Probe for measurement of air velocity in oscillating flows

Abstract

Measurement of air velocity when flow is oscillating is required in ocean wave energy studies. A special type of self-rectifying air turbine called "Wells turbine", coupled with induction generator is used for converting the air column movement in a wave energy basin to electrical energy. So far no attempts have been made to study the air velocity variations into and out of the turbine at site. Some efforts for measurement of oscillating air column at laboratory using hot-wire anemometer have been reported. A novel probe, comprising miniature pressure transducers, for the measurement of air velocity variations into and out of the turbine, was designed and developed. The probe was first calibrated and tested at the laboratory before shifting to site for actual measurements. An unidirectional oscillating air flow facility was initially setup at the existing air flow laboratory, which has a variable speed blower as the prime mover. Oscillating flow was generated by a butterfly valve, operated through a function generator. Tests at a nominal frequency of 0.1 Hz and flow velocities upto 35 m/s were conducted. Accuracies of the order of /spl plusmn/2% were estimated for the probe.