Anemometer with direct velocity indication using 3 thin wires for low wind velocity

An anemometer using a heat wake method for low wind velocity was constructed. Mean flow velocity is indicated by using thin wires mounted on a simple body. The parallel wires are held perpendicular to the flow direction. Heating the upstream wire with a periodical current, thermal oscillation was introduced into the flow. The time taken for thermal oscillation to connect between the two downstream wires which serve as thermal sensors, is inversely proportional to mean velocity. When the lowest thermal frequency was adjusted to keep the ratio of convection time and thermal period constant, its frequency should be proportional to velocity. The system with two sensors 0.4 mm apart was calibrated using one half of this value. Convection velocity of thermal oscillation independent of its frequency was found to be equal to about 80 percent of the mean velocity. Mean velocity from 0.3m/sec to 2m/sec was measured with good linearity to the heating frequency. If the ratio were reduced to one fourth or one eighth, the high velocity limit for velocity measurement could be easily extended to two or four times respectively larger than that in the present calibration.