Abstract: The 4 main structural parameters of double row suction nozzles for 150mm reverse circulation drill bits used in multilayer goaf drilling were optimized by orthogonal design method and CFD(computational fluid dynamics) analysis. The analysis results indicated the primary and secondary orders as follows: the inclination angle(θ_s)， the horizontal deflection angle(θ_d)， the vertical space (L) and the horizontal space (S)， with the most optimal parameter combination being θ_s=30°， θ_d=10°， L=-15mm and S=10mm. At the same time， the 150mm reverse circulation drill bit which adopts the most optimal parameter combination was carried on the multilayer goaf drilling test. The test results showed that the reverse circulation drilling can still be achieved through the first layer goaf， and the rock sample with large particles can be continuously discharged from the borehole bottom to the earth surface. The problem on multilayer goaf drilling and measurement in mines can thus be resolved.

Key words: reverse circulation drill bit, double row suction nozzle, orthogonal design, CFD analysis, multilayer goaf drilling