An advanced digital filter method to generate synthetic turbulence is presented for efficient two-and three-dimensional leading edge noise predictions. The technique, which is based on the Random Particle-Mesh method, produces a turbulent inflow that matches a target isotropic energy spectrum. The discretized equations for the synthetic eddies, and the input parameters needed to recover the desired turbulence statistics, are presented. Moreover, a simple and fast implementation strategy, which does not require an additional boundary condition, is presented under the frozen turbulence assumption. The method is used in a linearized Euler solver to predict turbulence-airfoil interaction noise from a number of configurations, including variations in airfoil thickness, angle of attack and Mach number. For the first time, noise predictions from a digital filter method are directly compared to those provided by synthetic turbulence based on a summation of Fourier modes. The comparison indicates that the advanced digital filter method gives enhanced performance in terms of computational cost and simulation accuracy. In addition, initial tests show that this method is capable of reproducing experimental noise measurements within 3 dB accuracy.

This paper is the first part of a series of three papers dedicated to the prediction of lowspeed interaction noise of an isolated contra-rotating open rotor (CROR). The objective of this study is to assess available analytical and numerical methodologies in terms of robustness, performance and accuracy. The analytical procedure follows the classical Sears' theory, while the numerical procedure follows a two-step approach based on CFD coupled with the analogy of Ffowcs Williams-Hawkings (FWH). Concerning the numerical tools, both chorochronic (single-passage) and Chimera (full-annulus) approaches are considered. The prediction of interaction noise requires fulfilling three modelling steps: the aerodynamic perturbations, the rotor unsteady blade response and the resulting noise radiation. Comparisons with noise measurements are provided. It is shown that the results are highly sensitive to the description of the incoming wake deficit. The chorochronic approach, as a single blade passage is computed, allows the use of much finer meshes than the Chimera approach and requires a lower computational cost. This approach is therefore highly attractive for computing isolated axisymmetric configurations. Nomenclatureunsteady lift k X = chord-wise wave number M ri = relative Mach number across blade i mR = Rear rotor tones frequency, m×BPF (rear rotor) nF = Front rotor tones frequency, n×BPF (front rotor) nF+mR = Rotor-to-rotor tones frequency, n×BPF (front rotor) + m×BPF (rear rotor) RPM = Revolutions Per Minute R i = radius of rotor i S = Incompressible Sears function S c,hf = High-frequency compressible Sears function S c,lf = Low-frequency compressible Sears function SPL = Sound Pressure Level 2 U ri = relative velocity across blade i (X i , Y i ) = coordinate system attached to the blade row i α i = local stagger angle of the section i ß r = relative Mach number function Ω i = rotational speed of blade row i σ 2 = reduced frequency φ = reception angle

A benchmark of Reynolds-Averaged Navier-Stokes (RANS)-informed analytical methods, which are attractive for predicting fan broadband noise, was conducted within the framework of the European project TurboNoiseBB. This paper discusses the first part of the benchmark, which investigates the influence of the RANS inputs. Its companion paper focuses on the influence of the applied acoustic models on predicted fan broadband noise levels. While similar benchmarking activities were conducted in the past, this benchmark is unique due to its large and diverse data set involving members from more than ten institutions. In this work, the authors analyze RANS solutions performed at approach conditions for the ACAT1 fan. The RANS solutions were obtained using different CFD codes, mesh resolutions, and computational settings. The flow, turbulence, and resulting fan broadband noise predictions are analyzed to pinpoint critical influencing parameters related to the RANS inputs. Experimental data are used for comparison. It is shown that when turbomachinery experts perform RANS simulations using the same geometry and the same operating conditions, the most crucial choices in terms of predicted fan broadband noise are the type of turbulence model and applied turbulence model extensions. Chosen mesh resolutions, CFD solvers, and other computational settings are less critical.

Broadband noise is a significant part of the noise emitted by contra-rotating open rotors. Several noise sources can contribute to the total broadband sound field, with the most dominant ones probably being trailing edge noise, rotor-wake interaction noise and pylon-wake interaction noise. This paper addresses the prediction of these noise sources using analytical models based on Amiet's flat plate airfoil theory and also to empirical turbulence models, fed by input data extracted from steady and unsteady CFD RANS simulations. The models are assessed against wind tunnel tests of Rolls-Royce's rig 145 (build 1) conducted at the DNW anechoic open jet test facility using Rolls-Royce blades and Airbus pylons. The study showed promising results in terms of the ability of the models to predict acoustic power spectrum shapes, peak frequencies and absolute levels. The effects of changes in thrust on broadband wake-interaction noise are well reproduced. However, the models significantly underestimate the effect of thrust on trailing edge noise and the effect of rotational velocity on pylon interaction noise. Nomenclature

A semi-empirical analytical model is developed that predicts the noise produced by a rotor ingesting a boundary layer in proximity to a hard-wall. The rotor boundary layer ingestion noise source is an important source to include when a rotor is installed close to an aircraft fuselage. This is the case for a tail mounted