It is well known that interactions between the leading edge of a blade and incoming vortical structures produce a sharp rise in fluctuating pressure nearby,contributing significantly to the noise production in various...It is well known that interactions between the leading edge of a blade and incoming vortical structures produce a sharp rise in fluctuating pressure nearby,contributing significantly to the noise production in various types of rotorcrafts.To suppress this fluctuating pressure and subsequently induced noise,as the first step,active control of interactions between an airfoil and incoming cylinder-generated vortices,which mimics the practical phenomenon,was experimentally investigated.The essence of the control is to create a local perturbation,using piezo-ceramic actuators,on the surface near the leading edge of the airfoil,thus modifying the airfoil-vortex interactions.Both open-and closed-loop methods were used,where the surface perturbation was controlled by an external sinusoidal wave and a feedback pressure signal from a pressure transducer installed at the leading edge,respectively.It was observed that the closed-loop control was superior to the open-loop one;the closed-and open-loop controls achieve a maximum reduction in the pressure fluctuation at the dominant vortex frequency by 32% and 11%,respectively.The detailed physics behind the observations was discussed.展开更多
Polycrystalline of[(Na_(0.535)K_(0.480))_(0.966)Li_(0.058)](Nb_(0.90)Ta_(0.10))O_(3)samples were prepared using the high-temperature solid-state reaction technique.X-ray diffraction(XRD)analysis indicates the formatio...Polycrystalline of[(Na_(0.535)K_(0.480))_(0.966)Li_(0.058)](Nb_(0.90)Ta_(0.10))O_(3)samples were prepared using the high-temperature solid-state reaction technique.X-ray diffraction(XRD)analysis indicates the formation of a single-phase with orthorhombic structure.AC impedance plots were used as tool to analyze the electrical behavior of the sample as a function of frequency at different temperatures.The AC impedance studies revealed the presence of grain effect,from 425℃onwards.Complex impedance analysis indicated non-Debye type dielectric relaxation.The Nyquist plot showed the negative temperature coefficient of resistance(NTCR)characteristic of NKLNT.The AC conductivity results were used to correlate with the barrier hopping(CBH)model to evaluate the binding energy(W_(m)),the minimum hopping distance(R_(min)),the density of states at Fermi level(N(E_(f))),and the activation energy of the compound.展开更多
We have investigated the structure,dielectric and electrical properties of lead-free polycrystalline (Na_(0.47)K_(0.47)Li_(0.06))NbO_(3) ceramics as a function of temperature and frequency in order to understand the i...We have investigated the structure,dielectric and electrical properties of lead-free polycrystalline (Na_(0.47)K_(0.47)Li_(0.06))NbO_(3) ceramics as a function of temperature and frequency in order to understand the intrinsic contribution of grain/bulk and grain boundary effects toward the dielectric response as well as the electrical conduction mechanism in the samples fabricated by microwave sintering method.X-ray diffraction analysis exhibits perovskite structure with orthorhombic symmetry,which is well supported by the Raman spectroscopic analysis.A minor secondary impurity phase of tungsten bronze structure was observed for samples sintered at 1050℃,which gets weaker for samples sintered at 1150℃.Dielectric permittivity was enhanced by 50%,although there was a reduction in the dielectric loss by about 50%at Curie temperature(450℃)for samples sintered at 1150℃.Complex impedance spectroscopic analysis indicated non-Debye-type dielectric relaxation present in the samples,and this phenomenon followed thermally activated process related to hopping mechanism.Nyquist plot showed the negative temperature coefficient of resistance,characteristic of the samples.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 51076153, 50836006) and‘Hundred Talent Program’ of Chinese Academy of Sciences
文摘It is well known that interactions between the leading edge of a blade and incoming vortical structures produce a sharp rise in fluctuating pressure nearby,contributing significantly to the noise production in various types of rotorcrafts.To suppress this fluctuating pressure and subsequently induced noise,as the first step,active control of interactions between an airfoil and incoming cylinder-generated vortices,which mimics the practical phenomenon,was experimentally investigated.The essence of the control is to create a local perturbation,using piezo-ceramic actuators,on the surface near the leading edge of the airfoil,thus modifying the airfoil-vortex interactions.Both open-and closed-loop methods were used,where the surface perturbation was controlled by an external sinusoidal wave and a feedback pressure signal from a pressure transducer installed at the leading edge,respectively.It was observed that the closed-loop control was superior to the open-loop one;the closed-and open-loop controls achieve a maximum reduction in the pressure fluctuation at the dominant vortex frequency by 32% and 11%,respectively.The detailed physics behind the observations was discussed.
文摘Polycrystalline of[(Na_(0.535)K_(0.480))_(0.966)Li_(0.058)](Nb_(0.90)Ta_(0.10))O_(3)samples were prepared using the high-temperature solid-state reaction technique.X-ray diffraction(XRD)analysis indicates the formation of a single-phase with orthorhombic structure.AC impedance plots were used as tool to analyze the electrical behavior of the sample as a function of frequency at different temperatures.The AC impedance studies revealed the presence of grain effect,from 425℃onwards.Complex impedance analysis indicated non-Debye type dielectric relaxation.The Nyquist plot showed the negative temperature coefficient of resistance(NTCR)characteristic of NKLNT.The AC conductivity results were used to correlate with the barrier hopping(CBH)model to evaluate the binding energy(W_(m)),the minimum hopping distance(R_(min)),the density of states at Fermi level(N(E_(f))),and the activation energy of the compound.
基金financially supported by UGC-DAE-CSR Indore,India(Project Ref.No.CSR-IC/CSR-85/2014-15/592).
文摘We have investigated the structure,dielectric and electrical properties of lead-free polycrystalline (Na_(0.47)K_(0.47)Li_(0.06))NbO_(3) ceramics as a function of temperature and frequency in order to understand the intrinsic contribution of grain/bulk and grain boundary effects toward the dielectric response as well as the electrical conduction mechanism in the samples fabricated by microwave sintering method.X-ray diffraction analysis exhibits perovskite structure with orthorhombic symmetry,which is well supported by the Raman spectroscopic analysis.A minor secondary impurity phase of tungsten bronze structure was observed for samples sintered at 1050℃,which gets weaker for samples sintered at 1150℃.Dielectric permittivity was enhanced by 50%,although there was a reduction in the dielectric loss by about 50%at Curie temperature(450℃)for samples sintered at 1150℃.Complex impedance spectroscopic analysis indicated non-Debye-type dielectric relaxation present in the samples,and this phenomenon followed thermally activated process related to hopping mechanism.Nyquist plot showed the negative temperature coefficient of resistance,characteristic of the samples.
