# 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. ### 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. ### 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. ### 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. ### How Do You Calculate the Flow Rate of Oxygen in a Pressurized System?

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. ### 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. ### 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. ### 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...
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32. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### Understanding the Reynolds Number

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...