What is Fluid mechanics: Definition and 754 Discussions

Fluid mechanics is the branch of physics concerned with the mechanics of fluids (liquids, gases, and plasmas) and the forces on them.:3
It has applications in a wide range of disciplines, including mechanical, civil, chemical and biomedical engineering, geophysics, oceanography, meteorology, astrophysics, and biology.
It can be divided into fluid statics, the study of fluids at rest; and fluid dynamics, the study of the effect of forces on fluid motion.:3
It is a branch of continuum mechanics, a subject which models matter without using the information that it is made out of atoms; that is, it models matter from a macroscopic viewpoint rather than from microscopic. Fluid mechanics, especially fluid dynamics, is an active field of research, typically mathematically complex. Many problems are partly or wholly unsolved and are best addressed by numerical methods, typically using computers. A modern discipline, called computational fluid dynamics (CFD), is devoted to this approach. Particle image velocimetry, an experimental method for visualizing and analyzing fluid flow, also takes advantage of the highly visual nature of fluid flow.

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  1. V

    Aerodynamics: flow separation's effect on lift and drag

    In aerodynamics, how does flow separation reduces the lift and drag of a wing at the same time?
  2. A

    Airbag Simulation using LS-DYNA: start from filled airbag

    Hello! I'd like to model the impact of an object on an inflated air cushion (effectively an airbag) at rest in LS-DYNA, however all the tutorials I see start from a deflated airbag. I would like to skip this computation if possible to save computing time, since I would have to run the simulation...
  3. 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...
  4. D

    Quantitative Risk Assessment Of buried crude Oil Pipelines

    Currently, I am working on a project that necessitates a quantitative risk assessment (frequency analysis and consequence analysis) of buried crude oil pipelines, considering specific hazard scenarios. Most of the hazard analyses I have come across were conducted on gas pipelines, and there...
  5. D

    Time to empty gas cylinder (problem worked, but would like feedback)

    Hi everyone I am trying to solve a specific problem. I already have an idea on how to solve it, but I hoped someone else could tell me if my general approach is somewhat sensible or not. So I would really appreciate some feedback. Situation: A long, narrow cylinder filled with gas that is at...
  6. lifeisstrange444

    Fluid flow and elevation vs pressure

    Hey guys! does anyone have a graph of the relationship between elevation change and pressure loss in pipes? I currently have experimental data of a negative gradient graph. know it's theoretically correct however, I just need supporting research for this - have tried finding everywhere but...
  7. Florian Geyer

    B The application of Newton's laws to fluid equilibrium

    Hello respected members, I have been studying Sears and Zemansky's university physics, and I have encountered the following statement. I could not understand it well, so my question is: Why is fluid equilibrium based on Newton's first and third laws? Here is my try: - Newton's first law...
  8. R

    Programs Universities for Research in Dynamical Systems of Fluids

    Hi everyone, (this is my first post so be gentle) I am currently getting my masters is mechanical engineering, was admitted to aero Ph.D. programs as Vtech, MSU, and Cinci last year but decided to get masters locally and apply to "better" schools (UofM) for next cycle with a better resume and...
  9. RCH

    What kind of pump can do this?

    Hello -- I am working on a project where I need to recirculate a fluid which has a large quantity of glass spheres of say, 1mm diameter suspended in it, but without the pump crushing the spheres. I would appreciate any advice. To give a simple description of the desired function: it will be a...
  10. chandrahas

    A Why are the Navier-Stokes equations inconsistent in this case?

    Consider the case of a one-dimensional incompressible, non-viscous fluid flowing down a vertical pipe under the influence of gravity. Since we assume the flow is constant along the cross section of the pipe from the one dimensional assumption, let us denote the velocity of the fluid down the...
  11. E

    Why is solid density used in this thermodynamics problem?

