7/29/2019 Discussion Osborne Lab

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Discussion

The existence of these laminar, transitional, and turbulent flow regimes by injecting some dyes

streaks into the flow in a glass pipe, as the British engineer Osborne Reynolds (1842-1912) did over a

century ago. Laminar flow characterized by smooth streamlines and highly ordered motion. Turbulent is

characterized by velocity fluctuations and highly disordered motion. The transition from laminar to

turbulent does not occur suddenly. It occurs over some region in which the flow fluctuates between

laminar and turbulent flows before it becomes fully turbulent. Under most practical condition, the flow

in circular pipe is laminar for Re≤2300, turbulent for Re≥4000 and transitional is in between.

According to the Reynolds`s experiment, laminar flow will occur when a thin filament of dye

injected into laminar flow appears as a single line. There is no dispersion of dye throughout the flow,

except the slow dispersion due to molecular motion. While for turbulent flow, if a dye filament injected

into a turbulent flow, it disperse quickly throughout the flow field, the lines of dye breaks into myriad

entangled threads of dye.

In this experiment need to observe the characteristic of the flow of the fluid in the pipe, which

may be laminar or turbulent flow by measuring the Reynolds number and the behavior of the flow,

secondly to calculate the range for the laminar and turbulent flow and lastly to prove the Reynolds

number is dimensionless by using the Reynolds number formula.

After complete preparing and setup the equipment we run this experiment. The shape change

from thin threads to slightly swirling which still contains smooth thin threads and then fully swirling. This

change is from laminar flow to transitional flow and then to turbulent flow. In this experiment we fix the

volume of the water to 600mL. When the beaker occupied by 600mL, the observer sharp and carefully

removes the beaker from the exit valve. From the time taken, we get the volume flow rate, Q. To get

precise value we repeat this step 3 times to take its average volumetric flow rate. Then, from the

volumetric flow rate we can find the velocity. Last step of calculation is calculating the Reynolds number

by using the Reynolds equation. From Reynolds number calculated, we can estimate the condition of the

flow whether it is laminar, transition or turbulent by comparing with appropriate given Reynolds

number range.

7/29/2019 Discussion Osborne Lab

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Differences between laminar flow and turbulent flow:

Laminar Flow Turbulent Flow

Can be steady and unsteady. It always unsteady, because there are

always random, swirling motions.

Can be one, two, or three

dimensional

It always three dimensional

Occur at low Reynolds number. Occur at high Reynolds number

During the experiment there are several precaution steps that need to be alert. The experiment

should be done at suitable and unshaken place. To get appropriate laminar smooth stream flow, the clip

and the valve which control the injection of blue dye must be regulate slow and carefully. When

removing the beaker from the exit valve, notice that some water still enter the beaker because of the

slow response between the person who guide the stop watch and the collecting beaker. So to avoid this

parallax error, it is better to take same person who guard the stop watch and the collecting beaker.

There are bit different between the results collected. This might be some of parallax error such

as the slow response during collecting the water, the position of eyes during taking the value of water

volume, and regulating the valve which control the flow rate of water unstably.