Atmospheric boundary layer simulation in a wind tunnel, using air injection

The inner part of a neutral atmospheric boundary layer has been simulated in a wind tunnel, using air injection through the wind tunnel floor to thicken the boundary layer. The flow over both a rural area and an urban area has been simulated by adapting the roughness of the wind tunnel floor. Due to the thickening of the boundary layer the scaling factor of atmospheric boundary layer simulation with air injection is considerably smaller than that without air injection. This reduction of the scaling factor is very important for the simulation of atmospheric dispersion problems in a wind tunnel.The time-mean velocity distribution, turbulence intensity, Reynolds stress and turbulence spectra have been measured in the inner part of the wind tunnel boundary layer. The results are in rather good agreement with atmospheric measurements.Nomenclature d Zero plane displacement, m - h Height of roughness elements, m - k Von Kármán's constant - n Frequency of turbulence velocity component, s^–1 - S_u(n) Energy spectrum for longitudinal turbulence velocity component, m² s^–1 - S_v(n) Energy spectrum for lateral turbulence velocity component, m² s^–1 - S_w(n) Energy spectrum for vertical turbulence velocity component, m² s^–1 - U_o Free stream velocity outside the boundary layer, m s^–1 - Time-mean velocity inside the boundary layer, m s^–1 - u* Wall-friction velocity, m s^–1 - u Longitudinal turbulence intensity, m s^–1 - v Lateral turbulence intensity, m s^–1 - w Vertical turbulence intensity, m s^–1 - Reynolds stress, m² s^–2 - z Height above earth's surface or wind tunnel floor, m - z_o Roughness length, m - Thickness of inner part of boundary layer, m - Thickness of boundary layer, m - Kinematic viscosity, m² s^–1