Reynolds Definition and 117 Threads

Hi guys, I'm working on a project for school and I have measured the influence of the angle of attack, the wingspan and the speed of the air on the lift force the wing is producing. Now I have the question what these data say about real wings from planes. I've already red it has something to do...

For my senior design project, I have to reduce the aerodynamic drag of a truck and trailer. I am doing CFD simulations and wind tunnel testing. The dimensions of the wind tunnel (test section) are 94 in long, 13.5 in tall and 20 in wide and a cross-sectional area of 270 in^2 and it could go up...

Hi Guys, I've just started a HND Building Services Engineering course (for Work) and I have been given my first assignment for hand in on the 11th Nov 2014. I've not completed any Maths or Physics since Secondary School - 18 years ago (and didn't really pay attention then!) and I'd appreciate...

Hi people! I'm studying the problem of a house in a valley with a wind at 5m/s. If I'd like to compute Reynolds number here and know if the flow is laminar or turbulent which is the charateristic dimension? The height of the house?

Homework Statement Hi guys, I just wanted to verify my calculation of a reynolds number of a wind turbine. I understand that the reynolds number will vary in a spanwise direction along the blade due to changes in the characteristic length(chord width) and velocity(due to the tip speed...

Hi guys, I just wanted to verify my calculation of a reynolds number of a wind turbine. I understand that the reynolds number will vary in a spanwise direction along the blade due to changes in the characteristic length(chord width) and velocity(due to the tip speed ratio). As a way to...

Calculate the Reynolds number at a location χ= 0.3m along the chord length of an aircraft wing at each of the following velocities;u= 20,40,60,80 and 100 knots. Assume International Standard Atmosphere (ISA) conditions for pressure and temperature. Take; R =287 J/KG;μ= 18 X10 -6 Kg/m s; 1 knot =...

Homework Statement Hi, I am doing a theoretical investigation which will be compared to an experimental I'll do later. I am trying to calculate how much time will it take an object to fall a heigh H. the object is a 5x5x5 cm cube. I have the Reynolds number as this Re=3546*Velocity; and I...

Homework Statement Substance water Temperature 60 degrees c Density 983kg Pipe size 10" Flow rate 10 m/s Abs viscosity 432 centipoise Homework Equations The Attempt at a Solution (Velocity of fluid or flow rate ) (diameter of pipe) divided by (viscosity of fluid)...

hey pf! when it comes to calculating the reynolds number, i realize it is defined as \frac{inertia forces}{viscous forces}=\frac{ L V}{\nu} thus, if we have a plate of length 20 ft. with fluid flowing around it, would L=20? if so, is this always the case? would we always have L=the length of...

When calculating Reynolds number, when do I use dynamic viscosity and when do I use kinematic viscosity? In a pipe with air flowing inside it, what would you use when calculating Reynolds number and why?

I am trying to work out a reynolds number for an impinging jet using air. If I have: μ=1.8*10-5 kg/ms ρ=1.2 kg/m3 Velocity = 90m/s Nozzle Diameter=15mm is it Re = ρ u dh / μ Which is (1.2 kg/m3*90m/s*0.015m)/1.8*10-5 kg/ms Thanks M

Lately, I have conducted an experiment where I dragged various circular cylinders through water in order to find the resistance, and hopefully also the drag coefficient. It seems to me that this coefficient is dependent on what is called the Reynolds number. Using some sources, I can easily find...

Hi I am a little confused as to what length to use as the characteristic length of the Reynolds number for a body in and incompressible flow that has no boundary conditions(ie there all open). im going to try and draw a few examples to help me out..(i have no idea why..) from what i have read...

So I understand that Reynolds number is the ratio of intertial forces to viscous forces but how exactly does this relate to flow? Why is it that when viscous forces dominate one gets a laminar flow? How to conceptualize?

Just as the thread says, I am looking for some good flow visualization techniques at low Reynolds numbers. I am working on the design of a small recirculating water tunnel that I think can be built for ~$100. I cannot get a specific RE at the moment as I am still doing a preliminary feasibility...

