The primary impediments impeding the implementation of high-order methods in simulating viscous flow over complex configurations are robustness and convergence.These challenges impose significant constraints on comput...The primary impediments impeding the implementation of high-order methods in simulating viscous flow over complex configurations are robustness and convergence.These challenges impose significant constraints on computational efficiency,particularly in the domain of engineering applications.To address these concerns,this paper proposes a robust implicit high-order discontinuous Galerkin(DG)method for solving compressible Navier-Stokes(NS)equations on arbitrary grids.The method achieves a favorable equilibrium between computational stability and efficiency.To solve the linear system,an exact Jacobian matrix solving strategy is employed for preconditioning and matrix-vector generation in the generalized minimal residual(GMRES)method.This approach mitigates numerical errors in Jacobian solution during implicit calculations and facilitates the implementation of an adaptive Courant-Friedrichs-Lewy(CFL)number increasing strategy,with the aim of improving convergence and robustness.To further enhance the applicability of the proposed method for intricate grid distortions,all simulations are performed in the reference domain.This practice significantly improves the reversibility of the mass matrix in implicit calculations.A comprehensive analysis of various parameters influencing computational stability and efficiency is conducted,including CFL number,Krylov subspace size,and GMRES convergence criteria.The computed results from a series of numerical test cases demonstrate the promising results achieved by combining the DG method,GMRES solver,exact Jacobian matrix,adaptive CFL number,and reference domain calculations in terms of robustness,convergence,and accuracy.These analysis results can serve as a reference for implicit computation in high-order calculations.展开更多
An improved constant volume cycle （CVC） model is developed to analyze the nozzle effects on the thrust and specific impulse of pulse detonation rocket engine （PDRE）. Theoretically, this model shows that the thrust...An improved constant volume cycle （CVC） model is developed to analyze the nozzle effects on the thrust and specific impulse of pulse detonation rocket engine （PDRE）. Theoretically, this model shows that the thrust coefficient/specific impulse of PDRE is a function of the nozzle contraction/expansion ratio and the operating frequency. The relationship between the nozzle contraction ratio and the operation frequency is obtained by introducing the duty ratio, by which the key problem in the theoretical design can be solved. Therefore, the performance of PDRE can be accessed to guide the preliminary shape design of nozzle conveniently and quickly. The higher the operating frequency of PDRE is, the smaller the nozzle contraction ratio should be. Besides, the lower the ambient pressure is, the larger the expansion ratio of the nozzle should be. When the ambient pressure is 1.013 × 105 Pa, the optimal expansion ratio will be less than 2.26. When the ambient pressure is reduced to vacuum, the extremum of the optimal thrust coefficient is 2.236 9, and the extremum of the specific impulse is 321.01 s. The results of the improved model are verified by numerical simulation.展开更多
Subsonic jet nozzles,commonly used in passenger aircrafts,generate significant noise that travels both downstream and upstream due to large-scale or fine-scale turbulence in the jet plume.To reduce jet noise,a novel w...Subsonic jet nozzles,commonly used in passenger aircrafts,generate significant noise that travels both downstream and upstream due to large-scale or fine-scale turbulence in the jet plume.To reduce jet noise,a novel wall treatment method,termed the wavy inner wall(WIW),is proposed.With this method,the smooth inner wall near the exit of the nozzle is replaced by treated walls that carry small wavy patterns.Numerical simulations were conducted to investigate the effects of the WIW treatment.Large eddy simulations(LES)were used to predict the unsteady flow field and the far-field noise,followed by the analogy method proposed by Ffowcs Williams and Hawkings.To better understand the mechanism behind the noise reduction achieved by the WIW treatment,the shear-layer instability,radial and azimuthal auto-correlation functions,turbulent kinetic energy,and acoustic source term from the Tam-Auriault(TA)jet-noise model were analyzed.Results indicated that the WIW treatment advances the onset of jet flow instability in the shear-layer,leading to the early breakdown of jet shear-layer and production of different scales of downstream turbulent structures.As a result,the distribution and production of turbulent kinetic energy are affected,and the genera-tion and emission of jet noise are controlled.The WIW treatment enables the control of fine scale turbulence,resulting in the reduction of mid-to high-frequency noise in the far field,while ensuring a low thrust loss.This feature makes the WIW method a promis-ing approach for jet noise control.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.12102247)the Technology Development Program(Grant No.JCKY2022110C119).
