The Experts below are selected from a list of 216 Experts worldwide ranked by ideXlab platform
Georges Guiochon - One of the best experts on this subject based on the ideXlab platform.
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Single-component Shock Layer analysis in elution chromatography.
Analytical chemistry, 2004Co-Authors: Tarab Ahmad, Fabrice Gritti, Bingchang Lin, Georges GuiochonAbstract:One of the fundamental results of the theory of nonlinear chromatography is that a propagation velocity is associated with each concentration. This velocity is related to the slope of the isotherm at the corresponding concentration. It follows that if a continuous concentration gradient is injected into a column, the gradient profile will not propagate in a mere translation but will progressively change shape. In the most common case of a convex upward isotherm (e.g., Langmuir), a linear gradient will become curved upward, the high concentrations migrating faster than the low ones. However, high concentrations cannot pass low ones, so the concentrations pile up, a concentration Shock forms, and its height increases. In practice, axial dispersion and the mass-transfer resistances combine and prevent the formation of a true Shock. A Shock Layer, a region where the concentration gradient is very steep, is formed. This Shock Layer migrates at the same velocity as the ideal Shock would. Many characteristics of concentration Shocks and Shock Layers have been determined previously, but not the time that it takes for a continuous gradient to turn into a Shock Layer, the circumstances of the birth of the Shock Layer, and of its growth. Yet, this is important to know to understand certain aspects of gradient elution. We have derived simple equations relating the circumstances of the birth of Shocks to the phase equilibrium isotherm and to the column characteristics. The results of experimental measurements made with a high-efficiency analytical column are in excellent agreement with these theoretical predictions.
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Extension of the Shock Layer theory to the case of a linear dependence of the axial dispersion and the mass transfer coefficients on the concentration
Journal of Chromatography A, 1997Co-Authors: Peter Sajonz, Guoming Zhong, Georges GuiochonAbstract:The classical Shock Layer theory assumes that the coefficients of axial dispersion and of mass transfer kinetics are constant. Experimental results have shown that this assumption is not always valid. The influence of a linear dependence of these coefficients on the concentration is investigated. The Shock Layer theory is easily extended to this case and an analytical solution is reported. Changes in the shape of the breakthrough curves and in the thickness of the Shock Layer are discussed. Excellent agreement was observed between the results of numerical calculations of breakthrough curves and the Shock Layer thickness derived from the analytical solution. The agreement found with experimental results previously reported was also excellent.
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Optimum liquid and solid-phase velocity for minimum Shock Layer thickness in counter-current chromatography
Journal of Chromatography A, 1996Co-Authors: Guoming Zhong, Georges GuiochonAbstract:The Shock-Layer theory is applied to counter-current liquid chromatography, in the single-component case. This model uses a Langmuir isotherm to account for nonlinear effects, a finite axial dispersion coefficient and a linear driving force (LDF) kinetics to account for the nonideal effects, e.g., the axial dispersion and the mass transfer resistance. The Shock-Layer velocity and its thickness are explicitly formulated in closed forms. Based on these expressions, the optimum velocities of the solid and liquid phases are derived for minimum Shock-Layer thickness.
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Shock Layer analysis for a single-component in preparative elution chromatography
Journal of Chromatography A, 1995Co-Authors: Bingchang Lin, Guoming Zhong, Tong Yun, Georges GuiochonAbstract:The onset of the nonlinear behavior of band profiles in elution chromatography is investigated by studying the profile of the Shock Layer caused by a finite mass transfer resistance in the absence of axial dispersion for a single component. A closed-form analytical expression of the Shock Layer is obtained for a parabolic isotherm. This solution depends on a dimensionless number which may be used to characterize the degree of nonlinear behavior of the band profiles and to select the model most appropriate for their accurate description. The profiles resulting from this solution are compared with those obtained by numerical calculations under different conditions to assess the influence of the assumptions made. The differences observed illustrate the sensitivity of the elution profiles to small changes in the equilibrium isotherm.
