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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781724700643
Category :
Languages : en
Pages : 230
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Book Description
An 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. Taghavi, Rahmat and Farokhi, Saeed Unspecified Center NASA-CR-180895, NAS 1.26:180895 NCC3-56; RTOP 505-62-21...
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781724700643
Category :
Languages : en
Pages : 230
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Book Description
An 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. Taghavi, Rahmat and Farokhi, Saeed Unspecified Center NASA-CR-180895, NAS 1.26:180895 NCC3-56; RTOP 505-62-21...
Author: Sara Toutiaei
Publisher:
ISBN: 9781321238839
Category : Jets
Languages : en
Pages : 52
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Book Description
In this study, velocity distributions of a swirling and a non-swirling jet flows were obtained using Laser Doppler Anemometer (LDA) in the near field where both jets are at the same stages of development. The resulting mean velocity and Reynolds stress distributions and the energy budgets of the axial Reynolds stresses are assessed. All Reynolds stresses showed higher magnitude in the swirling case compared to the non-swirling one at the same measurement axial locations. The swirling jet is found to exhibit larger production, mean convection and turbulence transport terms in the energy budget of axial Reynolds stress. The result shows faster development of the swirling jet compared with the non-swirling jet and is in consistency with previous studies. The turbulent transport term is found to be responsible for the faster development of the turbulence in the swirling jet.
Author: David Jorgen Ettestad
Publisher:
ISBN:
Category : Jets
Languages : en
Pages : 520
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Author: Eric J. DeMillard
Publisher:
ISBN: 9781085621250
Category : Fluid dynamics
Languages : en
Pages : 56
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Book Description
Experimental investigations were carried out in both non-swirling and swirling jets at a Re = 105. A stereoscopic particle image velocimetry (SPIV) system was used to acquire the measurements in both axial-radial and radial-tangential planes at x/D = (1-10). Multiple test cases were taken where both the swirl magnitude and swirl distribution was adjusted. Proper Orthogonal Decomposition (POD) was then applied to the measurements to characterize turbulence structure. The results indicate that swirl causes the structure to be more ordered and shifts the relative amount of energy from axisymmetric structure to azimuthal structure.
Author: R. Taghavi
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Jonathan Wayne Naughton
Publisher:
ISBN:
Category : Eddies
Languages : en
Pages : 30
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Book Description
Swirling jet flows have been studied experimentally and computationally and the results have been compared with theory. Three-component Laser Doppler Anemometry (LDA) measurements have been carried out for swirling jets of various strengths and swirl distributions. Radial profiles of velocity have been obtained from the jet exit to 50 diameters downstream. The experimental results are consistent with previous results and with similarity theory for weakly swirling turbulent jets. However, the parametric range and spatial domain of the current data set makes it suitable for validation. Computational simulations have also been performed using a combination of Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) approaches. The results have been validated with experimental data and used to explore the mechanisms behind the increased mixing enhancement observed. The combined experimental/computational effort is still ongoing, but the experiences to date have demonstrated the effectiveness of such an approach.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 173
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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722385910
Category :
Languages : en
Pages : 48
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Book Description
Passive and active control of swirling turbulent jets is experimentally investigated. Initial swirl distribution is shown to dominate the free jet evolution in the passive mode. Vortex breakdown, a manifestation of high intensity swirl, was achieved at below critical swirl number (S = 0.48) by reducing the vortex core diameter. The response of a swirling turbulent jet to single frequency, plane wave acoustic excitation was shown to depend strongly on the swirl number, excitation Strouhal number, amplitude of the excitation wave, and core turbulence in a low speed cold jet. A 10 percent reduction of the mean centerline velocity at x/D = 9.0 (and a corresponding increase in the shear layer momentum thickness) was achieved by large amplitude internal plane wave acoustic excitation. Helical instability waves of negative azimuthal wave numbers exhibit larger amplification rates than the plane waves in swirling free jets, according to hydrodynamic stability theory. Consequently, an active swirling shear layer control is proposed to include the generation of helical instability waves of arbitrary helicity and the promotion of modal interaction, through multifrequency forcing. Farokhi, Saeed and Taghavi, R. Unspecified Center NCC3-56...
Author:
Publisher:
ISBN:
Category : Air jets
Languages : en
Pages : 762
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Author: Zahir Uddin Ahmed
Publisher:
ISBN:
Category : Fluid-structure interaction
Languages : en
Pages :
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