Yukio Yamao

Particle-Image Velocimetry Measurements of Separation and Re-attachment of Airflow over Two-Dimensional Hills with Various Slope Angles and Approach-Flow Characteristics

Airflow over two-dimensional hills was investigated in a wind tunnel using particle image velocimetry. We focus on the flow separation behaviour. A trapezoidal hill shape was used in most of the experimental runs, but the critical slope angle for flow separation was approximately the same as that established for smooth hill shapes. The re-attachment point of the separated flow became farther from the hill as the slope angle

A wind-tunnel study on exhaust gas dispersion from road vehicles—Part I: Velocity and concentration fields behind single vehicles

\theta

A wind-tunnel study on exhaust-gas dispersion from road vehicles—Part II: Effect of vehicle queues

increased, reaching a saturation of about seven times the hill height for

Velocity Adjustment and Passive Scalar Diffusion in and Above an Urban Canopy in Response to Various Approach Flows

\theta \gtrsim 60^\circ

Wind-tunnel Experiments on Improving the Natural Ventilation of a Street-Canyon

. Increasing the upwind surface roughness length was found to suppress flow separation. This tendency is analogous to the previous experimental results for turbulent boundary layers on flat plates. The boundary-layer thickness varied by the presence or absence of Counihan-type spires and a castellated fence at the test-section entrance had negligible effect on the flow separation.

Passive scalar diffusion in and above urban-like roughness under weakly stable and unstable thermal stratification conditions

This paper proposes an atmospheric diffusion model for traffic-related emission in urban areas within a few hundred meters from relevant roads. The model adopts the mass-conservation (MC) principle for the velocity calculation and the advection-diffusion (AD) equation for the concentration calculation. This MC+AD combination was chosen to achieve fast calculation for complex geometries. To compensate for the inherent deficiencies of MC and AD, as many known properties possible of turbulent boundary-layer flow over obstacles are incorporated into the MC calculation, and the diffusivity in AD is derived from the velocity spectrum as a function of distance from the emission source. The model is evaluated against wind-tunnel experiments ranging from point-source emission in uniform urban canopy to along-road emission in real city geometries. The model performs well in relatively simple configurations, but the performance deteriorates considerably as the complexity increases. However, in real city geometries, the model exhibits distinctly better performance in terms of statistical indices than a conventional Gaussian-plume model that neglects the effect of individual buildings. The model is therefore a viable option for environmental assessment.