Formation mechanism and control of microclimate zone with low velocity ratio jet in coal mining face

Optimizing cooling efficiency in confined spaces with high-temperature crossflows, such as underground mines, remains a major challenge. This study investigates the formation and control of localized head–neck microclimates using multi-stage, low-velocity-ratio (R) jets in crossflow. The work establishes a vortex-structure–guided spacing principle that links the evolution of hairpin vortices to the continuity of cooling zones. Experimental flow visualization combined with large-eddy simulation reveals that the evolution and breakdown of hairpin vortices divide the flow field into four regions—strong attachment, weak attachment, fragmentation, and dissipation—each with distinct cooling characteristics. Based on this classification, a variable-spacing strategy is proposed, positioning downstream jets within the weak attachment zone of upstream vortices to effectively utilize residual cooling energy and maintain a continuous low-temperature region. Compared with uniform-spacing arrangements, the proposed design reduces the dimensionless temperature decay rate by 54.4% at the fifth-stage jet and suppresses excessive mixing, leading to lower energy dissipation and extended cooling coverage. These findings provide new insights and practical guidance for airflow management in mitigating heat hazards at coal mining faces.