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Sanford Fleeter - One of the best experts on this subject based on the ideXlab platform.
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Forcing Function Effects on Unsteady Aerodynamic Gust Response: Part 1—Forcing Functions
Journal of Turbomachinery, 1993Co-Authors: Gregory H. Henderson, Sanford FleeterAbstract:The fundamental gust modeling assumption is investigated by means of a series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady periodic flow field is generated by rotating rows of perforated plates and airfoil cascades. In this paper, the measured unsteady flow fields are compared to Linear-Theory vortical gust requirements, with the resulting unsteady gust response of a downstream stator cascade correlated with Linear Theory predictions in an accompanying paper. The perforated-plate forcing functions closely resemble Linear-Theory forcing functions, with the static pressure fluctuations small and the periodic velocity vectors parallel to the downstream mean-relative flow angle over the entire periodic cycle
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forcing function effects on unsteady aerodynamic gust response part 2 low solidity airfoil row response
Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls Diagnostics and Instrumentation; Education, 1992Co-Authors: Gregory H. Henderson, Sanford FleeterAbstract:The fundamental gust modeling assumption is investigated by means of a series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady periodic flow field is generated by rotating rows of perforated plates and airfoil cascades, with the resulting unsteady periodic chordwise pressure response of a downstream low solidity stator row determined by miniature pressure transducers embedded within selected airfoils. When the forcing function exhibited the characteristics of a Linear-Theory gust, as was the case for the perforated-plate wake generators, the resulting response on the downstream stator airfoils was in excellent agreement with the Linear-Theory models. In contrast, when the forcing function did not exhibit Linear-Theory gust characteristics, i.e., for the airfoil wake generators, the resulting unsteady aerodynamic response of the downstream stators were much more complex and correlated poorly with the Linear-Theory gust predictions. Thus, this investigation has quantitatively shown that the forcing function generator significantly affects the resulting gust response, with the complexity of the response characteristics increasing from the perforated-plate to the airfoil-cascade forcing functions.Copyright © 1992 by ASME
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forcing function effects on unsteady aerodynamic gust response part 1 forcing functions
Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls Diagnostics and Instrumentation; Education, 1992Co-Authors: Gregory H. Henderson, Sanford FleeterAbstract:The fundamental gust modeling assumption is investigated by means of a series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady periodic flow field is generated by rotating rows of perforated plates and airfoil cascades. In this paper, the measured unsteady flow fields are compared to Linear-Theory gust requirements, with the resulting unsteady gust response of a downstream stator cascade correlated with Linear Theory predictions in an accompanying paper. The perforated-plate forcing functions closely resemble Linear-Theory forcing functions, with the static pressure fluctuations small and the periodic velocity vectors parallel to the downstream mean-relative flow angle over the entire periodic cycle. In contrast, the airfoil forcing functions exhibit characteristics far from Linear-Theory gusts, with the alignment of the velocity vectors and the static pressure fluctuation amplitudes dependent on the rotor-loading condition, rotor solidity and the inlet mean-relative flow angle. Thus, these unique data clearly show that airfoil wakes, both compressor and turbine, are not able to be modeled with the boundary conditions of current state-of-the-art Linear unsteady aerodynamic Theory.Copyright © 1992 by ASME
Stirling A. Colgate - One of the best experts on this subject based on the ideXlab platform.
