Abstract

Base drag constitutes a major fraction of the total drag on aerospace vehicles at sonic and supersonic speeds, arising from the low-pressure, recirculating wake behind a blunt rear face. Reducing it yields large gains in range and payload, motivating the study of base flow control. This study reviews active methods—principally micro-jet injection and base bleed—and evaluates them against established passive techniques. The governing flow physics is examined through shear-layer separation, the dead-air recirculation zone, and the reattachment process that fixes base pressure, characterized via the base pressure coefficient. Drawing on experimental and computational studies of suddenly-expanded ducts and nozzles, the report assesses how active control raises base pressure relative to the uncontrolled baseline and identifies where each method is most effective.

Keywords

base flow, base pressure, active flow control, supersonic; sonic, micro-jet, base bleed, drag reduction