Breakup processes of pressure swirl spray in gaseous cross-flow

• First systematic experimental investigation of pressure swirl spray in cross flow.
• Breakup regimes, their orderly transitions and dependence on swirl number explained.
• Breakup structures and their transient developments are closely investigated.
• Tri-modal distribution of resultant droplets from bag breakup process is studied.
• Correlation for spray trajectory and instability waves on windward liquid sheet.

Injection of liquid fuel in cross flowing air has been a strategy for future aircraft engines in order to control the emissions. In this context, breakup of a pressure swirl spray in gaseous cross-flow is investigated experimentally. The atomizer discharges a conical swirling sheet of liquid that interacts with cross-flowing air. This complex interaction and the resulting spray structures at various flow conditions are studied through flow visualization using still as well as high speed photography. Experiments are performed over a wide range of aerodynamic Weber number (2–300) and liquid-to-air momentum flux ratio (5–150). Various breakup regimes exhibiting different breakup processes are mapped on a parameter space based on flow conditions. This map shows significant variations from breakup regime map for a plain liquid jet in cross-flow. It is observed that the breakup of leeward side of the sheet is dominated by bag breakup and the windward side of the sheet undergoes breakup through surface waves. Similarities and differences between bag breakup present in plain liquid jet in cross-flow and swirl spray in cross-flow are explained. Multimodal drop size distribution from bag breakup, frequency of bag breakup, wavelength of surface waves and trajectory of spray in cross-flow are measured by analyzing the spray images and parametric study of their variations is also presented.