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rossby wave instability of thin accretion disks ii detailed Linear Theory
The Astrophysical Journal, 2000Co-Authors: J M Finn, R V E Lovelace, Stirling A. ColgateAbstract:In an earlier work we identi—ed a global, nonaxisymmetric instability associated with the presence of an extreme in the radial pro—le of the key function L(r) 4 (&)/i2)S2@! in a thin, inviscid, nonmagnetized accretion disk. Here &(r) is the surface mass density of the disk, )(r) is the angular rotation rate, S(r )i s the speci—c entropy, ! is the adiabatic index, and i(r) is the radial epicyclic frequency. The dispersion relation of the instability was shown to be similar to that of Rossby waves in planetary atmospheres. In this paper, we present the detailed Linear Theory of this Rossby wave instability and show that it exists for a wider range of conditions, speci—cally, for the case where there is a ii jump ˇˇ over some range of r in &(r) or in the pressure P(r). We elucidate the physical mechanism of this instability and its dependence on various parameters, including the magnitude of the ii bump ˇˇ or ii jump,ˇˇ the azimuthal mode number, and the sound speed in the disk. We —nd a large parameter range where the disk is stable to axisym- metric perturbations but unstable to the nonaxisymmetric Rossby waves. We —nd that growth rates of the Rossby wave instability can be high, for relative small jumps or bumps. We discuss possible D0.2) K conditions which can lead to this instability and the consequences of the instability. Subject headings: accretion, accretion diskshydrodynamicsinstabilitieswaves
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rossby wave instability of thin accretion disks ii detailed Linear Theory
arXiv: Astrophysics, 1999Co-Authors: J M Finn, R V E Lovelace, Stirling A. ColgateAbstract:In earlier work we identified a global, non-axisymmetric instability associated with the presence of an extreme in the radial profile of the key function ${\cal L}(r) \equiv (\Sigma \Omega/\kappa^2) S^{2/\Gamma}$ in a thin, inviscid, nonmagnetized accretion disk. Here, $\Sigma(r)$ is the surface mass density of the disk, $\Omega(r)$ the angular rotation rate, $S(r)$ the specific entropy, $\Gamma$ the adiabatic index, and $\kappa(r)$ the radial epicyclic frequency. The dispersion relation of the instability was shown to be similar to that of Rossby waves in planetary atmospheres. In this paper, we present the detailed Linear Theory of this Rossby wave instability and show that it exists for a wider range of conditions, specifically, for the case where there is a ``jump'' over some range of $r$ in $\Sigma(r)$ or in the pressure $P(r)$. We elucidate the physical mechanism of this instability and its dependence on various parameters, including the magnitude of the ``bump'' or ``jump,'' the azimuthal mode number, and the sound speed in the disk. We find large parameter range where the disk is stable to axisymmetric perturbations, but unstable to the non-axisymmetric Rossby waves. We find that growth rates of the Rossby wave instability can be high, $\sim 0.2 \Omega_{\rm K}$ for relative small ``jumps'' or ``bumps''. We discuss possible conditions which can lead to this instability and the consequences of the instability.
R V E Lovelace - One of the best experts on this subject based on the ideXlab platform.
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rossby wave instability of thin accretion disks ii detailed Linear Theory
The Astrophysical Journal, 2000Co-Authors: J M Finn, R V E Lovelace, Stirling A. ColgateAbstract:In an earlier work we identi—ed a global, nonaxisymmetric instability associated with the presence of an extreme in the radial pro—le of the key function L(r) 4 (&)/i2)S2@! in a thin, inviscid, nonmagnetized accretion disk. Here &(r) is the surface mass density of the disk, )(r) is the angular rotation rate, S(r )i s the speci—c entropy, ! is the adiabatic index, and i(r) is the radial epicyclic frequency. The dispersion relation of the instability was shown to be similar to that of Rossby waves in planetary atmospheres. In this paper, we present the detailed Linear Theory of this Rossby wave instability and show that it exists for a wider range of conditions, speci—cally, for the case where there is a ii jump ˇˇ over some range of r in &(r) or in the pressure P(r). We elucidate the physical mechanism of this instability and its dependence on various parameters, including the magnitude of the ii bump ˇˇ or ii jump,ˇˇ the azimuthal mode number, and the sound speed in the disk. We —nd a large parameter range where the disk is stable to axisym- metric perturbations but unstable to the nonaxisymmetric Rossby waves. We —nd that growth rates of the Rossby wave instability can be high, for relative small jumps or bumps. We discuss possible D0.2) K conditions which can lead to this instability and the consequences of the instability. Subject headings: accretion, accretion diskshydrodynamicsinstabilitieswaves
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rossby wave instability of thin accretion disks ii detailed Linear Theory
arXiv: Astrophysics, 1999Co-Authors: J M Finn, R V E Lovelace, Stirling A. ColgateAbstract:In earlier work we identified a global, non-axisymmetric instability associated with the presence of an extreme in the radial profile of the key function ${\cal L}(r) \equiv (\Sigma \Omega/\kappa^2) S^{2/\Gamma}$ in a thin, inviscid, nonmagnetized accretion disk. Here, $\Sigma(r)$ is the surface mass density of the disk, $\Omega(r)$ the angular rotation rate, $S(r)$ the specific entropy, $\Gamma$ the adiabatic index, and $\kappa(r)$ the radial epicyclic frequency. The dispersion relation of the instability was shown to be similar to that of Rossby waves in planetary atmospheres. In this paper, we present the detailed Linear Theory of this Rossby wave instability and show that it exists for a wider range of conditions, specifically, for the case where there is a ``jump'' over some range of $r$ in $\Sigma(r)$ or in the pressure $P(r)$. We elucidate the physical mechanism of this instability and its dependence on various parameters, including the magnitude of the ``bump'' or ``jump,'' the azimuthal mode number, and the sound speed in the disk. We find large parameter range where the disk is stable to axisymmetric perturbations, but unstable to the non-axisymmetric Rossby waves. We find that growth rates of the Rossby wave instability can be high, $\sim 0.2 \Omega_{\rm K}$ for relative small ``jumps'' or ``bumps''. We discuss possible conditions which can lead to this instability and the consequences of the instability.
