Reynolds Definition and 117 Threads

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”

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?

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...

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?

∂/∂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)

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")...

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...

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...

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?

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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?

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...

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...

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...

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...

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.

"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...

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...

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...

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...

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...

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?

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?

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...

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

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...

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

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"...

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...

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...

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)...

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...

I completed 4a successfully, and with 4b, i have 2 queries: a)why can't I let Reynolds # equal to 2.19 x 10^5 (from part a) then simply sub v=4 instead of 5m/s and rearrange for viscosity? I tried it this way first and got a very wrong answer. Why do we, essentially, need to work backwards to...

I have been given the assignment to model the entrance of meteorite in Earth's atmosphere, and ultimately it's impact with earth. The meteorite weighs 0.025kg, and has the speed 28.6km/s 50km vertically above the surface of the earth, giving it a Reynolds number of approximately 3.5*10^7. The...