I suggest to read some fundamental textbook, this example is really misleading.

Try to start thinking about the flow over a flat plate that starting from laminar regime reaches a turbulent regime after a transition. The Re number is local, along the x-direction of the plate

dear Filippo Maria Denaro thanks for the reply but I didn't post this example, many websites post this example to differentiate laminar flow vs turbulent flow....I got this doubt.....I do accept with you...

Use classical textbooks, even if this example runs around social networks that does not mean it is the best representation you can think about the difference between laminar and turbulence regimes.

First I didn’t agree with this example 2nd my question how to compute Reynolds number for scattered flow. I do know that I need to refer text book

Ijaz Fazil Syed Ahmed Kabir

you are not getting the key ... in the Reynolds number you have to insert a lenght and a velocity. Any choice could be lecit but the problem is about the resulting meaning of the value.

In a same flow problem you can chose several lenghts, each one providing different values.

In a pipe flow we use the geometrical diameter and there are some estimation about the change of regime from laminar to turbulent if the Re number exceeds a threshold value. But if the fluid leaves the pipe outlet you have then a different physics. In the case in figure, the flow letting the pipe is in laminar regime thus we assume it is also entering in laminar regime (Re below a certain value). The "jet" of water exiting now in air has no longer a characteristic geometric lenght but only a local distance from the exit. You can see transition to turbulence after the distance has reached a certain value (that is a certain local Re number). What is more is that the jet is impinging a surface and that produces strong vorticity that is then stretched and diffused along a wide range of scales (that is at different Re numbers).

The figure shows a set of different flow problems.