Abstract :

The investigation of fluid mechanical processes that act as facilitators in the excitation of combustion driven instabilities. The basic motivation for such studies lies in the fact that once such a process has been identified to a sufficient level of confidence, suitable design or operational modifications can be suggested which can inhibit the process under consideration and can improve the overall stability of a given combustor. In particular, I will talk about a particular problem related to the problem of combustion instability in liquid rocket engines. Through controlled flame acoustic interaction experiments, in which a turbulent GH2-GO2-GH2 diffusion flame is acoustically forced by a driver unit mounted in a transverse direction, it will be shown that the fluid mechanical process of baroclinicity, generated due to the interactions between misaligned pressure gradient (in the transversely directed acoustic wave) and density gradient (at the fuel-oxidizer interface) could cause large scale wrinkling of the flame front thereby causing significant modulations in heat release oscillations. At the early stages of flame development, any such mechanism that modulates heat release could make the combustor susceptible to thermo-acoustic instabilities once conditions for coupling with pressure oscillations become favorable. To the knowledge of the author, this kind of mechanism involving intermittent baroclinic torque arising from the interactions between misaligned pressure and density gradients has never been reported in liquid rocket engine instability studies. Since the physical process of baroclinicity depends on the density gradient between fuel and oxidizer, a tailoring of the density gradient between fuel and oxidizer could be suggested as a method to discourage this process from occurring, thereby improving the stability of the engine.