I used this Venturi pipe for my Masters thesis to measure the gas flow rate of a Biogas burner. It can be used with 10mm-13mm Inner diameter flexible hoses. The two small outlets for 4mm inner diameter hose were connected to an MPX5010DP pressure sensor (https://www.nxp.com/files-static/sensors/doc/data_sheet/MPX5010.pdf).
As I had relatively low flow rates, this Sensor was at the very bottom of its measuring range, but was the only one I found both affordable and suitable for this purpose.
The small outlets could also be simply connected to a U shaped tube filled with water mounted next to ruler to indicate the pressure difference with a sensitivity of 9.8Pa/mm: https://en.wikipedia.org/wiki/Pressure_measurement#Liquid_column_(manometer)
For this specific pipe, I measured a relation of about 5.04 (l/min)/mBar * (pressure difference in mBar)+2.24l/min in a 3 to 8l/min range. Standard deviation for my measurements was 5.6%.
I added the Fusion 360 file, so you can adjust the narrow Venturi pipe section, which is advisable for higher flow rates. Then, the tube would also be more accurate as it now can switch from laminar to turbulent flow in the narrow section. But, of course, you have to calibrate it.
The Part was printed standing with brim and supports for the small outlets