In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing. At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross-currents perpendicular to the direction of flow, nor eddies or swirls of fluids. In laminar flow, the motion of the particles of the fluid is very orderly with particles close to a solid surface moving in straight lines parallel to that surface.
Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection.
When a fluid is flowing through a closed channel such as a pipe or between two flat plates, either of two types of flow may occur depending on the velocity and viscosity of the fluid: laminar flow or turbulent flow. Laminar flow occurs at lower velocities, below a threshold at which the flow becomes turbulent. The threshold velocity is determined by a dimensionless parameter characterizing the flow called the Reynolds number, which also depends on the viscosity and density of the fluid and dimensions of the channel. Turbulent flow is a less orderly flow regime that is characterized by eddies or small packets of fluid particles, which result in lateral mixing. In non-scientific terms, laminar flow is smooth, while turbulent flow is rough.
I'm interested in the very basics of drag, both for ships in water and airplanes in air. Here's what I have so far :
Flow of the medium can be laminar or turbulent. As the relative speed of the vessel increases, the more likely the flow is to be turbulent.
Laminar drag increases linearly...
Is it possible to create (nearly?) laminar flow in a tube with rectangular C.S. , around 1 cm X 5 cm , with air moving at around 100 to 150 m/sec?
Turbulence will likely set in sooner or later, but can the laminar flow be made to last over say 20 cm?
Hello,i am just a college student who has a little confusion on when to consider both laminar and turbulent flow -say over a flat plate,should i assume turbulent flow all over the plate and use the related equations(nusselt number) or use the laminar and turbulent equation(Nusslet number) but if...
I have been tasked by my fluid dynamics professor to create a 3 minute video showing and explaining laminar flow vs turbulant flow. It must be engaging and explain the concepts simply enough with no math.
I will be re-writting this definition below to suite the needs
""Laminar flow occurs...
Good evening everybody.
I am new here I hope it is okay to ask this question here.
As part of a project I am trying to examine the effect of a pulsating laminar duct flow on the heat transfer behavior for constant heat flux at the wall for a Newtonian incompressible fluid.
As such I am...
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...
Hi there,
Hopefully this is a very easy question and you all can just confirm this for me.
When calculating heat transfer into a fluid from a heated tube, is it correct to say that the heat transfer coefficient is *not* dependent on the tube diameter?
So, if we solve for T_{out}, we get...
Is it true that the laminar to turbulent flow transition has been finally solved? From what I've read, it seems to be well described by the Directed Percolation Model. I can hardly believe it since I haven't seen the news in the press (from my point of view, it's a long standing unsolved issue...
Hi guys,
I've been working through some notes on Transport Phenomena by Bird and I've basically been just developing velocity and shear stress profiles for various (simple) models by a differential momentum balance and I'm trying to understand why a certain result happens.
When looking at...
In the equation characterizing the mass transfer in laminar flow, the radial variation of velocity and concentration can be lumped into the axial dispersion term as below:
After reading the original paper about Taylor dispersion, I know how to derive this equation. But I am still not able to...
While deriving Poiseuille's law (the relation between flow rate and pressure gradient for fluid flow in a rigid cylindrical tube under a pressure gradient) , we make an assumption that flow is both laminar and steady.Why we need the flow to be laminar. Is it not enough to consider only steady...
Homework Statement
A reasonable approximation for the two-dimensional incompressible laminar boundary layer on the flat surface in Fig. P4.17 is
u ≈ U(2*(y/δ) - 6*(y3/δ4) + y4/δ4)
δ = Cx1/2 where C is a constant
y ≤ δ
Homework EquationsThe Attempt at a Solution
Incompressible so...
When compared to laminar flows, the fluid "sticks" with the solid surface longer in case of turbulent flows. For example, the angle of separation for flow over a circular cylinder is 80 degrees for laminar flows, and 140 degrees for turbulent flows. What is the reason?
Homework Statement
We know for Laminar flow in which Re<2000 that
##Δhloss=K*\frac{u^{2}} {2g}##
What about if Re>10000 and is turbulent?
