Nicolas Tantot

Advanced Open Rotor Performance Modelling for Multidisciplinary Optimization Assessments

As a consequence of increased stringent engine emission regulations, in a highly competitive market, it has become necessary to explore innovative, economic and environmentally friendly cycles to sustain competitive advantages. Among these innovative cycles, both the geared and the direct drive counter-rotating open rotors, due to their relatively higher propulsive efficiency, have the potential to significantly reduce fuel consumption and emissions relative to conventional high bypass ratio turbofans. A detailed TERA (Technoeconomic Environmental Risk Analysis), multidisciplinary optimisation framework, can be used to optimise both engines and thereby assess their potential as well as quantify their risks on a formal and consistent basis. This technique is based on detailed and rigorous engine performance, aircraft performance, engine geometry, engine weight, noise, gaseous emissions and environmental impact simulation models. No specific performance simulation methodology for counter rotating open rotors is available in the public domain. An innovative technique is introduced, comprising novel models of: • Counter-rotating propellers (including their interaction); • Counter-rotating turbines; • Planetary differential gearboxes. A thorough description of the modelling methodology (with a justification of the main assumptions) of each of these three components is presented and an indication of work in progress is provided. These components are then used to develop direct drive and geared open rotor performance models. The results of steady state design point and off design performance simulations of these two engine models are subsequently presented via two case studies. Some of the differences in the performance of the low pressure system of geared and direct drive open rotors are highlighted. It was observed that the impact of the key OR performance DP parameters is different for the two engines. Consequently the optimal design and control strategies of theses two configurations will differ. The flexibility of the new simulation technique makes it a suitable candidate to perform multi-disciplinary TERA design space exploration and optimisation studies assess and optimise open rotor designs and control strategies in a multidisciplinary framework.Copyright

A Method for Predicting Contra Rotating Propellers Off-Design Performance

This article presents a method for predicting contra rotating propellers individual and total performance which is fast and robust enough to be used in performance engine cycle and engine subsystems detailed design. The method is based on the use of single propeller maps and models mutual induced velocities thanks to one-dimensional theories. These velocities are responsible for interferences between propellers. This article goes through the assumptions on which stands the proposed method and shows that it is relevant compared against more complex methods such as lifting line theory and definitively provides a valuable easy-to-enforce preliminary design tool for open rotor propulsor controls sizing.Copyright

Prediction of Certification Noise Levels Generated by Contra-Rotating Open Rotor Engines

The tendency for environmentally friendlier aeronautic engines, led to the re-examination of the contra rotating open rotor (CROR) as a more efficient and less polluting propulsion system, thanks to its noticeably high propulsive efficiency. The geometrical and operational characteristics of these contra rotating propellers are examined in order to optimize the noise emissions, given the challenging regulation context for such an unducted concept. For this research, computational techniques have been used to develop a numerical model for prediction of noise levels generated by CRORs propellers. An extended database of unsteady CFD simulations, generated with innovative methods, namely a non-linear harmonic flow solver and an acoustic propagation model based on the Ffowcs Williams–Hawkings approach, have been used to assess the noise spectra measured in the certification points. Sound pressure levels and frequencies have been afterwards converted into EPN levels along the aircraft flight path, according to the ICAO regulation. The whole procedure has been applied to 102 different cases to establish the influence of several independent parameters on noise emissions. A surface response model has finally been developed, providing an easy tool of fast utilization to be implemented in optimization platforms.Copyright

Innovative Approaches to Propellers Off-Design Performance Modeling

This article provides an overview on the challenges related to the prediction of propellers performance at preliminary design stage, ranging from numerical stability to simplicity required for being integrated into engine cycle models. After a description of the usual approach to propeller performance based on maps, and a discussion on its limitations, innovative methods are proposed, lying on the identification of losses trends combined with the use of propeller characteristic operating points over the whole usable area. These innovative approaches significantly reduce the number of required simulations or test cell points to be able to describe the full propeller range of operation, adding physics to the mathematical approach usually considered for turbomachinery component maps elaboration. Accuracy and stability of the considered approaches are discussed, along with an assessment of the required effort to set them up.Copyright