In this study we investigate, both numerically and experimentally, the interplay between the intrinsic Darrieus-Landau (DL) or hydrodynamic instability of a premixed flame and the moderately turbulent flow field in which the flame propagates. The objective is threefold: to establish, unambiguously, through a suitably defined marker, the presence or absence of DL-induced effects on the turbulent flame, to quantify the DL effects on the flame propagation and morphology and, finally, to asses whether such effects are mitigated or suppressed as the turbulence intensity is increased. The numerical simulations are based on a deficient reactant model which lends itself to a wealth of results from asymptotic theory, such as the determination of stability limits. The skewness of the flame curvature probability density function is identified as an unambiguous morphological marker for the presence or absence of DL effects in a turbulent environment. In addition, the turbulent propagation speed is shown to exhibit a distinct dual behavior whereby it is noticeably enhanced in the presence of DL instability while it is unchanged otherwise. Furthermore, increasing the turbulence intensity is found to be mitigating with respect to DL-induced effects such as the mentioned dual behavior which disappears at higher intensities. Experimental propane and/or air Bunsen flames are also investigated, utilizing two distinct diameters, respectively, above and below the estimated DL cutoff wavelength. Curvature skewness is still clearly observed to act as a marker for DL instability while the turbulent propagation speed is concurrently enhanced in the presence of the instability.

This study is devoted to the investigation, by means of direct numerical simulation, of the interaction between turbulent motions and the pseudo-boiling process. To this end, fully resolved data of a transcritical nitrogen jet are used, obtained via high order methods and using detailed thermodynamic and transport properties. A laminar pseudo-boiling process is simulated in a quiescent setting and used as a consistent reference to shed light on the mutual effects of the jet evolution and thermodynamic non-linearities. In the turbulent scenario, pseudo-boiling is shown to be faster, in an average sense, to the laminar reference case. A consistent definition of the pseudo-boiling rate, based on the concept of the displacement speed, commonly used in premixed flame propagation, is introduced and, for a better physical interpretation, split into a normal diffusion component and a curvature component. The pseudo-boiling rate is statistically analyzed to evaluate the rate of mass transfer from the liquid-like state to the gas-like state during the jet evolution. Normal diffusion is found to be the dominant component of the pseudo-boiling rate, while the curvature component is shown to have a role only when warm fluid pockets are deeply entrained in the jet cold core.