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Turbulent swirling jets with excitationAn existing cold-jet facility at NASA Lewis Research Center was modified to produce swirling flows with controllable initial tangential velocity distribution. Two extreme swirl profiles, i.e., one with solid-body rotation and the other predominated by a free-vortex distribution, were produced at identical swirl number of 0.48. Mean centerline velocity decay characteristics of the solid-body rotation jet flow exhibited classical decay features of a swirling jet with S - 0.48 reported in the literature. However, the predominantly free-vortex distribution case was on the verge of vortex breakdown, a phenomenon associated with the rotating flows of significantly higher swirl numbers, i.e., S sub crit greater than or equal to 0.06. This remarkable result leads to the conclusion that the integrated swirl effect, reflected in the swirl number, is inadequate in describing the mean swirling jet behavior in the near field. The relative size (i.e., diameter) of the vortex core emerging from the nozzle and the corresponding tangential velocity distribution are also controlling factors. Excitability of swirling jets is also investigated by exciting a flow with a swirl number of 0.35 by plane acoustic waves at a constant sound pressure level and at various frequencies. It is observed that the cold swirling jet is excitable by plane waves, and that the instability waves grow about 50 percent less in peak r.m.s. amplitude and saturate further upstream compared to corresponding waves in a jet without swirl having the same axial mass flux. The preferred Strouhal number based on the mass-averaged axial velocity and nozzle exit diameter for both swirling and nonswirling flows is 0.4.
Document ID
19890019958
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Taghavi, Rahmat (Kansas Univ. Center for Research, Inc. Lawrence, KS, United States)
Farokhi, Saeed (Kansas Univ. Center for Research, Inc. Lawrence, KS, United States)
Date Acquired
September 6, 2013
Publication Date
March 1, 1988
Subject Category
Aerodynamics
Report/Patent Number
NASA-CR-180895
NAS 1.26:180895
Accession Number
89N29329
Funding Number(s)
PROJECT: RTOP 505-62-21
CONTRACT_GRANT: NCC3-56
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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