The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform

Roque Corral - One of the best experts on this subject based on the ideXlab platform.

  • The Low Reduced Frequency Limit of Vibrating Airfoils—Part II: Numerical Experiments
    Journal of Turbomachinery, 2015
    Co-Authors: Almudena Vega, Roque Corral
    Abstract:

    This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced Frequency regime with special emphasis on its impact on the scaling of the work-per-cycle curves by means of numerical experiments. Simulations using a Frequency domain linearized Navier–Stokes solver have been carried out on rows of a low-pressure turbine (LPT) airfoil section, the NACA0012 and NACA65 profiles, and a flat-plate cascade operating at different flow conditions. Both the traveling wave (TW) and the influence coefficient (IC) formulations of the problem are used in combination to investigate the nature of the unsteady pressure perturbations. All the theoretical conclusions derived in Part I of the paper have been confirmed, and it is shown that the behavior of the unsteady pressure modulus and phase, as well as the work-per-cycle curves, are fairly independent of the geometry of the airfoil, the operating conditions, and the mode-shape in first-order approximation in the reduced Frequency. The second major conclusion is that the airfoil loading and the symmetry of the cascade play an essential role in this trend. Simulations performed at reduced Frequency ranges beyond the low reduced Frequency Limit reveal that, in this regimen, the ICs modulus varies linearly with the reduced Frequency, while the phase is always π/2, and then, the classical sinusoidal antisymmetric shape of work-per-cycle curves in the low reduced Frequency Limit turns into a cosinusoidal symmetric shape. It is then concluded that the classical cosinusoidal shape of compressor airfoils is not neither a geometric nor a flow effect, but a direct consequence of the fact that the natural frequencies of the lowest modes of compressors are higher than that of high aspect ratio cantilever LPT rotor blades. Numerical simulations have also confirmed that the actual mode-shape of the airfoil motion does not alter the conclusions derived in Part I of the paper.

  • the low reduced Frequency Limit of vibrating airfoils part ii numerical experiments
    Journal of Turbomachinery-transactions of The Asme, 2015
    Co-Authors: Almudena Vega, Roque Corral
    Abstract:

    This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced Frequency regime with special emphasis on its impact on the scaling of the work-per-cycle curves by means of numerical experiments. Simulations using a Frequency domain linearized Navier–Stokes solver have been carried out on rows of a low-pressure turbine (LPT) airfoil section, the NACA0012 and NACA65 profiles, and a flat-plate cascade operating at different flow conditions. Both the traveling wave (TW) and the influence coefficient (IC) formulations of the problem are used in combination to investigate the nature of the unsteady pressure perturbations. All the theoretical conclusions derived in Part I of the paper have been confirmed, and it is shown that the behavior of the unsteady pressure modulus and phase, as well as the work-per-cycle curves, are fairly independent of the geometry of the airfoil, the operating conditions, and the mode-shape in first-order approximation in the reduced Frequency. The second major conclusion is that the airfoil loading and the symmetry of the cascade play an essential role in this trend. Simulations performed at reduced Frequency ranges beyond the low reduced Frequency Limit reveal that, in this regimen, the ICs modulus varies linearly with the reduced Frequency, while the phase is always π/2, and then, the classical sinusoidal antisymmetric shape of work-per-cycle curves in the low reduced Frequency Limit turns into a cosinusoidal symmetric shape. It is then concluded that the classical cosinusoidal shape of compressor airfoils is not neither a geometric nor a flow effect, but a direct consequence of the fact that the natural frequencies of the lowest modes of compressors are higher than that of high aspect ratio cantilever LPT rotor blades. Numerical simulations have also confirmed that the actual mode-shape of the airfoil motion does not alter the conclusions derived in Part I of the paper.

