Investigation of nonlinear effects in constant-temperature anemometers

The nonlinear behavior of constant-temperature anemometers is investigated experimentally and numerically for three commercially available anemometers. The experiments are performed in the potential core of a subsonic jet by injecting electrical signals of varying amplitudes and frequencies in the hot wire and recording the anemometer output signals. The numerical model is based on Freymuth's theoretical analysis (1977 J. Phys. E: Sci. Instrum. 10 705-10). The two approaches are in good agreement, which demonstrates the validity of Freymuth's nonlinear theory of constant-temperature anemometers. The results confirm that significant errors are made in the third-order turbulence moment, also called the skewness factor, when the amplitude of velocity fluctuations is large and their frequency is not small compared to the cut-off frequency of the system.