# 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. ### 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. ### Biology Equations governing cavitation, flow speed, and delta vapor pressure...

Looking for the flow speed for cavitation to occur
3. ### 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...
4. ### 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...
5. ### 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...

31. ### 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...
32. ### 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}##...
33. ### 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...
34. ### 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...
35. ### 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...
36. ### 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...
37. ### 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...
38. ### 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...
39. ### 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...
40. ### 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...
41. ### 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...
42. ### 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...
43. 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...
44. 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...
45. 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...
46. ### 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...
47. ### 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...
48. ### 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 /...
49. ### 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?
50. ### 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...