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Shock Layer thickness and optimum linear velocity in displacement chromatography
Journal of Chromatography A, 1994Co-Authors: Jie Zhu, Georges GuiochonAbstract:The width of the mixed zones between two successive bands in the isotachic train represents the loss in recovery yield achieved in displacement chromatography. Intuitively, this width depends on the mobile phase flow velocity, but no systematic study of this effect has yet been performed. On the other hand, constant pattern behavior and the theory of Shock Layer are well known in chemical engineering. Using this approach, and assuming competitive Langmuir isotherm behavior, an analytical equation is derived which relates the Shock Layer thickness (SLT) in displacement chromatography and the column design and operating parameters. Using this equation, it is possible to investigate the dependence of the SLT between two consecutive bands in the isotachic train on the mobile phase velocity, the concentration and the retention factor of the displacer and the separation factor of the two components. In displacement chromatography, the optimum mobile phase linear velocity (uopts) for minimum Shock Layer thickness, or maximum recovery yield depends not only on the coefficients of axial dispersion and mass transfer resistance of the two components, as does the optimum mobile phase velocity (uoptL) in linear chromatography, but also on the retention factor and the concentration of the displacer. The results of the study of this analytical equation are in excellent agreement with those of numerical calculations.
Anatoly A. Maslov - One of the best experts on this subject based on the ideXlab platform.
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Active control of hypersonic Shock Layer disturbances
Progress in Flight Physics, 2012Co-Authors: T.v. Poplavskaya, Anatoly A. MaslovAbstract:This is a brief review of the investigations of receptivity and control of hypersonic Shock Layers. The present paper describes comprehensive numerical and experimental investigations of evolution of disturbances generated in the hypersonic viscous Shock Layer (VSL) on a flat plate by external acoustic waves and by perturbations introduced into the Shock Layer from the surface of model. The active control of intensity of pulsations is possible because both external acoustic waves and the periodic controlled disturbances introduced on the plate surface generate, in a Shock Layer, entropy-vorticity disturbances with identical spatial distributions and phase velocities.
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Wave processes in the Shock Layer on a flat plate at an angle of attack
Journal of Applied Mechanics and Technical Physics, 2010Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, I. S. TsyryulnikovAbstract:A numerical and experimental study of receptivity of the viscous Shock Layer on a flat plate aligned at an angle of attack to external acoustic perturbations is performed. Density and pressure fluctuations are measured in experiments at the free-stream Mach number M ∞ = 21 and Reynolds number Re 1 = 6·10 5 m −1 . Direct numerical simulations of receptivity of the viscous Shock Layer to external acoustic perturbations in wide ranges of the governing parameters are performed by solving the Navier-Stokes equations with the use of high-order Shock-capturing schemes. The calculated intensities of density and pressure fluctuations are found to be in good agreement with experimental data. Results of the study show that entropy-vortex disturbances dominate in the Shock Layer at small angles of attack, whereas acoustic perturbations prevail at angles of attack above 20°.
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Wave processes in a viscous Shock Layer and control of fluctuations
Journal of Fluid Mechanics, 2010Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, Alexey Kudryavtsev, I. S. TsyryulnikovAbstract:Generation and development of disturbances in a hypersonic viscous Shock Layer on a flat plate is studied both experimentally and numerically. The study is performed at the Mach number M∞ = 21 and the Reynolds number ReL = 1.44 × 105 and is aimed at elucidating the physical mechanisms that govern the receptivity and instability of the Shock Layer at extremely high hypersonic velocities. The experiments are conducted in a hypersonic nitrogen-driven wind tunnel. An electron-beam fluorescence technique, a Pitot probe and a piezoceramic transducer are used to measure the mean density and Mach number contours, as well as density and pressure fluctuations, their spectra and spatial distributions in the Shock Layer. Direct numerical simulations are performed by solving the Navier–Stokes equations with a high-order Shock-capturing scheme in a computational domain including the leading and trailing edges of the plate, so that the bow Shock wave and the wake behind the plate are also simulated. It is demonstrated that computational and experimental data characterizing the mean flow field, intensity