Homework Equations
##Δhloss=K*\frac{u^{2}} {2g}##
where ##K=\frac{f*4L} {D}##
The Attempt at a Solution
How would Δhloss look like for turbulent...
Homework Statement
why the shaer stress ( tau) formula is given by μ(dv/ dy ) = μ(-dV / dR) , why there is a negative sign there ?
Homework EquationsThe Attempt at a Solution
Homework Statement
as we all know , D=4R , D=hydraulic diameter , in the equation of P= (8μLV_avg) / (R^2) , i would get (128μLV_avg)/ (D^2) , am i right ? why the author gave (32μLV_avg)/ (D^2) ?
Homework EquationsThe Attempt at a Solution
The Nusselt number for an entire flat plate in the turbulent region has two different equations: One for Turbulent and one for Combined Laminar and Turbulent. How do I know when to use one or the other?
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Consider the fully developed laminar flow due to gravity of water in a vertical circular tube. Assume atmospheric pressure at inlet and outlet. Show that the relationship between diameter and...
Hi!
I read from Perry Green's ChE Handbook that the friction factor for Re ≤ 2,100 can be approximated by ƒ = 16/Re. But there was this question that I encountered (though I don't know the source) and according to it, ƒ = 64/Re for laminar flow. Can someone clarify which is which? Thank you!
So, there's a project I'm working on (no, it's not school related), where I'm trying to figure out how to measure thermal conductivity of a material using laminar flow. The idea is to integrate this into a larger system, and it's a measurement I'd like to take in the process.
I know the...
Please could someone verify this statement as I understand things:
If an object has a low reynolds number (or the fluid is very viscous) then it is dominated by viscous forces and inertia plays no role. The object is in a laminar flow regime.
That last part, is it correct? What I'm asking is...
Homework Statement
a viscous fluid with viscosity η flows through a circular vessel of length L and radius R under a pressure difference of P. Assuming the flow is laminar, calculate:
a)the force on the walls of the vessel.
b)the net force on the vessel.
Homework Equations
Hagen-Poiseuille...
I am working on a problem in which viscous flow comes out from an inclined tube, forming some kind of a fountain. In the tube the fluid is Newtonian and the flow can be treated as Poiseuille flow. I want to study the movement of the fluid after it leaves the tube. Can someone point me about the...
Hello. I'm new to the forums. I apologize if I have posted this in the wrong topic area.
I'm new to this hydrodynamics area and I'm trying to learn the concepts of boundary layer thicknesses. My question is about laminar pipe flow and calculating displacement and momentum thicknesses. I was...
Homework Statement
I am trying to derive Poiseuille's equation using an infinitesimal volume element of the pipe in cylindrical coordinates as seen below. I am using x for the flow direction, u for the velocity in the flow direction, and μ for the viscosity constant...
Hi, I was just going over the moment of inertia for a 2D lamina, I've been happy with writing the small mass element dM as dM = ρdxdy where ρ is the area density, but for some reason decided on doing it like this,
M(x,y) = ρxy
so
dM = \frac{∂M}{∂x}dx + \frac{∂M}{∂y}dy
= ρ(ydx +...
Hi,
I need clarification on the difference in head loss for turbulent flow and laminar flow. I understand how the head loss due to friction is different for the two regimes. For friction head loss, the friction factor is 64/Re for laminar flow, and a more complex formula for turbulent flow. I...
A ridig sphere is rolling from left to right down an incline plane with an angle elevation of β
In the y -direction, FN = mg cos β.
In the x-direction, mg sin β - f
(where f is the frictional force: μsFN)
The laminar motion is then given by Icmdω/dt = Rf (where R is the radius of the sphere)...
Hi,
Consider a 2D laminar only rotating about the z axis, with the axis origin at the bottom left hand corner and adjacent sides coinciding with the z and x axes.
so ω = (0,0,ωz)
y = 0
I don't understand how the IXZ component is 0 to just leave the IZZ component?
