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  • 1
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    Stability of compressible boundary layers over a smooth backward-facing step (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An investigation is conducted into the determination of the credibility of interacting boundary layers in predicting compressible subsonic flows over smooth surface imperfections. The case of smooth backward-facing steps is considered. The predicted mean flows are compared with those obtained using a Navier-Stokes solver. Moreover, the linear 2-D compressible stability characteristics of both mean flows are compared. The results show that the interacting boundary-layer formulation produces accurate mean flows that yield accurate linear stability characteristics, such as growth rates and amplification factors.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-184962 , NAS 1.26:184962 , NR-4325201
    Format: application/pdf
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  • 2
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    Goertler instability (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Goertler instability for boundary-layer flows over generally curved walls is considered. The full-linearized disturbance equations are obtained in an orthogonal curvilinear coordinate system. A perturbation procedure to account for second-order effects is used to determine the effects of the displacement thickness and the variation of the streamline curvature on the neutral stability of the Blasius flow. The streamwise pressure gradient in the mean flow is accounted for by solving the nonsimilar boundary-layer equations. Growth rates are obtained for the actual mean flow and compared with those for the Blasius flow and the Falkner-Skan flows. The results demonstrate the strong influence of the streamwise pressure gradient and the nonsimilarity of the basic flow on the stability characteristics.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids; 24; Aug. 198
    Format: text
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  • 3
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    Effect of streamwise vortices on Tollmien-Schlichting waves (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The method of multiple scales is used to determine a first order uniform expansion for the effect of counter rotating steady streamwise vortices in growing boundary layers on Tollmien-Schlichting waves. The results show that such vortices have a strong tendency to amplify three dimensional Tollmien-Schlichting waves having a spanwise wavelength that is twice the wavelength of the vortices. An analytical expression is derived for the growth rates of these waves. These growth rates increase linearly with increasing amplitudes of the vortices.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-162654 , VPI-E-79-12
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  • 4
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    Effect of streamwise vortices on Tollmien-Schlichting waves (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The method of multiple scales is used to determine a first-order uniform expansion for the effect of counter-rotating steady streamwise vortices in growing boundary layers on oblique Tollmien-Schlichting waves. The results show that such vortices have a strong tendency to amplify oblique Tollmien-Schlichting waves having a spanwise wavelength that is twice the wavelength of the vortices. An analytical expression is derived for the growth rates of these waves. These exponential growth rates increase linearly with increasing amplitudes of the vortices. Numerical results are presented. They suggest that this mechanism may dominate the instability.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics; 107; June 198
    Format: text
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  • 5
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    Nonparallel stability of boundary layers with pressure gradients and suction (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An analysis is presented for the linear nonparallel stability of boundary layer flows with pressure gradients and suction. The effect of the boundary layer growth is included by using the method of multiple scales. The present analysis is compared with those of Bouthier and Gaster and the roles of the different definitions of the amplification rates are discussed. The results of these theories are compared with experimental data for the Blasius boundary layer. Calculations are presented for stability characteristics of boundary layers with pressure gradients and nonsimilar suction distributions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AGARD Laminar-Turbulent Transition; 21 p
    Format: text
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  • 6
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    Nonlinear propagation of a wave packet in a hard-walled circular duct (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The method of multiple scales is used to derive a nonlinear Schroedinger equation for the temporal and spatial modulation of the amplitudes and the phases of waves propagating in a hard-walled circular duct. This equation is used to show that monochromatic waves are stable and to determine the amplitude dependance of the cut off frequencies.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-146326 , VPI-E-74-9
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  • 7
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    Nonlinear interaction of two waves in boundary-layer flows (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: First-order nonlinear interactions of Tollmien-Schlichting waves of different frequencies and initial amplitudes in boundary-layer flows are analyzed using the method of multiple scales. Numerical results for flow past a flat plate show that the spatial detuning wipes out resonant interactions unless the initial amplitudes are very large. Thus, a wave having a moderate amplitude has little influence on its subharmonic although it has a strong influence on its second harmonic. Moreover, two waves having moderate amplitudes have a strong influence on their difference frequency. The results show that the difference frequency can be very unstable when generated by the nonlinear interaction, even though it may be stable when introduced by itself in the boundary layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids; 23; Mar. 198
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  • 8
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    Stability of compressible boundary layers over a smooth backward-facing step (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An investigation is conducted into the determination of the credibility of interacting boundary layers in predicting compressible subsonic flows over smooth surface imperfections. The case of smooth backward-facing steps is considered. The predicted mean flows are compared with those obtained using a Navier-Stokes solver. Moreover, the linear 2-D compressible stability characteristics of both mean flows are compared. The results show that the interacting boundary-layer formulation produces accurate mean flows that yield accurate linear stability characteristics, such as growth rates and amplification factors.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 90-1449
    Format: text
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  • 9
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    Finite amplitude waves in two-dimensional lined ducts (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A second-order uniform expansion is obtained for nonlinear wave propagation in a two-dimensional duct lined with a point-reacting acoustic material consisting of a porous sheet followed by honeycomb cavities and backed by the impervious wall of the duct. The waves in the duct are coupled with those in the porous sheet and the cavities. An analytical expression is obtained for the absorption coefficient in terms of the sound frequency, the physical properties of the porous sheet, and the geometrical parameters of the flow configuration. The results show that the nonlinearity flattens and broadens the absorption vs. frequency curve, irrespective of the geometrical dimensions or the porous material acoustic properties, in agreement with experimental observations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Sound and Vibration; 37; Nov. 8
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  • 10
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    The relation between temporal and spatial stability in three-dimensional flows (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An analysis is presented of the nonparallel spatial or temporal stability of three-dimensional incompressible, isothermal boundary-layer flows taking into account the transverse velocity component as well as the axial and crossflow variations of the mean flow. The method of multiple scales is used to derive partial differential equations that describe the axial and crossflow variations of the disturbance amplitude, phase and wavenumbers. This equation is used to derive the expressions that relate the temporal and spatial instabilities. These relations are functions of the complex group velocities. Moreover, this equation is used to derive the expression that relates the spatial amplification in any direction to a calculated amplification in any other direction. These relations are verified by numerical results obtained for two- and three-dimensional disturbances in two- and three-dimensional flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 78-1126 , Fluid and Plasma Dynamics Conference; Jul 10, 1978 - Jul 12, 1978; Seattle, WA
    Format: text
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