Wind Tunnel Experiment on Flow and Tracer Gas Diffusion in Convective Planetary Boundary Layer

Abstract

The temperature of a flat wind tunnel floor was increased almost uniformly to 80°C to simulate an unstable atmospheric boundary layer. The velocity, temperature and surface temperature heat flux on the wind tunnel floor were measured using a laser Doppler anemometer, a resistance thermometer and a thin-film-type heat flowmeter. The tracer gas was released from continuous point sources located in the simulated unstable boundary layer, and its spatial concentration was measured by flame ionization detectors. The measured turbulent flow and tracer gas concentration characteristics such as turbulence intensities and plume spreads showed good agreement with those obtained from field experiments and water tank experiments when normalized by the convective velocity. The universal functions for velocity and temperature profiles were applied and the empirical constants were optimized. The length scales of turbulent motion were estimated by means of the universal functions. It appeared that the convective velocity and convective temperature could be applied as the similarity parameter for the flow and tracer gas diffusion when considering the corresponding equivalent atmospheric conditions.