Periodic Reporting for period 1 - PANDORA (OPEN FAN VALIDATION FOR CARBON-FREE AIRCRAFTS)
Reporting period: 2023-02-01 to 2024-07-31
The open fan concept has been around for decades. Its high propulsive efficiency combined with the elimination of the nacelle drag and weight has been always appealing to replace high by-pass ratio ducted fans and reduce CO2 and NOx emissions. The CS1 and CS2 programs have also made relevant efforts to pursue the contra-rotating open rotor (CROR) concept. Though CROR has not made it to market, progress has been made in reducing noise levels to that of ducted fans. Open fans exhibit several differences concerning ducted fans, which today are highly sophisticated components accumulating decades of research. The chasm between the OP concept and its product is too big to be covered by a single demonstrator since a wrong materialization of the idea can give rise to misleading conclusions. Turbomachinery simulations have been perfected for decades and are essential to close the gap between the concept and the detailed product implementation. However, open rotors exacerbate existing problems (e.g. blade-to-blade variations even for small angles of attack, strong coupling between CO2 and noise emissions, etc.) .
Moreover, open fans lack publicly available data or test cases, preventing researchers from validating their ideas. The first global assessment of CS2 reported an expected noise reduction of -9dB in the innovative TP 130 pax project with respect to the last generation of ducted fans, though at a lower flight Mach number. This project aims to obtain relevant noise and performance experimental data of an unducted single fan (USF) for short/medium-range aircraft with two objectives. Firstly, confirm that about 5-10 dB noise reduction is achievable at the expense of a slight penalty in fan efficiency, and secondly, validate and expand the scope of numerical tools. An experimental database with the key results of the projects will be built to unlock the application of the USF for SAF, Hydrogen, and Hybrid-electric engine and aircraft configurations.
Moreover, open fans lack publicly available data or test cases, preventing researchers from validating their ideas. The first global assessment of CS2 reported an expected noise reduction of -9dB in the innovative TP 130 pax project with respect to the last generation of ducted fans, though at a lower flight Mach number. This project aims to obtain relevant noise and performance experimental data of an unducted single fan (USF) for short/medium-range aircraft with two objectives. Firstly, confirm that about 5-10 dB noise reduction is achievable at the expense of a slight penalty in fan efficiency, and secondly, validate and expand the scope of numerical tools. An experimental database with the key results of the projects will be built to unlock the application of the USF for SAF, Hydrogen, and Hybrid-electric engine and aircraft configurations.
The most relevant activities in WP1 were related to the design of the test article. The industrial partner (Safran Aeroengines) prepared the specifications, and DLR mainly performed the aerodynamic design. The level of detail in the aerodynamics was high since the test specimen is intended to deliver relevant industrial information for Open Rotor design, not only in terms of noise but also aerodynamic performances. Regarding the optimizations carried out for the design, an automatic optimizer for multi-objective optimization using an evolutionary algorithm with Meta Models to accelerate the process was used. The cost function included thrust and global efficiency obtained using low-resolution steady RANS analyses. The design involved multiple operating pòints (Cruise, maximum take-off, etc.), making the overall exercise complex.
A conceptual design review (CDR) was conducted with Safran's specialists, and feedback was given, especially concerning mechanical constraints. A second iteration was conducted to implement CDR considerations. Potential subcontractors have been contacted to carry out the mechanical design and complete the design of the test specimen.
The experimental work has been oriented towards understanding the potential test facilities for conducting the test. The fact that the consortium's researchers are largely unaware of these two facilities (one for low-speed and another for high-speed testing) and the donor rig has posed serious difficulties in advancing preparatory work. However, conceptual designs and test strategies have been devised.
Simulation activities have progressed steadily. CFD has been progressively adapted to Open Rotor configurations. Most turbomachinery codes have been designed for ducted blading, for which several open test cases are available. Moreover, consortium partners, with the sole exception of DLR, have developed their experience in ducted fans. The partners have adapted and improved their simulation codes for open rotor configurations and have shown that they are in the position of conducting most of the simulations needed for the project.
A conceptual design review (CDR) was conducted with Safran's specialists, and feedback was given, especially concerning mechanical constraints. A second iteration was conducted to implement CDR considerations. Potential subcontractors have been contacted to carry out the mechanical design and complete the design of the test specimen.
The experimental work has been oriented towards understanding the potential test facilities for conducting the test. The fact that the consortium's researchers are largely unaware of these two facilities (one for low-speed and another for high-speed testing) and the donor rig has posed serious difficulties in advancing preparatory work. However, conceptual designs and test strategies have been devised.
Simulation activities have progressed steadily. CFD has been progressively adapted to Open Rotor configurations. Most turbomachinery codes have been designed for ducted blading, for which several open test cases are available. Moreover, consortium partners, with the sole exception of DLR, have developed their experience in ducted fans. The partners have adapted and improved their simulation codes for open rotor configurations and have shown that they are in the position of conducting most of the simulations needed for the project.
It is too soon to show any progress beyond the state-of-the-art. Moreover, state-of-the-art in this field is proprietary and lies within the major overall engine manufacturers (OEMs). No data are available in the public or semi-public domain.The judgement about the competitiveness of the proposed design relies on Safran. So far, all the comments are positive and encourage further development of the Open Rotor configuration.
An interesting by-product of the project is the strategy developed to conduct open rotor simulations under angle of attack using harmonic methods. These simulations are needed not only to assess noise under these conditions but to compute low frequency aerodynamic unsteady loading on the rotor blades (1p loads). The proposed strategy has brought the attention of the industrial partner and is deemed novel.
An interesting by-product of the project is the strategy developed to conduct open rotor simulations under angle of attack using harmonic methods. These simulations are needed not only to assess noise under these conditions but to compute low frequency aerodynamic unsteady loading on the rotor blades (1p loads). The proposed strategy has brought the attention of the industrial partner and is deemed novel.