Download A Combo Setup for Atmospheric Turbulence Measurements

A combo (Sonic & 2 x-hot-films or 3D-multisensor probe) setup for
atmospheric turbulence measurements
Eliezer Kit, Tel Aviv University
The fine-scale structure of turbulence is a largely unexplored aspect of the
atmospheric boundary layer since it eludes conventional probing techniques. The direct
measurement of fine structure using high resolution instruments such as hot-film or hotwire anemometers that can resolve smallest (dissipation) scales has been rare, given the
intricacy of the instruments involved.
Standard hot film/wire techniques work on the premise that the change of
resistance produced in a heated wire due to cooling of a passing flow is a function of
velocity. Thus, a reliable calibration procedure is necessary to convert measured voltage
to velocity. In addition, more frequent calibrations are necessary in view of slowly
changing probe performance due to contamination. In the talk, there is a recall to
feasibility study conducted by Kit et al. (2010) where a strikingly successful method, the
Neural Network (NN) approach was suggested and applied.
By employing an effective velocity approach to mimic behavior of multi-sensor
hot-film probe in a given velocity field, a “virtual” probe algorithm was developed. It
enabled to study several aspects of the suggested calibration scheme based on NN:
determination the turbulence intensity bounds of the flow which permit acceptable
calibration, the effect of anisotropy of the flow on calibration quality and the effect of
hot-wire nonlinearity on the calibration process.
The combos were installed on towers and continuous measurements of the fine
turbulence structure were conducted in the frame of MATERHORN-X program during
the fall and spring campaigns. The preliminary results from fall campaign are presented.
The further data processing is in progress.