This work reports that the flame oscillation induced by acoustic excitation can effectively suppress soot generation in Rijke-type burners.When the acoustic frequency is close to the natural frequency of the burner sy...This work reports that the flame oscillation induced by acoustic excitation can effectively suppress soot generation in Rijke-type burners.When the acoustic frequency is close to the natural frequency of the burner system,it can produce resonance resulting in intense oscillation of the flame.The relationship between the soot suppression efficiency and the acoustic field of standing wave at different flame positions is discussed.Compared with that under self-excited oscillation,when there is external forced acoustic force introduced to the flame,oscillation combustion occurred in a lager zone in the glass tube.The fundamental cause of different soot suppression efficiency at different positions is that the standing wave acoustic field causes the particles to move at different speeds in different positions of the glass tube.The axial particle velocity difference results in the formation of acoustic vortexes and the change of the flame shape.The high particle velocity causes the air in the glass tube to turn into the turbulent condition and make the flame temperature rise.Simulation results show that the surface growth rate of soot is reduced,while the oxidation rate of soot is enhanced,which result in the soot suppression under acoustic oscillation.This study can provide some reference for the practical application of oscillate combustion in soot suppression.展开更多
A robust immersed boundary-lattice Boltzmann method(IB-LBM)is proposed to simulate fluid-structure interaction(FSI)problems in this work.Compared with the conventional IB-LBM,the current method employs the fractional ...A robust immersed boundary-lattice Boltzmann method(IB-LBM)is proposed to simulate fluid-structure interaction(FSI)problems in this work.Compared with the conventional IB-LBM,the current method employs the fractional step technique to solve the lattice Boltzmann equation(LBE)with a forcing term.Consequently,the non-physical oscillation of body force calculation,which is frequently encountered in the traditional IB-LBM,is suppressed greatly.It is of importance for the simulation of FSI problems.In the meanwhile,the no-slip boundary condition is strictly satisfied by using the velocity correction scheme.Moreover,based on the relationship between the velocity correction and forcing term,the boundary force can be calculated accurately and easily.A few test cases are first performed to validate the current method.Subsequently,a series of FSI problems,including the vortex-induced vibration of a circular cylinder,an elastic filament flapping in the wake of a fixed cylinder and sedimentation of particles,are simulated.Based on the good agreement between the current results and those in the literature,it is demonstrated that the proposed IB-LBMhas the capability to handle various FSI problems effectively.展开更多
This paper presents a novel mechanical attachment, i.e., nonlinear energy sink （NES）, for suppressing the limit cycle oscillation （LCO） of an airfoil. The dynamic responses of a two-degree-of-freedom （2-DOF） air...This paper presents a novel mechanical attachment, i.e., nonlinear energy sink （NES）, for suppressing the limit cycle oscillation （LCO） of an airfoil. The dynamic responses of a two-degree-of-freedom （2-DOF） airfoil coupled with an NES are studied with the harmonic balance method. Different structure parameters of the NES, i.e., mass ratio between the NES and airfoil, NES offset, NES damping, and nonlinear stiffness in the NES, are chosen for studying the effect of the LCO suppression on an aeroelastic system with a supercritical Hopf bifurcation or subcritical Hopf bifurcation, respectively. The results show that the structural parameters of the NES have different influence on the supercritical Hopf bifurcation system and the subcritical Hopf bifurcation system.展开更多
The aeroelastic behavior of a thin flat rudder model was numerically simulated and experimentally investigated in a hypersonic wind tunnel. In particular, a flutter suppression system taking advantage of collision wit...The aeroelastic behavior of a thin flat rudder model was numerically simulated and experimentally investigated in a hypersonic wind tunnel. In particular, a flutter suppression system taking advantage of collision within small gaps was proposed and a novel system for the flutter simulation of the whole nonlinear aeroelastic system including the flutter suppression system was developed. First, the critical flutter dynamic pressure of the rudder without the flutter suppression system was calculated with different methods. Then, the whole nonlinear aeroelastic system, including theflutter suppression system, was simulated to design the gap size. Finally, the flutter suppression system was experimentally validated in a hypersonic wind tunnel operating at Mach number 5. The typical phenomenon of Limit Cycle Oscillation(LCO) was observed, avoiding the structural failure of the model and the consistency between numerical and experimental results was demonstrated.The proposed suppression system can improve the design and reusability of test models of hypersonic flutter experiments.展开更多
基金financially supported by the National Natural Science Foundation of China (51776188, 21805244)the key program of Natural Science Foundation of Zhejiang Province (LZ21E060001)Fundamental Research Funds of Zhejiang University of Science and Technology (No.2021QN029)。
文摘This work reports that the flame oscillation induced by acoustic excitation can effectively suppress soot generation in Rijke-type burners.When the acoustic frequency is close to the natural frequency of the burner system,it can produce resonance resulting in intense oscillation of the flame.The relationship between the soot suppression efficiency and the acoustic field of standing wave at different flame positions is discussed.Compared with that under self-excited oscillation,when there is external forced acoustic force introduced to the flame,oscillation combustion occurred in a lager zone in the glass tube.The fundamental cause of different soot suppression efficiency at different positions is that the standing wave acoustic field causes the particles to move at different speeds in different positions of the glass tube.The axial particle velocity difference results in the formation of acoustic vortexes and the change of the flame shape.The high particle velocity causes the air in the glass tube to turn into the turbulent condition and make the flame temperature rise.Simulation results show that the surface growth rate of soot is reduced,while the oxidation rate of soot is enhanced,which result in the soot suppression under acoustic oscillation.This study can provide some reference for the practical application of oscillate combustion in soot suppression.
