Turbulence Distortion Effects in Airfoil Leading-Edge Noise:Insights from Lattice Boltzmann Simulations

Kurzfassung

Turbulence-airfoil interaction constitutes a primary broadband noise source in numerous aeroacoustic applications. Classical prediction frameworks, following Amiet's flat-plate model, assume that incoming turbulence convects to the leading edge without modification. The present work challenges this assumption by demonstrating, through high-fidelity lattice Boltzmann simulations of a NACA 0012 airfoil at chord-based Reynolds number Re_c approximately 5.1 x 10^5 and free-stream Mach number M = 0.059, that the turbulence field undergoes a systematic, scale-dependent, and component-dependent transformation before impacting the airfoil surface.

A distortion mapping operator D(k, theta) is introduced that relates the upstream spectral tensor Phi_infinity_ij to the pre-impact tensor Phi_LE_ij in the stagnation region, with the non-dimensional wavenumber kappa = k r_LE governing the transition between strong and weak distortion regimes. Reynolds-stress budgets and Lumley invariant trajectories reveal irreversible tensorial reorganisation of the turbulence state, including a transient eigenvalue reordering that cannot be captured by scalar or isotropic corrections.

Patch-based spectral comparisons confirm that the mapping Phi_infinity to Phi_LE is frequency-dependent and component-dependent, with wall-normal fluctuations preferentially suppressed at large scales, kappa less than or approximately equal to 1, and cross-plane energy redistributed non-uniformly around the leading edge at smaller scales. These results establish turbulence distortion as a physically necessary pre-conditioning stage that must be accounted for explicitly in predictive models of leading-edge noise, rather than absorbed implicitly into acoustic transfer functions or empirical attenuation factors.