In order to reduce fuel consumption the propulsion efficiency of aircraft have to be improved. A most effective method to do that is to increase the bypass ratio of the turbofan engines. However, this leads to engines with a larger diameter which become difficult to install...
In order to reduce fuel consumption the propulsion efficiency of aircraft have to be improved. A most effective method to do that is to increase the bypass ratio of the turbofan engines. However, this leads to engines with a larger diameter which become difficult to install under a wing. In particular the wing leading edge large lift devices such as slats can not be kept in the area above the large diameter nacelle. As a consequence this leads to a less efficient high lift performance of the aircraft in take-off, but especially in landing configuration. Measures are sought to recover at least part of this high lift degradation, by using active flow control in the leading edge slat gap area of the wing. Within the AFLoWtest project subscale tests with active flow control are made with an modified model from DLR (HINVA model). Most of the tests are made in cryogenic conditions in order to reach sufficient high and representative Reynolds numbers.
The tests are needed to confirm the benefits of active flow control for high lift efficiency, both for an aircraft configuration that is supposed to be flight tested in Clean Sky project and for a potential future Ultra High Bypass configuration having an even larger bypass ratio.
The overall objective of the project is to demonstrate the effectiviness of active flow control for high lift efficiency.
\"In the first phase of the project the inboard leading edge parts of the existing DLR HINVA halfmodel have been replaced by newly designed and manufactured leading edge parts, including a new shortened slat and a leading edge part with installed active flow control unit. The pulsed jet active flow control unit and a continuous blowing unit were designed and manufactured within the DECOROUS project. The high lift performance of the modified model with standard V2500 nacelle was tested at realistic high Reynoldsnumbers in the subcontracted DNW-KKK wind tunnel in November/December 2017. The measurements included load measurements on the half model, detailed pressure distribution measurements, unsteady pressure measurements in the pylon region and in the active flow control unit, flow visualisations with mini-tufts, detailed flow field PIV measurements. The measurements confirmed the favourable effect of active flow control on high lift performance.
NLR developed a PIV setup including 2 high speed cameras and high speed laser, allowing for each measurement plane to take 125 images with a sampling rate of 1500 Hz. The complete NLR PIV setup was placed on a traversing mechanism. Measurements were made at 8 streamwise positions. In addition TU-Delft performed measurements with a low speed PIV system at a fixed position close behind the active flow control unit. Prior to the test NLR installed double glass windows for the PIV cameras. The PIV seeding was performed by DLR in subcontract to NLR. The efficiency and quality of the PIV measurements was influenced by contamination of the model surface, due to the PIV seeding. This necessitated a time-consuming cleaning on the model in model lock, reducing the PIV data volume. In addition, paint was detaching in some areas of the new leading edge model parts which caused large laser reflections and made it hardly possible to yield any sensible PIV data on the most forward position measured by TU-Delft. Finally, the large laser reflections in the windtunnel and laser light reflections between the standard KKK heated windows and the second NLR installed windows, cause problems for the quality of the PIV measurements.
In parallel with these activities NLR designed a new UHBR nacelle and pylon, an even further shortened slat and a new LE part for the installation of the larger spanwise active flow control unit to be employed for the UHBR configuration. In the DECOROUS project new pulsed blowing active flow control units for V2500 and UHBR nacelle configuration were designed and manufactured. The new active flow control units had a somewhat different blowing direction than during phase 1 test. The new blowing direction had been defined based on CFD sensitivity studies. Following the results from phase 1 tests, NLR and TUD made considerable changes to the PIV setup: the traversing system was kept identical but the high speed PIV camera and laser were replaced by a low speed system (150 double images at 15 Hz sampling rate), having also higher resolution cameras. The TUD laser was used. The TUD PIV measurements at the fixed upstream position were no longer performed. In an attempt to reduce laser light reflections, the double glass windows were replaced by new single glass non-reflecting windows. In the second test phase (November 2018) both the V2500 and UHBR configuration were tested. Initial test results for V2500 configuration showed no or only minor effect of active flow control on aerodynamic performance. It was concluded that the changed blowing direction interfered with the wake of the most outboard \"\"dummy\"\" slat bracket. It required a time consuming model modification to remove the dummy bracket, after which the favourable effect of active flow control was again found. Subsequently the model with the new UHBR nacelle was tested and also for this configuration the favourable effect of active flow control was demonstrated.
Unfortunately the volume of PIV measurements was not very large sin\"
The AFLoWTest project confirmed a substantial favourable effect of active flow control, both for the V2500 and the UHBR nacelle configuration. These results add to the favourable effects demonstrated in the AFLoNext test campaign at TsAGI, especially since the half wing configuration used in the AFLoWTest project is much more realistic than the wing segment tested in AFLoNext. The results can be used by Airbus to take a decision to test the active flow control concept in a flight test.
For NLR the PIV measurements made in a challenging test environment have enable NLR to apply the traversing PIV setup also in other tests.