What is Reynolds: Definition and 124 Discussions

The Reynolds and Reynolds Company is a private corporation based in Dayton, Ohio. Its primary business is providing business forms, management software and professional services to car dealerships. Its software is used to manage sales logistics at dealerships. It also produces forms used in medicine and insurance.
Reynolds and Reynolds was founded in 1866 as a printer of standardized business forms. It began developing and marketing digital products in the 1960s. This was followed by a major downsizing of the printing division and subsequent advancements in its software products. By the 1980s, Reynolds and Reynolds had won contracts with all of the Big Three automotive manufacturers, as well as some insurance businesses. The company went public in 1961, but was re-formed as a private company in 2006, when it was merged with Universal Computer Systems, resulting in a culture clash between the two companies.

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  1. ergospherical

    B Swimming at the Same Reynolds Number as Sperm: A Reflection on Purcell's Talk

    https://www2.gwu.edu/~phy21bio/Reading/Purcell_life_at_low_reynolds_number.pdf “It helps to imagine under what conditions a man would be swimming at, say, the same Reynolds number as his own sperm”
  2. C

    I Reynolds Number and Turbulence: Why Does Increasing Density Affect Flow?

    hi. I have a question regarding rheology. the Reynolds number increases when density of a fluid increases. so the flow becomes more turbulent. but I wonder why it is that the flow becomes more turbulent when density increases. why is that?
  3. L

    Pressure drag and the Reynolds number

    Ok, I am kind of lost in my fluid dynamics course on a specific topic. I understand the reynolds number and how it works. What i do not get:: if Re = VD/v, and if we increase V(velocity) which in turn will increase the inertial effects of the number, why is it called a pressure drag? pressure...
  4. 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?
  5. R

    Transformation of Reynolds Equation from Cartesian to cylindrical

    ∂/∂x ((ρh^3)/12μ ∂p/∂x) + ∂/∂z ((ρh^3)/12μ ∂p/∂z) = ∂/∂x (ρh (U_1+U_2)/2) + ∂/∂z (ρh (W_1+W_2)/2) + (∂(ρh))/∂t (1) 1/r ∂/∂r (r (ρh^3)/12μ ∂p/∂r) + 1/r ∂/∂θ ((ρh^3)/12μ ∂p/r∂θ) = rω/2 ∂(ρh)/r∂θ + (∂(ρh))/∂t (2)
  6. B

    Nozzle loss coefficient that increases with Reynolds number?

    Hi, I started to think about the drag coefficient of a sphere. At high Reynolds number Cd drops of suddenly when the boundary layer separates. If the Reynolds number is increased further, Cd increases with increasing Re. (I'm thinking about what is referred to as "post critical separated flow")...
  7. curiously new

    I Laminar-turbulent transition and Reynolds number

    Hi all! This is my first post here, so hopefully I am not in violation of any rules or etiquette. I'm looking to derive an equation for Reynolds number as function of pressure for a pinhole leak in a pressurized gas line. The line is regular air and is pressurized to 1 atmosphere and is leaking...
  8. E

    B Control volumes and Reynolds transport theorem

    If we consider a system of fixed mass as well as a control volume which is free to move and deform, then Reynolds transport theorem says that for any extensive property ##B_{S}## of that system (e.g. momentum, angular momentum, energy, etc.) then$$\frac{dB_{S}}{dt} = \frac{d}{dt} \int_{CV} \beta...
  9. S

    Pipe Friction, Reynolds number & Bernoilli's Equation

    First calc reynolds no. Re Flow = 1.5ms-2 Re = (density x mean velocity x diameter) / viscosity = (1007 kgm-3)(1.5ms-1)(0.1m) / 0.002 Pa s = 75,525 = Turbulent flow I used this chart Here And I am getting friction factor of 0.02 Would you agree with this?
  10. V

    I Reynolds Number in Organism-Fluid Interactions

    Recently I read an article that relates fish larval survival to Reynolds number. It is a new and very interesting concept to me. After some researching, the definition "ratio of inertial forces to viscous forces" still confuses me. As I understand it, both are resistant while the former to...
  11. George5356

