Vibration-based flowmeters are useable in inaccessible nuclear reactor spaces. Flowmeters include an extension that blocks fluid flow in a path and a detector that detects vibrations caused by vortex shedding in the fluid flow around the extension. The detected frequency of the vibrations determines the flow rate. A Strouhal number may be used to calculate the flow speed using extension surface diameter and detected vortex shedding frequency. Several extensions may cover a range of frequencies and flow speeds. Pipe-organ-type flowmeters include a passage with an opening constricted, and subsequent widening section. An extension and outlet that create turbulence in the flow at the outlet create a standing wave and vibration in the extension and/or entire flowmeter. A flow rate of the fluid through the flowmeter can be calculated using length of the passage and/or known properties of the fluid. Multiple, flowmeters of customized physical properties and types are useable together.