Near Field Modeling of the Effects of Sound Barriers on Flow and Dispersion

Master of Science, Graduate Program in Mechanical Engineering
University of California, Riverside, December 2012
Dr. Marko Princevac, Chairperson

Previous  research  of  air  quality  in  the  vicinity  of  roadways  has  used  either  field measurements, where results are site specific, or modeling, which can be computationally expensive or too simplified and misleading. The presented research consists of a systematical laboratory  and  numerical investigation  of  the  influence  of  different  sound  barrier  (SB) configurations on the dispersion from roadways. Sound Barriers can be seen along the sides of freeways, especially in Southern California. The primary purpose of SBs is to dampen roadway  noise;  however  this  research  focuses  on  their  influence  on  the  dispersion  of pollutants from roadways. Vehicular emissions have been shown to be a major source of pollution in urban areas and that long term exposure can lead to adverse health effects. There is a need for reliable models to predict the effectiveness of SBs. These models need to be validated  and  the  best  way  to  accomplish  that  is  through  laboratory  experiments.  The laboratory  experiments  are  being  conducted  at  the  Laboratory  for  Environmental  Flow Modeling (LEFM) at the University of California, Riverside, which has a custom made water channel with the capability of performing Particle Image Velocimetry (PIV) and Fiber Optic Assisted  Laser  Induced  Fluorescence  (FOALIF)  measurements.  This  water  channel  is commonly used to investigate the flow and dispersion within complex urban geometries. The water channel is also being used for qualitative flow visualizations by releasing fluorescence tracer  dye.  The  presented  measurements  have  been  made  with  a  neutrally  buoyant  dye (mixture of dye with water). The laboratory experiments are accompanied with numerical modeling using Quick Urban and Industrial Complex (QUIC) model, which consists of a wind  and  a  dispersion  module.  The  wind  module  has  two  options:  1)  parametric  flow description  (QUIC-URB)  or  2)  flow  results  from  Reynolds  Averaged  Navier-Stokes equations (QUIC-CFD). The dispersion module deploys Lagrangian particle tracking method. It was found that in both the water channel and QUIC simulations, the presence of SBs increases the vertical spread of the plume relative to that of no SBs. The presence of SBs has been shown to decrease the downwind concentrations due to the enhanced vertical mixing, however in certain situations, such as during conditions of low wind speeds, the SBs tend to trap the pollutants on the roadway.