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Numerical investigation of flow over a two-dimensional square cylinder with a synthetic jet generated by a bi-frequency signal 被引量:2
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作者 Yiran LU Yuan QU +1 位作者 jiangsheng wang Jinjun wang 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI CSCD 2022年第10期1569-1584,共16页
The flow around a square cylinder with a synthetic jet positioned at the rear surface is numerically investigated with the unsteady Reynolds-averaged Navier-Stokes(URANS)method.Instead of the typical sinusoidal wave,a... The flow around a square cylinder with a synthetic jet positioned at the rear surface is numerically investigated with the unsteady Reynolds-averaged Navier-Stokes(URANS)method.Instead of the typical sinusoidal wave,a bi-frequency signal is adopted to generate the synthetic jet.The bi-frequency signal consists of a basic sinusoidal wave and a high-frequency wave.Cases with various amplitudes of the high-frequency component are simulated.It is found that synthetic jets actuated by bi-frequency signals can realize better drag reduction with lower energy consumption when appropriate parameter sets are applied.A new quantity,i.e.,the actuation efficiency Ae,is used to evaluate the controlling efficiency.The actuation efficiency Ae reaches its maximum of 0.2668 when the amplitude of the superposed high-frequency signal is 7.5%of the basic signal.The vortex structures and frequency characteristics are subsequently analyzed to investigate the mechanism of the optimization of the bi-frequency signal.When the synthetic jet is actuated by a single-frequency signal with a characteristic velocity of 0.112 m/s,the wake is asymmetrical.The alternative deflection of vortex pairs and the peak at half of the excitation frequency in the power spectral density(PSD)function are detected.In the bi-frequency cases with the same characteristic velocity,the wake gradually turns to be symmetrical with the increase in the amplitude of the high-frequency component.Meanwhile,the deflection of the vortex pairs and the peak at half of the excitation frequency gradually disappear as well. 展开更多
关键词 synthetic jet flow control signal superposition vortex dynamics
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Quantifying the influence of vortex instability on mean velocity field statistics of wingtip vortex
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作者 Zepeng Cheng Chong Pan jiangsheng wang 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2024年第11期13-21,共9页
During its evolution to the far field,the wingtip vortex exhibits complex instability behaviors such as long-wave/short-wave instability and vortex wandering.However,the quantification influence of vortex instability ... During its evolution to the far field,the wingtip vortex exhibits complex instability behaviors such as long-wave/short-wave instability and vortex wandering.However,the quantification influence of vortex instability on its velocity field statistics has not been well investigated.To this end,experimental measurements of a canonical wingtip vortex generated by an elliptical wing under various angles of attack and Reynolds numbers were conducted using particle image velocimetry.It is found that the streamwise variation of wandering amplitude presents an exponential growth within the middle-to-far wake region and asymptotically saturates to 10−1b in the far wake,which differs from the previous report of a linear growth trend in the nearwake region.Further,two average methods,i.e.,time average(TA)and ensemble average(EA),were adopted to compare the velocity field statistics.In both TA-and EA-obtained flow fields,the vortex radius rc,peak vorticity x p,and vortex circulationΓall demonstrate a power-law scaling with respect to the streamwise location,rc∝x^(kr),Ω_(x)^(p) ∝x^(-kω) and Г∝x^(kГ),respectively.For a full rolling-up wingtip vortex in the middle-to-far wake region,the fact that kГ=k_(ω)-2k_(r) demonstrates that the vortex circulation can be scaled Г=Ω_(x)^(p)(r_(c))^(2).On the other hand,TA overestimates the decay rate of peak vorticity k and the growth rate of vortex radius kr.Furthermore,the TA-introduced bias level of the peak vorticity and vortex radius is found to be scaled with an empirical scaling between the wandering amplitude by a power law,respectively.These findings provide significant practical value for detecting wake vortex in wake vortex spacing systems. 展开更多
关键词 Vortex flow Vortex instability Wingtip vortex PIV
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Numerical investigation of efficient synthetic jets generated by multiple-frequency actuating signals 被引量:4
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作者 Yiran Lu jiangsheng wang Jinjun wang 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2022年第1期70-80,共11页
The synthetic jets generated by multiple-frequency actuating signals composed of a basic sinusoidal wave and a superposed high-frequency signal is investigated by two-dimensional simulation in the present study.The ef... The synthetic jets generated by multiple-frequency actuating signals composed of a basic sinusoidal wave and a superposed high-frequency signal is investigated by two-dimensional simulation in the present study.The effect of the frequency and amplitude of the high-frequency signal on the synthetic jet in the quiescent flow is investigated in detail with stroke length ratio L and Reynolds number Re_(U0)kept as constant.It is found that,with the high-frequency signal superposed,the vortex pairs induced by the synthetic jets are strengthened and accelerated.The distance that the vortex pairs can propagate downstream is also elongated.The entrainment of the synthetic jets is thus enhanced as well.The optimal design is reached when the frequency ratio,defined as the ratio between the superposed signal frequency and the basic signal frequency,is fixed at f^(+)=2.At this optimal frequency ratio,the jet entrainment increases monotonously with the amplitude of the high-frequency signal. 展开更多
关键词 Synthetic jet Jet entrainment Signal superposition Vortex pairs
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Flow-structure interaction of an inverted flag in a water tunnel 被引量:2
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作者 YaoWei Hu jiangsheng wang +1 位作者 JinJun wang Christian Breitsamter 《Science China(Physics,Mechanics & Astronomy)》 SCIE EI CAS CSCD 2019年第12期57-67,共11页
Herein, the dynamics and flow fields of an inverted flag are studied using hydrogen bubble flow visualization and particle image velocimetry technologies at different height-to-length ratios and flow velocities in a w... Herein, the dynamics and flow fields of an inverted flag are studied using hydrogen bubble flow visualization and particle image velocimetry technologies at different height-to-length ratios and flow velocities in a water tunnel. Results show that the heightto-length ratio of the inverted flag at which the critical flow velocity remains nearly constant is approximately 1.4. Moreover, a nonperiodic flapping phenomenon is observed under various height-to-length ratios. This phenomenon may be attributed to the existence of multiple equilibrium solutions to the self-excited vibration system, thus engendering chaos in the system comprising an inverted flag and surrounding fluid. Other indications that the system has entered chaos include multiple frequencies, nonoverlapping phase diagram, and positive Lyapunov exponent. Further discussion of the flow fields around the inverted flag reveals that the large-amplitude oscillation is due to the flow separation, while the flapping instability is a static divergence instability. In the large flapping mode, the starting leading-edge vortex(LEV) is wrapped by Kelvin-Helmholtz instabilities,which are arranged at almost uniform spacing along a circular path. In addition, the variation in position, circulation, and radius of the starting LEV are discussed in detail. 展开更多
关键词 INVERTED FLAG MODES aperiodic FLAPPING LEV
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