A significant way to achieve energy saving and emission reduction is to optimize the design of heat transfer devices.As is widely applied in industry,a corrugated tube constructed by B-spline curve is numerically inve...A significant way to achieve energy saving and emission reduction is to optimize the design of heat transfer devices.As is widely applied in industry,a corrugated tube constructed by B-spline curve is numerically investigated and the profile is optimized,using a surrogate model with considerations of performance evaluation criterion(PEC)as single objective or minimum flow resistance(f)and maximum Nusselt number(Nu)as multi-objective.The machine learning technique is used to determine the candidate samples to update the surrogate model for improving the optimization efficiency and reliability,which is validated to be effective in this paper.The optimization results show that the comprehensive performance of the corrugated tube is more sensitive to the vertical coordinates of the control points,with the appropriate increase in the number of control points for Bspline,and the better performance of corrugated tubes is achieved.The optimal profile corresponding to the best comprehensive performance is a double-crest shape.With Reynolds number(Re)increased,the wave-amplitude of the first wave gradually gets smaller,and the profile of the corrugated tube becomes smoother.With the increasing consideration of heat transfer performance over multi-objective optimization,the optimal shape gradually changes from a double-trough to a single-trough shape.Finally,the maximum PEC of 1.2415,1.1845,and 1.1504 are acquired with the Re=8000,10000,and 12000,respectively,and the maximum Nu increases from 358.540 to 478.821.Compared with the design with the maximum thermal performance,the best compromise solution from multi-objective optimization is determined at Re=8000,10000,and 12000,showing improved flow resistance of 83.917%,85.465%,and 84.473%,but with sacrificed thermal performance of 36.754%,37.088%,and 35.005%,respectively.展开更多
The dynamic response of the rotor depends on not only itself but also the dynamical characteristics of the structures that support it. In this paper, the coupling vibration characteristics of the rotor and supporting ...The dynamic response of the rotor depends on not only itself but also the dynamical characteristics of the structures that support it. In this paper, the coupling vibration characteristics of the rotor and supporting structure are studied using one simple rotor-supports model firstly, and then the dynamic stiffness of the typical supporting structure of an aero-engine is investigated in use of both numerical and experimental methods. While, one simulation strategy is developed to include dynamic stiffness of realistic supports in the dynamical analysis of the rotor system. The simulated and tested results show that the dynamic stiffness of the supporting structure not only depends on the structural parameters but also is related to the frequency of the excitation force. The dynamic stiffness is affected by the damping and inertia effect when the excitation frequency is high and closed to the resonance frequency of the support, which may decrease the dynamic stiffness sharply.More resonance frequencies may be induced and the critical speed could be reduced or increased.While higher vibration response peak and overload of the bearing may also be caused by the varied dynamic stiffness, which needs to be avoided in the design of the rotor-supports system.展开更多
In aero engine design, determining whether the preliminary design will have disruptive effects on the detailed design is the key to multidisciplinary design optimization in the preliminary design stage. In order to ad...In aero engine design, determining whether the preliminary design will have disruptive effects on the detailed design is the key to multidisciplinary design optimization in the preliminary design stage. In order to adapt to the non-orthogonal parameter value range caused by the selfconstrained parametric modeling method, a non-orthogonal space mapping method that maps the optimal Latin hypercube sampling points of the traditional orthogonal design space to the non-orthogonal design space is proposed. Based on the logical regression method in machine learning field, a kind of feasible domain boundary identification method is employed to identify whether the sample spatial response meets the relevant criteria. The method proposed in this paper is used to identify and analyze the key technologies of the high-pressure turbine mortise joint structure. It is found that the preliminary design of the aero engine may lead to the failure to obtain a mortise joint structure meeting the design requirements in the detailed design stage. The mortise joint structure needs to be pre-optimized in the preliminary design stage.展开更多
