对于高超声速飞行器在临近空间形成的连续与稀薄混合流场,DSMC(direct simulation of Monte Carlo)方法需要消耗巨大的计算资源,CFD(computational fluid dynamics)方法,无法对稀薄效应进行准确模拟。在对连续/稀薄耦合数值方法深入研...对于高超声速飞行器在临近空间形成的连续与稀薄混合流场,DSMC(direct simulation of Monte Carlo)方法需要消耗巨大的计算资源,CFD(computational fluid dynamics)方法,无法对稀薄效应进行准确模拟。在对连续/稀薄耦合数值方法深入研究的基础上,提出了一套非结构网格的CFD/DSMC耦合方法。该方法具有通用强、适应性良好的特点,进行耦合计算时对不规则复杂分界面无需进行光滑处理。对超声速圆柱绕流和钝锥体流场进行了模拟,数值结果表明:该方法对不规则分界面和复杂外形具有高度适用性,通过与重叠网格结果进行比较验证了该方法的有效性和计算效率,相较于传统的DSMC方法,计算效率分别提高了2.3倍和3.16倍,具有高效性。展开更多
In this work,computational fuid dynamics(CFD)is used to study elbow erosion due to a gas-solid two-phase fow.In particular,the direct simulation Monte Carlo(DSMC)method is used to study the impact of inter-particle co...In this work,computational fuid dynamics(CFD)is used to study elbow erosion due to a gas-solid two-phase fow.In particular,the direct simulation Monte Carlo(DSMC)method is used to study the impact of inter-particle collision on the erosion behavior.The two-way coupled Euler-Lagrange method is used to solve the gas-solid fow,and the DSMC method is used to consider the collision behavior between particles.The efects of key factors,such as the particle concentration distribution and inter-particle collision,on the erosion ratio are evaluated and discussed.The efectiveness of the method is verifed from experimental data.The results show that the inter-particle collision signifcantly infuences the particle movement path and erosion ratio.When the inter-particle collision is considered,the maximum erosion position is ofset.The erosion model proposed by Oka et al.,who used the DSMC method,agrees best with the experimental data,and the average percentage error decreases from 39.2 to 27.4%.展开更多
In this paper,a high-fidelity computational fluid dynamics(CFD)and rigid body dynamics(RBD)coupled platform for virtual flight simulation is developed to investigate the flight stability of fixed canard dual-spin proj...In this paper,a high-fidelity computational fluid dynamics(CFD)and rigid body dynamics(RBD)coupled platform for virtual flight simulation is developed to investigate the flight stability of fixed canard dual-spin projectile.The platform's reliability is validated by reproducing the characteristic resonance instability of such projectiles.By coupling the solution of the Unsteady Reynolds-Averaged Navier-Stokes equations and the seven-degree-of-freedom RBD equations,the virtual flight simulations of fixed canard dual-spin projectiles at various curvature trajectories are achieved,and the dynamic mechanism of the trajectory following process is analyzed.The instability mechanism of the dynamic instability during trajectory following process of the fixed canard dual-spin projectile is elucidated by simulating the rolling/coning coupled forced motion,and subsequently validated through virtual flight simulations.The findings suggest that an appropriate yaw moment can drive the projectile axis to precession in the tangential direction of the trajectory,thereby enhancing the trajectory following stability.However,the damping of the projectile attains its minimum value when the forward body equilibrium rotational speed(-128 rad/s)is equal to the negative of the fast mode frequency of the projectile.Insufficient damping leads to the fixed canard dual-spin projectile exiting the dynamic stability domain during the trajectory following,resulting in weakly damped instability.Keeping the forward body not rotating or increasing the spin rates to-192 rad/s can enhance the projectile's damping,thereby improving its dynamic stability.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
The value of form factor k at different drafts is important in predicting full-scale total resistance and speed for different types of ships. In the ITTC community, most organizations predict form factor k using a low...The value of form factor k at different drafts is important in predicting full-scale total resistance and speed for different types of ships. In the ITTC community, most organizations predict form factor k using a low-speed model test. However, this method is problematic for ships with bulbous bows and transom. In this article, a Computational Fluid Dynamics(CFD)-based method is introduced to obtain k for different type of ships at different drafts, and a comparison is made between the CFD method and the model test. The results show that the CFD method produces reasonable k values. A grid generating method and turbulence model are briefly discussed in the context of obtaining a consistent k using CFD.展开更多
