Leminar and Turbulent Flow

For a given rate of flow (volume) Reynold's No. varies inversely with pipe diameter. So it is higher after the reducer, and possibilities are a) turbulent before, turbulent after, b) laminar before, turbulent after, c) laminar before, laminar after.

You need to calculate Reynold's Nos to find which. But if it's water flowing, at anything like normal velocities and pipe sizes, laminar flow is very unlikely.

Cheers.........Codey

thats correct,

The reynolds number is a dimensionaless number that determines if it is a turbulent flow, and you determine if it reaches the threshold of turbulent flow.

As flow is increased, your laminar boundry layers decrease as the threshold changes to turbulent flow.

Is it practical question or theoretical question? If it is theoretical, both the posts already received fro guest and codemaster are correct. I fully agree with both. But if you calculate Re, for your problem, the flow before the reducer also may be turbulent. It is very difficult to find laminar flow in practice. It will be laminar only if the velocities are very small or viscosity of the fluid is too large. Can you put the flow conditions for which you are looking for the solution? Pipe diameter, pipe material and surface condition, liquid, velocity. liquid viscosity. Let us calculate Re.

Surely all the replies are correct. but one thing i would like to add is that one parameter that is viscosity is most important if the viscosity of the fluid is low than most probably the flow would be turbulent after the reducer and if its high than most probably it would be laminar even though turbulent for some initial lenghth but would become laminar later on.

Calculate Reynold's Number R_e to define the type of flow, is it laminar or turbulent.

And note that R_e depends on Velocity, Diameter, and Kinematics Viscosity.

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Dear Mr.Shanii,

The flow type, whther it is in up-streme or down streme, depends only upon the REYNOLD's NUMBER.

Upto 2000 Re.No., the flow is defined as LAMINAR FLOW. Re. No. 2001 TO 2800 Flow is defined as TRANSITION FLOW. Above this Re.No., the flow is defined as TURBULENT FLOW .

If the pipe line size is reduced, the down streme flow Velocity will increase depending upon the reducer size, and for the increased Velocity of flow the Re will increase and even the INCREASED Re. No.is STILL less than 2000 (inspite of reducer in the line) the FLOW IS STILL LAMINAR FLOW, and just because the reducer is in line it cannot be decided as TURBULENT FLOW.

DHAYANANDHAN.S

To be a little pedantic, it's not a matter of definition, it's one of experiment. Based on Reynolds's tests, the figure usually given for the onset of turbulent flow is 4000. But laminar flow can occur at higher Reynolds nos if special care is taken, flow increased gradually etc. However, below 2000 the flow is always laminar, as there is insufficient energy of flow to cause turbulence.

Cheers..........Codey