基金J.W.acknowledges the support of the Natural Science Foundation of Jiangsu Province(Grant No.BK20130778)the National Natural Science Foundation of China(Grant No.11302104)N.Z.acknowledges the support of the National Program on Key Basic Research Project(Grant No.2014CB046201).This work is also supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘A robust immersed boundary-lattice Boltzmann method(IB-LBM)is proposed to simulate fluid-structure interaction(FSI)problems in this work.Compared with the conventional IB-LBM,the current method employs the fractional step technique to solve the lattice Boltzmann equation(LBE)with a forcing term.Consequently,the non-physical oscillation of body force calculation,which is frequently encountered in the traditional IB-LBM,is suppressed greatly.It is of importance for the simulation of FSI problems.In the meanwhile,the no-slip boundary condition is strictly satisfied by using the velocity correction scheme.Moreover,based on the relationship between the velocity correction and forcing term,the boundary force can be calculated accurately and easily.A few test cases are first performed to validate the current method.Subsequently,a series of FSI problems,including the vortex-induced vibration of a circular cylinder,an elastic filament flapping in the wake of a fixed cylinder and sedimentation of particles,are simulated.Based on the good agreement between the current results and those in the literature,it is demonstrated that the proposed IB-LBMhas the capability to handle various FSI problems effectively.
基金Project supported by the National Natural Science Foundation of China(No.11172199)the KeyProgram of Tianjin Natural Science Foundation of China(No.11JCZDJC25400)
文摘This paper presents a novel mechanical attachment, i.e., nonlinear energy sink （NES）, for suppressing the limit cycle oscillation （LCO） of an airfoil. The dynamic responses of a two-degree-of-freedom （2-DOF） airfoil coupled with an NES are studied with the harmonic balance method. Different structure parameters of the NES, i.e., mass ratio between the NES and airfoil, NES offset, NES damping, and nonlinear stiffness in the NES, are chosen for studying the effect of the LCO suppression on an aeroelastic system with a supercritical Hopf bifurcation or subcritical Hopf bifurcation, respectively. The results show that the structural parameters of the NES have different influence on the supercritical Hopf bifurcation system and the subcritical Hopf bifurcation system.
基金co-supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)the National Natural Science Foundation of China (No. 11472133)
文摘The aeroelastic behavior of a thin flat rudder model was numerically simulated and experimentally investigated in a hypersonic wind tunnel. In particular, a flutter suppression system taking advantage of collision within small gaps was proposed and a novel system for the flutter simulation of the whole nonlinear aeroelastic system including the flutter suppression system was developed. First, the critical flutter dynamic pressure of the rudder without the flutter suppression system was calculated with different methods. Then, the whole nonlinear aeroelastic system, including theflutter suppression system, was simulated to design the gap size. Finally, the flutter suppression system was experimentally validated in a hypersonic wind tunnel operating at Mach number 5. The typical phenomenon of Limit Cycle Oscillation(LCO) was observed, avoiding the structural failure of the model and the consistency between numerical and experimental results was demonstrated.The proposed suppression system can improve the design and reusability of test models of hypersonic flutter experiments.
