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Aerodynamic and acouStic for high-by-Pass ratIo tuRbofan intEgration

Periodic Reporting for period 3 - ASPIRE (Aerodynamic and acouStic for high-by-Pass ratIo tuRbofan intEgration)

Reporting period: 2018-01-01 to 2018-09-30

The latest engine technologies, which are about to enter into service around 2025 via the new generation of engines of for new Aircraft (Short range or Long range), will offer a substantial specific fuel consumption (SFC) improvement of 15-17% compared with reference EIS 2000 technology. Those benefits have mainly been achieved by successively improving engine component and cycle efficiency, based on increased overall pressure ratio (OPR = 40) and by-pass ratio (BPR = 10 to 12). New light weight and reduction gearbox technologies are key enablers for the mentioned cycle improvements.
Increasing the by-pass ratio for turbofans further towards UHBR technology (BPR between 12 and 20) is expected to bring substantial additional SFC improvement comparable or even superior to the expected gain of CROR technologies. The use of innovative technologies such as new light weight materials, allows a shift to higher values of the optimal BPR value of HBR or UHBR engines which is driven by a compromise between propulsive efficiency, aerodynamic drag and weight.
However, the integration of UHBR engines under the wing is a challenge. Indeed, because of the size of these engines tremendous interactions occur with other aircraft components such as the nacelle, the pylon, the wing or the high-lift devices.
In this context, the overall objective of the ASPIRE project is to demonstrate to ability of existing numerical and experimental methods to accurately assess the aerodynamic and acoustic performance of such configurations thanks to a reliable modelling of fan/airframe physical interactions. In more details, the technical objectives are:
1. Design generic fan/OGV combinations representative of future UHBR engine;
2. Demonstrate the ability of CFD codes (NLR ENFLOW , ONERA elsA, DLR TAU, DLR TRACE) to predict aerodynamic performance of aircraft equipped with UHBR engines;
3. Demonstrate the ability of aero-acoustic methods to predict aeroacoustic performance of aircraft equipped with UHBR engines;
4. Identify and assess the experimental capabilities for the characterization of UHBR installation noise sources.
Based on the Top Level Aircraft Requirements provided by Airbus, DLR designed a generic fan/OGV combination representative of future UHBR engine and ONERA, two derivative configurations with laminar fan blades and heterogeneous OGV. The detailed geometries were provided to Airbus, ONERA and NLR as a basis for aerodynamic and aero-acoustic computations.

Based on these geometries and the other geometric elements provided by Airbus (isolated nacelle, Air inlet and Nozzle), aerodynamic steady and unsteady URANS 360° computations were performed and compared by NLR, DLR and ONERA in different aerodynamic conditions to assess the impact of the fan/OGV combination on the airframe performance and vice et versa (see Figure 1). Active Flow Control strategies were also evaluated to reduce flow separation in the air inlet at high angle of attack.

These aerodynamic computations were completed by numerical aero-acoustic analysis for fan and jet noise prediction. Some activities conducted by the partners aimed at evaluating the ability of numerical methods to assess the impact of distortions in the air inlet, of heterogeneous OGV or of laminar fan blade on fan noise (Tone, Broadband and buzz Saw noise - Figure 2). Other tasks are dedicated to the jet noise prediction and the use of advanced numerical methods (LES or DES coupled with CAA).

Regarding experimental acoustic mean development, the activities conducted in ASPIRE by the consortium aimed at improving the inflow instrumentation for WTT, at developing dedicated post-processing procedure to correct WT or Flight-Test measurements and at developing specific means and features for noise reduction. In this framework, a common liner test case has been defined and tested in several facilities by ONERA, DLR and TsAGI in order to compare the results of impedance eduction model and the different measurement techniques applied by the partners.
On the generic configuration (fan, OGV, nacelle, air, inlet, nozzle), a detailed cross-comparison of CFD codes and acoustic methods was performed by ONERA, DLR and NLR. This was achieved in order to define the best numerical strategies to accurately predict the impact of the fan on airframe performance and noise. For this, all unsteady URANS 360° computations were analysed in detail to extract the most relevant data. Moreover, aero-elastic URANS 360° computations were performed by NLR to assess the impact of the aero-elastic behaviour of the fan on the overall aerodynamic performance. In parallel, ONERA evaluated the potential of Active Flow Control strategies to reduce detached flow in very short inlet. All these activities brought a valuable insight in the potential of UHBR engine and provide guidelines to Airbus for the integration of future UHBR engine. This will have a strong impact on the development of future aircraft equipped with UHBR engines. All these numerical activities also permitted to identify and quantify possible acoustic penalties and risks that could appear in future UHBR engines featuring short inlets and heterogeneous OGVs.

Regarding experimental activities, the test case defined to compare the results obtained in different acoustic liner test benches on a unique liner sample provided very relevant results to improve existing numerical and experimental prediction methods. This also provided to Airbus useful indications regarding the real noise reduction level obtained with acoustic liners.

Furthermore, original experimental acoustic approaches were tested to measure the interactions between airframe and engine (e.g. jet-flap interaction noise, boundary layer refraction correction with rotating sources). These approaches will be strategic tools during future wind tunnel and flight tests of future aircraft equipped with UHBR engines.