A Numerical Analysis of Transonic/Supersonic Flows in the Axisymmetric Main Nozzle of an Air-Jet Loom

Abstract

This paper reports a numerical analysis of transonic flows in the axisymmetric backward-facing step main nozzle of an air-jet loom. To obtain basic design data for the optimum main nozzle shape of an air-jet loom and to predict transonic/supersonic internal flows, a characteristic-based, upwind flux difference-splitting, compressible Navier-Stokes method is used. Wall static pressure and flow velocity distributions in the nozzle are analyzed by changing air tank pressures and acceleration tube lengths. The flow inside the nozzle experiences double choking, first at the needle tip and then at the acceleration tube exit at air tank pressures near 4 kgf/cm2. The air tank pressure that leads to critical conditions depends on acceleration tube length, i.e., higher air tank pressures for longer acceleration tubes. The air pressure required to bring the acceleration tube exit to sonic conditions is nearly constant regardless of acceleration tube length. The round needle tip shape could lead to less total pressure loss when compared with step shape.