Helicity is an important quantity that represents the topological interpretation of vortices;however,helicity is not a Galilean invariant.In this study,VR helicity density(HVR)is derived via taking the dot product of ...Helicity is an important quantity that represents the topological interpretation of vortices;however,helicity is not a Galilean invariant.In this study,VR helicity density(HVR)is derived via taking the dot product of vorticity with the unit real eigen vector of the velocity gradient tensor when the complex eigenvalues exist.The analytical solution of HVR is derived to resolve it in a local pointwise manner,and the Galilean invariance of HVR is proved.Tip leakage flow structures in a direct numerical simulation of a tip leakage flow model and a delayed detached eddy simulation of a low-speed large-scale axial compressor rotor are extracted using helicity,eigen helicity density and HVR methods.Results show that the utilization of HVR permits the identification and accentuation of concentrated vortices.Vortices identified by HVR appear in more connective states.As in the case of helicity,the sign of HVR distinguishes between primary and secondary vortices,while eigen helicity density fails.The normalized HVR is superior to the normalized helicity density in locating the vortex axis,especially for the induced vortex structures.Hence,HVR is a strong candidate to replace the helicity density,especially when Galilean invariance is required.展开更多
In this work,a discrete unified gas kinetic scheme(DUGKS)is developed for radiative transfer in anisotropic scattering media.The method is an extension of a previous one for isotropic radiation problems[1].The present...In this work,a discrete unified gas kinetic scheme(DUGKS)is developed for radiative transfer in anisotropic scattering media.The method is an extension of a previous one for isotropic radiation problems[1].The present scheme is a finite-volume discretization of the anisotropic gray radiation equation,where the anisotropic scattering phase function is approximated by the Legendre polynomial expansion.With the coupling of free transport and scattering processes in the reconstruction of the flux at cell interfaces,the present DUGKS has the nice unified preserving properties such that the cell size is not limited by the photon mean free path even in the optical thick regime.Several one-and two-dimensional numerical tests are conducted to validate the performance of the present DUGKS,and the numerical results demonstrate that the scheme is a reliable method for anisotropic radiative heat transfer problems.展开更多
基金supported by the National Natural Science Foundation of China (No. 51676007, No. 51376001, No. 51420105008)supported by the China Scholarship council (CSC)
基金supported by the National Natural Science Foundation of China(Grant Nos.51736004,and 52076088)the Foundation of State Key Laboratory of Coal Combustion(Grant No.FSKLCCA2007)。
文摘A significant way to achieve energy saving and emission reduction is to optimize the design of heat transfer devices.As is widely applied in industry,a corrugated tube constructed by B-spline curve is numerically investigated and the profile is optimized,using a surrogate model with considerations of performance evaluation criterion(PEC)as single objective or minimum flow resistance(f)and maximum Nusselt number(Nu)as multi-objective.The machine learning technique is used to determine the candidate samples to update the surrogate model for improving the optimization efficiency and reliability,which is validated to be effective in this paper.The optimization results show that the comprehensive performance of the corrugated tube is more sensitive to the vertical coordinates of the control points,with the appropriate increase in the number of control points for Bspline,and the better performance of corrugated tubes is achieved.The optimal profile corresponding to the best comprehensive performance is a double-crest shape.With Reynolds number(Re)increased,the wave-amplitude of the first wave gradually gets smaller,and the profile of the corrugated tube becomes smoother.With the increasing consideration of heat transfer performance over multi-objective optimization,the optimal shape gradually changes from a double-trough to a single-trough shape.Finally,the maximum PEC of 1.2415,1.1845,and 1.1504 are acquired with the Re=8000,10000,and 12000,respectively,and the maximum Nu increases from 358.540 to 478.821.Compared with the design with the maximum thermal performance,the best compromise solution from multi-objective optimization is determined at Re=8000,10000,and 12000,showing improved flow resistance of 83.917%,85.465%,and 84.473%,but with sacrificed thermal performance of 36.754%,37.088%,and 35.005%,respectively.