    Dynamic Viscosity in Reynolds Number

    I am trying to run a calculation to work out the overall heat transfer coefficient of an arbitrary ten plate exchanger where the fluid is not determined using Re=puD/mu where mu is dynamic viscosity. When mu is such a strong function of temperature how should I determine which valye to use, say...
  12. ntdiemai

    Critical Reynolds number and characteristic length

    What are the critical Reynolds number for fluid and characteristic length when a cylinder immerses and then rotates in the fluid (The fluid is initially static)? Please suggest the critical number for the transition from concentric flow to laminar and from laminar to turbulent flow. I would...
  13. J

    Uncertainty - Reynolds number and the friction factor

    Homework Statement Correctly present the table of information. The values in the table are deliberately in a wrong format. The calculated Re values have been analysed to have an uncertainty of ± 0.4% and the calculated f values an uncertainty of ± 0.1%. Homework EquationsThe Attempt at a...
  14. P

    Can Reynolds Number < 70 Cause Turbulence in Elbow Fittings?

    Hello people, If we are working on the flow with reynolds number less than 70 as we all know the flow will be laminar in pipe. Now if the flow continues to flow through elbow fittings like 90 degrees, will we get any turbulence because of the elbow bend ? How to deal with this problem in ansys...
  15. Jeviah

    Aerofoil Reynolds number, meaning of a statement in my homework

    Homework Statement hello, i have been given a piece of homework which is determining the characteristics on an aerofoils boundary layer. In the brief the following statement is made with no context “Aerofoil is flying in chord Reynolds number 0.2x10^6” am i correct in saying that is the point...
  16. stockzahn

    I Exploring Reynolds Vortices: Fact or Fiction?

    Dear all, recently I read in a belletristic book about Reynolds Vortices. In the fictitious story the author writes about special (Reynolds) vortices generated in the whitewater, which can be passed in only one direction by objects of a "critical" density, which then will be kept in the vortex...
  17. G

    Beyond Viscous Drag, Cavitation, Laminar Flow, & Reynolds

    When using Computational Fluid Dynamic (CFD) modeling you are able to see incredible complexity in water energy transfer. The Thermodynamic energy transfer occurs at much higher velocity so it does not apply in most of the cases I am looking at. What are the other parasitic energy transfers that...
  18. A

    At what critical Reynolds number does vortex shedding begin?

    In: "Fluid Dynamics", Chapter 3 (Turbulence), Section 26, Landau and Lifchitz analyze the problem of the stability of a steady flow past a body of finite size. The fluid is assumed to be incompressible and they reach the conclusion that perturbations that deviate from steady flows start to...
  19. M

    How can I calculate the Reynolds number if the particle velocity is unknown?

    Hello, The particle Reynolds number makes me confused, and I hope someone can help me with this, please! Reynolds number is calculated by Re = ρfUD/μ where U is particle velocity, D can be particle diameter, and ρf and μ are density and viscosity of the continuous fluid. How I can Reynolds...
  20. I

    Hydrodynamic forces on a foil, Reynolds number, viscosity

    Hi! I know little about physics, but I am very well educated , with an inquisitive mind. First the context, then my specific question A. Context The practice of windsurfing has brought me to try and understand the principles of hydrodynamics, in order to make my sailing more efficient. As...
  21. M

    Effective Reynolds Number for a swept wing

    Suppose we have an infinite straight wing, using a given airfoil. Also, suppose for simplicity the B.L. is completely turbulent, and M<<1 (incompressible fluid). As we know, the forces per unit length are: L=q⋅c⋅cl, D=q⋅c⋅cd, where cl and cd are the coefficients of the 2D airfoil for the given...
  22. M

    How to replicate a realistic Reynolds number for an airfoil

    Homework Statement Hi I am doing a project of designing and testing a wing in a wind tunnel, the wing is based a cessna 172 skyhawk wing and I am trying to determine what chord length it should be to try and replicate similar reynolds numbers that a cessna 172 wing would experience in real...
  23. D

    Characteristic linear dimension (Reynolds' number)

    How can I choose the characteristic linear dimension? For example in pipe it is its diameter, but on a surface is the length, on a flat plane it can be measured as 4A/P. I was having problems determining the characteristic linear dimension for a diffusion problem in a "rectangular" pipe. I don't...
  24. W

