In this study, the effects of several geometry factors (fin front angle, clearance, number of fins, and honeycomb cell diameter and depth) on the mass flow function of solid and honeycomb land were studied experimentally. The fin front angle considered in the experiment ranged from 60 to 90 degrees, the number of fins was varied between two and three, and the diameter and depth of the honeycomb cell ranged from 1.33 to 4.00 times and 8.08 to 13.08 times the thickness of the fin tip, respectively. The experimental results showed that the mass flow function decreased as the number of fins increased for the solid land labyrinth seal, and the mass flow function increased as the clearance increased. A fin front angle of 60 degrees was found to have the minimum mass flow function. For the honeycomb land labyrinth seal, the mass flow function decreased as the number of fins increased, and the effect of the cell depth was shown to be insignificant compared to the effect of the cell diameter. The effects of cell diameter and cell depth on the mass flow function depended on the conditions of other variables. In addition, the correlation equations of the mass flow functions of the solid land and honeycomb land labyrinth seals are presented based on the experimental results, which represent the effects of the fin front angle, clearance, pressure ratio, and diameter and depth of the honeycomb cell. The correlation equation for the solid land labyrinth seal had an $r^2$ value of 0.9822, while the correlation equation for honeycomb land had an $r^2$ value of 0.9621.

Micromix combustion is a promising approach to addressing issues such as flashback, combustion instability, and nitrogen oxide (NO_x) emissions in hydrogen-fueled gas turbines. In this study, a numerical analysis was conducted to investigate key factors influencing NO_x emissions in a lab-scale micromix combustor under atmospheric pressure and room temperature. The effects of air flow rate, equivalence ratio, and combustor component surface temperature on NO_x formation were systematically evaluated. The results show that increasing the air and hydrogen flow rates at a constant equivalence ratio reduced NO_x emissions due to shorter residence times. In addition, higher surface temperatures of combustor components increased flame temperatures and NO_x production. Lastly, high equivalence ratios led to partial flame merging, increasing NO_x emissions. These findings highlight that the efficient cooling of combustor components and proper selection of air flow rate and equivalence ratio are critical to minimizing NO_x emissions in micromix combustors. The study provides design and operational guidelines for the future development of hydrogen-fueled gas turbines.

Spiders utilize their fine silk fibers for their aerial dispersal, known as ballooning. With this method, spiders can disperse hundreds of kilometers, reaching as high as 4.5 km. However, the passive dynamics of a ballooning model (a highly flexible filament and a spider body at the end of it) are not well understood. Here, we introduce a bead–spring model that takes into account the anisotropic drag of a fiber to investigate the passive dynamics by the various non-uniform flows: (i) a shear flow, (ii) a periodic vortex flow field, and (iii) a homogeneous turbulent flow. For the analysis of the wide range of parameters, we defined a dimensionless parameter, which is called “a ballooning number.” The ballooning number is defined as the ratio of Stokes’ fluid-dynamic force on a fiber by the non-uniform flow field to the gravitational force of a body. Our simulations show that the present model in a homogeneous turbulent flow exhibits the biased characteristic of slow settling with increasing turbulence. Upon investigating this phenomenon for a shear flows, it was found that the drag anisotropy of the filament structure is the main cause of the slow settling. Particularly, the cause of slow settling speed lies not only in the deformed geometrical shape but also in its generation of fluid-dynamic force in a non-uniform flow. Additionally, we found that the ballooning structure could become trapped in a vortex flow. These results help deepen our understanding of the passive dynamics of spiders ballooning in the atmospheric boundary layer.