Within the frame of the ongoing 7th Framework European Project DREAM, this article presents a synthesis of Cenaero, DLR, and Onera's joint effort to demonstrate the aerodynamic and acoustic optimization potential of a contra-rotating open rotor. Within WP 3.2 led by Snecma, the objective was to maximize the propellers efficiency at top-of-climb conditions and to minimize the noise emission at take-off focusing on interaction noise while fulfilling the thrust and torque split specifications at both operating points. These objectives were successfully met by the development and exploitation of efficient multi-objective three-dimensional Reynolds-averaged Navier–Stokes (RANS)-based surrogate-assisted optimization strategies. In order to assess the aerodynamic and acoustic characteristics of both baseline and optimized geometries, coupled unsteady RANS (URANS) simulation and farfield prediction based on an integral Ffowcs Williams–Hawkings approach were then carried out. The results demonstrate that although the acoustic criterion driving the optimization process did not lead to an improvement of the noise characteristics over the whole directivity range, it may be regarded as a cost-effective way to incorporate noise-related aspects into the design intent.

Turbomachinery components are designed to achieve high performances while being exposed to a complex flow environment with varying operating conditions. Whereas the purpose of a new design optimisation is straightforward — obtaining a better design than the already existing one — the actual process itself remains a challenging task, permanently confronted to the dual need to reduce the cycle time and to further integrate complexity and multiple physics. The extensive use of numerical simulations has contributed in a significant way to the design of state-of-the-art blade geometries. To deal with expensive high-fidelity computations, surrogate-based optimisation (SBO) has become an established and recognised approach. In order to be useful within an industrial context, it is crucial that this SBO process is capable of efficiently handling high-dimensional design spaces as well as managing highly constrained design problems. This work presents innovative auto-adaptive surrogates, exploiting a blend of interpolation/regression and classification, implemented in the integrated optimisation platform Minamo. As a demonstrator based on NASA Rotor 37, an aero-mechanical multi-point optimisation has been performed. For a design space with 60 parameters, significant performance gains have been obtained (+4% after 250 evaluations or less than a fortnight’s runtime) while considering over 30 constraints. The proposed SBO approach offers therefore many opportunities for turbomachinery applications tackling highly constrained design problems. Despite the unavoidable curse of dimensionality, the proposed approach is able to efficiently achieve reliable results at a cost that is in line with industrial needs and it provides a conclusive asset in the frame of design specifications evolving along the design cycle.

For several years, Safran has been involved in the design and optimization of contra rotating open rotors. This innovative architecture is known for allowing drastic reduction in fuel burn, but its development is facing complex technological challenges such as acoustics, aerodynamics, and weight penalty due to the mechanical complexity of an Open Rotor. Since 2010, Safran has been developing the experimental test bench HERA (1/5 mock-up scale) to improve the understanding of the complex aerodynamics and acoustics phenomena involved in the counter rotating propellers configuration. Isolated and installed low speed and high speed wind tunnel campaigns, including PIV measurements have been extremely helpful in defining design guidelines for full scale open rotor specification. These tests have been used as CFD feed-back among other purposes. An iterative process involving CFD optimization (in close collaboration with Cenaero) and wind tunnel test campaigns has been developed over the last 4 years and has led to the definition of an innovative design strategy, which has been successfully tested during the process of the full scale counter rotating propellers design for the SAGE2 ground test demonstrator engine. This phase has evidenced the absolute necessity of a multi-disciplinary design method when it comes to full scale and “rig-ready” design. Ensuring high propulsive efficiency and at the same time, minimizing the acoustic level, while maintaining severe mechanical constraints such as weight, inertia and proper dynamic positioning under control, requires a dedicated and integrated “all inclusive” design process. The aim of this paper is to present the design methodology and some of the wind tunnel tests results carried out over the last 4 years, which have led to the definition of a novel multidisciplinary design methodology that involves CFD, FEM and acoustics.

State-of-the-art turbomachinery design processes rely more and more on the extensive use of numerical simulations. To deal with expensive high-fidelity computations, surrogate-based optimisation (SBO) has become a very interesting approach. In order to cope with industrial cases, the capability to handle variables of a mixed nature appears key. Innovative and auto-adaptive surrogates have been implemented within Minamo that are capable of natively handling the different natures of the design parameters. The present work discusses this mixed-variable SBO framework applied to a multi-profile combinational problem inside the bypass duct. A proof of concept is given followed by a more advanced application. It is demonstrated that the proposed mixed-variable SBO efficiently delivers reliable results and that it offers many opportunities during a conceptual design phase.

The current research focuses on the aerodynamic design of a centrifugal compressor and the effect of tip tailoring on the aerodynamic impeller efficiency. To this extent a high-fidelity multi-point design optimization process has been developed and exploited on a high pressure ratio transonic impeller. By manipulating the shape of the impeller blades and endwalls and by including advanced geometrical features such as winglets on the impeller blades, the behavior of the impeller flow has been investigated. Here, the results of three-dimensional RANS simulations with the Spalart-Allmaras turbulence model on a structured multi-block mesh is used for the evaluation of the flow characteristics. In the context of radial machines, the results of the aerodynamic design optimization show an important improvement of the impeller isentropic efficiency compared to the reference impeller, with a significant contribution from the presence of the impeller tip winglets. Furthermore, the integration of the impeller winglet has encouraged this study to provide a detailed analysis on the impeller flow structures in order to have a better understanding of the effects of tip tailoring on impeller performance.