Synthesis of convection velocity and turbulence measurements in three-stream jets

• Published in: Experiments in fluids 2019-05, Vol.60 (5), p.1-12, Article 83
• Main Authors: Stuber, Marcie, Lowe, K. Todd, Ng, Wing F.
• Format: Article
• Language: English
• Subjects: Acoustic noise; Acoustic tests; ADVANCED PROPULSION SYSTEMS; Aerodynamics; Configurations; Convection; ENGINEERING; Engineering Fluid Dynamics; Engineering Thermodynamics; Fluid dynamics; Fluid- and Aerodynamics; Heat and Mass Transfer; High speed; Jet aircraft noise; Noise; Noise generation; Nozzles; Particle image velocimetry; Photomultiplier tubes; Reduction; Research Article; Turbulence intensity; Velocity; Velocity measurement
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-019-2730-5

Key flow regions linked to jet noise sources are investigated through comparison of convection velocity and turbulence measurements in high-speed three-stream nozzles. Time-resolved flow imaging using a photomultiplier tube array was applied in the Nozzle Acoustic Test Rig at NASAs Aero-Acoustic Propulsion Lab to measure 250 kHz repetition laser scattering signals arising from seeding particles at 32 points in high-speed flow. Particle image velocimetry measurements previously reported by NASA provided mean velocity and turbulence intensity. Results for convection velocity of the particle concentration field were obtained from the time-resolved data for three-stream nozzle configurations using a cross-correlation approach. The three-stream cases included an axisymmetric and an asymmetric, offset nozzle configuration. For the axisymmetric case, areas of high convection velocity and turbulence intensity were found to occur 4–6 area-equivalent nozzle diameters downstream from the nozzle exit. Comparison of convection velocity between the axisymmetric and offset cases shows this same region as having the greatest reduction in convection velocity due to the offset, up to 20% reduction for the offset case compared to the axisymmetric case. These findings suggest that this region along the centerline near the end of the potential core is an important area for noise generation with jets and contributes to the noise reductions seen from three-stream offset nozzles. Graphical abstract