    Callen asks us the following question in his famous textbook: I have answered as follows: However, I get the wrong answer and, in fact, the correct answer obtains from using ##\Delta P = -\rho_s g h##; that is, using the solid density for the change in pressure. Now why on earth should this...
  12. Valour549

    Fluid Mechanics Force Body Diagrams

    Let me start off by saying that I have found (or is given) all of these: ρ, Q, V1, V2, P1, P2, A1, A2 (V being the velocity here). So no problem with Bernoulli or the Continuity equation calculations. I am just struggling with drawing the FBD in order to evaluate the axial force, Fx I know we...
  13. K

    Engineering How Does Cup Anemometer Design Utilize Fluid Mechanics Principles?

    First, this class uses Frank White's Fluid Mechanics textbook. This particular problem is taken straight from chapter 7, which is on "Flow Past Immersed Bodies" and is basically focused on external flow, geometry effects, and boundary-layer conditions. So I imagine that the problem makes use of...
  14. N

    I A specific case of an exception to Archimedes' Principle?

    First post on this forum, hopefully in the correct category and conforming to forum rules. Will the object in below scenario move upwards, downwards or will it remain stationary? An object is submersed in a container 'A' which contains a fluid 'B' (e.g. water) The trapezium shaped object...
  15. Austin_Tx_Rockets

    Does the discharge coefficient of an injector depend on the fluid?

    The discharge coefficient is the ratio of the actual discharge to the ideal discharge and can be measured experimentally. If one were to experimentally measure the discharge coefficient using water, would this value be constant for all incompressible fluids? What does the discharge coefficient...
  16. G

    I How can I integrate variable velocity in fluid mechanics?

    Do you know of any place where I can look up things about the momentum (linear momentum) in fluid mechanics? It's just that when I have a variable velocity and it has to be integrated, I don't quite understand how to do it. I have looked for videos and things and I can't find that they are...
  17. G

    Fluid mechanics: water jet impacting an inclined plane

    I was looking at an example of fluid mechanics and I don't understand this. Statement figures: CONTINUITY EQUATION $$\left. \dfrac{dm}{dt}\right]_{MC}=(\dot{m}_2+\dot{m}_3)-\dot{m}_1=0$$ $$\dot{m}_1=\dot{m}_2+\dot{m}_3$$ $$\rho c_1A_1=\rho c_2A_2+\rho c_3A_3$$ $$\rho c_1 h1=\rho c_2 a1+\rho...
  18. V

    Why are the three different surface tensions in the directions shown?

    I think in the explanation below a very small element of the liquid at the line of contact between the horizontal solid surface, air outside the liquid and the liquid itself is being taken, and forces acting on such a small element are being shown. This very small element is to the left of shown...
  19. V

    Calculating Pressure in a Flowing Liquid

    According to what I get, the problem clearly says that ##p_2= 500 ## kPa. I can also see that ##p_1 > p_2## since higher velocity means lower pressure in a flowing liquid and we can say that ##v_1<v_2##.
  20. Gustavo Reis

    I Air Resistance: Exploring Hooke's Law

    Basically the air works like a spring, it always tries to get back to its resting state. And it's like Hooke's law, the more it deforms the more elastic potential energy it has. That's why the faster you are, the air resistance is greater. Thinking in this way, I imagine that in fluid mechanics...
  21. 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...
  22. samy4408

    I Relationship between viscosity and velocity in fluid mechanics

    hello, I read in a lecture paper about fluid mechanics that velocity is not related to viscosity, i found this odd and i think it is an error , can someone confirm that?
  23. M

    How to find velocity of gas pump flowing into car tank

    The general balance equation is as follow: d[m{u+gz+v2/2)sys=(u+gz+v2/2)dmin-(u+gz+v2/2)dmout +dq+dw. I understand that I would take in consideration the cross sectional area as well as the mass flow rate. However I can't figure out what else to consider as if atm pressure should be considered...
  24. lavalite

    Thin-walled sphere and fluid mechanics question

    Suppose you had a thin-walled sphere fully submerged in a liquid. The sphere is filled to the equator with a liquid of sufficient density to reach buoyant equilibrium. Will the lateral cross-sectional areas of the thin-walled sphere experience tensile stresses in the longitudinal axis? Why or...
  25. AJSayad

