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Due to the increasing bypass ratios of modern engines, the fan stage is increasingly becoming the dominant source of engine noise. Accordingly, it is becoming more and more important to develop not only efficient but also quiet fan stages. In this paper the noise emission of a fan for an aero-engine with a bypass ratio of 19 is reduced within a multidisciplinary design optimization (MDO) by means of an hybrid noise prediction method while at the same time optimizing the aerodynamic efficiency. The aerodynamic performance of each configuration in the optimization is evaluated by stationary Reynolds-Averaged Navier-Stokes (RANS) simulations. These stationary flow simulations are also used to extract the aerodynamic excitation sources for the analytical fan noise prediction. The resulting large database of the optimization provides new insights into which extent an MDO can contribute to the design of both quiet and efficient fan stages. In addition to that the hybrid approach of numerical flow solutions and analytical description of the noise sources enables to understand the noise reduction mechanisms. In particular, the influence of rotor blade loading on the aerodynamic efficiency and the noise sources as well as the potential of configurations with a comparatively low number of outlet guide vanes (OGV) is explored. The acoustic results of selected configurations are confirmed by unsteady RANS simulations.

Ultra-High Bypass Ratio Geared (UHBRG) turbofan technology allows a significant reduction in fuel burn, noise and emissions — key metrics for aircraft engine performance. However, one of the main challenges in this technology is the large amount of waste heat generated by the Power Gearbox (PGB). Therefore, having a practical tool for precise prediction of the PGB-generated thermal loads in UHBRGs is becoming a necessity. Such a tool would assist in analyzing engine performance, as well as ensuring that engine physical limitations/restrictions are not breached (e.g. over-temperature in fuel and oil, cocking, etc.). This paper presents a methodological approach to mathematically model the waste heat generated by a PGB on a UHBRG for different points on a typical flight profile. To do this, the total power loss in a PGB system is firstly defined as the summation of load-dependent and load-independent losses. Physics-based equations for each heat loss mechanism are introduced and, through a combination of the associated equations, a simulation model for the thermal loads calculation in PGBs is developed. In addition, the heat losses and efficiency of the PGB has been analyzed across a simulated flight. The developed PGB model calculates the main power losses generated in a gear reduction system of a turbofan engine. It is found that in a typical flight, the heat loss generated by the PGB can reach about 80% of the total waste heat generated by the engine. The values of the mechanical efficiency calculated by the tool at different flight points are above 97% which is in good agreement with publicly available data for planetary gearboxes. This tool is intended to be utilized by engine thermal management system designers to predict and analyze the heat loads generated by the PGB at different flight conditions.

International audience; Organized structures in turbulent jets can be modeled as wavepackets. These are characterized by spatial amplification and decay, both of which are related to stability mechanisms, and they are coherent over several jet diameters, thereby constituting a noncompact acoustic source that produces a distinctive directivity in the acoustic field. In this review, we use simplified model problems to discuss the salient features of turbulent-jet wavepackets and their modeling frameworks. Two classes of model are considered. The first, that we refer to as kinematic, is based on Lighthill's acoustic analogy, and allows an evaluation of the radiation properties of sound-source functions postulated following observation of jets. The second, referred to as dynamic, is based on the linearized, inhomogeneous Ginzburg–Landau equation, which we use as a surrogate for the linearized, inhomogeneous Navier–Stokes system. Both models are elaborated in the framework of resolvent analysis, which allows the dynamics to be viewed in terms of an input–ouput system, the input being either sound-source or nonlinear forcing term, and the output, correspondingly, either farfield acoustic pressure fluctuations or nearfield flow fluctuations. Emphasis is placed on the extension of resolvent analysis to stochastic systems, which allows for the treatment of wavepacket jitter, a feature known to be relevant for subsonic jet noise. Despite the simplicity of the models, they are found to qualitatively reproduce many of the features of turbulent jets observed in experiment and simulation. Sample scripts are provided and allow calculation of most of the presented results.

Hearing protection with standard passive earmuffs is for many military applications insufficient. Low frequency noises (diesel engines, helicopter rotor) require increased attenuation. Active Noise Reduction (ANR) is specifically suited for reduction at low frequencies. Assessment of ANR for military applications is an important topic as the adverse military environment may cause unexpected reduced performance (e.g. very low rotor-blade noise may overload a for civil applications designed system). This study contains assessment methods for ANR in military applications from five laboratories.