    Reynolds Transport Theorem Derivation Sign Enquiry

    Hi, Our lecturer explained us the Reynold Transport theorem, its derivation , but I don't get where the - sign in control surface 1 comes from? He said that the Area goes in opposite direction compared with this system. I can't visualise this on our picture. Can you please help me understand...
  25. Pete Moore

    Particle Reynolds number / max entrained particle size

    I am not a student; this is for work. Would some kind soul: a) direct me to an online calculator to enable answering the following or b) give me the answer and show how you arrived at it :) or c) advise me of the formula / process by which I can arrive at the answer? THANK YOU! What is the...
  26. U

    Reynolds transport theorem derivation - linear momentum

    I've managed to derive the form of Reynolds transport theorem as a bilance of linear momentum of the system: \left (\frac{\vec{\mathrm{d} p}}{\mathrm{d} \tau} \right )_{system}=\frac{\mathrm{d} }{\mathrm{d} x}(\int_{V}^{ }\vec{v}\cdot \rho dV)+\int_{A}^{ }\vec{a}dm+\int_{A}^{ }\vec{v}\cdot \rho...
  27. M

    Reynolds Transport Theorem and Volume calculation

    I cannot understand the the relation between Reynolds Transport Theorem and Volume Calculation. Volume calculation is an simple, straightforward process which, I think, have much connection between Reynolds Transport Theorem. We calculate volumes in thermodynamics, heat transfer and fluid...
  28. mastermechanic

    Characteristic lengh in Reynolds number

    As we know $$Re= \frac{ρ.v.l}{μ}$$ The characteristic length (l) is said to be representative of the problem but according to what should we choose this length? I mean if we want to calculate Reynolds number of a wing of plane, should we choose the length or the width?
  29. Jehannum

    I Can someone explain this equation for Reynolds' number?

    The following is quoted from British Standard 6891:2015, the standard for the installation of domestic gas pipework: "In the UK, the Reynolds number is taken to be equivalent to: 25 043 x Q/d for natural gas; and 83 955 x Q/d for LPG." [Q = flow rate, cubic metre per hour, d = pipe...
  30. EnumaElish

    Timeline jump in Alastair Reynolds' Redemption Ark

    I have been reading Reynolds's space opera Redemption Ark. In it, the villain Skade attempts to have her ship make a "state 4" jump, meaning jump to a faster-than-light speed. At the heart of the jump is a machinery that creates and contains a state 4 quantum vacuum. A state 4 vacuum is...
  31. EternusVia

    I Interpretation of the Reynolds Transport Theorem?

    Background: I am taking an undergraduate fluid mechanics class. I seem to have a misunderstanding with my interpretation of Reynolds Transport theorem (RTT), which I have written below: $$\frac{DB_{sys}}{Dt} = \frac{\partial}{\partial t}\int_{CV}\rho bd V +\int_{CS}\rho b \vec{V}\cdot...
  32. F

    Is this definition of Reynolds' Transport Theorem correct?

    One thing I find frustrating when trying to get a handle on this theorem is the number of different forms presented in the literature. I understand this to be due to it being very general theorem applicable to many different contexts. Not that the world needs a new, slightly different looking...
  33. F

    I Reynolds number of washing machine like object

    What would the reynolds number be for a closed pipe spinning like a washing machine? would the characteristic length be the diameter... if so why. Everything I have read is so vauge on this. How can I determine it for strange situations? Can I skip it and figure out if flow is laminar or...
  34. Jimmy

    News Debbie Reynolds: Beloved Actress and Singin' in the Rain Star Dies at 84

    http://www.nytimes.com/2016/12/28/movies/debbie-reynolds-dead.html Debbie Reynolds, the wholesome ingénue in 1950s films like “Singin’ in the Rain” and “Tammy and the Bachelor,” died Wednesday, a day after the death of her daughter, the actress Carrie Fisher. She was 84.
  35. MaxKang

    Reynolds number & Mach number for flow regime

    "An adverse pressure gradient strongly favors transition to turbulent flow. In contrast, strong favorable pressure gradients (where p decreases in the downstream direction) tend to preserve initially laminar flow." "High values of M∞ and low values of Re tend to encourage laminar flow" Looking at...
  36. M

    Understanding the Importance of Particle Reynolds Number in Fluid Dynamics

    Hello, The particle Reynolds number makes me confused and I hope someone can help me on this please! Normally (as I read in every books and papers) that when a bubble or drop rises in a fluid, the bubble/drop Reynolds number is calculated by: Re = ρUD/μ where U is particle velocity, D can...
  37. H

    Why Reynolds Stress vanishes on boundary of closed volume?