    Engineering Experimental Fluid Mechanics Vs. Computational Fluid Mechanics

    Hi everyone, I just started graduate school and I've been working in an experimental fluid mechanics lab. We have a shock tube and run tests on studying supersonic and hypersonic airflow under different conditions. We use Schileren imaging and transducers to take measurements during tests. We...
  26. A

    Fluid mechanics - Additional liquid capacity due to compression

    A cylindrical tube (diameter = D, width = L) is completely filled with a liquid (density = ρ). A pump pressurizes the system with a pressure P. Consequently, 1) the solid tube is compressed and deformed according to Hooke's law (σ = ε.E), and 2) the liquid is compressed and deformed, following...
  27. A

    I Drag equation - relative flow velocity

    Hello! I have a question about aerodynamic drag. It sounds simple but when trying to understand why the relative velocity can be used in calculations I have some trouble. The formula is 0.5*rho*u2*cd*A where u is the relative velocity between the object and the fluid. The cd value depends on the...
  28. A

    Engineering Need Advice on Fundamentals of Fluid Mechanics Textbook

    I would like to buy a Fundamentals of Fluid Mechanics for Engineer textbook. I have 2 options, they are: 1. https://www.amazon.com/dp/0133521702/?tag=pfamazon01-20 2. https://www.amazon.com/dp/0132788128/?tag=pfamazon01-20 Can someone please tell me which one of above Fluid Mechanics textbook...
  29. mohamed_a

    I Acoustic wave properties and momentum

    I have read about doppler effect in acoustics so i searched for the relation ship between wavelength of wave produced by linear movement of body and its momentum along with other dependent variables such as density of fluid (leaving acoustics for a second) and temperature but souldn't find a...
  30. Franklie001

    Engineering Fluid mechanics question and the Bernoulli Equation

    Good afternoon, I am struggling to find the solution at Q2 and Q3. For Q2 the absolute pressure at point 1 is at the bottom of the tank, so do i need to use the formula P=Patm+qgh ? If using this formula I've got a bigger number than 100Pa. Same issue for Q3, isn't the pressure at point 2...
  31. J

    A Is fluid mechanics (aerodynamics) still being discovered?

    Is fluid mechanics,particularly aerodynamics still being discoverd (like math for example) or everything has already done long time ago?
  32. A

    Is Throwing a Knife with No Spin Actually More Effective?

    They say that a rotating knife thrown is more dangerous than a knife thrown straight I find it weird If the knife is rotating, it will experience more air drag than if thrown straight which will also depend on plane of rotation(For some reason, I don't know, it experiences more drag if...
  33. jdgotts

    I Help Regarding Application of Bernoulli in a Boundary Layer

    Hey all, I recently took an aerodynamics exam that included the question "Please Explain how the Bernoulli Equation can be Applied Inside a Boundary Layer". Now, it is my belief that the Bernoulli equation, defined by my textbook as P+0.5ρV2=ℂ, requires inviscid flow to be properly applied...
  34. AJSayad

    Grad School Flow Simulation PC Build

    Hey everyone, I'm coming to the end of my Mechanical Engineering B.S. degree and I've been in the process of applying to mechanical and aerospace PhD programs. I want to do research in fluid mechanics; I have some expereience in hypersonics from a Research Expereince for Undergraduates NSF...
  35. T

    Why Does Rain Create Waves on My Street? - Investigating Fluid Mechanics

    Hello (Perhaps this should be in physics, but perhaps it should be mechanical engineering (fluid mechanics). I attach a picture of water running down the street near my house. The street is a nearly constant 15 degree incline that goes on for about 1 kilo-meter with no speed bumps. The...
  36. knotted_pine

    Engineering Finding arc length of a pipe between two tanks

    I can't seem to find the arclength between A and B. I tried using L = integral (0.6 to 0.4) of sqrt (1+ (dz/dx)^2) to no avail. Would it be roughly similar to 400 km (the length from A to B) since the change in elevation could be considered negligible? Furthermore, how might I go about...
  37. M

