Identification and characterization of coherent structures in gasoline injector nozzle flow using proper orthogonal decomposition

Proper orthogonal decomposition (POD) methodology is used to identify and characterize coherent structures in the gasoline nozzle flow. A correlation matrix is generated from the fluctuating velocity data snapshots produced by in-house Large Eddy simulations (LES) of an internal flow of a gasoline nozzle at a pressure of 1.1 MPa (11 bar). The modes obtained from the solution of correlation matrix identify the most energetic and dominant recirculation zones along with strong axial and radial pulsations. Initial modes show big vortical structures and inter-mode coupling but later modes identify less energetic, smaller and uncoupled structures. The dominant modes demonstrate the key role of highly energetic large coherent structures in the flow organization at the exit of the injector. The frequencies obtained from Fast Fourier transform (FFT) analysis of axial and radial fluctuating velocities give an additional insight to the characteristics of important coherent structures that govern the nozzle flow.