Influence of g-jitter on a laminar boundary layer type diffusion flame

Abstract

A numerical study was conducted to analyze the effect of g-jitter on micro-gravity flames. A boundary layer laminar diffusion flame was used as a test case. This configuration is commonly used to study flame spread in microgravity, thus it is essential to understand the role of g-jitter in these flames. Furthermore, the role of buoyancy increases with the stream-wise coordinate permitting a systematic study of the impact of acceleration perturbations with a reduced number of experimental results. The evolution of experimental stand-off distances defined during parabolic flights compared well, in a qualitative manner, with numerical simulations, validating the aerodynamic aspects of the model. A systematic study using a sinusoidal function showed that perturbations characterized by high frequencies (>1 Hz) do not affect the flame stand-off distance. This is independent of the amplitude within the range of typical perturbations observed during parabolic flights. Perturbations occurring at lower frequencies significantly affected the flame geometry. Averaging over time through periods much longer than the perturbation cycle did not eventually reveal departure from purely zero-gravity flames. Fuel and oxidizer velocities have opposite effects on the sensitivity of the flames to gravity fluctuations. An increase in oxidizer velocity results in a sensitivity decrease. The influence of the multiple parameters of the problem can qualitatively be combined within a previously reported non-dimensional group. Nevertheless, it cannot account for the influence of frequency.