of density fluctuations and their spatial distributions in the Shock Layer are in close agreement. It is found that excitation of the Shock Layer by external acoustic waves leads to generation of entropy–vortex disturbances with two maxima of density fluctuations: directly behind the Shock wave and on the external edge of the boundary Layer. At the same time, the pressure fluctuations decay inward into the Shock Layer, away from the Shock, which agrees with the linear theory of interaction of Shock waves with small perturbations. Thus, the entropy–vortex disturbances are shown to dominate in the hypersonic Shock Layer at very high Mach numbers, in contrast with the boundary Layers at moderate hypersonic velocities where acoustic modes are most important. A parametric numerical study of wave processes in the Shock Layer induced by external acoustic waves is performed with variations of frequency, amplitude and angle of propagation of external disturbances. The amplitude of generated disturbances is observed to grow and decay periodically along the streamwise coordinate, and the characteristics of these variations depend on the frequency and direction of incident acoustic waves. The hypersonic Shock Layer excited by periodic blowing and suction near the leading edge is also investigated; in the experiments, this type of excitation is obtained by using an oblique-cut whistle. It is shown that blowing/suction generates disturbances resembling those generated by external acoustic waves, with similar spatial distributions and phase velocities. This result paves the way for active control of instability development in the Shock Layer by means of destructive interference of two types of disturbances. Numerical simulations are performed to show that instability waves can be significantly amplified or almost entirely suppressed, depending on the relative phase of blowing/suction and acoustic disturbances. Wind-tunnel experiments completely confirm this numerical prediction. Thus, the feasibility of delaying instability development in the hypersonic Shock Layer has been demonstrated for the first time.
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Stability of the Hypersonic Shock Layer on a Flat Plate
Fluid Dynamics, 2004Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, B. V. SmorodskiiAbstract:The stability of hypersonic viscous gas flow in a Shock Layer in the neighborhood of a flat plate is considered. The stability of the velocity, temperature, density, and pressure profiles calculated on the basis of the complete viscous Shock Layer equations is investigated within the framework of the linear stability theory with allowance for the Shock wave relations. The calculated perturbation growth rates and phase velocities are compared with the experimental data obtained by means of electron-beam fluorescence.
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Stability of a hypersonic Shock Layer on a flat plate
Comptes Rendus Mécanique, 2004Co-Authors: Anatoly A. Maslov, T.v. Poplavskaya, B. V. SmorodskyAbstract:Abstract Stability of a hypersonic Shock Layer on a flat plate is examined with allowance for disturbances conditions on the Shock wave within the framework of the linear stability theory. The characteristics of the main flow are calculated on the basis of the Full Viscous Shock Layer model. Conditions for velocity, pressure, and temperature perturbations are derived from steady Rankine–Hugoniot relation on the Shock wave. These conditions are used as boundary conditions on the Shock wave for linear stability equations. The growth rates of disturbances and density fluctuations are compared with experimental data obtained at ITAM by the method of electron-beam fluorescence and with theoretical data of other authors. To cite this article: A.A. Maslov et al., C. R. Mecanique 332 (2004).
S. G. Mironov - One of the best experts on this subject based on the ideXlab platform.
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Wave processes in the Shock Layer on a flat plate at an angle of attack
Journal of Applied Mechanics and Technical Physics, 2010Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, I. S. TsyryulnikovAbstract:A numerical and experimental study of receptivity of the viscous Shock Layer on a flat plate aligned at an angle of attack to external acoustic perturbations is performed. Density and pressure fluctuations are measured in experiments at the free-stream Mach number M ∞ = 21 and Reynolds number Re 1 = 6·10 5 m −1 . Direct numerical simulations of receptivity of the viscous Shock Layer to external acoustic perturbations in wide ranges of the governing parameters are performed by solving the Navier-Stokes equations with the use of high-order Shock-capturing schemes. The calculated intensities of density and pressure fluctuations are found to be in good agreement with experimental data. Results of the study show that entropy-vortex disturbances dominate in the Shock Layer at small angles of attack, whereas acoustic perturbations prevail at angles of attack above 20°.
