antisymmetric parts then ##\frac{\partial v^i}{\partial x^j}=\sigma_{ij}+\omega_{ij}## where ##\sigma _{ij}=\frac{1}{2}(\frac{\partial v^i}{\partial x^j}+\frac{\partial v^j}{\partial x^i})## and...
  29. T

    Maximum height for water from a fire hose

    Homework Statement Fire hose has diameter of 4.0 cm and flow rate of 10 L/s. There is pressure of 2.2 bar inside the hose. How high the water can go at best? Water density is 1.00E3 kg/m^3 and air pressure outside the hose is 1.0 bar. Homework Equations Flow rate $$ Q = Av $$ Newtons...
  30. Rahulx084

    Shear stress direction and the velocity gradient

    1)In a flowing fluid in laminar fashion we know that it flows in planes which slides over each other, Let's take a fluid element (cylindrical) in a pipe(Radius=R) the resistive force is (stress)(cross section area of cylinder with radius 'r') acting in backward direction, now if I take Flow...
  31. J

    Pressure and heights of a manometer -- Find the fluid flow rate

    Homework Statement Find the flow rate of water. The fluid in the manometer is mercury. ##d_{1},d_{2}## are the diameters in the figure Homework Equations Bernoulli, continuity equations The Attempt at a Solution We know that ##p_{1}=p_{1Top}+\rho_{water}gh_{2}##...
  32. B

    Effective Resistance (Fluid Mechanics)

    Imagine you have a vertical pressure head 2m tall with water flowing down to height 0m and emptying. Through this length we have 3 identical tubes of resistance R and length L. Assuming I know the volumetric flow rate(Q) as a function of height, how can I calculate the resistance of each tube...
  33. R

    Hydraulic head as a function of flow rate

    Hello! 1. Homework Statement Symbols and variables: ##\dot{V}## : flow rate ##H## : Hydraulic head ##g = 9.81 \frac{N}{kg}## ##P_{atmosphere} = 101325Pa## ##\rho = 1000\frac{kg}{m^3}## I am given a piping system, with serie and parallel pipes, they start from one point and go back into one...
  34. P

    Fluid flow over part of an aircraft wing

    Recently, on a conversation with PhD in Engineering, I came to know that if, instead of the whole wing, air/fluid flows over part of it, then that will cause great turbulence and swirl. When I asked him for reference, he said that it can be found in any book on Aerodynamics. But still today, I...
  35. Domenico94

    I How does a fluid behave inside of a spherical cavity?

    Suppose you have a spherical cavity, with a flow of a fluid ( in particular water), entering it from one side. What will happen to this flow? Will it create turbulences? Will speed increase? Will eventual waves entering the cavity be reflected, so creating waves with bigger amplitude? Suppose...
  36. S

    Air resistance in projectile motion

    In lower-division physics classes, air resistance is usually ignored to make the mathematics of projectile motion easier to understand. When air resistance is included, it's often stated that at lower velocities, air resistance is proportional to the velocity of the object, Fair ∝ kv At...
  37. JorgeM

    I Variation of Torriceli's theorem?

    Hi there. Everyone knows about Torricelli's theorem that says about , in a too big container (opened) the speed of the liquid is given by: v=√(2gh) This result is just for containers that have a hole in the side and the fluid goes out perpendicular to the gravity. And also this result is just...
  38. K

    Sound Generation from Fluid Flow

    Hi guys, I am involved in some research on modelling sound from fluids through mirco annuli and i have been trying to get some of the basic fundamentals on generation of sounds from turbulent flow. Unfortunately most of the online literature do not give much details on the physics of such...
  39. dRic2

    Calculating Heat Exchange Surface for Fluid Flow

    Fluid comes in at ##T_1## and comes out at ##T_2## and I know that heat is exchanged with steam at constant ##T_{steam}##. If I want to know the Surface of the exchanger then ##US(T_{steam}-T_{fluid}) = \dot m_{fluid} cp_{fluid} (T_2-T_1)## My question is, since ##T_{fluid}## changes, which...
  40. H

    Difficuilt and/or interesting problems in fluid mechanics

    Homework Statement Can anyone please give me hard and interesting problems regarding fluid mechanics problems such as hydrostatic and air prssure bouyance force and Bernoullis equation(Bernoullis equation problems only for liquids)? I tried looking for them but the ones I found were quite...
  41. F

    I Fluid flow through a pipe constriction - what would you feel

    Hi. Imagine a large pipe 10 m wide through which water is flowing at 10 m/s. You are in the stream flowing at the same speed, two other people are stationary at the entrance and in the middle of the venturi. You flow to the a venturi constriction that is 5 m wide. Apart from the acceleration you...
  42. 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...
  43. M

    Fluid flow through branched nozzles

    Homework Statement I wanted to know if the flow rate and velocity would stay constant or change in nozzles 1,2 and 3 in a incompressible fluid flow through a rectangular duct. (Illustrated image in attachment). Aim is to have the same amount of fluid flowing out of each of the nozzles...
  44. M

    Fluid flow through branched nozzles

    I wanted to know if the flow rate and velocity would stay constant or change in nozzles 1,2 and 3 in a incompressible fluid flow through a rectangular duct. (Illustrated image in attachment). Aim is to have he same amount of fluid flowing out of each of the nozzles. Would the flow rate be...
  45. 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...
  46. MexChemE

    Modeling a multiple inlet piping system

    Hello, PF! I’m trying to model a real piping system, which has multiple inlets and one outlet, so I can’t use Bernoulli’s equation. Instead, I’m planning to use the generalized macroscopic energy balances as shown in BSL, which allow for any number of inlets and outlets. However, first I want...
  47. 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 /...
  48. H

    A Azimuthal Symmetry in fluid flow

    I am looking at evaporating droplets and I am interested in looking at when there is azimuthal symmetry, and I need to write the Navier-Stokes equations for this. I just set all \varphi terms in the spherical case equal to zero right?
  49. C

    Cellular Automaton, Random Walks, and Fluid Mechanics

    Hi I'm trying to understand a paper that approximates the solution to Burger's equation (1D Navier Stokes) by a doing a one-dimensional cellular automaton simulation. I'm having a hard time understanding how all these topics connect. I have seen and walked through various demonstrations that...