    Turbulence of square fractal grid

    Hi all, Whats the significance/application of square fractal grid turbulence studies?
  38. R

    I Minimize supported weight of a water pipe

    I’m trying to calculate the weight I have to support at one end of a pipe with flowing water. So suppose you had a water pipe that extended from the ground upwards some distance away both horizontally and vertically, i.e., at an angle. Normally, you don’t have to worry about this issue because...
  39. Angelo Pascal

    Geophysics: Fluid Dynamics Problem

    (a) Write down an expression for the velocity field corresponding to uniform rotation. Find the vorticity corresponding to this flow. (b) Consider a small perturbation u' to the state of uniform rotation with angular velocity Ω, which has the form of a plane harmonic wave u'= A exp i(k·x−ω t) +...
  40. R

    Classical Looking for the absolute best fluid mechanics book available

    Dear physics forum dwellers, Currently on search for an advanced fluid mechanics book that covers all the nitty gritty details. Not looking for general introduction books like Munson, Rothmayer, ... or Cengel that are used in bachelor physics classes or engineering classes. Even after skimming...
  41. AJSayad

    Finding Your Path to the Aerospace Engineering Industry

    Summary:: What is the best way to get into the Aerospace Engineering Industry? Hi everyone, I'm new to the physics forums. My name is Andrew, I'm going to be in my undergrad Senior year in mechanical engineering this coming fall. I've recently been looking into PhD programs and I've been...
  42. binbagsss

    Drop out of PhD in fluid mechanics and switch to Mres in mathematical physics?

    A post doc in an area that differs from my PhD? I am currently doing a PhD in fluid mechanics but want to do mathematical physics tbh. In another thread I got an answer about a user who had done a PhD in accelerator physics and went to do a post-doc in condensed matter, vice versa even, but in...
  43. C

    Intro Physics Best textbook for properties of matter and fluid mechanics

    I am a First Year Undergraduate Physics student. Which will be the best textbook for me to study properties of matter (Elasticity) and fluid mechanics? I prefer a better theoretical understanding.
  44. kmot

    Fluid mechanics - Linearized shallow water equations

    Hi, In a text describing solution to linearized shallow water equations, I am not able to move forward. It's a 1 dimensional shallow water setup. There is a steady state (velocity) and (height of free surface). On top of this steady state there are u' and h' as disturbances. The goal is to...
  45. WhiteWolf98

    Calculating Discharge Rate of Fluid in Circular Area

    This is actually right at the start of another derivation, but I can't understand how the author gets the formula for ##q##. So the discharge per unit thickness is the circumference of the circle, multiplied by the velocity at that point (at ##r##)? I thought the formula for flow rate was...
  46. person123

    Bernoulli Principle For Pitot Tubes

    Here is the setup: Apply Bernoulli Principle to the top (free surface) of the two pitot tubes (1 for static and 2 for dynamic with the points colored in red): $$\frac{p_1}{\rho_w g}=h+\frac{p_2}{\rho_w g}$$ The difference in air pressure would give the following:$$p_1=p_2+h\rho_{air} g$$...
  47. person123

    Parabolic Pressure Distribution in a Jet

    Assume the jet is straight but the radius of the jet varies over it's length (like a jet of water falling which narrows due to gravitational acceleration). Also ignore viscosity. A pressure gradient would be required to accelerate the fluid radially. Because during an expansion transformation...
  48. person123

    Inertial Force in Fluid Mechanics

    According to one explanation, the left hand acceleration terms of Navier Stokes equations are the called the inertial terms. If you were to balance forces on the fluid particle, they would have to be equal and opposite to the forces on the right hand side (pressure gradient, viscous, and body)...
  49. T

    Is this a valid way to calculate capillary force / pressure?

    When figuring out the capillary pressure on a liquid in a tube of a certain cross-section, the typical approach is to consider the Young-Laplace pressure and the curvature etc. I was looking through some of my old notes and I had an equation for the capillary force: fc = γ cosθ dS/dx where γ...
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