Screech is a high frequency tonal noise generated from afterburners (AB, for short and used for thrust augmentation in gas turbine engines) as a result of coupling of combustion heat release fluctuations with the acoustic modes of the afterburner. Liner, which is a perforated annular chamber enclosing the flame holder and extending through the length of the AB acts as passive damping device to suppress amplification of acoustic oscillations. The damping characteristics of the liner are dependent on the size, number and more importantly the Mach numbers of the bias and grazing flow. We are developing a CFD based tool for design of acoustic liners for ABs.
A new and novel approach to modeling composite propellant burn rate behavior is proposed based on the fact that composite propellant combustion is largely boxed between the premixed limits – of pure AP and fine AP-binder (HTPB, here) whose burn behaviors are taken as known. The current strategy accounts for particle size distribution using the burn time averaging approach. The specialty of the present approach is that it invokes local extinction for fuel rich conditions for specific particle sizes when the heat balance causes the surface temperature to drop below the low pressure deflagration limit of AP; this feature allows for the prediction of extinction of propellant combustion. Comparisons of burn rate data over nearly thirty compositions from different sources appear excellent to good. (Read More...)
S. Varunkumar et al. Combust. Flame, 173 (2016)