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. RandomDude123

    Fluid Dynamics - Calculating Coefficient of Drag

    How would one calculate the drag on a projectile (in this case a 1cm3 cube) that was launched at 0°. The vertical drop, initial velocity, distance, and time (taken to travel distance) where measured. I want to say that I could compare these experimental drop (bellow hight that projectile was...
  2. G

    When will the house be flooded?

    Homework Statement [/B] A simplified schematic of the rain drainage system for a barn is shown in the figure. Rain falling on the slanted roof runs off into gutters around the roof edge; it then drains through several downspouts (only one is shown) into a main drainage pipe M below the...
  3. Wanna_be_Feynman

    Distance a bullet will travel while shot underwater

    Homework Statement hey I am trying to work out the problem: If I shoot an ak47 underwater with 7.62x39mm ammunition, how far will the bullet travel before coming to a stop? Homework Equations The equation that I have used to find the drag force is the drag equation: F =1/2 p*A*C_d*v^2...
  4. Z

    Fluid Dynamics question -- compressibily of brake fluids "oil"

    As part of a racing community, there is a discussion going on that talks about compressibility of brake fluid. the Street car versions have a value of 6.5E-05 and the racing stuff is 4.5E-05 both at a pressure of near 5000psi. there is talk about the difference of the racing fluids which...
  5. Alfreds9

    Is a motionless liquid-floating object possible?

    1. Homework Statement Do you think it's possible for an object to be relatively motionless if floating on rippled water surface? Could this be achieved by have it float inside one (or several nested) water/oil-containing containers? 2. Homework Equations ES = - n2(k-m)2 Lucassen's...
  6. W

    Bernoulli equation exercise from Fanning and Moody

    Homework Statement I would really appreciate it if you could give me a hand with this exercise, not sure on what I've done. Data: Moody: L=55*10-3m D=10-1m k=0.0002m Homework Equations ##Re=\frac{D*u*ρ} {μ}## ##Re=\frac{4*m} {pi*D*μ}## Relative roughness ##ξ=\frac k D## where k=rougness...
  7. R

    B Lenovo Thinkpad E460: Ideal Laptop for Research and Code Writing

    Hi, I am starting at a CDT (Integrated MSc, and PhD) next month in Fluid Dynamics, a large part of my work will include running simulations and writing code. I am in need of a new laptop, I am going to dual boot windows and fedora scientific. Between the student discount and mobility of the...
  8. J

    Diameter of hole vs time to submerge

    Hey everyone, I'm new to physics forums and I would really like some help with my physics report. For my high school physics topic I have chosen an experiment where holes with differing diameters are drilled into the centre of the bottom of PVC pipe caps and the time taken for the each cap to...
  9. W

    Bernoulli equation with losses dilemma

    Homework Statement Hello,Could you please lend me a hand with this problem?I would really appreciate it. Question:[/B] Their Answer: KL=2*0.75(2 elbows) D=5*10^-2 m ;f=0.001(fanning friction factor) Assumptions I made: Point 1 which is at the top of the liquid in the tank: h1=23 m...
  10. VMP

    Energy fighting in combat flight sims

    Hello everyone, I have a question regarding energy fighting. Suppose you're flying a plane and you want to boom and zoom a target that is lower than you, flying at similar velocity. What is the optimal* way of diving and then zooming up again. *optimal wrt energy conservation. I'm aware of the...
  11. N

    How High is the Water in the Bottle Based on Fluid Dynamics?

