In the conventional configurations of transport aircraft, the turbofan engines are mounted either under the wings or on the rear part of the fuselage. In both configurations the engine flow interferes with the airflow over the aerodynamic configuration of the airframe in various different manners. The engine intake and exhaust can affect the circulation around the wing section in the vicinity of the engines. The slipstream can interact with the high lift elements and the empennage of the aircraft. Those interactions can be quantitatively evaluated in the properly designed wind tunnel testing of powered models.
In the domain of aircraft power/thrust simulations, DNW has specialized in air driven Turbofan Propulsion Simulators (TPS) for both cruise as well as take-off and approach flight regime simulation. The TPS provide sufficient power density for both regimes to be representative of the flight regime at the model scale. They combine the effects of engine intake and slipstream, required for a realistic simulation of the interference of the engine induced flow with the wings, the empennage and the fuselage of the aircraft. The power supply of the TPS is integrated in such a way that it does not falsify the aerodynamic measurements. In addition to that, aeroacoustic measurements of shielding effects can be performed. This means that the TPS technique provides a much richer set of data than, for instance, tests performed with a simple through-flow nacelle that ignore the power integration effects. However, through-flow nacelles are often used as a primary test by engine manufacturers, representing the engine idle condition.
The TPS testing requires careful calibration of the simulators prior to each testing campaign in order to achieve the required resolution for the thrust/drag bookkeeping in the wind tunnel. For this a dedicated facility on the Noordoostpolder site, called the Engine Calibration Facility (ECF) is used.
When testing with Turbofan Propulsion Simulators it is possible utilize both external and internal balances to measure the overall performance of the powered aircraft model. External balances are used for supporting half models both in high-speed and low-speed testing. Internal balances are used in full models, both at high and at low speed.
Turbofan propulsion simulation is often combined with the moving belt in order to obtain information on the effect of ground clearance on all essential forces and moments, including the influence of the engine on the effectiveness of an aircraft’s stabilizer and rudder. The moving belt is also applied for measuring the effects of thrust reversal. In addition, DNW applies Particle Image Velocimetry (PIV) to visualize complex flow fields, for instance of the engine fan exhaust.