Automatic identification and characterization of turbulent bursting from single-point records of the velocity field

A new identification method allowing accurate detection of time periods corresponding to turbulent bursts in single point velocity field records is presented. The discrimination between bursting and burst free periods is made by locating the time corresponding to elevated TKE dissipation rate levels, i.e. examining variations of "instantaneous" dissipation rates obtained by implementing window averaging and proper normalization. In turn, use of the record rms and mean values for normalization eliminates the need of a flow specific threshold, detecting bursting periods by a twofold increase in the instantaneous normalized TKE dissipation rate variations. Hence, the suggested technique is potentially universally applicable across various flow fields of different characteristics. The performance of the new identification method is examined using a data set of up slope flow, constituting a buoyancy driven turbulent boundary layer flow recorded during a field experiment. Spectral shapes of non-bursting periods show high level of similarity to those expected in canonical turbulence, while the bursting periods spectral shapes are significantly indifferent. In addition, the statistical behavior of the temperature fluctuations during bursting periods is examined, revealing a significant decrease in temperature fluctuation intensity during bursts. This opens the possibility to examine the bursting period generation mechanism based on statistical findings in the duration of bursts. Examination of other scalar variations, i.e. particulate matter and/or gaseous pollutant concentrations, in connection with turbulent bursting periods using the proposed methodology can assist in further understanding of bursting generation and scalar transfer mechanisms.