Abstract
It is envisaged that the next generation of civil aero-engines will employ high bypass ratios to lower specific thrust and improve propulsive efficiency. This trend is likely to be accompanied with the integration of compact nacelle and exhausts in podded under-wing installation positions that are close coupled to the airframe. This leads to the requirement for a comprehensive methodology able to predict aerodynamic performance for combined airframe-engine architectures. This paper presents a novel thrust and drag accounting approach for the aerodynamic analysis of integrated airframe-engine systems. An integral metric is synthesised based on the concept of net vehicle force. This is accomplished through the consolidation of aerodynamic coefficients, combined with the engine cycle characteristics obtained from a thermodynamic matching model. The developed approach is coupled with an in-house tool for the aerodynamic design and analysis of installed aero-engines. This framework is deployed to quantify the impact of engine installation position on the aerodynamic performance of a future large turbofan installed on a commercial wide-body airframe. The governing flow mechanisms are identified and their influence is decomposed in terms of the impact on airframe, nacelle, and exhaust performance. It is shown that it is essential to include the impact of installation on the exhaust for the correct determination of overall airframe-engine performance. The difference in net vehicle force for a close coupled position can reach up to -0.70% of nominal standard net thrust relative to a representative baseline engine location.
Highlights
Scope of present work This paper presents a novel thrust and drag accounting approach based on Computational Fluid Dynamics (CFD), for the aerodynamic analysis of installed aero-engines
Aerodynamic analyses were conducted at DP mid-cruise conditions with M∞ = 0.85, ReCref
590 metric was proposed based on the concept of “net vehicle force”, which quantifies the overall performance of coupled airframe-engine configurations
Summary
5 an increase in BP R for a given net thrust is typically accompanied by an increase in engine size, nacelle wetted-area, and fan diameter Dfan [2]. This increase in BP R results in higher exchange rates between nacelle and exhaust aerodynamic performance, and engine Specific Fuel Consumption (SFC) [3]. Since gross thrust is dependent on the exhaust velocity coefficient Cv [5], this change in BP R can increase the exchange rate between exhaust performance and SFC by 33% relative to contemporary engines [6].
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