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  • 1
    Electronic Resource
    Electronic Resource
    Passive scalar tagging for the study of coherent structures in the plane mixing layer (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 2034-2041 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data obtained from the two-dimensional numerical simulation of a plane mixing layer have been used to study the feasibility of tagging one side of the flow by a passive scalar and using the instantaneous concentration of the scalar to detect the typical coherent events in the flow. The study has shown that this technique works quite satisfactorily and yields results similar to those obtained by using the instantaneous vorticity as a detection criterion. The contribution from the coherent events to the time-averaged turbulent momentum and scalar transport has been estimated. It is found that this contribution is of the same order as the time-mean transport during most of the dynamical evolution of the coherent structure. However, it may attain very large values for short periods of time in the neighborhood of pairing. The increase is particularly spectacular in the case of the Reynolds shear stress. While the present findings obtained from a two-dimensional simulation seem to support earlier results obtained from actual experiments, it is desirable to conduct additional studies with three-dimensional simulations when they become available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857477
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of compressibility on vortex pairing (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 1063-1072 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct numerical simulations are conducted to investigate in detail the effect of Mach number on vortex pairing in a mixing layer. The pairing process is found to be delayed at higher Mach numbers and the paths followed by the vortices change. To investigate the effect of the initial shape of the vortices a simple vortex dynamical model of pairing is constructed which accurately models pairing at low Mach numbers. Results from the model suggest that a variation in the initial shape of the vortices is not sufficient to explain the changes in the pairing process due to Mach number. Further simulations are conducted for isolated vortex pairs. There is little departure from the expected rotation rate as Mach number is increased, but strong core effects. Overall, changes in the pairing process reflect changes in the evolution of the primary instability, with vortex trajectories becoming more elongated as the Mach number is increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868339
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  • 3
    Electronic Resource
    Electronic Resource
    Instability of vortical and acoustic modes in supersonic round jets (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 1003-1013 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of "top-hat" and fully developed jet profiles is investigated by an inviscid linear stability theory for compressible flow. The study covers a wide range of the Mach number and the temperature ratio. Two types of instabilities are found: vortical and acoustic, each of which can be subdivided into non-radiating (subsonic) and radiating (supersonic) modes. The vortical mode is the continuation of the Kelvin-Helmholtz instability from incompressible flow. The acoustic mode is a compressible flow phenomenon, which becomes important at large Mach numbers. Temperature-ratio effects can be destabilizing or stabilizing, depending on the Mach number and mode of instability. A spectrum of unstable acoustic modes, including axisymmetric ones, are found to exist in the fully developed jet. For this jet, acoustic axisymmetric waves become more unstable than both vortical and acoustic helical waves at Mach numbers over about 3. Strong evidence of a resonance mechanism for acoustic modes is seen in the growth rate curves at high Mach numbers, where a spectrum of local peaks and valleys appears at regularly distributed frequencies. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869196
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  • 4
    Electronic Resource
    Electronic Resource
    Direct simulation of breakdown to turbulence following oblique instability waves in a supersonic boundary layer (1995)
    Springer
    Flow, turbulence and combustion 54 (1995), S. 223-234 
    Details
    ISSN: 1573-1987
    Keywords: transition ; compressible flow ; direct numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The late stages of transition to turbulence in a Mach two boundary layer are investigated by direct numerical simulation of the compressible Navier-Stokes equations. The primary instability at this Mach number consists of oblique waves, which are known to form a pattern of quasi-streamwise vortices. It is found that breakdown does not follow immediately from these vortices, which decay in intensity. The generation of new vortices is observed by following the evolution of the pressure and vorticity in the simulation, and analysed by consideration of vorticity stretching. It is found that the slight inclined and skewed nature of the quasi-streamwise vortices leads to a production of oppositely signed streamwise vorticity, which serves as a strong localised forcing of the shear layer alongside the original vortices, formed by convection and stretching of spanwise vorticity. The shear layer rolls up into many new vortices, and is followed by a sharp increase in the energy of higher frequencies and in the skin friction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00849118
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  • 5
    Electronic Resource
    Electronic Resource
    Numerical simulation of boundary-layer transition at Mach two (1993)
    Springer
    Flow, turbulence and combustion 51 (1993), S. 371-375 
    Details
    ISSN: 1573-1987
    Keywords: transition ; compressible flow ; direct numerical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The linear and early nonlinear stages of boundary-layer transition at free-stream Mach numberM ∞==2.0 are investigated by direct numerical simulation of the compressible Navier-Stokes equations. Results from simulations with a large computational box and small-amplitude random initial conditions are compared with linear stability theory. The growth rates of oblique waves are reproduced correctly. Two-dimensional waves show a growth that is modulated in time, indicating the presence of an extra unstable mode which moves supersonically relative to the free stream. Further simulations are conducted to investigate the nonlinear development of two- and three-dimensional disturbances The transition due to oblique disturbance waves is the most likely cause of transition at this Mach number, and is found to lead to the development of strong streamwise vortices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01082563
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  • 6
    Electronic Resource
    Electronic Resource
    Direct Numerical Simulation of Supersonic Jet Flow (1997)
    Springer
    Journal of engineering mathematics 32 (1997), S. 121-142 
    Details
    ISSN: 1573-2703
    Keywords: DNS ; jets ; supersonics ; finite differences ; shocks.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract A numerical method is given for direct numerical simulation of the nonlinear evolution of instability waves in supersonic round jets, with spatial discretisation based on high-order compact finite differences. The numerical properties of a class of symmetric and asymmetric schemes are analysed. Implementation for the Navier–Stokes equations in cylindrical polar coordinates is discussed with particular attention given to treatment of the origin to ensure stability and efficiency. Validation of the schemes is carried out by detailed comparison with linear stability theory. The computer code is applied to study the initial stages of nonlinear development of unstable modes in a Mach 3 jet. The modes of instability that are present include strongly unstable axisymmetric acoustic and helical vortical waves, as well as weakly unstable radiating acoustic and vortical modes. Three distinctive wave patterns are observed from the simulations including a cross-hatched internal shock structure. Nonlinear interactions between the vortical and acoustic modes are investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004244715140
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  • 7
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    Strong interaction of a turbulent spot with a shock-induced separation bubble (2007)
    American Institute of Physics
    Details
    Publication Date: 2007-01-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 8
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    Numerical simulation of boundary-layer transition at Mach two (1993)
    Springer
    Details
    Publication Date: 1993-06-01
    Print ISSN: 1386-6184
    Electronic ISSN: 1573-1987
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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  • 9
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    Direct simulation of breakdown to turbulence following oblique instability waves in a supersonic boundary layer (1995)
    Springer
    Details
    Publication Date: 1995-04-01
    Print ISSN: 1386-6184
    Electronic ISSN: 1573-1987
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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  • 10
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    Analysis of data on the relation between eddies and streaky structures in turbulent flows using the placebo method (2006)
    Springer
    Details
    Publication Date: 2006-09-01
    Print ISSN: 0015-4628
    Electronic ISSN: 1573-8507
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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