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Wave processes in a viscous Shock Layer and control of fluctuations
Journal of Fluid Mechanics, 2010Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, Alexey Kudryavtsev, I. S. TsyryulnikovAbstract:Generation and development of disturbances in a hypersonic viscous Shock Layer on a flat plate is studied both experimentally and numerically. The study is performed at the Mach number M∞ = 21 and the Reynolds number ReL = 1.44 × 105 and is aimed at elucidating the physical mechanisms that govern the receptivity and instability of the Shock Layer at extremely high hypersonic velocities. The experiments are conducted in a hypersonic nitrogen-driven wind tunnel. An electron-beam fluorescence technique, a Pitot probe and a piezoceramic transducer are used to measure the mean density and Mach number contours, as well as density and pressure fluctuations, their spectra and spatial distributions in the Shock Layer. Direct numerical simulations are performed by solving the Navier–Stokes equations with a high-order Shock-capturing scheme in a computational domain including the leading and trailing edges of the plate, so that the bow Shock wave and the wake behind the plate are also simulated. It is demonstrated that computational and experimental data characterizing the mean flow field, intensity of density fluctuations and their spatial distributions in the Shock Layer are in close agreement. It is found that excitation of the Shock Layer by external acoustic waves leads to generation of entropy–vortex disturbances with two maxima of density fluctuations: directly behind the Shock wave and on the external edge of the boundary Layer. At the same time, the pressure fluctuations decay inward into the Shock Layer, away from the Shock, which agrees with the linear theory of interaction of Shock waves with small perturbations. Thus, the entropy–vortex disturbances are shown to dominate in the hypersonic Shock Layer at very high Mach numbers, in contrast with the boundary Layers at moderate hypersonic velocities where acoustic modes are most important. A parametric numerical study of wave processes in the Shock Layer induced by external acoustic waves is performed with variations of frequency, amplitude and angle of propagation of external disturbances. The amplitude of generated disturbances is observed to grow and decay periodically along the streamwise coordinate, and the characteristics of these variations depend on the frequency and direction of incident acoustic waves. The hypersonic Shock Layer excited by periodic blowing and suction near the leading edge is also investigated; in the experiments, this type of excitation is obtained by using an oblique-cut whistle. It is shown that blowing/suction generates disturbances resembling those generated by external acoustic waves, with similar spatial distributions and phase velocities. This result paves the way for active control of instability development in the Shock Layer by means of destructive interference of two types of disturbances. Numerical simulations are performed to show that instability waves can be significantly amplified or almost entirely suppressed, depending on the relative phase of blowing/suction and acoustic disturbances. Wind-tunnel experiments completely confirm this numerical prediction. Thus, the feasibility of delaying instability development in the hypersonic Shock Layer has been demonstrated for the first time.
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Active Control of Hypersonic Shock Layer Instability: Direct Numerical Simulation and Experiments
Computational Fluid Dynamics 2008, 2009Co-Authors: T.v. Poplavskaya, S. G. Mironov, A. N. Kudryavtsev, I. S. TsyryulnikovAbstract:When a flying vehicle moves with a high velocity in the upper Layers of the atmosphere, a viscous Shock Layer is formed in the vicinity of its leading edges. The viscous Shock Layer consists of a thick boundary Layer and a thin zone of inviscid flow behind the bow Shock wave. The receptivity of a hypersonic Shock Layer to external and internal disturbances plays an important role in formation of a spectrum of initial distubances and influences laminartubulent transition in a hypersonic boundary Layer. In this connection, the investigation of wave processes in a hypersonic Shock Layer and development of methods of controlling their intensity is an important scientific problem.
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Stability of the Hypersonic Shock Layer on a Flat Plate
Fluid Dynamics, 2004Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, B. V. SmorodskiiAbstract:The stability of hypersonic viscous gas flow in a Shock Layer in the neighborhood of a flat plate is considered. The stability of the velocity, temperature, density, and pressure profiles calculated on the basis of the complete viscous Shock Layer equations is investigated within the framework of the linear stability theory with allowance for the Shock wave relations. The calculated perturbation growth rates and phase velocities are compared with the experimental data obtained by means of electron-beam fluorescence.
