A thermally stratified wind tunnel for environmental flow studies

A wind tunnel was constructed to study the effects of thermal stratification on flow and diffusion in the atmospheric boundary layer. The wind tunnel is of a suction type and has a 1.5 m wide, 1.2 m high, 13.5 m long, rectangular test section. Designed to produce thermally stratified flows, the tunnel is equipped with two independent temperature systems, an air-flow heating unit (AHU) and a floor temperature controlling unit (FTCU). Using the AHU and FTCU, a wide range of thermal stratification can be generated with a wind speed in the range of (U =) 0.2-2.0 m s^-1. Both in neutral and stably stratified flows, the tunnel can provide a uniform smooth flow with a low turbulence intensity of about 0.4% at a wind speed less than 1 ms^-1. The design features and performance of the wind tunnel are described. The characteristic of thermally stratified flows created in the test section is also discussed.