    Homework Statement A water bottle has a tap tube at the bottom. The diameter of the valve opening is 1 cm. If you turn on the tap, the water drains out with a velocity of 1.4 m / s. If the air pressure in the bottle is equal to the atmospheric pressure outside it, how high the water than in the...
  12. W

    Heat transfer and Fluid Flow Struggling Problems

    Homework Statement Hello, I am struggling with this heat transfer and fluid flow problem.I would really appreciate if someone could have a look over what I have done on it. I am not sure if what I have done is correct ,I would really appreciate if you could tell me if it is correct or wrong.And...
  13. N

    Fluid dynamics continuity equation

    Homework Statement Through a (cylindrical) heating tube, warm air has to flow with a velocity of 3m/s in order to heat a rectangular spacewhich is 12 m long, 10 m wide and 2.5 m high. How large the radius of the tube should be if the air in the room get refreshed every 15 minutes ? Assume that...
  14. H

    Question about pressure drops due to friction and valves

    If I'm designing an injector for a rocket engine, I have a specific mean flow rate (m/s) that must be met due to the pipe diameter and the required mass flow rate. I've calculated all the pressure drops due to lost work from friction, valves, and orifice geometries (not from change in area, but...
  15. Elien

    Fluid Dynamics in Pipe Lines Problem

    Hello! Please help me understand whether I'm going to the right direction with the solution or partially wrong or completely wrong. I have a basic Fluid Mechanics course at the uni, the following problem is from a past exam my teacher gave us to practice before the exam, so there're no answers...
  16. S

    Pump used to halve the time taken by fluid to flow out

    Homework Statement The tank in picture has section ##S_1## and it's linked with a tube of section ##S_2=\frac{1}{\sqrt{17}} S_1##. The tank is filled at an height ##h## and this level is kept constant by a sink ##R##, in such way that the exiting volumetric flow rate is ##Q=0.3 m^3/s## and...
  17. S

    Problem about Hagen-Poiseuille law and pump

    Homework Statement A tank contains an incompressible liquid of density ##\rho = 1. 4\cdot10^{3}kg / m^3 ## and viscosity ##\eta=1. 4\cdot10^{-3} Pa\cdot s##. The tank is open at the summit and the level of the liquid is kept constant through a sink. At the base of the tank there is a circular...
  18. Qais Hassan

    Confused about Reynolds Number- Fluid Mechanics

    Hi, I am working on the laminar flow and during my calculation at the outlet of my nozzle my Re was even greater than 120,000 however my other calculations seemed legit to me. And someone told me that I am calculating the Reynolds number of an open channel and for that flow can remain in laminar...
  19. K

    Why is the velocity of fluid on top a hydrofoil higher than on the bottom?

    I am trying to learn how hydrofoil works. A big part of it is Bernoulli's principles. I found this http://web.mit.edu/2.972/www/reports/hydrofoil/hydrofoil.html on MIT webisite. There are two explanation for how it works: 1. The conservation of linear momentum or Newton's third law.If water...
  20. I

    How does the change in area affect the velocity of helium gas in a vacuum?

    Hello here is a schematic of the problem: http://imgur.com/CgcybVT A stream of helium gas will be used to carry aerosolized particles. I am assuming conservation of mass (and mass flow) The mission is to find the exit stream velocity of the gas. For the time being, i am assuming the weight...
  21. M

    Modeling 2D vs. 3D Flow in a Circular Pipe

    Hi everyone! I have the following problem. I have a two phase flow in a circular pipe and I want to model it. I need to decide and justify whether the model should be 2D or 3D. For the moment, I can say only one thing: considering z-axis in the length direction (that it is the dominant one) I...
  22. faradayscat

    U-shaped tube fluid dynamics

    Homework Statement [/B] Suppose we have a u-shaped tube filled with water, with oil added at one end which disturbs the equilibrium. Now say one end is blocked off and the other is exposed to air flow which reduces the pressure above the water and causes the water to climb back to equilibrium...
  23. Umair Shariff

    Fluid Dynamics: Orthostatic Blood Pressure Equation

    Hi everyone, I have been hunting all over the Internet for an explanation to changes in the blood pressure when sitting, standing or lying down. I know the complex mechanisms that are involved but I need an equation for an ideal system with the heart in the middle and the pressure that needs to...
  24. Arsen

    Fluid Dynamic. Force on particles in carrying fluid (liquid)

    Good day to all! I have a question : We have a flowing fluid ( liquid ) with known pressure, flow in the pipe ( pump is pumping it). There are some spherical microparticles in the liquid, let's say 10-15 microns. I want to create force to stop them moving! Will the pressure force be in the form...
  25. Y

