Turbulent Mixing in a Far-Field Plume During the Transition to Upwelling Conditions: Microstructure Observations From an AUV

The main aim of this investigation is to analyze directional noise reduction resulting from asymmetric high momentum fluidic injection downstream of a Mach 0.9 nozzle. Jet noise has been identified as one of the primary obstacles to increasing commercial aviation capacity. Microjets in cross flow are known to enhance turbulent mixing in the shear layer due to the induced stream-wise vortices. This enhanced mixing can be used for reorganizing the spatial distribution of acoustic energy. Targeted reduction in the downward-emitted turbulent mixing noise can be achieved by strategically injecting high momentum fluid downstream of the jet exhaust. Detailed Large Eddy Simulations were performed on a hybrid block structured-unstructured mesh to generate the flow field which was then used for near field and far field noise computation. Aeroacoustic analogy based formulation was used for computing far-field noise estimation. Benchmark cases were validated with preexisting experimental data sets. Mean flow measurements suggest shorter jet core lengths due to the enhanced mixing resulting from fluidic injection. The induced asymmetry due to the fluidic injection gives rise to an asymmetric acoustic field leading to targeted directional noise reduction in the far field as measured by pressure probes.

Download Full-text

Far-Field Turbulent Mixing Efficiency and Large-Scale Outer-Fluid-Interface Dynamics

42nd AIAA Aerospace Sciences Meeting and Exhibit ◽

10.2514/6.2004-1280 ◽

2004 ◽

Author(s):

Jennifer Nathman ◽

Roberto Aguirre ◽

Haris Catrakis

Keyword(s):

Turbulent Mixing ◽

Large Scale ◽

Mixing Efficiency ◽

Far Field ◽

Fluid Interface ◽

Interface Dynamics

Download Full-text

Concurrent scale interactions in the far-field of a turbulent mixing layer

Physics of Fluids ◽

10.1063/1.4903970 ◽

2014 ◽

Vol 26 (12) ◽

pp. 125106 ◽

Cited By ~ 7

Author(s):

O. R. H. Buxton ◽

B. Ganapathisubramani

Keyword(s):

Turbulent Mixing ◽

Mixing Layer ◽

Far Field ◽

Turbulent Mixing Layer ◽

Scale Interactions

Download Full-text

Possible applications of fraunhofer holography in high resolution electron microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108258 ◽

1978 ◽

Vol 36 (1) ◽

pp. 222-223 ◽

Cited By ~ 1

Author(s):

N. Bonnet ◽

M. Troyon ◽

P. Gallion

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Transfer Function ◽

Radiation Damage ◽

High Resolution Electron Microscopy ◽

Far Field ◽

Field Region ◽

Crystalline Materials ◽

Resolution Electron ◽

The Ideal

Two main problems in high resolution electron microscopy are first, the existence of gaps in the transfer function, and then the difficulty to find complex amplitude of the diffracted wawe from registered intensity. The solution of this second problem is in most cases only intended by the realization of several micrographs in different conditions (defocusing distance, illuminating angle, complementary objective apertures…) which can lead to severe problems of contamination or radiation damage for certain specimens.Fraunhofer holography can in principle solve both problems stated above (1,2). The microscope objective is strongly defocused (far-field region) so that the two diffracted beams do not interfere. The ideal transfer function after reconstruction is then unity and the twin image do not overlap on the reconstructed one.We show some applications of the method and results of preliminary tests.Possible application to the study of cavitiesSmall voids (or gas-filled bubbles) created by irradiation in crystalline materials can be observed near the Scherzer focus, but it is then difficult to extract other informations than the approximated size.

Download Full-text