文摘The primary impediments impeding the implementation of high-order methods in simulating viscous flow over complex configurations are robustness and convergence.These challenges impose significant constraints on computational efficiency,particularly in the domain of engineering applications.To address these concerns,this paper proposes a robust implicit high-order discontinuous Galerkin(DG)method for solving compressible Navier-Stokes(NS)equations on arbitrary grids.The method achieves a favorable equilibrium between computational stability and efficiency.To solve the linear system,an exact Jacobian matrix solving strategy is employed for preconditioning and matrix-vector generation in the generalized minimal residual(GMRES)method.This approach mitigates numerical errors in Jacobian solution during implicit calculations and facilitates the implementation of an adaptive Courant-Friedrichs-Lewy(CFL)number increasing strategy,with the aim of improving convergence and robustness.To further enhance the applicability of the proposed method for intricate grid distortions,all simulations are performed in the reference domain.This practice significantly improves the reversibility of the mass matrix in implicit calculations.A comprehensive analysis of various parameters influencing computational stability and efficiency is conducted,including CFL number,Krylov subspace size,and GMRES convergence criteria.The computed results from a series of numerical test cases demonstrate the promising results achieved by combining the DG method,GMRES solver,exact Jacobian matrix,adaptive CFL number,and reference domain calculations in terms of robustness,convergence,and accuracy.These analysis results can serve as a reference for implicit computation in high-order calculations.
基金supported by the National Natural Science Foundation of China(No.11472167)
文摘An improved constant volume cycle （CVC） model is developed to analyze the nozzle effects on the thrust and specific impulse of pulse detonation rocket engine （PDRE）. Theoretically, this model shows that the thrust coefficient/specific impulse of PDRE is a function of the nozzle contraction/expansion ratio and the operating frequency. The relationship between the nozzle contraction ratio and the operation frequency is obtained by introducing the duty ratio, by which the key problem in the theoretical design can be solved. Therefore, the performance of PDRE can be accessed to guide the preliminary shape design of nozzle conveniently and quickly. The higher the operating frequency of PDRE is, the smaller the nozzle contraction ratio should be. Besides, the lower the ambient pressure is, the larger the expansion ratio of the nozzle should be. When the ambient pressure is 1.013 × 105 Pa, the optimal expansion ratio will be less than 2.26. When the ambient pressure is reduced to vacuum, the extremum of the optimal thrust coefficient is 2.236 9, and the extremum of the specific impulse is 321.01 s. The results of the improved model are verified by numerical simulation.
基金the National Natural Science Foundation of China(No.11702329,No.12102247)the National Science and Technology Major Project(J2019-II-0013-0033)the Shanghai Key Lab of Vehicle Aerodynamics and Vehicle Thermal Management Systems(No.VATLAB-2021-01).
文摘Subsonic jet nozzles,commonly used in passenger aircrafts,generate significant noise that travels both downstream and upstream due to large-scale or fine-scale turbulence in the jet plume.To reduce jet noise,a novel wall treatment method,termed the wavy inner wall(WIW),is proposed.With this method,the smooth inner wall near the exit of the nozzle is replaced by treated walls that carry small wavy patterns.Numerical simulations were conducted to investigate the effects of the WIW treatment.Large eddy simulations(LES)were used to predict the unsteady flow field and the far-field noise,followed by the analogy method proposed by Ffowcs Williams and Hawkings.To better understand the mechanism behind the noise reduction achieved by the WIW treatment,the shear-layer instability,radial and azimuthal auto-correlation functions,turbulent kinetic energy,and acoustic source term from the Tam-Auriault(TA)jet-noise model were analyzed.Results indicated that the WIW treatment advances the onset of jet flow instability in the shear-layer,leading to the early breakdown of jet shear-layer and production of different scales of downstream turbulent structures.As a result,the distribution and production of turbulent kinetic energy are affected,and the genera-tion and emission of jet noise are controlled.The WIW treatment enables the control of fine scale turbulence,resulting in the reduction of mid-to high-frequency noise in the far field,while ensuring a low thrust loss.This feature makes the WIW method a promis-ing approach for jet noise control.
