What is the laminar pressure ratio in T-junction block?

In the documentation for T-junction block, "laminar pressure ratio" is mentioned in the following definition:

"Pressure ratio — The transition from laminar to turbulent regime is smooth and depends on the value of the Laminar flow pressure ratio parameter".

 <https://www.mathworks.com/help/releases/R2019a/physmod/hydro/ref/tjunction.html#buimxs6-5>

What variables are the pressure ratio referring to? For example, Inlet and Outlet. How does that determine whether the flow is laminar or turbulent?

Answer 1

[MathWorks Support Team]

The Laminar pressure ratio is the ratio between the downstream pressure and the upstream pressure. When this ratio is reached, it will transition to a laminar regime.