Improvement of the constant temperature anemometer and measurement of energy spectra in a turbulent jet

• We developed the constant temperature anemometer (CTA) for the measuring of velocity fluctuations.
• Roll-off frequency of our CTA was 20 kHz–40 kHz given a free stream flow velocity of 20 m/s.
• Mean and fluctuating velocity are precisely measured by means of our CTA.
• Measured energy spectra in turbulent jets by means of our CTA well agreed with LDIA theory.

This paper presents a rearranged electrical circuit for a constant temperature anemometer (CTA), along with details of calibration results and velocity measurement results for a plane jet and square jet that were obtained by using the rearranged CTA. In this rearranged CTA, the ratio of the electrical resistance of the Wheatstone bridge was set at one, and the feedback circuit used two operational amplifiers whose gain-bandwidth product and slew rate were 110 MHz and 20V/μs, respectively. The results of a frequency response test showed that the roll-off frequency of the rearranged CTA was 20 kHz for a 5-μm5-μm hot-wire and 40 kHz for a 3-μm3-μm hot-wire, given a free stream flow velocity of 20 m/s; those of a basic CTA were 5 kHz and 6 kHz, respectively. It was also found that the energy spectra measured by the rearranged CTA yielded a power spectrum that agreed with the profile derived numerically from the Lagrangian direct-interaction approximation (LDIA) theory in the range of non-dimensional wave numbers smaller than 0.5. These results indicate that the rearranged CTA could be used for more accurate investigations of fine-scale structures in turbulent flows. Further, the profile obtained by the LDIA theory was valid and useful for discussing the turbulent flows.