  • the low reduced Frequency Limit of vibrating airfoils part i theoretical analysis
    Journal of Turbomachinery-transactions of The Asme, 2015
    Co-Authors: Roque Corral, Almudena Vega
    Abstract:

    This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced Frequency regime with special emphasis in its impact on the scaling of the work per cycle curves using an asymptotic approach (Part I) and numerical simulations (Part II). A perturbation analysis of the linearized Navier-Stokes equations for real modes at low reduced Frequency is presented and some conclusions are drawn. The first important result is that the loading of the airfoil plays an essential role in the trends of the phase and modulus of the unsteady pressure caused by the vibration of the airfoil. For lightly loaded airfoils the unsteady pressure and the influence coefficients scale linearly with the reduced Frequency whereas the phase departs from π/2 and changes linearly with the reduced Frequency. As a consequence the work-per-cycle scales linearly with the reduced Frequency for any inter-blade phase angle and it is independent of its sign. For highly loaded airfoils the unsteady pressure modulus is fairly constant exhibiting only a small correction with the reduced Frequency, while the phase departs from zero and varies linearly with it. In this case only the mean value of the work-per-cycle scales linearly with the reduced Frequency. This behavior is independent of the geometry of the airfoil and the modeshape in first approximation. For symmetric cascades the work-per-cycle scales linearly with the reduced Frequency irrespectively of whether the airfoil is loaded or not. Simulations using a Frequency domain linearized Navier-Stokes solver have been carried out on a low-pressure turbine airfoil section, the NACA0012 and NACA65 profiles and a flat plate to show the generality and correctness of the analytical conclusions (Part II of the corresponding paper). Both, the traveling-wave and influence coefficient formulations of the problem are used in combination to increase the understanding and explore the nature of the unsteady pressure perturbations.Copyright © 2015 by ASME

J. Q. You - One of the best experts on this subject based on the ideXlab platform.

  • Floquet engineering of long-range p -wave superconductivity: Beyond the high-Frequency Limit
    Physical Review B, 2017
    Co-Authors: Chi-hang Lam, J. Q. You
    Abstract:

    It has been shown that long-range p-wave superconductivity in a Kitaev chain can be engineered via an ac field with a high Frequency [M. Benito et al., Phys. Rev. B 90, 205127 (2014)]. For its experimental realization, however, theoretical understanding of Floquet engineering with a broader range of driving frequencies becomes important. In this paper, focusing on the ac-driven tunneling interactions of a Kitaev chain, we investigate effects from the leading correction to the high-Frequency Limit on the emergentp-wave superconductivity. Importantly, we find new engineered long-range p-wave pairing interactions that can significantly alter the ones in the high-Frequency Limit at long interaction ranges. We also find that the leading correction additionally generates nearest-neighbor p-wave pairing interactions with a renormalized pairing energy, long-range tunneling interactions, and, in particular, multiple pairs of Floquet Majorana edge states that are destroyed in the high-Frequency Limit

  • floquet engineering of long range p wave superconductivity beyond the high Frequency Limit
    Physical Review B, 2017
    Co-Authors: Chi-hang Lam, J. Q. You
    Abstract:

    It has been shown that long-range p-wave superconductivity in a Kitaev chain can be engineered via an ac field with a high Frequency [M. Benito, Phys. Rev. B 90, 205127 (2014)PRBMDO1098-012110.1103/PhysRevB.90.205127]. For its experimental realization, however, theoretical understanding of Floquet engineering with a broader range of driving frequencies becomes important. In this paper, focusing on the ac-driven tunneling interactions of a Kitaev chain, we investigate effects from the leading correction to the high-Frequency Limit on the emergent p-wave superconductivity. Importantly, we find new engineered long-range p-wave pairing interactions that can significantly alter the ones in the high-Frequency Limit at long interaction ranges. We also find that the leading correction additionally generates nearest-neighbor p-wave pairing interactions with a renormalized pairing energy, long-range tunneling interactions, and, in particular, multiple pairs of Floquet Majorana edge states that are destroyed in the high-Frequency Limit. (Less)

Alexander Oron - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear dynamics of a thin liquid film deposited on a laterally oscillating corrugated surface in the high-Frequency Limit
    Physics of Fluids, 2016
    Co-Authors: Selin Duruk, Alexander Oron
    Abstract:

    The nonlinear dynamics of thin liquid films deposited on various periodically corrugated substrates, both left-right symmetric and asymmetric, subjected to lateral vibration in the high-Frequency Limit is investigated. The method used to derive the governing evolution equation is based on the long-wave approximation, multiscale time expansion, and averaging over the fast time scale. The resulting evolution equation contains the effects of gravity, capillarity, vibration, and the substrate topology. The initial-boundary-value problem associated with this evolution equation is numerically solved and the system behavior is investigated for a variety of parameter sets. Typical patterns emerging as a result of the film evolution include hump formation within the troughs of the substrate and homogenized coatings whose configuration resembles that of the substrate, as well as the possibility of film rupture. We show that the choice of the vibration parameters and the topological features of the substrate may be ...

  • Stability analysis of a thin liquid film on an axially oscillating cylindrical surface in the high-Frequency Limit.
    Physical review. E Statistical nonlinear and soft matter physics, 2014
    Co-Authors: Selin Duruk, Alexander Oron
    Abstract:

    We consider an axisymmetric liquid film on a horizontal cylindrical surface subjected to axial harmonic oscillation in the high-Frequency Limit. We derive and analyze the nonlinear evolution equation describing the nonlinear dynamics of this physical system in terms of the averaged film thickness. The method used for the derivation of the evolution equation is based on long-wave theory and the separation of the relevant fields into fast and slow components. We carry out the linear stability analysis for a film of a constant thickness which shows that axial forcing of the cylinder may result in either stabilization or destabilization of the axisymmetric flow with respect to the unforced one, depending on the choice of the parameter set. The analysis is extended to the weakly nonlinear stage and it reveals that the system bifurcates subcritically from the equilibrium.

Nam Kim - One of the best experts on this subject based on the ideXlab platform.

  • Upper Frequency Limit depending on potential shape in a QD-based single electron pump
    Journal of Applied Physics, 2017
    Co-Authors: Ye-hwan Ahn, Changki Hong, Young-seok Ghee, Yunchul Chung, Young-pyo Hong, Myung-ho Bae, Nam Kim
    Abstract:

    Our quantum-dot (QD) electron pump has uniqueness in design in that the QD potential shape can be manipulated, especially its potential depth can be controlled by a plunger gate. We find that there exist strong correlations between the potential depth of the QD and the upper Frequency Limit, fm, when the modulating microwave power is fixed. As the depth of the QD potential is deepened, fm shows decreasing characteristics while the flatness of the 1st current plateau is increased. We have semi-quantitatively analyzed these correlations by using the notion of so-called “non-adiabatic Coulomb blockade gap energy,” ΔELU. We find that ΔELU parameter being under control by a plunger gate is proportional to the pumping Frequency f.

Almudena Vega - One of the best experts on this subject based on the ideXlab platform.

  • The Low Reduced Frequency Limit of Vibrating Airfoils—Part II: Numerical Experiments
    Journal of Turbomachinery, 2015
    Co-Authors: Almudena Vega, Roque Corral
    Abstract:

    This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced Frequency regime with special emphasis on its impact on the scaling of the work-per-cycle curves by means of numerical experiments. Simulations using a Frequency domain linearized Navier–Stokes solver have been carried out on rows of a low-pressure turbine (LPT) airfoil section, the NACA0012 and NACA65 profiles, and a flat-plate cascade operating at different flow conditions. Both the traveling wave (TW) and the influence coefficient (IC) formulations of the problem are used in combination to investigate the nature of the unsteady pressure perturbations. All the theoretical conclusions derived in Part I of the paper have been confirmed, and it is shown that the behavior of the unsteady pressure modulus and phase, as well as the work-per-cycle curves, are fairly independent of the geometry of the airfoil, the operating conditions, and the mode-shape in first-order approximation in the reduced Frequency. The second major conclusion is that the airfoil loading and the symmetry of the cascade play an essential role in this trend. Simulations performed at reduced Frequency ranges beyond the low reduced Frequency Limit reveal that, in this regimen, the ICs modulus varies linearly with the reduced Frequency, while the phase is always π/2, and then, the classical sinusoidal antisymmetric shape of work-per-cycle curves in the low reduced Frequency Limit turns into a cosinusoidal symmetric shape. It is then concluded that the classical cosinusoidal shape of compressor airfoils is not neither a geometric nor a flow effect, but a direct consequence of the fact that the natural frequencies of the lowest modes of compressors are higher than that of high aspect ratio cantilever LPT rotor blades. Numerical simulations have also confirmed that the actual mode-shape of the airfoil motion does not alter the conclusions derived in Part I of the paper.

