The effect of second-harmonic generation （SHG） by primary （fundamental） circumferential guided wave （CGW） propagation is investigated from a numerical standpoint. To enable that the second harmonic of the primar...The effect of second-harmonic generation （SHG） by primary （fundamental） circumferential guided wave （CGW） propagation is investigated from a numerical standpoint. To enable that the second harmonic of the primary CGW mode can accumulate along the circumferential direction, an appropriate mode pair of primary and double frequency CGWs is chosen. Finite element simulations and evaluations of nonlinear CGW propagation are analyzed for the selected CGW mode pair. The numerical simulations performed directly demonstrate that the response of SHG is completely generated by the desired primary CGW mode that satisfies the condition of phase velocity matching at a specific driving frequency, and that the second harmonic of the primary CGW mode does have a cumulative effect with circumferential angles. The numerical perspective obtained yields an insight into the complicated physical process of SHG of primary CGW propagation unavailable previously.展开更多
The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential gui...The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential guided wave desired and to detect its fundamental-frequency and second-harmonic amplitudes on the outside surface of the circular tube. The amplitudes of the fundamental waves and the second harmonics of the circumferential guided wave propagation are measured for different separations between the two wedge transducers. At the driving frequency where the primary and the double-frequency circumferential guided waves have the same linear phase velocities, the clear second-harmonic signals can be observed. The quantitative relationships between the second-harmonic amplitudes and circumferential angle are analyzed. It is experimentally verified that the second harmonics of primary circumferential guided waves do have a cumulative growth effect with the circumferential angle.展开更多
This study numerically investigates the aeromechanic behavior of a transonic fan model with a flat tip-leading-edge on the NASA rotor 67 test case.Single-passage unsteady calculations at a near stall operating point o...This study numerically investigates the aeromechanic behavior of a transonic fan model with a flat tip-leading-edge on the NASA rotor 67 test case.Single-passage unsteady calculations at a near stall operating point of 82%design speed show that the dominant frequencies of mass flow were not the harmonics of the rotor rotational frequency.A full-annulus fluid–structure interaction analysis was subsequently carried out to examine the unsteady flows and their interactions with blade vibrations.The results show that the modal displacement of the backward traveling seventh nodal diameter of the second torsion mode grew exponentially,which reveals that the blade vibration was non-synchronous.The vibration pattern indicates that the aerodynamic mode was resonant with the structural vibration mode.Around the rotor tip,the circumferential vortical propagation induced by interactions among the main flow,tip leakage flow,and tip clearance vortex was the source of aerodynamic excitation.To clarify the mechanism of the non-synchronous vibration,the coupling between aerodynamic disturbance and structural response,i.e.,aliasing,was summarized.The frequency spectra of the fluctuating pressure show that an aerodynamic Back-ward Traveling Wave(BTW)was co-aliased to a structural BTW due to the propagation of the cir-cumferential vortex.The correlation between the frequency and free convective speed of the aerodynamic disturbance determined the directions of aliasing.展开更多
Numerical analysis of three-dimensional sound propagation in soft-soft or soft-hard circular ducts with circumferential and axial modes of sound sources at the inlet has been carried out. In this paper , the numerical...Numerical analysis of three-dimensional sound propagation in soft-soft or soft-hard circular ducts with circumferential and axial modes of sound sources at the inlet has been carried out. In this paper , the numerical method and the samples are offered and the effects of circumferential and axial modes on numerical results are discussed in detail .展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474361,11474093 and 11274388
文摘The effect of second-harmonic generation （SHG） by primary （fundamental） circumferential guided wave （CGW） propagation is investigated from a numerical standpoint. To enable that the second harmonic of the primary CGW mode can accumulate along the circumferential direction, an appropriate mode pair of primary and double frequency CGWs is chosen. Finite element simulations and evaluations of nonlinear CGW propagation are analyzed for the selected CGW mode pair. The numerical simulations performed directly demonstrate that the response of SHG is completely generated by the desired primary CGW mode that satisfies the condition of phase velocity matching at a specific driving frequency, and that the second harmonic of the primary CGW mode does have a cumulative effect with circumferential angles. The numerical perspective obtained yields an insight into the complicated physical process of SHG of primary CGW propagation unavailable previously.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474361 and 11274388
文摘The experimental observation of cumulative second-harmonic generation of the primary circumferential guided wave propagation is reported. A pair of wedge transducers is used to generate the primary circumferential guided wave desired and to detect its fundamental-frequency and second-harmonic amplitudes on the outside surface of the circular tube. The amplitudes of the fundamental waves and the second harmonics of the circumferential guided wave propagation are measured for different separations between the two wedge transducers. At the driving frequency where the primary and the double-frequency circumferential guided waves have the same linear phase velocities, the clear second-harmonic signals can be observed. The quantitative relationships between the second-harmonic amplitudes and circumferential angle are analyzed. It is experimentally verified that the second harmonics of primary circumferential guided waves do have a cumulative growth effect with the circumferential angle.
基金co-supported by the National Science and Technology Major Project,China(No.2017-Ⅱ-0009-0023).
文摘This study numerically investigates the aeromechanic behavior of a transonic fan model with a flat tip-leading-edge on the NASA rotor 67 test case.Single-passage unsteady calculations at a near stall operating point of 82%design speed show that the dominant frequencies of mass flow were not the harmonics of the rotor rotational frequency.A full-annulus fluid–structure interaction analysis was subsequently carried out to examine the unsteady flows and their interactions with blade vibrations.The results show that the modal displacement of the backward traveling seventh nodal diameter of the second torsion mode grew exponentially,which reveals that the blade vibration was non-synchronous.The vibration pattern indicates that the aerodynamic mode was resonant with the structural vibration mode.Around the rotor tip,the circumferential vortical propagation induced by interactions among the main flow,tip leakage flow,and tip clearance vortex was the source of aerodynamic excitation.To clarify the mechanism of the non-synchronous vibration,the coupling between aerodynamic disturbance and structural response,i.e.,aliasing,was summarized.The frequency spectra of the fluctuating pressure show that an aerodynamic Back-ward Traveling Wave(BTW)was co-aliased to a structural BTW due to the propagation of the cir-cumferential vortex.The correlation between the frequency and free convective speed of the aerodynamic disturbance determined the directions of aliasing.
基金The project is supported by National Natural Science Foundation of China and National Education Commission Foundaion of China
文摘Numerical analysis of three-dimensional sound propagation in soft-soft or soft-hard circular ducts with circumferential and axial modes of sound sources at the inlet has been carried out. In this paper , the numerical method and the samples are offered and the effects of circumferential and axial modes on numerical results are discussed in detail .