Gregory H. Henderson - One of the best experts on this subject based on the ideXlab platform.
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Forcing Function Effects on Unsteady Aerodynamic Gust Response: Part 1—Forcing Functions
Journal of Turbomachinery, 1993Co-Authors: Gregory H. Henderson, Sanford FleeterAbstract:The fundamental gust modeling assumption is investigated by means of a series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady periodic flow field is generated by rotating rows of perforated plates and airfoil cascades. In this paper, the measured unsteady flow fields are compared to Linear-Theory vortical gust requirements, with the resulting unsteady gust response of a downstream stator cascade correlated with Linear Theory predictions in an accompanying paper. The perforated-plate forcing functions closely resemble Linear-Theory forcing functions, with the static pressure fluctuations small and the periodic velocity vectors parallel to the downstream mean-relative flow angle over the entire periodic cycle
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forcing function effects on unsteady aerodynamic gust response part 2 low solidity airfoil row response
Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls Diagnostics and Instrumentation; Education, 1992Co-Authors: Gregory H. Henderson, Sanford FleeterAbstract:The fundamental gust modeling assumption is investigated by means of a series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady periodic flow field is generated by rotating rows of perforated plates and airfoil cascades, with the resulting unsteady periodic chordwise pressure response of a downstream low solidity stator row determined by miniature pressure transducers embedded within selected airfoils. When the forcing function exhibited the characteristics of a Linear-Theory gust, as was the case for the perforated-plate wake generators, the resulting response on the downstream stator airfoils was in excellent agreement with the Linear-Theory models. In contrast, when the forcing function did not exhibit Linear-Theory gust characteristics, i.e., for the airfoil wake generators, the resulting unsteady aerodynamic response of the downstream stators were much more complex and correlated poorly with the Linear-Theory gust predictions. Thus, this investigation has quantitatively shown that the forcing function generator significantly affects the resulting gust response, with the complexity of the response characteristics increasing from the perforated-plate to the airfoil-cascade forcing functions.Copyright © 1992 by ASME
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forcing function effects on unsteady aerodynamic gust response part 1 forcing functions
Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls Diagnostics and Instrumentation; Education, 1992Co-Authors: Gregory H. Henderson, Sanford FleeterAbstract:The fundamental gust modeling assumption is investigated by means of a series of experiments performed in the Purdue Annular Cascade Research Facility. The unsteady periodic flow field is generated by rotating rows of perforated plates and airfoil cascades. In this paper, the measured unsteady flow fields are compared to Linear-Theory gust requirements, with the resulting unsteady gust response of a downstream stator cascade correlated with Linear Theory predictions in an accompanying paper. The perforated-plate forcing functions closely resemble Linear-Theory forcing functions, with the static pressure fluctuations small and the periodic velocity vectors parallel to the downstream mean-relative flow angle over the entire periodic cycle. In contrast, the airfoil forcing functions exhibit characteristics far from Linear-Theory gusts, with the alignment of the velocity vectors and the static pressure fluctuation amplitudes dependent on the rotor-loading condition, rotor solidity and the inlet mean-relative flow angle. Thus, these unique data clearly show that airfoil wakes, both compressor and turbine, are not able to be modeled with the boundary conditions of current state-of-the-art Linear unsteady aerodynamic Theory.Copyright © 1992 by ASME
C L Hung - One of the best experts on this subject based on the ideXlab platform.
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Linear analysis of a coaxial waveguide gyrotron traveling wave tube
Physics of Plasmas, 2006Co-Authors: C L HungAbstract:Linear Theory provides an efficient analysis model for the preliminary design of a gyrotron traveling-wave tube (gyro-TWT). This study presents a Linear Theory, which is applicable to amplifications or self-excited oscillations induced by absolute instabilities in a coaxial waveguide of finite length. The effects of wall losses are incorporated in the theoretical formalism. The validity of the Linear Theory is verified by comparison with calculation results obtained using an existing self-consistent nonLinear Theory. The Linear Theory is applied to analyze a TE01 mode coaxial gyro-TWT at the fundamental cyclotron harmonic. Numerical analysis of coupling between the beam cyclotron mode and the waveguide mode provides physical insight into the wave-growing mechanisms of various oscillations. The critical parameters for the onset of threatening oscillation modes are analyzed to determine the stable operating conditions. Finally, the dependencies of small-signal amplifications on system parameters are studied...
