Pierre Philippe Marie Loheac

Aeroacoustic Numerical Method Assessment for a Double Stream Nozzle

Industrial results obtained from different steady and unsteady numerical and analytical methods for a double stream jet in confluent flow configuration are presented. These results are compared with measurements from anechoic wind tunnel tests of a model nozzle. The test campaign was conducted in the ONERA CEPRA19 facility, and exhaust parameters are representative of take-off, with and without simulated flight effects. During this campaign, in addition to acoustic measurements, LDV (Laser Doppler Velocimetry) technique was used in order to measure steady and unsteady aerodynamic data in several planes downstream the exhaust plane. Those data are used to assess several RANS methods (Reynolds Averaged Navier Stokes - steady calculation) on structured and unstructured 2D meshes using k-e turbulence model. Particularly, the effects of the refinement and of the structure of the mesh, as well as flight effects are investigated. Those data are also used to assess LES method (Large Eddy Simulations - 3D unsteady calculation) performed for the same model nozzle in confluent flow configuration, but without plug. Because results of both steady and unsteady aerodynamic calculations are usually used as inputs of acoustic prediction methods, an assessment of two different aeroacoustic prediction processes is also achieved, with different RANS calculations as input of an improvement of MGB (Mani Gliebe Balsa), and LES calculations as input of an acoustic integral method in the time domain (FfowcsWilliams and Hawkings surface integration). Particularly, flight effects and the ability of the whole aeroacoustic chain to predict them are studied.

CFM56 Jet Noise Reduction with the Chevron Nozzle

Over the past few years, chevron nozzles have shown promising results to reduce jet noise on moderate to high bypass ratio engines. To support CFM noise reduction packages, GE Aircraft Engines and Snecma Moteurs have performed series of acoustic test campaigns in anechoic wind tunnel jet noise facilities equipped with external flow simulation to assess the jet noise reduction that could be achieved with chevron nozzles on the CFM56 engine. The chevron technology has been applied both to the current nozzle with an internal plug and to a new nozzle design with an external plug. Screening tests have been performed on isolated nozzle configurations at GE Aircraft Engine’s Cell41 scale model acoustic test facility with the most promising configurations tested installed on a partial scale model of an aircraft, in the CEPRA19 anechoic wind tunnel at ONERA. Core and fan chevrons were tested with the pylon for various engine operating conditions and different installed configurations including take-off, cut-back and approach, with appropriate angle of attack and flap settings. The most promising scaled configuration has recently been evaluated during an in flight test campaign with an aircraft equipped with two CFM56 engines. This paper presents the results of tests relative to the jet noise reduction levels achieved at high power setting conditions. Under wing installation effects on jet noise and their impact on the chevron nozzle effectiveness are discussed.