    Question: pressure inside an object submerged in water

    I'm doing a question relating to the pressure inside on object submerged in water. Here is the question: A tube, height 1.2m, is submerged vertically in the ocean where the waters density is 10^3 kg/m^3. A diver initially holds the tube vertically directly on top of the water. He then dives to...
  26. M

    Fluid mechanics civil engineering

    As shown in the attached image, a tank has an inclined wall at an angle of 450 to the horizontal. On this wall, there is a 1m square door that is hinged at A and has a simple latch at B. The distance between A and the free surface of sea water measured along the inclined wall is 2 m. (Specific...
  27. Tazerfish

    I Oscillations and Waves in Fluids

    I first wanted to ask a very specific question: There is something called the Brunt-Vaisala frequency. It describes the frequency of oscillation in a fluid with a density gradient. Because if a parcel of fluid is pushed up or down from its stable state it will oscillate around it. What i don't...
  28. S

    Volume flow rate variation of a free air jet

    Hi, I recently did an experiment whereby we investigated the velocity distribution of air expelled from a round nozzle whose diameter, D, was 30mm. We have been asked to calculate the volume flow rate at distances of 2D, 6D and 10D along the centreline. We found the flow rates to INCREASE...
  29. Narayanan KR

    I Strange Magnus Force in a Whirlpool

    1. Imagine a big river with water flowing constant velocity , assume there is a whirlpool at center as shown in the figure. 2. Because of the magnus force the whirlpool should move towards left or right towards river bank depending on the spin, but it does't happens it just stays fine in its...
  30. G

    Engineering Fundamentals of Fluid Dynamics

    I'm looking for a book to really help hit home what my fluids class is teaching because I'd like to eventually learn the Navier Stokes Equation. Syllabus: 1. Introduction, definitions, fluid kinematics 2. Hydrostatics, including nanometers, Bourdon gauges and pressure transducers 3. Control...
  31. S

    Solve question using Excel or Matlab

    water moves over a stationary horizontal flat plate of one-meter length. if velocity of water is 1 m/s, draw boundary layer and friction coefficient versus x for this plate. hint: start your curves from x=1cm.Professor asked us to do it in Matlab or Excel and I'm not sure I understand how to...
  32. T

    I How Can Boundary Layer Suction Reduce Flow Separation in Pipe Expansion?

    I have a question about the following scenario involving a flow separation issue in a pipe expansion The angle of the expansion is 30* - doubling the diameter from 1D to 2D We can consider this flow fully developed with a Reynolds of 5000+ Associated with this expansion is a head loss...
  33. Max KL

    Can I Learn Fluid Mechanics for Hobby Interests?

    Hello ! I'm a new member here and want to learn about fluid dynamics/ mechanics for several hobby interests specifically to do with impellers and flow rates. Look forward to becoming part of the community! :):)
  34. S

    I Solving Navier Stokes & energy equations with different coordinates

    Hi all I am conducting a fluid analysis on water flowing through a subsea pipe. Having used navier stokes equation, i derived the equation for velocity in the r-direction (using cylindrical coordinates. But when initially solving the energy equation to determine temperature distribution I...
  35. D

    Design of a Lightweight Waterproof (IP 67/68) Winch

    Hello, I am currently designing a lightweight waterproof winch system using off the shelf electrical or hand winches. My problem is that most electric winches that are waterproof are too heavy (design weight limit ~10lbs) and have a much higher force rating than needed (design max force ~500...
  36. S

    Pressure vs speed in an immersed object

    Hi all, In case of a fully immersed and standing object (i.e. a plate or sphere) in a steady moving fluid (i.e. water or oil), what is the type of the mathematical relationship between the pressure of a point of the object? Might exponential be right? I need this information because I measured...
  37. S

    MHB Combination of field and particle methods for fluid dynamics

    hello, in numerical fluid dynamics there are field methods like finite-volume, finite-element, etc. and particle methods like Smoothed-Particle-Hydrodynamics – SPH and others. Both approaches have advantages and disadvantages depending on the application. Both, in principal completely different...
  38. L

    Does an eductor work on the Bernoulli equation?

