Experimental Study on Base Drag Reduction with Combined Lateral and Axial Injection

Abstract

Experiments have been performed in a two-dimensional (2D), planar Mach 2 wind tunnel to study injection and combustion processes around a simulated projectile base. Lateral injection and external burning (EB) of hot fuel-rich reaction products from solid propellants, axial base injection (BI) of helium and nitrogen, and combined EB and BI have been studied. Test results show that the two base pressure rise mechanisms associated with EB and BI can be superimposed. Moreover, the base pressure rise associated with combined EB and BI was found to be higher than with EB or BI alone. NomenclatureA =area BB =base burning with axial fuel injection through projectile base into viscous near-wake region BI =base injection through projectile base without combustionburning in inviscid flow region achieved by lateral supersonic injection velocity EB/BR = external burning/base reaction achieved by lateral subsonic injection velocity h = base height / = injection parameter = m J /u 1 p 1 A b 7 sp = specific impulse = &p b A b /rhj M -Mach number m -mass flow p = static pressure RSP = rear stagnation point u = axial velocity component T = temperature X = axial coordinate measured from base a. = corner flow turning angle A/? = pressure rise due to injection and/or combustion K = ratio of specific heats p = density Subscripts 1 = condition before base corner expansion b = base £(ax) =in connection with A/?: base pressure rise due to axial injection in tests with EB and BI [A/7 Max) = (Ap b with BI and EB) -(Ap b with EB)] PM= primary motor j = injector ax = axial lat = lateral tot = total (in connection with 1:7 tot = 7 ax + 7 lat ) t = total (in connection with p: total pressure as determined with pressure probe) t(PM) = throat (primary motor)Presented as Paper 78-25 at