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  • 1
    Electronic Resource
    Electronic Resource
    The mechanism of mixing enhancement and suppression in a circular jet under excitation conditions (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2062-2074 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The present work is a numerical study of the shear layer's growth in a turbulent round jet under forced axisymmetric periodic disturbances. The forced oscillation is found to either enhance or reduce the momentum thickness along the jet depending on the forcing Strouhal number St, where St is defined as fd/Ue. Here, f is the frequency in Hertz, d is the nozzle exit diameter, and Ue is the jet exit velocity. At low Strouhal numbers (St〈0.5), no subharmonic of the forced fundamental is amplified. The momentum thickness is found to increase monotonically with the forcing level, and the effect is pronounced for forcing levels higher than 0.5% of the jet exit velocity. At forcing Strouhal numbers in the range of 0.6–1.0, the first subharmonic of the fundamental is amplified. The increase in the momentum thickness caused by forcing at this Strouhal number range is proportional to the forcing level and is pronounced at low forcing levels in the range of 0.01%–1% of the jet exit velocity. If the forcing Strouhal number is close to the "shear layer instability mode,'' Stθ≈0.015, several subharmonics are generated and the forcing is found to result in a reduction in the momentum thickness along the jet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865387
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    Paper (German National Licenses)
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  • 2
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    The mechanism of mixing enhancement and suppression in a circular jet under excitation conditions (1985)
    American Institute of Physics
    Details
    Publication Date: 1985-01-01
    Print ISSN: 0031-9171
    Topics: Physics
    Published by American Institute of Physics
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    PAPER CURRENT
  • 3
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    Large Eddy Simulation in the Computation of Jet Noise (1999)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Noise can be predicted by solving Full (time-dependent) Compressible Navier-Stokes Equation (FCNSE) with computational domain. The fluctuating near field of the jet produces propagating pressure waves that produce far-field sound. The fluctuating flow field as a function of time is needed in order to calculate sound from first principles. Noise can be predicted by solving the full, time-dependent, compressible Navier-Stokes equations with the computational domain extended to far field - but this is not feasible as indicated above. At high Reynolds number of technological interest turbulence has large range of scales. Direct numerical simulations (DNS) can not capture the small scales of turbulence. The large scales are more efficient than the small scales in radiating sound. The emphasize is thus on calculating sound radiated by large scales.
    Keywords: Acoustics
    Type: First NASA/Industry High Speed Research Program Nozzle Symposium; 25-1 - 25-7; NASA/CP-1999-209423
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Validation of a High-Order Compact Code for Nonlinear Flows About Complex Geometric (2001)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: The slides review computational requirements for nozzle exhaust flow and noise calculations and the current numerical method, validation of prefactored compact scheme on CAA benchmark problems, a curvilinear grid performance test of gust response of a Joukowski airfoil, airfoil surface RMS pressure distribution and far field noise radiation results for Joukowski airfoil in a vortical gust, boundary distance study for Joukowski airfoil problem, and performance of ICOMP parallel Macintosh cluster.
    Keywords: Aircraft Propulsion and Power
    Type: Proceedings of the Jet Noise Workshop; 951-965; NASA/CP-2001-211152
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    A rapid-distortion-theory turbulence model for developed unsteady wall-bounded flow (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new approach to turbulence modeling in unsteady developed flows has recently been introduced, based on results of rapid distortion theory. The approach involves closing the k-epsilon equations for the organized unsteady component of the flow by modeling local unsteadiness as a rapid distortion of the local structure of the parent turbulent flow, in terms of an effective strain parameter alpha(sub eff). In this paper, the phase-conditioned equations of motion are developed to accommodate a new unsteady dissipation model and local effects of the slow-relaxation time scale of the parent flow. The model equations are tested against measurements of the response of a fully-developed turbulent pipe flow to the superposition of sinusoidal streamwise oscillation. Good agreement is found between measurements and predictions over a wide range of frequencies of unsteadiness, indicating that this approach may be particularly well suited to modeling of unsteady turbulent flows which are perturbations about a well characterized mean.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-106249 , ICOMP-93-22 , E-7971 , NAS 1.15:106249
    Format: application/pdf
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  • 6
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    Sound Radiated by a Wave-Like Structure in a Compressible Jet (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper extends the analysis of acoustic radiation from the source model representing spatially-growing instability waves in a round jet at high speeds. Compared to previous work, a modified approach to the sound source modeling is examined that employs a set of solutions to linearized Euler equations. The sound radiation is then calculated using an integral surface method.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 2003-1063 , 41st AIAA Aerospace Sciences Meeting; Jan 06, 2003 - Jan 09, 2003; Reno, NV; United States
    Format: application/pdf
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  • 7
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    Direct Computation of Sound Radiation by Jet Flow Using Large-scale Equations (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Jet noise is directly predicted using large-scale equations. The computational domain is extended in order to directly capture the radiated field. As in conventional large-eddy-simulations, the effect of the unresolved scales on the resolved ones is accounted for. Special attention is given to boundary treatment to avoid spurious modes that can render the computed fluctuations totally unacceptable. Results are presented for a supersonic jet at Mach number 2.1.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA-TM-106877 , E-9503 , NAS 1.15:106877 , ICOMP-95-6 , AIAA Paper 95-0680 , Aerospace Sciences Meeting; Jan 09, 1995 - Jan 12, 1995; Reno, NV; United States
    Format: application/pdf
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  • 8
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    Turbulence enhancement in free shear flows under multifrequency excitation (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The interactions of multifrequency wave-packet with the background turbulence in a round jet are studied. The process explains the mechanisms governing the later stages of the laminar-turbulent transitions as well as the effect of multifrequency excitation on turbulent jets. In a multifrequency-excited jet, mixing enhancement was found to be a result of the turbulence enhancement rather than simply the amplification of forced wave components. The excitation waves pump energy from the mean flow to the turbulence, thus enhancing the latter. The high-frequency wave enhance the turbulence close to the jet exit, but the low-frequency waves are most effective further downstream.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Joint CSME/ASME Spring Meeting; Jun 04, 1990 - Jun 07, 1990; Toronto; Canada
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Heat transfer in oscillating flows (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The heat transfer in a sudden-expansion flow subjected to upstream periodic disturbances is investigated. In order to study the unsteady turbulent flow for the present symmetrical sudden-expansion flow, the phase-averaging technique of Hussain and Reynolds (1970) is used to derive the governing equations. The imposed periodic disturbances are found to increase the turbulent kinetic energy and the heat transfer rates at the wall. The phenomenon is discovered to be sensitive to the frequency of the imposed disturbances. At the optimum frequency and at a 3 percent disturbance level, the time-averaged heat transfer rate near the reattachment point can be increased by as much as 14 percent.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Symposium on Nonsteady Fluid Dynamics; Jun 04, 1990 - Jun 07, 1990; Toronto; Canada
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Validation of a High-Order Prefactored Compact Code on Nonlinear Flows with Complex Geometries (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-11
    Description: A finite-difference time domain solution of the airfoil gust problem is obtained using a high-accuracy nonlinear computational aeroacoustics code. For computational efficiency, the equations are cast in chain-rule curvilinear form, and a structured multiblock solver is used in parallel. In order to fully investigate the performance of this solver, a test matrix of eight problems are computed (two airfoil geometries, two gust frequencies, and two gust configurations). These results are compared to solutions obtained by the GUST3D frequency-domain solver both on the airfoil surface and in the far field. Grid density and domain size studies are included.
    Keywords: Aerodynamics
    Format: application/pdf
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