An experimental study on the performance of fire extinguishing system according to the agent charging condition and nozzle type.

In confined environments such as aircraft, an increase in mass impacts the overall system's performance, thus requiring sophisticated management. To verify whether the performance characteristics of fire extinguishing systems used in aircraft are satisfied, in this study was built a 1:1 scale test model. We examined the influence of the initial charge state and nozzles. Further, it measured the pressure inside the pipelines and vessels where multiple nozzles are installed to identify the flow and diffusivity characteristics of HFC-125 inside the pipelines and vessels. At a charging ratio of 54%, the initial pressure drop was smaller, and the lowest pressure before the bubble release point appeared 0.26 s later than when the charging ratio was 76%. The average pressure of each nozzle was 275.8 kPa higher under a charging ratio of 54% than 76% and increased further when the average concentration change was 54%, indicating that diffusivity increased. Although improvements occurred according to the charging ratio, the improvements according to the HFC-125 charging mass were more significant.

High frequency formulation for the acoustic power spectrum due to cascade-turbulence interaction.

This paper investigates the noise radiated by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. An analytic formulation for the spectrum of acoustic power of a two-dimensional flat-plate is derived. The main finding of this paper is that the acoustic power spectrum from the cascade of flat airfoils may be split into two distinct frequency regions of low frequency and high frequency, separated by a critical frequency. Below this frequency, cascade effects due to the interaction between neighboring airfoils are shown to be important. At frequencies above the critical frequency, cascade effects are shown to be relatively weak. In this frequency range, acoustic power is shown to be approximately proportional to the number of blades. Based on this finding at high frequencies, an approximate expression is derived for the power spectrum that is valid above the critical frequency and which is in excellent agreement with the exact expression for the broadband power spectrum. The formulation is used to perform a parametric study on the effects on the power spectrum of the blade number, stagger angle, gap-chord ratio, and Mach number. The theory is also shown to provide a close fit to the measured spectrum of rotor-stator interaction.