    The rate of working of the Reynolds Stress can be written as: where ui is the fluctuating velocity and Ūi is the time-averaged velocity. It is stated in the textbook that, if we integrate the above equation over a closed volume V, the divergence term on the left integrates to zero since τRij...
  38. H

    Chaos & Scales in Turbulent Flows

    Suppose you want to solve the Navier-Stokes equation for an incompressible turbulent flow. This is, in principle, possible. However, for higher Reynolds number, this isn't really feasible since the smallest eddy sizes are really small. First question 1) Why would this prevent you from...
  39. 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...
  40. 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?
  41. C

    Relationship between Mach number and Reynolds number

    Is there any correlation between Mach number and Reynolds number? Both of these nondimensional numbers involve speed, but they don't seem all that related other than that. For high speed flow, we have high Mach number. Is it incorrect to say that "generally" high speed flow is turbulent?
  42. K

    Understanding the Splitting of Velocity Fields in Reynolds Averaging Equations

    Okay, so the RANS equations use the idea that we can generate a statistical equation of motion from the Navier Stokes equations by using the idea that the velocity field is split into a mean field and a fluctuating field. I've had a great deal of trouble understanding this. From a purely...
  43. J

    Reynolds transport theorem (1st year undergrad fluids)

    hello all, I just wanted to check my worded interpretation of this otherwise messy result is ok:
  44. S

    Wall effect on falling sphere of small Reynolds number

    If I were to drop a sphere down a tube of fluid. What are the effects of the wall of the tube on the sphere? Assuming the sphere has an extremely low Reynolds number of less than 1. Is it right to say that the ratio of the radius of the tube and the radius of the sphere has an effect on the...
  45. H

    The Prefect by Alastair Reynolds: A Thrilling Sci-Fi Tale

    The Prefect by Alastair Reynolds. Very well crafted. The usual good-guys-bad-guys shtick.
  46. S

    Trouble calculating the Reynolds number

    Hi, I am having trouble calculating the reynolds number for 2 spear shafts underwater. The two shafts vary in diameter and velocity. The tips are identical, stream lined to a fine point so the flow should be laminar. Both spears are 1.9304 m long. The diameters are 11/32" (8.73125mm) and 3/8"...
  47. R

    Fully developed flow, Reynolds number

    Hi, For my experiment I was asked to determine the length of the tube for a fully developed flow to occur ( Entrance length as shown in the attachment) , with the following flow parameters. Flow rate : 1, 5, 15 lit/min Fluid: Water Tube Id: 1 inch. My question How do I find out the length of the...
  48. Mr.hev

    Calculating Reynolds number for a wind tunnel

    Hi All! as you can see I'm new here! i signed up in order to ask for a wee bit of help with my thesis! (now don't get me wrong I am not exactly asking anyone to write it for me!) I've found myself at a small bit of a loose end here, as a mechanical engineering student i am perfectly capable of...
  49. dragioden

    How is the head-flow curve dependant on reynolds number

    Homework Statement i trying to figure out why the head-flow curve changes at the speeds of 90, 80 and 70 revs and was told that i might want to look into reynolds number for this as the head coefficient is somewhat dependant on this. Homework Equations Ch=gH/(Nd)^2 Cf=Q/Nd^3 pi=f(Q/Nd^3, re)...
  50. M

    Understanding the Reynolds Number: A Guide

    Homework Statement I don't fully understand the Reynolds number and it has arisen in a problem. It says: Fluid with viscosity µ and density ρ fills the gap between two parallel plates at z = 0 and z = h. The upper plate at z = h moves with speed V in the x direction, while the lower plate at...
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