This paper presents an efficient time-domain method for simulating nonlinear ship waves.The proposed method,implemented in an earth-fixed coordinate system,integrates a compact boundary element domain within a high-or...This paper presents an efficient time-domain method for simulating nonlinear ship waves.The proposed method,implemented in an earth-fixed coordinate system,integrates a compact boundary element domain within a high-order spectral layer,enabling accurate modeling of both near-field and far-field ship waves.An overset mesh method and an attention mechanism are employed to track the moving ship.The effectiveness of the method is validated through simulations of Wigley and Series 60 ships sailing at various speeds.The numerical results,including the nonlinear wave run-up at the ship bow,surface pressure distribution on the hull,and the ship resistance,agree well with experimental data and published numerical results,confirming that the method is capable of accurately simulating the nonlinear ship waves.展开更多
Contra-rotating small-sized fans are used as cooling fans for electric equipment. The internal flow condition between the front and rear rotors of the contra-rotating small-sized fan is not known well especially at th...Contra-rotating small-sized fans are used as cooling fans for electric equipment. The internal flow condition between the front and rear rotors of the contra-rotating small-sized fan is not known well especially at the low flow rate. Furthermore, the blade row distance between the front and rear rotors is an important parameter for the contra-rotating small-sized fan and its influence on the internal flow condition is not clarified at the low flow rate. Therefore, the internal flow condition of the contra-rotating small-sized fan at the low flow rate is investigated by the numerical analysis in this research. The numerical analysis results are validated by comparing the fan static pressure curves of the numerical results to the experimental results. The internal flow condition at the low flow rate is clarified using the numerical models of the different blade row distance L = 10 mm and 30 mm. In the present paper, pressure fluctuations phase locked each front and rear rotor’s rotation are shown and the influences of the wake and the potential interference are discussed by the unsteady numerical analysis results at the low flow rate.展开更多
A hybrid Euler/full potential/Lagrangian wake method,based on single-blade simulation,for predicting unsteady aerodynamic flow around helicopter rotors in hover and forward flight has been developed.In this method,an ...A hybrid Euler/full potential/Lagrangian wake method,based on single-blade simulation,for predicting unsteady aerodynamic flow around helicopter rotors in hover and forward flight has been developed.In this method,an Euler solver is used to model the near wake evolution and transonic flow phenomena in the vicinity of the blade,and a full potential equation（FPE） is used to model the isentropic potential flow region far away from the rotor,while the wake effects of other blades and the far wake are incorporated into the flow solution as an induced inflow distribution using a Lagrangian based wake analysis.To further reduce the execution time,the computational fluid dynamics（CFD） solution and rotor wake analysis（including induced velocity up-date） are conducted parallelly,and a load balancing strategy is employed to account for the information exchange between two solvers.By the developed method,several hover and forward-flight cases on Caradonna-Tung and Helishape 7A rotors are per-formed.Good agreements of the loadings on blade surface with available measured data demonstrate the validation of the method.Also,the CPU time required for different computation runs is compared in the paper,and the results show that the pre-sent hybrid method is superior to conventional CFD method in time cost,and will be more efficient with the number of blades increasing.展开更多
Analysis of rotorcraft dynamics requires solution of the rotor induced flow field.Often,the appropriate model to be used for induced flow is nonlinear potential flow theory（which is the basis of vortex-lattice method...Analysis of rotorcraft dynamics requires solution of the rotor induced flow field.Often,the appropriate model to be used for induced flow is nonlinear potential flow theory（which is the basis of vortex-lattice methods）.These nonlinear potential flow equations sometimes must be solved in real time––such as for real-time flight simulation,when observers are needed for controllers,or in preliminary design computations.In this paper,the major effects of nonlinearities on induced flow are studied for lifting rotors in low-speed flight and hover.The approach is to use a nonlinear statespace model of the induced flow based on a Galerkin treatment of the potential flow equations.展开更多
基金supported by the YEQISUN Joint Funds of the National Natural Science Foundation of China(Grant No.U2141228).
文摘This paper presents an efficient time-domain method for simulating nonlinear ship waves.The proposed method,implemented in an earth-fixed coordinate system,integrates a compact boundary element domain within a high-order spectral layer,enabling accurate modeling of both near-field and far-field ship waves.An overset mesh method and an attention mechanism are employed to track the moving ship.The effectiveness of the method is validated through simulations of Wigley and Series 60 ships sailing at various speeds.The numerical results,including the nonlinear wave run-up at the ship bow,surface pressure distribution on the hull,and the ship resistance,agree well with experimental data and published numerical results,confirming that the method is capable of accurately simulating the nonlinear ship waves.
文摘Contra-rotating small-sized fans are used as cooling fans for electric equipment. The internal flow condition between the front and rear rotors of the contra-rotating small-sized fan is not known well especially at the low flow rate. Furthermore, the blade row distance between the front and rear rotors is an important parameter for the contra-rotating small-sized fan and its influence on the internal flow condition is not clarified at the low flow rate. Therefore, the internal flow condition of the contra-rotating small-sized fan at the low flow rate is investigated by the numerical analysis in this research. The numerical analysis results are validated by comparing the fan static pressure curves of the numerical results to the experimental results. The internal flow condition at the low flow rate is clarified using the numerical models of the different blade row distance L = 10 mm and 30 mm. In the present paper, pressure fluctuations phase locked each front and rear rotor’s rotation are shown and the influences of the wake and the potential interference are discussed by the unsteady numerical analysis results at the low flow rate.
基金National Natural Science Foundation of China (10872094)
文摘A hybrid Euler/full potential/Lagrangian wake method,based on single-blade simulation,for predicting unsteady aerodynamic flow around helicopter rotors in hover and forward flight has been developed.In this method,an Euler solver is used to model the near wake evolution and transonic flow phenomena in the vicinity of the blade,and a full potential equation（FPE） is used to model the isentropic potential flow region far away from the rotor,while the wake effects of other blades and the far wake are incorporated into the flow solution as an induced inflow distribution using a Lagrangian based wake analysis.To further reduce the execution time,the computational fluid dynamics（CFD） solution and rotor wake analysis（including induced velocity up-date） are conducted parallelly,and a load balancing strategy is employed to account for the information exchange between two solvers.By the developed method,several hover and forward-flight cases on Caradonna-Tung and Helishape 7A rotors are per-formed.Good agreements of the loadings on blade surface with available measured data demonstrate the validation of the method.Also,the CPU time required for different computation runs is compared in the paper,and the results show that the pre-sent hybrid method is superior to conventional CFD method in time cost,and will be more efficient with the number of blades increasing.
基金co-supported by the National Natural Science Foundation of China(No.51375104)the Heilongjiang Province Funds for Distinguished Young Scientists(No.JC201405)+1 种基金the China Postdoctoral Science Foundation(No.2015M581433)the Postdoctoral Science Foundation of Heilongjiang Province(No.LBH-Z15038)
文摘Analysis of rotorcraft dynamics requires solution of the rotor induced flow field.Often,the appropriate model to be used for induced flow is nonlinear potential flow theory（which is the basis of vortex-lattice methods）.These nonlinear potential flow equations sometimes must be solved in real time––such as for real-time flight simulation,when observers are needed for controllers,or in preliminary design computations.In this paper,the major effects of nonlinearities on induced flow are studied for lifting rotors in low-speed flight and hover.The approach is to use a nonlinear statespace model of the induced flow based on a Galerkin treatment of the potential flow equations.
