Simulated Flow and Dispersion of the Jack Rabbit II Field Experiment within EPA's Fluid Modeling Facility Wind Tunnel

Dense and irregular building morphologies within urban areas create complex turbulence, dispersion, and flow regimes that affect downwind and ground level pollutant concentrations. The urban canopy also alters boundary layer wind profiles due to wake turbulence generated from wind flow around buildings and within street canyons. While many dispersion models can capture the downwind effects from buildings, some fall short in terms of accuracy or ease of use, particularly when employed after chemical, biological, radiological, or nuclear (CBRN) releases. Therefore, thorough field and laboratory tests that simulate these potentially hazardous releases are critical in refining current dispersion models. This project leverages data from the Special Sonic Study that occurred during 2015 and 2016 as part of the Jack Rabbit II (JRII) field study. The JRII study was conducted at Dugway Proving Ground (DPG), UT, where 10-20-ton releases of chlorine gas were dispersed within an array of 83 CONEX shipping containers of various sizes. The individual CONEXs, as well as a 2x3 “tall building” stack, were meant to mimic buildings within an urban area in an effort to provide information to improve models and emergency response techniques. During the Special Sonic Study, flow and turbulence around the obstacles were measured from a network of 30 sonic anemometers dispersed around the CONEX array. In this project, a 1:50 scaled model of the JRII test area was constructed and tested within EPA’s Fluid Modeling Facility (FMF) Meteorological Wind Tunnel (MWT) to thoroughly examine the complex flow and dispersion patterns within this mock urban environment. The FMF wind tunnel, which is 3.6 m wide, 2.1 m high, and has an upwind fetch of 18 m, has been operational since the 1970’s for numerous regulatory dispersion applications. A neutrally buoyant scaled boundary layer for the smooth DPG desert surface was developed within the wind tunnel. Near-neutral boundary layer observation periods were identified from a 32 m sonic anemometer tower at the JRII test site and compared to the scaled FMF wind tunnel measurements. In the wind tunnel, velocity measurements were collected through Laser Doppler Velocimetry (LDV) to document the flow within the array. A neutrally-buoyant tracer was also released within the model to simulate ground-level and elevated releases. Concentrations were gathered with a hydrocarbon analyzer (HCA) system using Flame Ionization Detectors (FID). The goal of this presentation is to explain the results of the simulated JRII wind tunnel project, including flow and dispersion patterns. A particular emphasis is placed on comparing the wind tunnel data against observations at the test site, particularly in wakes and recirculation zones of the CONEX buildings. The ultimate goal is to use the wind tunnel and field datasets to inform improved urban parameterizations in Gaussian dispersion models, which are important tools for efficient and precise emergency preparation and response applications.