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.

Higher order nonreflecting blade row interfaces are today widely used for performing both steady and unsteady simulations of the flow withing axial turbomachines. In this paper, a quasithree-dimensional nonreflecting interface based on the exact, two-dimensional nonreflecting boundary condition for a single frequency and azimuthal wave number developed by Giles is presented. The formulation has been implemented to work for both steady simulations as well as unsteady simulations employing the nonlinear Harmonic Balance method. The theory behind the construction of the nonreflecting interface is presented and details on the numerical implementation is also provided. The implementation is verified for two dimensional wave propagation along a straight cascade. It is shown that the interface correctly absorbs incoming waves, but also found that the chosen implementation strategy may be ill-posed. A simple solution to stabilize the implementation is therefore implemented, but future work should seek a more generic solution to this problem.

No abstract

In the present work, a recently developed platform for turbomachinery design and optimization based on Evolutionary Algorithms (EAs) is presented. Two types of evolutionary algorithms are implemented. The first one based on Genetic Algorithms (GAs) and the second one on Differential Evolution (DE), both able to handle single-and multi-objective as well as constrained and unconstrained optimization problems. Meta-modeling based on Radial Basis Functions (RBFs) is used in order to help accelerate the optimization when the objective function is too expensive to be evaluated inside the EA. Details on the implementation as well as validation results for a set of well-known benchmark cases are presented. The platform is also combined with 3D CFD simulations to optimize the aerodynamic performance of a Counter Rotating Open Rotor (CROR). Results from the CROR optimization are discussed and analyzed.

The Counter Rotating Open Rotor (CROR) powerplant is an interesting architecture for future regional aircraft propulsion since it offers higher propulsive efficiency and thereby lower fuel consumption than the conventional Turbofan engine. The noise levels generated are however potentially larger compared to a Turbofan due in part to the absence of a ducting nacelle. This raises the need for efficient, high fidelity tools that can be used for the design and evaluation of new blade concepts capable of meeting strict noise regulations. In this paper, a Computational Aeroacoustics (CAA) platform for CRORs based on the Harmonic Balance method is presented. The method is formulated in the time domain and solves for the dominant frequencies of the flow by expressing the solution as a truncated Fourier series in time. Coupling between the resolved frequencies is furthermore possible since the nonlinear URANS equations are solved for. The far field acoustic signature is obtained by solving a convective form of the Ffowcs Williams-Hawkings equations for permeable surfaces. The CAA platform is applied to a generic, full scale, pusher type CROR operating at cruise conditions.