Effect of inter-module spacing on a clustered linear aerospike nozzle jet interacting with outer flow

This work experimentally characterizes the cold-flow field of a clustered, truncated linear aerospike nozzle with and without outer flow. Planar particle image velocimetry and time-resolved schlieren measurements are performed in a controlled wind tunnel environment. Two inter-module spacings are realized by means of a fully activated cluster and a layout with alternately deactivated modules. In the case of nozzle flow only, increased spacing splits the composite plume into largely uncorrelated plumes, each with a narrower shock cell system. The outer plumes expand laterally into the ambient, while the center plume experiences higher effective back pressure, resulting in shorter shock cells. Two unsteady modes appear across the nozzle pressure regimes: a plug base wake mode (shear layer–trailing shock interaction) and a jet screeching mode. When increasing the inter-module spacing, jet screeching is recorded to be suppressed, and two slightly offset plug base wake mode frequencies are observed. With outer flow, the jet unsteadiness increasingly localizes toward the plug base and shock interaction regions. The measured flow field is dominated by outer flow modes (bluff-body vortex shedding at sub/transonic, shear layer flapping at supersonic outer flow). No nozzle flow modes are detected within the field of view when the outer flow is present.