This is a numerical study of a falling droplet surrounding by air under the electric field modeled with finite volume method by means of CFD.The VOF method has been employed to model the two-phase flow of the present ...This is a numerical study of a falling droplet surrounding by air under the electric field modeled with finite volume method by means of CFD.The VOF method has been employed to model the two-phase flow of the present study.Various capillary numbers are investigated to analyze the effects of electric field intensity on the falling droplet deformation.Also,the effects of electric potential on the heat transfer coefficient have been examined.The obtained results showed that by applying the electric field at a capillary number of 0.2 the droplet tends to retain its primitive shape as time goes by,with a subtle deformation to an oblate form.Intensifying the electric field to a capillary number of 0.8 droplet deformation is almost insignificantwith time progressing;however,further enhancement in capillary number to 2 causes the droplet to deform as a prolate shape and higher values of this number intensify the prolate form deformation of the droplet and result in pinch-off phenomenon.Ultimately,it is showed that as the electric potential augments the heat transfer coefficient increases in which for electric potential values higher than 2400 V the heat transfer coefficient enhances significantly.展开更多
Spontaneous combustion(sponcom) is one of the issues of concern with the blasting gallery(BG) method of coal mining and has the potential to cause fires, and impact on production and safety, greenhouse gas(GHG) emissi...Spontaneous combustion(sponcom) is one of the issues of concern with the blasting gallery(BG) method of coal mining and has the potential to cause fires, and impact on production and safety, greenhouse gas(GHG) emissions and huge costs involved in controlling the aftermath situations. Some of the research attempts made to prevent and control coal mine fires and spontaneous combustion in thick seams worked with bord and pillar mining methods are presented in this paper. In the study, computational fluid dynamics(CFD) modelling techniques were used to simulate and assess the effects of various mining methods, layouts, designs, and different operational and ventilation parameters on the flow of goaf gases in BG panels. A wide range of parametric studies were conducted to develop proactive strategies to control and prevent ingress of oxygen into the goaf area preventing spontaneous combustion and mine fires.展开更多
In the present paper the rarefied gas how caused by the sudden change of the wall temperature and the Rayleigh problem are simulated by the DSMC method which has been validated by experiments both in global flour fiel...In the present paper the rarefied gas how caused by the sudden change of the wall temperature and the Rayleigh problem are simulated by the DSMC method which has been validated by experiments both in global flour field and velocity distribution function level. The comparison of the simulated results with the accurate numerical solutions of the B-G-K model equation shows that near equilibrium the BG-K equation with corrected collision frequency can give accurate result but as farther away from equilibrium the B-G-K equation is not accurate. This is for the first time that the error caused by the B-G-K model equation has been revealed.展开更多
To find out and improve the flow characteristics inside the intake system of cylinder head,the application of computational fluid dynamics(CFD)in the evaluation and optimization of the reconstructed intake system base...To find out and improve the flow characteristics inside the intake system of cylinder head,the application of computational fluid dynamics(CFD)in the evaluation and optimization of the reconstructed intake system based on slicing reverse method was proposed.The flow characteristics were found out through CFD,and the velocity vector field,pressure field and turbulent kinetic energy field for different valve lifts were discussed,which were in good agreement with experimental data,and the quality of reconstruction was evaluated.In order to improve its flow characteristic,an optimization plan was proposed.The results show that the flow characteristics after optimization are obviously improved.The results can provide a reference for the design and optimization of the intake system of cylinder head.展开更多
