Enstrophy transport in swirl combustion

Abstract

The contributions of vortex stretching, dilatation, baroclinic torque and viscous diffusion to Reynolds-averaged enstrophy transport in turbulent swirl flames were experimentally measured using tomographic particle image velocimetry and $\text{CH}_{2}\text{O}$ planar laser induced fluorescence at jet Reynolds numbers of 26 000–51 000. The mean baroclinic torque was determined by subtracting the other terms in the enstrophy transport equation from the mean Lagrangian derivative. Enstrophy production from baroclinic torque was found to be significant relative to the other transport terms across all conditions studies. This result contrasts with direct numerical simulations of flames in homogeneous isotropic turbulence, which show a decreasing relative significance of baroclinic torque with increasing turbulence intensity (e.g. Bobbitt, Lapointe & Blanquart, Phys. Fluids, vol. 28 (1), 2016, 015101). Hence, the significance of baroclinic enstrophy production in flames is not determined entirely by the local turbulence and flame properties, but also depends on the configuration-specific pressure field.

Physical space analysis of cross-scale turbulent kinetic energy transfer in premixed swirl flames

“…The experimental setup is identical to that described in Refs. [5,13,14] and only a brief summary is given here. The model gas turbine combustor (Fig.…”

Flame- and flow-conditioned vorticity transport in premixed swirl combustion

“…Experiments were performed using simultaneous tomographic particle image velocimetry (TPIV) and CH 2 O planar laser induced fluorescence (PLIF) in three unconfined premixed swirl flames. The experimental setup was identical to that presented in our previous work [24]; only a brief summary is given here. Flames were stabilized using a gas turbine model combustor (Fig.…”

“…Several methods of estimating c from the CH 2 O PLIF signal are discussed by Kazbekov et al [24], including assuming an infinitely thin flame [29,30] with c = 1 downstream of the CH 2 O; a three-value approach with c = 0 upstream of the CH 2 O, c = 0.5 in the CH 2 O, and c = 1 downstream of the CH 2 O; and based on linearly interpolating between the two bounding edges of the CH 2 O-containing region, with the reactant edge corresponding to c = 0 and the product edge corresponding to c = 1. The results were found to be qualitatively independent of the method of calculating c, with the latter two methods producing effectively identical quantitative results in the statistics.…”

“…Uncertainty in IV is controlled by under-resolution of the velocity field, which results in a systematic bias towards smoother velocity gradients. The effects of under-resolution were evaluated in Kazbekov et al [24] by performing the complete analysis with different spatial resolutions (i.e. final interrogation box sizes).…”

Numerical and experimental investigations on inflow loss in the energy recovery turbines with back-curved and front-curved impeller based on the entropy generation theory

“…On the right side of the equal sign, the first term is the unit work from the surface pressure gradient in the streamline direction, the second term is nonlinear effects of vorticity and velocity field in viscous fluids, and the last term is the loss of energy by viscosity and turbulent fluctuation. W ¼ mj6j 2 is defined as the entropy generation rate which is always a positive value and directly related to the loss of energy [34].…”