  • the low reduced Frequency Limit of vibrating airfoils part ii numerical experiments
    Journal of Turbomachinery-transactions of The Asme, 2015
    Co-Authors: Almudena Vega, Roque Corral
    Abstract:

    This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced Frequency regime with special emphasis on its impact on the scaling of the work-per-cycle curves by means of numerical experiments. Simulations using a Frequency domain linearized Navier–Stokes solver have been carried out on rows of a low-pressure turbine (LPT) airfoil section, the NACA0012 and NACA65 profiles, and a flat-plate cascade operating at different flow conditions. Both the traveling wave (TW) and the influence coefficient (IC) formulations of the problem are used in combination to investigate the nature of the unsteady pressure perturbations. All the theoretical conclusions derived in Part I of the paper have been confirmed, and it is shown that the behavior of the unsteady pressure modulus and phase, as well as the work-per-cycle curves, are fairly independent of the geometry of the airfoil, the operating conditions, and the mode-shape in first-order approximation in the reduced Frequency. The second major conclusion is that the airfoil loading and the symmetry of the cascade play an essential role in this trend. Simulations performed at reduced Frequency ranges beyond the low reduced Frequency Limit reveal that, in this regimen, the ICs modulus varies linearly with the reduced Frequency, while the phase is always π/2, and then, the classical sinusoidal antisymmetric shape of work-per-cycle curves in the low reduced Frequency Limit turns into a cosinusoidal symmetric shape. It is then concluded that the classical cosinusoidal shape of compressor airfoils is not neither a geometric nor a flow effect, but a direct consequence of the fact that the natural frequencies of the lowest modes of compressors are higher than that of high aspect ratio cantilever LPT rotor blades. Numerical simulations have also confirmed that the actual mode-shape of the airfoil motion does not alter the conclusions derived in Part I of the paper.

  • the low reduced Frequency Limit of vibrating airfoils part i theoretical analysis
    Journal of Turbomachinery-transactions of The Asme, 2015
    Co-Authors: Roque Corral, Almudena Vega
    Abstract:

    This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced Frequency regime with special emphasis in its impact on the scaling of the work per cycle curves using an asymptotic approach (Part I) and numerical simulations (Part II). A perturbation analysis of the linearized Navier-Stokes equations for real modes at low reduced Frequency is presented and some conclusions are drawn. The first important result is that the loading of the airfoil plays an essential role in the trends of the phase and modulus of the unsteady pressure caused by the vibration of the airfoil. For lightly loaded airfoils the unsteady pressure and the influence coefficients scale linearly with the reduced Frequency whereas the phase departs from π/2 and changes linearly with the reduced Frequency. As a consequence the work-per-cycle scales linearly with the reduced Frequency for any inter-blade phase angle and it is independent of its sign. For highly loaded airfoils the unsteady pressure modulus is fairly constant exhibiting only a small correction with the reduced Frequency, while the phase departs from zero and varies linearly with it. In this case only the mean value of the work-per-cycle scales linearly with the reduced Frequency. This behavior is independent of the geometry of the airfoil and the modeshape in first approximation. For symmetric cascades the work-per-cycle scales linearly with the reduced Frequency irrespectively of whether the airfoil is loaded or not. Simulations using a Frequency domain linearized Navier-Stokes solver have been carried out on a low-pressure turbine airfoil section, the NACA0012 and NACA65 profiles and a flat plate to show the generality and correctness of the analytical conclusions (Part II of the corresponding paper). Both, the traveling-wave and influence coefficient formulations of the problem are used in combination to increase the understanding and explore the nature of the unsteady pressure perturbations.Copyright © 2015 by ASME