For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics...For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics(CSD)module is introduced to handle blade flexibility.In CFD module,dual time-stepping algorithm is employed in temporal discretization,Jameson two-order central difference(JST)scheme is adopted in spatial discretization and B-L turbulent model is used to illustrate the viscous effect.The CSD module is developed based on Hamilton′s variational principles and moderate deflection beam theory.Grid deformation is implemented using algebraic method through coordinate transformations to achieve deflections with high quality and efficiency.A CFD/CSD loose coupling strategy is developed to transfer information between rotor flowfield and blade structure.The CFD and the CSD modules are verified seperately.Then the CFD/CSD loose coupling is adopted in airloads prediction of UH-60A rotor under high speed forward flight condition.The calculated results agree well with test data.Finally,effects of torsional stiffness properties on airloads of rotors with different tip swept angles(from 10° forward to 30° backward)are investigated.The results are evaluated through pressure distribution and airloads variation,and some meaningful conclusions are drawn the moderated shock wave strength and pressure gradient caused by varied tip swept angle and structural properties.展开更多
文摘对于高超声速飞行器在临近空间形成的连续与稀薄混合流场,DSMC(direct simulation of Monte Carlo)方法需要消耗巨大的计算资源,CFD(computational fluid dynamics)方法,无法对稀薄效应进行准确模拟。在对连续/稀薄耦合数值方法深入研究的基础上,提出了一套非结构网格的CFD/DSMC耦合方法。该方法具有通用强、适应性良好的特点,进行耦合计算时对不规则复杂分界面无需进行光滑处理。对超声速圆柱绕流和钝锥体流场进行了模拟,数值结果表明:该方法对不规则分界面和复杂外形具有高度适用性,通过与重叠网格结果进行比较验证了该方法的有效性和计算效率,相较于传统的DSMC方法,计算效率分别提高了2.3倍和3.16倍,具有高效性。
基金The authors acknowledge the fnancial support by the National Natural Science Foundation of China(No.51874340)by the Shandong Provincial Natural Science Foundation,China(No.ZR2018MEE004).
文摘In this work,computational fuid dynamics(CFD)is used to study elbow erosion due to a gas-solid two-phase fow.In particular,the direct simulation Monte Carlo(DSMC)method is used to study the impact of inter-particle collision on the erosion behavior.The two-way coupled Euler-Lagrange method is used to solve the gas-solid fow,and the DSMC method is used to consider the collision behavior between particles.The efects of key factors,such as the particle concentration distribution and inter-particle collision,on the erosion ratio are evaluated and discussed.The efectiveness of the method is verifed from experimental data.The results show that the inter-particle collision signifcantly infuences the particle movement path and erosion ratio.When the inter-particle collision is considered,the maximum erosion position is ofset.The erosion model proposed by Oka et al.,who used the DSMC method,agrees best with the experimental data,and the average percentage error decreases from 39.2 to 27.4%.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2141254 and U23B6009)。
文摘In this paper,a high-fidelity computational fluid dynamics(CFD)and rigid body dynamics(RBD)coupled platform for virtual flight simulation is developed to investigate the flight stability of fixed canard dual-spin projectile.The platform's reliability is validated by reproducing the characteristic resonance instability of such projectiles.By coupling the solution of the Unsteady Reynolds-Averaged Navier-Stokes equations and the seven-degree-of-freedom RBD equations,the virtual flight simulations of fixed canard dual-spin projectiles at various curvature trajectories are achieved,and the dynamic mechanism of the trajectory following process is analyzed.The instability mechanism of the dynamic instability during trajectory following process of the fixed canard dual-spin projectile is elucidated by simulating the rolling/coning coupled forced motion,and subsequently validated through virtual flight simulations.The findings suggest that an appropriate yaw moment can drive the projectile axis to precession in the tangential direction of the trajectory,thereby enhancing the trajectory following stability.However,the damping of the projectile attains its minimum value when the forward body equilibrium rotational speed(-128 rad/s)is equal to the negative of the fast mode frequency of the projectile.Insufficient damping leads to the fixed canard dual-spin projectile exiting the dynamic stability domain during the trajectory following,resulting in weakly damped instability.Keeping the forward body not rotating or increasing the spin rates to-192 rad/s can enhance the projectile's damping,thereby improving its dynamic stability.
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Supported by Ministry of Industry and Information(No.K24097)
文摘The value of form factor k at different drafts is important in predicting full-scale total resistance and speed for different types of ships. In the ITTC community, most organizations predict form factor k using a low-speed model test. However, this method is problematic for ships with bulbous bows and transom. In this article, a Computational Fluid Dynamics(CFD)-based method is introduced to obtain k for different type of ships at different drafts, and a comparison is made between the CFD method and the model test. The results show that the CFD method produces reasonable k values. A grid generating method and turbulence model are briefly discussed in the context of obtaining a consistent k using CFD.
