Search

Increased traffic emissions and reduced natural ventilation cause build up of high pollution levels in urban street canyons/intersections. Natural ventilation in urban streets canyons/intersections is restricted because the bulk of flow does not enter inside and pollutants are trapped in the lower region. Wind vortices, low-pressure zones and channeling effects may cause build up of pollutants under adverse meteorological conditions within urban street canyons. The review provides a comprehensive literature on wind tunnel simulation studies in urban street canyons/intersections including the effects of building configurations, canyon geometries, traffic induced turbulence and variable approaching wind directions on flow fields and exhaust dispersion.

The vertical dispersion parameter of Pasquill–Gifford needs some modification in the close vicinity of urban roadways by considering the influence of traffic-induced turbulence. Wind tunnel simulation experiments have been carried out with controlled traffic parameters to evaluate traffic-induced effect on vertical dispersion parameter (σz) in the near field of roadways. The aerodynamic similarities in atmospheric flow, vehicles size and speeds have been considered with appropriate similarity criteria. The tracer gas experiments have been performed to evaluate σz in the near field of the roadways for variable traffic volumes and two approaching wind directions (i.e. 90○ and 60○). The results showed that the value of σz increased monotonically with increase in traffic volumes and becomes nearly constant at a particular downwind distance. It has also been found that the σz was considerably affected by approaching wind directions. Further, the comparison of experimental σz values for both approaching wind directions with those of Chock (1978) and Rao and Keenan (1980), showed an agreement within ±15%.

The paper reports the results of an experimental investigation into the aeroacoustic performance of a contra-rotatingaxial flow compressor stage having a hub-tip ratio of 0.66. Aerodynamic superiority of a contra-stage is examined from the point of view of higher pressure rise, increased through flow and rotating stall suppression. Measurements of sound pressure level and real-time analysis of the noise signals is reported for different speed combinations for clean and distorted inlet flow for two axial gaps between the contra-rotors. The effect of pitch chord ratio and axial gap between the rotors on the aeroacoustic performance is discussed. The study reveals that the axial gap between the rotors significantly affects the aeroacoustic performance of a contra-stage.