Field and Experimental Research on Airflow Velocity Boundary Layer in Coal Mine Roadway

Abstract

There is an airflow velocity boundary layer near tunnel wall when the air is flowing in the undergro- und coal mine. The thickness and distribution of the airflow velocity boundary layer could influence the discharge of harmful and toxic gases that enter the ventilating airflow through this flow interface. It may also have a major impact in coal mine gas explosion. The results of field measurements and simulation experimental data are used to research airflow velocity boundary layer in a flat walled mine roadway, which is considered in turn: as unsupported, I-steel sectioned arch or bolted and shot create supported cross section. By referenced to other literature studies that consider boundary layer characteristics and the analysis of on-site and experimental data sets we obtain the corresponding airflow velocity boundary layer characteristics for each of the supported roadway sections. The airflow velocity within the boundary layer increase is assumed to follow a logarithmic law given by the expression: u = a Ln( x ) + b . It is concluded that the thickness of the airflow velocity boundary layer is observed to significantly decrease with the airflow center velocity and to increase with roadway wall roughness. The airflow velocity distribution is found to be described by the equation: u = ( m 1 v + n 1 )Ln( d ) + m 2 v + n 2 , for the three types coal mine tunnel taking into account the influence of center airflow velocity.