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Evolution of Controlled Disturbances in the Shock Layer on the Compression Surface
Journal of Applied Mechanics and Technical Physics, 2003Co-Authors: V. M. Aniskin, S. G. MironovAbstract:Results of an experimental study of density-wave characteristics in the Shock Layer are presented for the case of a hypersonic nitrogen flow around a model with a two-dimensional compression surface, which is an arc of a circle, and a sharp leading edge. Controlled periodic disturbances developed on the streaky structure are registered by the electron-beam fluorescence technique. The streaky structure of the type of two vortices rotating in the opposite directions is generated in the Shock Layer by an oblique gas-dynamic whistle.
I. S. Tsyryulnikov - One of the best experts on this subject based on the ideXlab platform.
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Control of disturbances of a hypersonic viscous Shock Layer on a flat plate
Journal of Applied Mechanics and Technical Physics, 2012Co-Authors: S. V. Kirilovskiy, T.v. Poplavskaya, I. S. TsyryulnikovAbstract:Receptivity of a viscous Shock Layer on a flat plate aligned at an angle of attack to external multiwave acoustic perturbations is studied. It is shown that external acoustic waves and periodic controlled perturbations introduced from the surface of the plate mounted at an angle of attack smaller than 20° generate entropy-vortex disturbances with a similar spatial distribution in the viscous Shock Layer. This result allows numerical implementation of the interference method of controlling disturbances generated in the viscous Shock Layer on the plate by external acoustic waves at one frequency and at a spectrum of frequencies by introducing blowing-suction perturbations on the plate surface with appropriate amplitudes and phases.
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Wave processes in the Shock Layer on a flat plate at an angle of attack
Journal of Applied Mechanics and Technical Physics, 2010Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, I. S. TsyryulnikovAbstract:A numerical and experimental study of receptivity of the viscous Shock Layer on a flat plate aligned at an angle of attack to external acoustic perturbations is performed. Density and pressure fluctuations are measured in experiments at the free-stream Mach number M ∞ = 21 and Reynolds number Re 1 = 6·10 5 m −1 . Direct numerical simulations of receptivity of the viscous Shock Layer to external acoustic perturbations in wide ranges of the governing parameters are performed by solving the Navier-Stokes equations with the use of high-order Shock-capturing schemes. The calculated intensities of density and pressure fluctuations are found to be in good agreement with experimental data. Results of the study show that entropy-vortex disturbances dominate in the Shock Layer at small angles of attack, whereas acoustic perturbations prevail at angles of attack above 20°.
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Wave processes in a viscous Shock Layer and control of fluctuations
Journal of Fluid Mechanics, 2010Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, Alexey Kudryavtsev, I. S. TsyryulnikovAbstract:Generation and development of disturbances in a hypersonic viscous Shock Layer on a flat plate is studied both experimentally and numerically. The study is performed at the Mach number M∞ = 21 and the Reynolds number ReL = 1.44 × 105 and is aimed at elucidating the physical mechanisms that govern the receptivity and instability of the Shock Layer at extremely high hypersonic velocities. The experiments are conducted in a hypersonic nitrogen-driven wind tunnel. An electron-beam fluorescence technique, a Pitot probe and a piezoceramic transducer are used to measure the mean density and Mach number contours, as well as density and pressure fluctuations, their spectra and spatial distributions in the Shock Layer. Direct numerical simulations are performed by solving the Navier–Stokes equations with a high-order Shock-capturing scheme in a computational domain including the leading and trailing edges of the plate, so that the bow Shock wave and the wake behind the plate are also simulated. It is demonstrated that computational and experimental data characterizing the mean flow field, intensity of density fluctuations and their spatial distributions in the Shock Layer are in close agreement. It is found that excitation of the Shock Layer by external acoustic waves leads to generation of entropy–vortex disturbances with two maxima of density fluctuations: directly behind the Shock wave and on the external edge of the boundary Layer. At the same time, the pressure fluctuations decay inward into the Shock Layer, away from the Shock, which agrees with the linear theory of interaction of Shock waves with small perturbations. Thus, the entropy–vortex disturbances are shown to dominate in the hypersonic Shock Layer at very high Mach numbers, in contrast with the boundary Layers at moderate hypersonic velocities where acoustic modes are most important. A parametric numerical study of wave processes in the Shock Layer induced by external acoustic waves is performed with variations of frequency, amplitude and angle of propagation of external disturbances. The amplitude of generated disturbances is observed to grow and decay periodically along the streamwise coordinate, and the characteristics of these variations depend on the frequency and direction of incident acoustic waves. The hypersonic Shock Layer excited by periodic blowing and suction near the leading edge is also investigated; in the experiments, this type of excitation is obtained by using an oblique-cut whistle. It is shown that blowing/suction generates disturbances resembling those generated by external acoustic waves, with similar spatial distributions and phase velocities. This result paves the way for active control of instability development in the Shock Layer by means of destructive interference of two types of disturbances. Numerical simulations are performed to show that instability waves can be significantly amplified or almost entirely suppressed, depending on the relative phase of blowing/suction and acoustic disturbances. Wind-tunnel experiments completely confirm this numerical prediction. Thus, the feasibility of delaying instability development in the hypersonic Shock Layer has been demonstrated for the first time.
