Impact of velocity and temperature fluctuations on the accuracy of low-velocity measurements indoors by thermal anemometers.

A study was made of the impact of well-documented random velocity fluctuations and periodic temperature fluctuations with different amplitudes and frequencies on the accuracy of the mean velocity and the standard deviation of the velocity measured by three low-velocity anemometers with omnidirectional probes. The anemometers were tested in an airflow at 225 combinations of mean velocity, amplitude of the velocity, and temperature fluctuations, as well as frequency of the temperature fluctuations, as identified during field measurements. The results show that random velocity fluctuations had no significant impact on the velocity measured by the anemometers. The amplitude and the frequency of the temperature fluctuations had no impact on the accuracy of the measured mean velocity. The temperature fluctuations had no impact on the standard deviation of the velocity measured by two of the anemometers. However, the standard deviation measured by the third anemometer was affected by the temperature fluctuations. The measurements in turbulent flow indicate that the impact of the directional sensitivity of omnidirectional probes on the accuracy of the measurements is smaller than identified during static tests.