CFD Modeling of a Realistic Turbofan Blade for Noise Prediction. Part 2: Analytical Acoustic Predictions

Abstract

Noise sources on the rotor of a scale-model turbofan are investigated at approach conditions. The fan geometry considered is the baseline configuration of the "Fan Noise Source Diagnostic Test" (SDT) experimental setup. Based on Reynolds Averaged Navier-Stokes simulations (RANS) competitive noise source mechanisms, the turbulent interaction noise and the trailingedge noise on the rotor are investigated. The noise estimations are compared to acoustic predictions from Large Eddy Simulations (LES) which consider only the rotor row and include a single blade, and to noise measurement performed by NASA. Focus is made on the modeling of the noise excitations in the analytical predictions. Nomenclature δ * Displacement thickness δ 99 Boundary layer thickness ∂p ∂s Streamwise wall pressure gradient Λ f Integral length scale of the turbulence ω Turbulent eddy frequency τ w Wall shear stress Θ Momentum thickness D Turbulent length scale coefficient I Intensity of the turbulence k Turbulent kinetic energy l y Spanwise coherence length Ma Mach number U c Turbulent eddy convective speeds U e Exterior stream velocity W Relative velocity FWH Ffowcs Williams & Hawking's analogy LE Leading-edge LES Large Eddy Simulation RANS Reynolds Averaged Navier-Stokes SDT Fan Noise Source Diagnostic Test TE Trailing-edge TEN Trailing Edge Noise TIN Turbulence Interaction Noise This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License CC-BY-NC-ND 4.0

Identification of Noise Sources in a Realistic Turbofan Rotor Using Large Eddy Simulation

“…It is capable to resolve the turbulent structures that may serve as effective rotor noise sources. The present study aims at decomposing and identifying these sources using the high-fidelity data obtained from rotor-only (RO) LES computations [8,[17][18][19]. The focus is put on the approach operating condition (62% of the operating point rotation speed), for which the fan is the dominant contributor in the overall turbofan noise [2].…”

“…The focus is put on the approach operating condition (62% of the operating point rotation speed), for which the fan is the dominant contributor in the overall turbofan noise [2]. The previous studies showed that the modeling of the trailing-edge and turbulence-interaction noise sources is not enough to correctly predict the total rotor broadband noise spectrum [17,18]. The analysis of the flow field showed that a complex tip flow, interacting with the neighbouring blades, can be an additional noise source along with the described two sources [8,19].…”

Turbomachinery Noise Review

“…Additional rotor-only configurations have now been simulated with quasi wall-resolved simulations (WR-LES) achieved by Kholodov and Moreau [71] that can serve as a reference simulation. Comparisons with the previous wall-modeled LES [72,73] using two different numerical schemes (Lax-Wendroff and Two-step Taylor-Galerkin TTG4A) show little differences on the blade and in the wake and noticeably similar overall global performances within 1% of measurements and good comparison with the hot-wire mean and root-mean-square (rms) velocity components downstream of the rotor. Only the tip vortices are better resolved as shown in Figure 3.…”

Turbomachinery Noise Review

“…Additional rotor-only configurations have now been simulated with quasi wall-resolved simulations (WR-LES) achieved by Kholodov & Moreau [71] that can serve as a reference simulation. Comparisons with the previous wall-modelled LES [72,73] using two different numerical schemes (Lax-Wendroff and TTG4A) show little differences on the blade and in the wake: noticeably similar overall global performances within 1% of measurements and good comparison with the hot-wire mean and root-mean-square (rms) velocity components downstream of the rotor. Only the tip vortices are better resolved as shown in Figure 3.…”