Adjoint-based control of turbulent jet noise

摘要: Noise is an important factor in certifying airplane and more restrictive noise regulations have demanded the design of quieter aircraft, with much emphasis focused on lower jet-noise emission. Previous passive active noise-reduction strategies required parametric experiments or cut-and-try approaches, a fact largely attributed to complexity turbulence as source sound subtlety sound-production mechanism. Both aeroacoustic theory high-fidelity simulation demonstrated that turbulence-generated can be predicted sufficient accuracy; however, they not been able generally guide efforts so far. Adjoint-based optimization provides unique useful tool pursue reduction systematic approach. The adjoint perturbed linearized Navier – Stokes equations crafted provide control sensitivity direction decreasing noise. Thus, despite jet physical space, noise-reducing controls directly explored parameter space. Prior work has shown adjoint-based are capable significantly suppressing from two-dimensional subsonic free shear flows via subtle modification large-scale vortex dynamics. The used here reduce radiation pressure-matched Mach 1.3 cold computed using high-fidelity, non-dissipative, high-order finite differences generalized curvilinear meshes. A large-eddy approximation conducted smallest scales turbulent motion approximated dynamic Smagorinsky sub-grid-scale model. For time horizon over which applied, most intense events almost completely removed. At exhaust angle 30 degree, far-field peak spectral 5.6 dB at column mode frequency overall pressure level reduced by 1.6 dB. 90 degree (sideline) angle, insignificant; there no adverse increase commonly found experimental efforts. Fourier analysis proper orthogonal decomposition investigate before after applied. coherent vortical slightly, but importantly, adjusted Most notably, coalescence associated intermittent sound-generating mechanisms. intermittently loud acoustic removed space–time localized alters tearing-like interaction appears lead for uncontrolled jet. There proofs available concerning convergence global minimum radiated sound, thus far applied this failed achieve same ~10 seen previous studies mixing layers. This greater…