Numerical Investigation of the Micro-Jets Efficiency for Jet Noise Reduction

Abstract

in this paper, we present aerodynamic and acoustic simulated results from a 50 mm single stream nozzle with continuous and pulsed micro-jets. It follows a former paper presenting the main results observed with continuous control and gives more detailed aerodynamic analyses on these configurations, as well as new results with pulsed micro-jets. Isothermal and hot main jet configurations are considered with an acoustic Mach number Ma = Vj/a∞ set to 0.9. Control is made through 12 micro-jets located around the nozzle exit with an impinging angle of 45 degrees to the jet axis; their temperature and velocity are identical to the main isothermal jet configuration. Instantaneous aerodynamic fields are obtained with a LES model using the MILES approach and the acoustic far field is computed with the Ffowcs-Williams and Hawkings surface integral formulation. When the control is active, jet flow investigations show a reduction of the turbulence in the shear layer and a decrease of the far field broadband noise, for all micro-jets configurations. Broadband noise reduction is more effective with pulsed control, which nevertheless generates penalizing tonal noises. Azimuthal analysis demonstrates that continuous control decreases all pressure modes in the near field. Pulsed control lead to a more complex behavior but also results in a global modes reduction for x/D ≥ 3. To end, computation of the thrust highlights the great interest of pulsed control for jet noise reduction, as it requires the minimum mass flow injection to work and gives the minimum thrust loss.