An Evaluation of Free- and Fixed-Vane Flowmeters with Curved- and Flat-Bladed Savonius Rotors

Abstract

Speed and direction performances of flowmeters, designed by the authors for in-house use, employing an Aanderaa-type curved-bladed Savonius rotor and a free vane and an Aanderaa-type flat-bladed Savonius rotor and a fixed vane, are discussed. It has been observed that accuracy, linearity, and tilt response of a meter using the Aanderaa curved-bladed rotor is superior to those of a meter using the Aanderaa flat-bladed rotor. Analysis showed that the azimuth response of a flowmeter is affected by the presence of support rods surrounding its rotor. The change in azimuth response arises from flow pattern modifications in the vicinity of the rotor, imposed by the changes in the horizontal angle of the support rods of the rotor relative to the flow streamlines. While the use of two support rods may be suitable for a fixed-vane system, it is undesirable for a free-vane system where the meter's orientation with respect to the flow direction is not defined. Flow direction calibration results indicated that a fixed-vane system exhibits superior direction performance compared to a free-vane system. The comparatively poor direction performance of the free-vane system stems from the poor coupling to the ?vane-follower? magnet from the external vane.