Hello, I have a question regarding Reynolds numbers. As I understand, the higher a Reynolds number, the more turbulent a flow becomes, with Re>4000 considered turbulent. I have a model where I've calculated a Reynolds number of 10^7, and when going to set my model boundary conditions I'm...

hey guys, I would like to know about reynold's number for a wing I have designed a NACA 4412 wing which has wingroot = a , wingtip = b and winglet tip = c (a,b,c are any integers or decimals) please tell me the formula of calculating D for the eqn of reynolds number = ρVD/μ additional...

Homework Statement If the Reynolds number is 4000, what is the Power (P) required in units of watts at a shaft speed (n) of 0.03 Hz? Assume the system contains acetone, with a kinematic viscosity of 0.419 stokes. The density of acetone is 0.785 grams per cubed centimeter. Us Curve B in the...

Reynolds numbers and "inertial force" I am an undergrad physics major taking an engineering course that just introduced the concept of reynolds numbers. When I try to get an idea of how the Reynolds number is physically derived, I keep running into the definition that it is the "ratio of...

Hello I am preparing for my aerodynamics exam and I'm having trouble with this question. Why is the Reynolds number of the airflow over a wing important in determining the value of lift and dragThe Reynolds number is important for determining laminar and turbulent flows over a body. It is a...

Homework Statement From dimensional analysis it is found that the drag force F that a fluid (density ρ, viscosity μ) exerts on a sphere (diameter d) moving through a fluid at a velocity u is given by cD = f(Re), where . The table below gives the relationship between the drag...

I'm trying to calculate the reynolds number for flow inside an air duct with an obstruction. Basically the set up involves cooling electronics by placing aerodynamic "shrouds" over the device to improve the heat transfer. So far a cube is being used to approximate the shape of the device. The...

when calculating a Reynolds number for an obstacle in wind tunnel Re = air density * air velocity * D / Dynamic viscosity D here is the characteristic length of the immersed body ( frontal length ) 2 dimensional problem Or the Hydraulic diameter which relates the tunnel dimensions to the...

Hi I know that for an airfoil, it's typical to describe stall in terms of angle of attack. I'm wondering, how does Re play a role in flow separation of an airfoil (and for objects in general such as a plate, sphere, or cylinder)? One Wikipedia (http://en.wikipedia.org/wiki/Flow_separation) it...

Wikipedia: "Reynolds Number is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces." What is meant by the inertial forces? I have a much better intuition of viscosity. But it seems to be like the Reynolds Number predicts turbulent flow for a...

In which range of Reynolds numeber is laminar flow for airfoil? Is it Re < 5 x 10^5? How about turbulence case?

Homework Statement For the following situations of steady flow, determine whether the flow is laminar or turbulent based on Reynolds number: water at 10oC flowing at an average velocity of 2 m/s in a 100-mm pipe, (Viscosity of water at 10oC: 1.31 cP, density: 1000 kg/m3) Homework...

Is there a simple mathematical way of proving the left hand side equals the right hand side (see attached image)? Any help will be much appreciated as I'm desperately trying to work out exactly where the magnetic Reynolds number comes from. I can derive the left hand side (its simply the ratio...

So, I understand that when reynolds number increases, the fluid becomes more turbulent, and there is a greater energy loss due to formation of eddies. However, shouldn't this increase in reynolds number cause an increase in friction as well? But, according to the moody diagram...

Homework Statement This is a part of an assignment for a computational modelling paper requiring the modelling of couette flow between two (infinite) parallel plates in MATLAB. The lower plate is stationary while the upper plate moves at 0.1m/s, the plates are 0.01m apart and the no slip...

Hi, I'm struggling to understand one step in the derivation of the Reynold's Transport Theorem. I get as far as: \begin{equation} \frac{d}{dt} \int_{V(t)} f(\mathbf x, t) \, dV = \frac {d} {dt} \int_{V_0} f(\mathbf X,t) J(\mathbf X,t) \, dV = \int_{V_0} J \frac {\partial f} {\partial t}...

Homework Statement Afluid with a viscosity of 9.1 x 10-4 Pa.s and density 1.1 g/cm3 flows through a tube with an inner diameter of 10 mm and fills a 10 mL container in 29 s. What is the Reynolds number for this flow? Homework Equations I am assuming its this equation for a tube...