文摘This is a numerical study of a falling droplet surrounding by air under the electric field modeled with finite volume method by means of CFD.The VOF method has been employed to model the two-phase flow of the present study.Various capillary numbers are investigated to analyze the effects of electric field intensity on the falling droplet deformation.Also,the effects of electric potential on the heat transfer coefficient have been examined.The obtained results showed that by applying the electric field at a capillary number of 0.2 the droplet tends to retain its primitive shape as time goes by,with a subtle deformation to an oblate form.Intensifying the electric field to a capillary number of 0.8 droplet deformation is almost insignificantwith time progressing;however,further enhancement in capillary number to 2 causes the droplet to deform as a prolate shape and higher values of this number intensify the prolate form deformation of the droplet and result in pinch-off phenomenon.Ultimately,it is showed that as the electric potential augments the heat transfer coefficient increases in which for electric potential values higher than 2400 V the heat transfer coefficient enhances significantly.
文摘Spontaneous combustion(sponcom) is one of the issues of concern with the blasting gallery(BG) method of coal mining and has the potential to cause fires, and impact on production and safety, greenhouse gas(GHG) emissions and huge costs involved in controlling the aftermath situations. Some of the research attempts made to prevent and control coal mine fires and spontaneous combustion in thick seams worked with bord and pillar mining methods are presented in this paper. In the study, computational fluid dynamics(CFD) modelling techniques were used to simulate and assess the effects of various mining methods, layouts, designs, and different operational and ventilation parameters on the flow of goaf gases in BG panels. A wide range of parametric studies were conducted to develop proactive strategies to control and prevent ingress of oxygen into the goaf area preventing spontaneous combustion and mine fires.
基金The project supported by the National Natural Science Foundation of China (19772059, 19889209)
文摘In the present paper the rarefied gas how caused by the sudden change of the wall temperature and the Rayleigh problem are simulated by the DSMC method which has been validated by experiments both in global flour field and velocity distribution function level. The comparison of the simulated results with the accurate numerical solutions of the B-G-K model equation shows that near equilibrium the BG-K equation with corrected collision frequency can give accurate result but as farther away from equilibrium the B-G-K equation is not accurate. This is for the first time that the error caused by the B-G-K model equation has been revealed.
基金“Strategic Cooperation of Science and Technology between Nanchong City and Southwest Petroleum University 2018” Special Fund Project,China(Nos.18SXHZ0030,18SXHZ0054)
文摘To find out and improve the flow characteristics inside the intake system of cylinder head,the application of computational fluid dynamics(CFD)in the evaluation and optimization of the reconstructed intake system based on slicing reverse method was proposed.The flow characteristics were found out through CFD,and the velocity vector field,pressure field and turbulent kinetic energy field for different valve lifts were discussed,which were in good agreement with experimental data,and the quality of reconstruction was evaluated.In order to improve its flow characteristic,an optimization plan was proposed.The results show that the flow characteristics after optimization are obviously improved.The results can provide a reference for the design and optimization of the intake system of cylinder head.
文摘For accurate aeroelastic analysis,the unsteady rotor flowfield is solved by computational fluid dynamics(CFD)module based on RANS/Euler equations and moving-embedded grid system,while computational structural dynamics(CSD)module is introduced to handle blade flexibility.In CFD module,dual time-stepping algorithm is employed in temporal discretization,Jameson two-order central difference(JST)scheme is adopted in spatial discretization and B-L turbulent model is used to illustrate the viscous effect.The CSD module is developed based on Hamilton′s variational principles and moderate deflection beam theory.Grid deformation is implemented using algebraic method through coordinate transformations to achieve deflections with high quality and efficiency.A CFD/CSD loose coupling strategy is developed to transfer information between rotor flowfield and blade structure.The CFD and the CSD modules are verified seperately.Then the CFD/CSD loose coupling is adopted in airloads prediction of UH-60A rotor under high speed forward flight condition.The calculated results agree well with test data.Finally,effects of torsional stiffness properties on airloads of rotors with different tip swept angles(from 10° forward to 30° backward)are investigated.The results are evaluated through pressure distribution and airloads variation,and some meaningful conclusions are drawn the moderated shock wave strength and pressure gradient caused by varied tip swept angle and structural properties.