    What i know is that the Bernoulli equation is applied only along a streamline. Is it correct to say that eductors work on the Bernoulli equation?
  39. L

    I What Causes Jets to Entrain Mass?

    I have done a research on google but still i can't find a reason why air is entrained in jets. An example of a jet is the fuel jet in a combustion chamber of a diesel engine. I suspect it has to do with the conservation of mass principle. Thank you in advance.
  40. L

    Why is mass entrained in jets and plumes?

    Could someone explain why mass is entrained in jets and plumes?
  41. Mingsliced

    Centrifugal/Reciprocating Pump Efficiency

    Homework Statement It is proposed to pump 1500 m3 of a liquid (density 1100 kg m–3) each day through a total head of 10 m (including all losses) by using either a centrifugal pump or a reciprocating pump. The centrifugal pump discharges 2.0 m3 min–1 when driven by an electric motor supplying...
  42. datf

    Solving Fluid Dynamics Questions: Pump Similarity Laws and Efficiency Comparison

    Hi guys, please help me with these questions. I've been racking my brain for days but I'm not sure of the answers. 1) (Assume that pump similarity laws are valid and that the effects of Reynolds number (Re) are small.) A centrifugal pump operating at speed N is combined in series with an...
  43. MrGianmarcoD

    I Hydrost Pressure Integration Problem (Environmental Physics)

    Hey guys! I'm working on a problem for which i somehow just can't figure out what I'm doing wrong. This is the problem: I think I've figured it out, but somehow i think i make an error with the maths. First of let's determine the equation for the temperature (in Kelvin): $$T(z) =...
  44. Mingsliced

    Fluid Mechanics - Head Loss Due to Friction

    Homework Statement This is simply a sanity check concerning the system described and attached. My concerns are detailed within my attempts at the solution. Any guidance will be greatly appreciated! The diagram attached represents a process for which a pump and associated pipe work require to...
  45. R

    Why does friction factor decrease with Reynolds number?

    As the flow rate increases frictional force increases but friction factor(Darcy,Fanning) decreases with Re. Can anyone explain what is the concept behind it?
  46. M

    Diesel injector sac pressure calculation

    I am trying to calculate the nozzle sac pressure required to deliver 60mm3/ms of diesel fuel into a pressurised cylinder (19MPa). The nozzle has 5 delivery holes of diameter 0.157mm and the discharge co-efficient is 0.87. The sac diameter= 0.7 mm and the sac volume= 0.12mm3. I have tried to use...
  47. MexChemE

    Boundary layer thickness confusion

    Hi, PF! Recently, while reading chapter 6 of Incropera's Fundamentals of Heat and Mass Transfer I got into a confusion regarding the velocity boundary layer. The book first states that, as the flow becomes more turbulent, the boundary layer gets thicker, as indicated by both figures attached at...
  48. tomdodd4598

    I What is a "Blunt Form Factor"?

    Hi there - a very simple question. On Wikipedia, it is stated that for the drag equation to be accurate, "the objects must have a blunt form factor and the fluid must have a large enough Reynolds number to produce turbulence behind the object". My question is what is a 'blunt form factor'? I...
  49. Alettix

    Choosing Reference Points in Bernoulli's Equation for Fluid Flow

    Hello! I have encountered some trouble with choosing the right reference points when using Bernoulli's equation and I would be glad if you could help me sort it out with this made up example. :) 1. Homework Statement There is a large, open, cylindrical water tank with a cross section area of...
  50. B

    Finding out Shear rate of a bent pipe which has different bend radius values

    which has different radiuses at both end. Its actually two pipes merging after the entrance going straight and somewhere close to middle of the pipe it's bent 90°. So for simple pipes it's =4*Q π*r^3 But what for the pipe I...
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