Suppose after t seconds.

The cross-sectional area of the tube is s=π*(a/2).

We can know the volume of natural gas flowing in t seconds V=vts=v*t*π(a/2).

So the flow is equal to V/t=v*π(a/2).

Generally speaking;

The flow rate of natural gas pipeline multiplied by the cross-sectional area of the pipeline is the natural gas flow rate of the pipeline.

The natural gas flowmeter is manufactured by using the principle of Karman vortex street, which has the advantages of high measurement accuracy, wide measurement range, low power consumption, convenient installation, simple operation and small pressure loss. It can measure working condition volume flow or standard volume flow (integrated with intelligent temperature and pressure compensation), and can provide pulse or 4 ~ 20m ADC current output function according to user's needs. It is an ideal natural gas metering instrument at present.

In the fluid pipeline, a cylindrical obstacle is inserted vertically, and vortices will be alternately generated at the back (relative to the direction of fluid flow). As the fluid flows downstream, a vortex train is formed, which we call Carmen vortex street. We define the cylindrical obstacle that produces vortex as vortex generator. Experiments show that under certain conditions, the separation frequency of vortex is linear with the flow velocity of fluid. Therefore, as long as the frequency of vortex separation is detected, the speed or flow rate of the pipeline can be calculated.