Utilizing Computational Fluid Dynamics to Estimate Drift Extent-from Aerial Spraying of Dispersants

Abstract

Abstract Aerial application of dispersants are an effective means of responding to oil spills in coastal waters and the deeper waters of the Outer Continental Shelf or Gulf of Mexico. To ensure the safety of responders and nearby wildlife, a buffer area is put in place around the spilled oil to be treated, within which spraying operations are conducted. In 2015, a research project was initiated to develop a prototype Decision Support Tool (DST) designed specifically for estimating the spray drift during the aerial application of dispersants on an oil spill. In 2019, an initiative was undertaken to further develop the DST and address known data gaps in the modeling used in the prototype, expand on the aircraft included in the tool, and include a contour plot output of dispersant deposition. The DST has been designed specifically for estimating the spray drift during the aerial application of dispersants on an oil spill through the use of complex Computational Fluid Dynamics (CFD) modeling. The DST program operational space was developed based on direct input from Oil Spill Response Operators (OSROs) for ten airframes currently used in the United States for aerial response operations, including both turbo propeller and turbo fan engine types. The DST employs a database of results generated using the latest in CFD modeling technology to examine flow structures and drift effects created by various operating conditions, coupled with specific configurations of different oil spill response aircraft and their spray systems (boom and nozzle configurations). The DST uses a Response Surface Curve (RSC) for each airframe to predict the drift extent of dispersant particles and mass deposition concentration, the RSC for each airframe was derived from a database of results generated using the latest CFD modeling technology. The studies conducted to generate data for the DST RSCs provided considerable insight into the relationships between the particle dispersant behavior for different airframe types. Trends were identified in particle dispersion behavior when airframes were flown with a heavy payload (full weight) compared to lighter payload (empty weight). These trends change depending on the airframe used and, more specifically, the location and arrangement of the boom used to release the droplets relative to the location of the main wing. Change in Particle Size Distribution (PSD) was also investigated for flight operations of one airframe and the impact on the drift extent reported. The DST will provide oil spill responders with information related to the extent of any areas potentially impacted by dispersant drift. This will assist the operational control personnel in establishing setback distances, information which becomes increasingly important as a spill escalates beyond a Tier 1 response where the size of the spill, and the resources committed, become significant. In addition, the DST generates a contour plot of mass deposition at ground level based on the operational and environmental parameters input to the program, providing the user with a graphical display of where the majority of the aerial dispersant is predicted to land. While the analysis and tool development are complete, a formal peer review has not been completed at the time of the paper publication.