The influence of engine thrust behaviour on the aerodynamics of engine airframe integration

Kurzfassung

The wind tunnel is still an important pillar for the aerodynamic investigations of engine installation effects, such as the strong aerodynamic interferences between an underwing mounted engine and the wing itself. To consider real engine effects on the aerodynamics in the wind tunnel environment the turbine powered simulator (TPS) technique is one of the widely applied technologis. Especially for underwing installed engines thrust affects the aerodynamic drag. Reflecting the fact that in modern aircraft design engine installation improvements on drag counts in small numbers, and considering that the TPS technology cannot match the real engine in all parameters, the questions arises if no matching parameters exist what is their influence on drag. Usually fan Mach numbers and total thrust coefficients of the real engine can be correctly realized by TPS. In the present contribution the essential parameters of engine simulation are determined and in particular the thrust ratios, i.e. turbine thrust to fan thrust of real engines and simulators at different bypass ratios (BPR) in the range of 6–17 at cruise conditions will be evaluated. Considerable differences of the thrust ratios between the engines and the simulators exist in particular at high freestream Mach numbers. Therefore, the aim of this contribution will be to clarify the influence of the thrust ratio on the drag behaviour of an aircraft configuration. First, the theoretical background on the drag determination theory is derived. Based on this theory the analysis of the thrust ratio is done using mainly experimental results. Additional numerical results by solving the Reynolds-averaged Navier–Stokes equations are used to support the analysis.