- Author
- Prasad, K. R. | Patnaik, G. | Kailasanath, K.
- Title
- Advanced Simulation Tool for Improved Damage Assessment. Part 2. Water-Mist Suppression of Large Scale Compartment Fires. NRL Memorandum Report.
- Coporate
- Naval Research Laboratory, Washington, DC Science Applications International Corp., VA
- Sponsor
- Office of Naval Research, Arlington, VA
- Report
- NRL/MR/6410-00-8507, December 29, 2000, 27 p.
- Keywords
- fire suppression | compartment fires | water mist | damage | large scale fire tests | formulations | vapor phases
- Identifiers
- multiblock techniques
- Abstract
- This report is the second in a series that discusses the development of an advanced simulation tool for improved damage assessment. In the first report, we described a multiblock technique to simulate the reactive fluid flow inside large complex enclosures. We adopted a domain decomposition method, based on the multiblock. Chimera technique, which allows a system of relatively simple grids, each describing a component of the complex geometry, to be combined into a composite mesh for solution to complex flow fields. Using this approach we studied fires in a single uncluttered compartment and predicted smoke spread in multi-compartment ship geometries. These simulations demonstrated the capability of the tool to simulate complex flow fields in large multi-compartment enclosures. In this report we focus on the suppression of fires in large compartments and conduct parametric studies to optimize various water mist injection characteristics for maximum fire suppression. Fine water mist relies on relatively small (less than 200 mum) droplet sprays to extinguish fires. For optimum use of water mist systems, the various physical processes involved in the interaction of water mist spray and the fire should be clearly understood. Typically, water mist is injected through various strategically located nozzles into a fire compartment. The turbulent flow field in the fire compartment may consist of a fire plume consisting of hot combustion products rising above the fuel source. The fire plume hits the ceiling and spreads along the ceiling. Vertical structures are continuously generated as fresh air is entrained into the fire. The flow of water droplets through such a, hot turbulent environment should be understood. Besides there might bc actual physical barriers or obstructions in the fire compartment that may prevent water mist from reaching the fire source. Once the water mist starts interacting with the fire source, the mechanism of fire suppression may include gas phase cooling (thermal effect), oxygen displacement by steam, wetting of fuel surface and attenuation of radiative heat transfer. Efforts to explain the mechanisms of extinguishment of fire, and to identify the parameters that are crucial to system design, benefit greatly from the application of computational models to simulate the dynamics of fires. Research indicates that the relationship between spray characteristics, fuel properties, compartment geometry and the probability of extinguishment is a multi-variable problem that can best be analyzed using computational models. This report describes numerical simulations of water-mist suppression of fires in large complex enclosures, to better understand and probe these issues.