First off, what we have on the shelf for such purposes would be subtended under the two product families below.
Flow Sensors - Industrial
Beyond that, the question could use a bit of refinement in terms of the fluid in question and whether you’re interested in mass or volumetric measurements. Typical approaches to flow measurement historically have involved placing an obstruction in the flow path and inferring flow rate from the pressure differential across it, placing some manner of whirlygig in the flow stream and watching how fast it spins, or measuring the rate at which fluid flow transfers heat from a warm object. Newer techniques may involve use of ultrasound, electromagnetics, and/or dark magic… All present varying tradeoffs in terms of measurement fidelity, material compatibility, cost, and sensitivity to various factors such as temperature, fluid properties, installation restrictions, etc.