Axisymmetric jet shear-layer excitation by laser energy and electric arc discharges

Two energy deposition methods (electric arcing and laser-induced optical breakdown) were used to force and control compressible mixing layers of axisymmetric jets. The effects of energy-deposition forcing methods have been experimentally investigated with schlieren imaging, particle image velocimetry, product formation flow visualizations, and high-frequency pressure measurements. Large-scale structures were forced in perfectly expanded jets with nozzle-exit Mach numbers of 1.38,1.5, and 2.0, utilizing single pulse-laser energy deposition focused at the nozzle exit. Structures were successfully forced over a range of convective Mach numbers from 0.63 to 0.85 using laser pulse energies from 5 to 40 mJ. The large-scale structure forced by laser perturbation in the Mach 1.38 jet was characterized with detailed measurements of the velocity and vorticity fields and the fluctuating pressure history. The measured convective velocity of the forced structure was approximately 25% above-isentropic theory, and the structures had a growth rate 2.1 times the undisturbed shear layer. Also, multiple-pulse electric arc discharges were induced locally at the nozzle exit and investigated with schlieren imaging. Electric arc frequencies ranging from 1 to 18 kHz for the Mach 1.38 jet were investigated with Strouhal numbers from 0.32 to 0.56 having the greatest effect.