This study presents a systematic investigation into the collapse jet and migration dynamics of bubbles near a cylindrical boundary and a free surface within confined spaces. A quantitative investigation is carried out to elucidate the impact of the cylinder radius, the bubble-free surface distance, and the bubble-cylinder distance. Three typical jet cases are classified: right-biased jet, downward jet, and left-biased jet. As the bubble-cylinder distance increases, the jet evolves from a right-biased jet to a downward jet and further to a left-biased jet. The regions are classified as cylinder dominated, co-dominated, and free surface dominated. As the cylinder radius increases, the cylinder dominated region expands, but the free surface dominated region remains larger. In addition, the bubble splits into two unequal parts in the terminal phase of collapse. The area ratio of the two split bubbles increases with increasing bubble-free surface distance and decreasing bubble-cylinder distance.
This study investigates the effect of shot peening (SP) on the fatigue strength and harmless defect behavior of solution-treated laser powder bed fusion (LPBF) 18
Conventional thermoacoustic network models often assume an acoustically compact flame, which can misrepresent elongated heat-release zones and their phase-lag effects. This study develops a low-order thermoacoustic network framework that accounts for the spatial flame structure by dividing the combustor into unburned, flame, and burned zones. The pseudo-one-dimensional model solves the linearized Euler equations within this specialized tri-zone formulation in each section, coupling them using cross-sectionally weighted properties and a spatially resolved flame transfer function. Axial distributions of local gain and time lag are extracted and incorporated into eigenfrequency and growth-rate analyses. The predictions are validated against a three-dimensional multiphysics simulation with detailed flame dynamics and compared with a conventional thin-flame network model. The proposed framework accurately reproduces the unstable modes and growth rates by accounting for localized Rayleigh driving mechanisms, whereas the conventional compact-flame approximation underestimates growth rates and shifts instability frequencies. These results demonstrate the importance of spatially resolved flame dynamics and structural zoning in low-order thermoacoustic modeling.
To address the trade-off between radiator soil protection and cooling efficiency in motorcycles, this study optimizes radiator cover structures to balance contamination resistance and thermal performance. A high-fidelity computational domain model of the motorcycle’s external flow field was established via STAR-CCM+ (k-ε turbulence model). Four structural parameters—cover-core gap, upper guide angle, grille hole inclination, and guide plate opening—were numerically evaluated. The optimal design was experimentally validated through vehicle chassis thermal balance tests and human thermal comfort assessments. CFD results reveal that the conventional standard cover induces a 13