Can someone explain to me how XFoil calculates the Reynolds Number for computational analysis. I have the XFoil manual which explains the method used in calculating the Reynolds Number. But what I don't understand is that it says that the "Reynolds Number is defined with the freestream velocity...

Could somebody please clarify a few things about Reynolds number for me? In class the lecturer approximated |u. \nabla |u by (u^2)/L where L is the characteristic length. In a specific example considering flow around a cylinder of diameter D, it was said that L=D. What does the characteristic...

Homework Statement I don't understand why flow coefficient increases with Re and why it becomes independent after a certain Re number for orifice plates and venturi meter! Homework Equations The Attempt at a Solution It seems than when the flow becomes turbulent, the flow...

The wake is made because the inertia forces in the system ,right? So if i have low Reynolds number the inertia forces are negligible and the flow doesn't separate ,right? So In every low Reynolds number the flow doesn't separate (no wake) but low Reynolds number also indicate a viscous flow...

Hello! First time poster, long time lurker. I've been doing my own independent study of fluid dynamics (not recommended, i know!) and I've hit a wall. I'm trying to imagine problems of fluid dynamics other than the "river and pipe" variety to confirm that I'm really getting this drag stuff. I'm...

Hello, can someone tell me how the reynolds number for flow through a pipe change along it's length? Is the only method that the boundary layer gets thicker along the pipe so the freestream velocity increases? Assuming no gas temperature change along the pipe's length. From thinking of the...

Hello, I have a problem I am trying to model analytically (please note: I am NOT a fluid mechanics expert -- I come from a chemistry background): A semi-infinite plate is oriented axially in the direction of flow. Please refer to the following page for an illustration of my problem...

Homework Statement At the moment, I am planning my I.B extended essay (last 2 years at school), and have chosen to do my EE on physics. I've done loads of background research about Reynolds Number and how it affects the type of flow present. There is an experiment I can recreate (Reynolds...

Homework Statement A pipe 0.15m in diameter has a roughness ratio (k/d) of 0.002 and carries water at a flow rate Q. Using the moody diagram, show that at high flow rates (where the friction factor is independent of reynolds number), the head loss per m length due to friction is approx...

Homework Statement Estimate a reynolds number for a pipe of 0.3m internal diameter, carrying water at a rate of 71 m/s, and say what that says about the likely nature of the flow. Homework Equations Re = (density x L x velocity of flow)/coefficient of dynamic viscosity for water...

Hi, I have been given a couple of questions in which i have to draw a velocity profile in a pipe etc. We are asked to find the mean & maximum velocitys, velocity pressure & pressure drop. the only 2 parameters we are given are the RE (Reynolds number) & pipe size. We are also told that the...

I have the density (ρ) of the particles and the fluid, as well as the complete dimensions of the non-spherical particles. I know the Force of drag (F) and the Coefficient of drag (C). But how do you get the Reynolds number from this? I can't use Stokes' equations because they only apply to spheres.

Does anyone here know how to calculate the reynolds number for a pulsating swirl flow? I've been trying to find the right expression for ages, I can't locate it. I'm sure it will be a integral equations based upon the frequency of swirl (i.e. 1Hz, 5Hz or 10Hz etc) Thanks

Perhaps someone can clear up some confusion for me. EQs (1) and (2) are synonymous, but use different notations for the derivative. In my textbook, the RTT is written in the following form: Given some fluid property 'B,' let \beta be the intensive property \beta = d\, B/d\, m. Then the rate...

Osbourne Reynolds: "The Sub-mechanics of the Universe" While reading a very interesting article/lecture called http://jilawww.colorado.edu/perkinsgroup/Purcell_life_at_low_reynolds_number.pdf, there was a reference to a publication by Osbourne Reynolds called The Sub-mechanics of the Universe...

hi i have to find out the reynolds number for a missile launched from a sub. i only have the temperature of the water, the dimensions of the missile and the velovity of a model of the of the actual missile at a scale of 1:10 i havn't given any quantities because i don't want a...

I have a question about Reynolds Number and wind tunnel tests. Last semester a few students at my university were conducting wind tunnel tests on a small model of a truck, they were trying to find ways to reduce the drag in order to save fuel. I would guess they were testing at a Reynolds Number...