Numerical and Experimental Study of Engine/Airframe Interference Effects for Engines with Different Bypass Ratios

Abstract

Due to environmental and economical demands future transport aircraft need to reduce the specific fuel consumption significantly. The installation of Very High and Ultra High Bypass Ratio engines requires a close coupling with the wing. It becomes therefore essential to accurately determine the installation drag of a powered configuration. Experimental and numerical research on this topic has been performed within various European projects. The results of the experimental data show very little influence of the bypass ratio on the drag and secondly, a drag decrease with increasing engine thrust settings. Since thrust cannot be measured directly in the wind tunnel, it has to be evaluated by a valid bookkeeping procedure. Within this contribution the shortcomings of the standard, static engine calibration bookkeeping procedure are identified when external flow at wind tunnel conditions is present. Additional terms of the thrust equation, which only result from effects of external flow, are presented and analysed using the experimental data as well as complementary CFD simulations. The paper will further give an insight on the effect of external flow on pressure distributions on engine parts, wetted by the fan jet. From these investigations thrust correction terms are evaluated and the corrected thrust/drag bookkeeping procedure is applied on the wind tunnel data, showing the necessity of a valid bookkeeping procedure for drag evaluation of powered transport aircraft configurations.