Computational Analysis of the Secondary Flow Injection for the Drag Reduction of the Plug Nozzle

Abstract

The flows over annular plug nozzles are numerically simulated and the effect of the clustered secondary flow injection on the boat-tail drag reduction is investigated. The plug nozzle configuration is taken from the ATREX (Air Turbo Ram jet) engine under development at the ISAS. The simulations are carried out using the three-dimensional thin-layer Navier-Stokes equations. First, the effect of the secondary flow injection through the clustered slots with the sonic condition given at the slot exits on the boat-tail surface is investigated and the result is compared to that of the axisymmetric slit injection in the previous study. The computed result for the clustered slot injection shows that the wall pressure downstream of the injection clearly increases and the boat-tail drag is reduced by about 40%. The result justifies that the effect of the secondary flow injection demonstrated by the simplified simulation with the axisymmetric slit injection also exits for the clustered slot injection. In addition, the result shows that the clustered secondary flow injection is more efficient than the axisymmetric slit injection. The flow field with the secondary flow injected directly fiom the inner nozzle to the boat-tail region is next investigated. The comparison of the result for the secondary flow injected directly fiom the inner nozzle and the reslt for the secondary flow given as a sonic condition at the exit shows that there is little difference in the flow structure and the pressure distributions over the boat-tail region. The pressure thrust decreases by 12% since a part of the exhaust gas in the inner nozzle is used as the secondary flow. The total thrust of the plug nozzle inmases by about 7.5% even with the pressure thrust reduced by the secondary flow injection.