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Active Control of Hypersonic Shock Layer Instability: Direct Numerical Simulation and Experiments
Computational Fluid Dynamics 2008, 2009Co-Authors: T.v. Poplavskaya, S. G. Mironov, A. N. Kudryavtsev, I. S. TsyryulnikovAbstract:When a flying vehicle moves with a high velocity in the upper Layers of the atmosphere, a viscous Shock Layer is formed in the vicinity of its leading edges. The viscous Shock Layer consists of a thick boundary Layer and a thin zone of inviscid flow behind the bow Shock wave. The receptivity of a hypersonic Shock Layer to external and internal disturbances plays an important role in formation of a spectrum of initial distubances and influences laminartubulent transition in a hypersonic boundary Layer. In this connection, the investigation of wave processes in a hypersonic Shock Layer and development of methods of controlling their intensity is an important scientific problem.
T.v. Poplavskaya - One of the best experts on this subject based on the ideXlab platform.
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Control of disturbances of a hypersonic viscous Shock Layer on a flat plate
Journal of Applied Mechanics and Technical Physics, 2012Co-Authors: S. V. Kirilovskiy, T.v. Poplavskaya, I. S. TsyryulnikovAbstract:Receptivity of a viscous Shock Layer on a flat plate aligned at an angle of attack to external multiwave acoustic perturbations is studied. It is shown that external acoustic waves and periodic controlled perturbations introduced from the surface of the plate mounted at an angle of attack smaller than 20° generate entropy-vortex disturbances with a similar spatial distribution in the viscous Shock Layer. This result allows numerical implementation of the interference method of controlling disturbances generated in the viscous Shock Layer on the plate by external acoustic waves at one frequency and at a spectrum of frequencies by introducing blowing-suction perturbations on the plate surface with appropriate amplitudes and phases.
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Active control of hypersonic Shock Layer disturbances
Progress in Flight Physics, 2012Co-Authors: T.v. Poplavskaya, Anatoly A. MaslovAbstract:This is a brief review of the investigations of receptivity and control of hypersonic Shock Layers. The present paper describes comprehensive numerical and experimental investigations of evolution of disturbances generated in the hypersonic viscous Shock Layer (VSL) on a flat plate by external acoustic waves and by perturbations introduced into the Shock Layer from the surface of model. The active control of intensity of pulsations is possible because both external acoustic waves and the periodic controlled disturbances introduced on the plate surface generate, in a Shock Layer, entropy-vorticity disturbances with identical spatial distributions and phase velocities.
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Wave processes in the Shock Layer on a flat plate at an angle of attack
Journal of Applied Mechanics and Technical Physics, 2010Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, I. S. TsyryulnikovAbstract:A numerical and experimental study of receptivity of the viscous Shock Layer on a flat plate aligned at an angle of attack to external acoustic perturbations is performed. Density and pressure fluctuations are measured in experiments at the free-stream Mach number M ∞ = 21 and Reynolds number Re 1 = 6·10 5 m −1 . Direct numerical simulations of receptivity of the viscous Shock Layer to external acoustic perturbations in wide ranges of the governing parameters are performed by solving the Navier-Stokes equations with the use of high-order Shock-capturing schemes. The calculated intensities of density and pressure fluctuations are found to be in good agreement with experimental data. Results of the study show that entropy-vortex disturbances dominate in the Shock Layer at small angles of attack, whereas acoustic perturbations prevail at angles of attack above 20°.