I have a doubt about the difference between laminar and streamlined flow. What is difference between those to flows of the liquid. Waht is the reason for the top layer of a liquid to have maximum speed in laminar flow. When does laminar and streamlined flows occur.
Homework Statement
Finding the viscosity of oil...
Homework Equations
η = b/(6∏r)
Fr = -bv
The Attempt at a Solution
The question only gives a radius, mass, density of oil, and terminal velocity. Is it possible to get the viscosity with the given information?
I was hoping someone could give me an explanation as to why resistance of a fluid moving through a tube changes from being determined by viscosity in conditions of laminar flow to being determined by density in conditions of turbulent flow.
Thanks in advance.
Homework Statement
Consider the flow of air over an aerofoil.
The critical Reynolds number marking the transition from laminar to turbulent flow is 6 x 10^5, the dynamic viscosity is 2.0 x 10^-5 Ns/m^2, the density of air is 1.100 kg/m^3 and the aircraft velocity is 180 m/s.
What is the length...
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?
If we're considering fluid flow over a plate and found that at one location the flow is turbulent. Is it always the case that there is also a transition and laminar region before that turbulent region on the plate?
http://books.google.com/books?id=p7WsoU-CfPkC&pg=PA224&lpg=PA224&dq=6.132+fluid+mechanics&source=bl&ots=7q6rcCGewf&sig=EvcrqTJCxqLSPbKrkiztkPS4I6Q&hl=en&sa=X&ei=6vo6UYusIenFyAHHt4GYAQ&ved=0CDoQ6AEwAw#v=onepage&q=6.132%20fluid%20mechanics&f=false
Can someone please tell me how they arrived at...
I am calculating Reynolds number for a automotive ac suction line with 16mm Id 300kpa and 10 deg C and 230 kg/hr. I am getting around 200,000. I think I got laminar flow, but the equation says turbulent. greater than 10,000. dynamic viscosity is my most questionable variable. i checked...
Hello everyone,
I am studying laminar airflow in a channel (2D) and trying to simulate it with FLUENT software but I need to know about the entrance length, and I want to know how I can be sure that a flow is fully developed? is it just by looking at the velocity profile? or looking at the...
Homework Statement
Consider a flat plate moving at V = 105 ft/s in an atmosphere with P = 2100 psf and T =
75F, with a viscosity of vis = 3.7373e-7 slug/ft-s. The plate has a 2 foot chord and a 3.5
foot span.
a. Find the drag on the plate for:
i. A boundary layer that is laminar over the...
Homework Statement
Q) Water (p = 998 kg/m^3
, n = 1.0*10^-3 Pa.s at 20C) at 20C flows through a pipe of
diameter 50.0 mm. What is the maximum average flow velocity if the flow is
guaranteed to be laminar? Give your answer in mm/s.Homework Equations
Reynolds number=(pvd)/n
The Attempt at a...
I am absolutely stumped on this last question for my assignment, I have no idea what to or how to calculate the flow from just these given constants.
Q) Water (p = 998 kg/m^3
, n = 1.0*10^-3 Pa.s at 20C) at 20C flows through a pipe of
diameter 50.0 mm. What is the maximum average flow...
Hi
I was wondering, if I have two different liquid in two separate branches, and then the two branch lead to a single branch such that the two flows now go together in one branch, I was wondering what are the factors (qualitatively) affecting the degree of mixing of the two liquid? What about...
Hi all,i'm new here and i really hope that you could help me with this problem that is blocking the progression of my graduation thesis.
I'm working on a 3D stationary simulation of brachiocefalic artery; I'm using laminar flow physics with a known velocity in inlet and a normal stress in...
Hi there,
I am working an a stationary, laminar flow model and would like to calculate the drag of that model.
Now the Comsol forum guys suggest to use the operator reacf(u). It is also used in the "Flow over a circular cylinder" tutorial. Does anyone know where to get it from or how to use...
1)Can two streamlines(line of flow) converge to a single one ?
2) When water flows from the tap, as it flows down the horizontal area of cross-section decreases...An argument using the Equation of Continuity is given...but I have two doubts regarding those
i) Is water in freefall Laminar...