Multidisciplinary Design Optimization of a Low-Noise and Efficient Next-Generation Aero-Engine Fan
The aim of the presented design study is to design a fan stage from scratch for a generic next-generation aero-engine of a long-hole aircraft with an ultra-high bypass ratio of 19. The fan stage should be both efficient and quiet. For this purpose, a Multi-Disciplinary Design Optimization (MDO) is carried out with the aim to optimize the aerodynamic efficiency at Cruise condition and to reduce the interaction noise sources at the acoustic certification points Approach and Sideline with consideration of the mechanical constraints. Each configuration in the optimization is evaluated in view of the aerodynamic efficiency by performing stationary Reynolds-Averaged Navier-Stokes (RANS) simulations and the mechanical feasibility is ensured by Finite Element Method (FEM) simulations. The fan noise emission is evaluated with a RANS-informed analytical prediction method. For the analytical fan noise prediction based on steady flow simulations, methods are used to reconstruct the unsteadiness of the flow field seen by the OGVs. These models enable both the reconstruction of the mean flow field for the calculation of the tonal interaction noise and the turbulent flow field for the calculation of the broadband interaction noise. The analytical fan noise calculation relies on a strip theory, which approximates the fan blades by equidistantly distributed profiles over the span. At each radial position the acoustic response of the profiles to the aerodynamic excitation is calculated independently of each other. For the calculation of the radiated three-dimensional acoustical field the acoustical pressure fluctuations of the profiles are integrated over the span.
The fan stage is parametrized with 87 degrees of freedom describing the fan parameters and the shape of the blades. These parameters are optimized using evolutionary algorithms. Surrogate models are used to accelerate the convergence of the optimization. Especially the rotor blade loading and the number of outlet guide vanes (OGV) are varied in a wide range within the optimization. The impact of the rotor blade loading and number of OGV's on the aerodynamic efficiency and in particular on the interaction noise sources are analyzed in detail. It is found that the aerodynamic efficiency, the tonal noise and the broadband interaction noise have opposing dependencies on the rotor stage loading. While the highest aerodynamic efficiency is found at supersonic flow conditions, the tonal noise is substantially lower at subsonic flow conditions due to the absence of self-noise sources and due to the decrease of tonal interaction noise by increasing the stage loading, i.e. lowering the rotational speeds and keeping the pressure raise constant. However it is found that broadband interaction noise increases with increasing stage loading due to the increase of turbulence in the rotor wakes.
Regarding the number of the vanes it is found, that for broadband interaction noise the number should be as low as possible. For the tonal interaction noise it could be shown that an optimized number of comparatively few blades can achieve similarly low sound power levels as a conventional cut-off design.
All trends found are also checked for plausibility and compared against results from other studies or measurements.
In summary, the study shows that the design of a low-noise and efficient fan stage requires a compromise with regard to certain design parameters.
Multidisciplinary Design Optimization of a Low-Noise and Efficient Next-Generation Aero-Engine Fan
Category
Technical Paper Publication
Description
Session: 38-12 Fan and Propeller Design Optimization
ASME Paper Number: GT2020-14580
Start Time: September 21, 2020, 12:45 PM
Presenting Author: Robert Jaron
Authors: Robert Jaron German Aerospace Center (DLR)
Antoine Moreau German Aerospace Center (DLR)
Sébastien Guérin German Aerospace Center (DLR)
Lars Enghardt German Aerospace Center (DLR)
Timea Lengyel-KampmannGerman Aerospace Center (DLR)
Tom Otten German Aerospace Center (DLR)
Eberhard Nicke German Aerospace Center (DLR)