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Wave processes in a viscous Shock Layer and control of fluctuations
Journal of Fluid Mechanics, 2010Co-Authors: Anatoly A. Maslov, S. G. Mironov, T.v. Poplavskaya, Alexey Kudryavtsev, I. S. TsyryulnikovAbstract:Generation and development of disturbances in a hypersonic viscous Shock Layer on a flat plate is studied both experimentally and numerically. The study is performed at the Mach number M∞ = 21 and the Reynolds number ReL = 1.44 × 105 and is aimed at elucidating the physical mechanisms that govern the receptivity and instability of the Shock Layer at extremely high hypersonic velocities. The experiments are conducted in a hypersonic nitrogen-driven wind tunnel. An electron-beam fluorescence technique, a Pitot probe and a piezoceramic transducer are used to measure the mean density and Mach number contours, as well as density and pressure fluctuations, their spectra and spatial distributions in the Shock Layer. Direct numerical simulations are performed by solving the Navier–Stokes equations with a high-order Shock-capturing scheme in a computational domain including the leading and trailing edges of the plate, so that the bow Shock wave and the wake behind the plate are also simulated. It is demonstrated that computational and experimental data characterizing the mean flow field, intensity of density fluctuations and their spatial distributions in the Shock Layer are in close agreement. It is found that excitation of the Shock Layer by external acoustic waves leads to generation of entropy–vortex disturbances with two maxima of density fluctuations: directly behind the Shock wave and on the external edge of the boundary Layer. At the same time, the pressure fluctuations decay inward into the Shock Layer, away from the Shock, which agrees with the linear theory of interaction of Shock waves with small perturbations. Thus, the entropy–vortex disturbances are shown to dominate in the hypersonic Shock Layer at very high Mach numbers, in contrast with the boundary Layers at moderate hypersonic velocities where acoustic modes are most important. A parametric numerical study of wave processes in the Shock Layer induced by external acoustic waves is performed with variations of frequency, amplitude and angle of propagation of external disturbances. The amplitude of generated disturbances is observed to grow and decay periodically along the streamwise coordinate, and the characteristics of these variations depend on the frequency and direction of incident acoustic waves. The hypersonic Shock Layer excited by periodic blowing and suction near the leading edge is also investigated; in the experiments, this type of excitation is obtained by using an oblique-cut whistle. It is shown that blowing/suction generates disturbances resembling those generated by external acoustic waves, with similar spatial distributions and phase velocities. This result paves the way for active control of instability development in the Shock Layer by means of destructive interference of two types of disturbances. Numerical simulations are performed to show that instability waves can be significantly amplified or almost entirely suppressed, depending on the relative phase of blowing/suction and acoustic disturbances. Wind-tunnel experiments completely confirm this numerical prediction. Thus, the feasibility of delaying instability development in the hypersonic Shock Layer has been demonstrated for the first time.
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Active Control of Hypersonic Shock Layer Instability: Direct Numerical Simulation and Experiments
Computational Fluid Dynamics 2008, 2009Co-Authors: T.v. Poplavskaya, S. G. Mironov, A. N. Kudryavtsev, I. S. TsyryulnikovAbstract:When a flying vehicle moves with a high velocity in the upper Layers of the atmosphere, a viscous Shock Layer is formed in the vicinity of its leading edges. The viscous Shock Layer consists of a thick boundary Layer and a thin zone of inviscid flow behind the bow Shock wave. The receptivity of a hypersonic Shock Layer to external and internal disturbances plays an important role in formation of a spectrum of initial distubances and influences laminartubulent transition in a hypersonic boundary Layer. In this connection, the investigation of wave processes in a hypersonic Shock Layer and development of methods of controlling their intensity is an important scientific problem.