Numerical Simulation of Dispersion of Fire Extinguishing Agents in Turbulent Flow in the Presence of Clutter Elements of Aircraft Engine Nacelles

Abstract

The combination of highly turbulent airflow, flammable fluids, and numerous ignition sources makes aircraft engine nacelles a difficult fire zone to protect. Better understanding of nacelle air flow and how it influences the spread of fires and fire extinguishing agents is needed to improve the efficiency of fire suppression. The principal objective of this study is to analyze the flow field and the dispersion of fire extinguishing agents in the presence of various clutter elements of aircraft engine nacelles. Three dimensional simulations of the transport of liquid droplets in highly turbulent flow past clutter elements are performed in this study. A three dimensional model with 2000 mm length, 915 mm width and 610 mm height was first created. The clutter package consists of 16 cylindrical elements; each element has an outer diameter D of 50.8 mm and assembled to form three separate arrays of 5, 6 and 5 elements. The stream wise spacing between each clutter array is set to twice the diameter (2 D). The three dimensional geometry is similar to the one used in the experimental study at Sandia National Laboratory. This will help to validate the numerical results before performing a parametric study. Water with initial droplet size of 150 to 280 μm, and flow rate of 0.285 Kg/s is used as suppressant agent. The three velocity components, turbulence intensity, and droplet concentrations and trajectories behind the clutter package are obtained in this study. The droplet X-velocity and Y-velocity and the droplet size distribution downstream the clutter elements show a good agreement with the experimental data. The effect of initial turbulence intensity, the air flow velocity at the inlet, and droplet diameter at the injection on the transport and dispersion of fire extinguishing agent in this complex geometry is presented in this paper.