Large-scale Jet Noise Testing, Reduction and Methods Validation "EXEJET" : 4 - Flows characterization with PIV in the CEPRA19 anechoic wind tunnel of Onera

The "CEPRA19" large anechoic wind tunnel of the "FRENCH AEROSPACE LAB ONERA" is particularly adapted to the aeroacoustic studies of the nozzle jets. In the "EXEJET" test (EXpErimental modelling of JET noise with installation effects), besides the measurements of far and near noise fields, PIV (Particle Imaging Velocimetry) measurements were carried out in order to characterize the flow of a HBPR (High bypass ratio) turbofan dual-stream nozzle with forward flight effects. This paper documents the technological achievement of implementing PIV at large scale. The experimental methodology is described, along with the resolution of the PIV measurement issues incident to the complexity of such a test due to the size of the investigated area, the velocity ranges and the flow turbulence characteristics. Experimental techniques were focused in a systematic manner on a “simple” axisymmetric nozzle configuration with validation of simulations in mind. Our PIV methodology allowed documenting the flow field over a large volume, from the nearnozzle region of 1 diameter up to 13 diameters downstream. Acquiring reliable PIV data very close to the nozzle remains a challenge. Models complexity was increased gradually. The PIV was able to measure effects of chevrons and of pylon simulator. The "EXEJET" test has offered the construction of a significant aerodynamic database on industrial designs by an adapted implementation of the PIV method.