基金the financial support from the National Natural Science Foundation of China(No.52075018)the National Science and Technology Major Project of the Ministry of Science and Technology of China(Nos.2017-Ⅳ-0011-0048 and 2017-I-0008-0009)。
文摘The dynamic response of the rotor depends on not only itself but also the dynamical characteristics of the structures that support it. In this paper, the coupling vibration characteristics of the rotor and supporting structure are studied using one simple rotor-supports model firstly, and then the dynamic stiffness of the typical supporting structure of an aero-engine is investigated in use of both numerical and experimental methods. While, one simulation strategy is developed to include dynamic stiffness of realistic supports in the dynamical analysis of the rotor system. The simulated and tested results show that the dynamic stiffness of the supporting structure not only depends on the structural parameters but also is related to the frequency of the excitation force. The dynamic stiffness is affected by the damping and inertia effect when the excitation frequency is high and closed to the resonance frequency of the support, which may decrease the dynamic stiffness sharply.More resonance frequencies may be induced and the critical speed could be reduced or increased.While higher vibration response peak and overload of the bearing may also be caused by the varied dynamic stiffness, which needs to be avoided in the design of the rotor-supports system.
文摘In aero engine design, determining whether the preliminary design will have disruptive effects on the detailed design is the key to multidisciplinary design optimization in the preliminary design stage. In order to adapt to the non-orthogonal parameter value range caused by the selfconstrained parametric modeling method, a non-orthogonal space mapping method that maps the optimal Latin hypercube sampling points of the traditional orthogonal design space to the non-orthogonal design space is proposed. Based on the logical regression method in machine learning field, a kind of feasible domain boundary identification method is employed to identify whether the sample spatial response meets the relevant criteria. The method proposed in this paper is used to identify and analyze the key technologies of the high-pressure turbine mortise joint structure. It is found that the preliminary design of the aero engine may lead to the failure to obtain a mortise joint structure meeting the design requirements in the detailed design stage. The mortise joint structure needs to be pre-optimized in the preliminary design stage.
基金supported by the National Natural Science Foundation of China(Nos.52106039,51976006 and 51790513)the National Science and Technology Major Project,China(No.2017-Ⅱ-003-0015)+3 种基金the Aeronautical Science Foundation of China(No.2018ZB51013)the Open Fund from State Key Laboratory of Aerodynamics,China(No.SKLA2019A0101)the China Postdoctoral Science Foundation(Nos.2020M670097 and 2021T140037)also supported by the High-Performance Computing(HPC)resources at Beihang University,China。
文摘Helicity is an important quantity that represents the topological interpretation of vortices;however,helicity is not a Galilean invariant.In this study,VR helicity density(HVR)is derived via taking the dot product of vorticity with the unit real eigen vector of the velocity gradient tensor when the complex eigenvalues exist.The analytical solution of HVR is derived to resolve it in a local pointwise manner,and the Galilean invariance of HVR is proved.Tip leakage flow structures in a direct numerical simulation of a tip leakage flow model and a delayed detached eddy simulation of a low-speed large-scale axial compressor rotor are extracted using helicity,eigen helicity density and HVR methods.Results show that the utilization of HVR permits the identification and accentuation of concentrated vortices.Vortices identified by HVR appear in more connective states.As in the case of helicity,the sign of HVR distinguishes between primary and secondary vortices,while eigen helicity density fails.The normalized HVR is superior to the normalized helicity density in locating the vortex axis,especially for the induced vortex structures.Hence,HVR is a strong candidate to replace the helicity density,especially when Galilean invariance is required.
基金The National Key R&D Program of China(No.2018YFE0180900)the Fundamental Research Funds for the Central Universities(No.2019kfyXMBZ040).
文摘In this work,a discrete unified gas kinetic scheme(DUGKS)is developed for radiative transfer in anisotropic scattering media.The method is an extension of a previous one for isotropic radiation problems[1].The present scheme is a finite-volume discretization of the anisotropic gray radiation equation,where the anisotropic scattering phase function is approximated by the Legendre polynomial expansion.With the coupling of free transport and scattering processes in the reconstruction of the flux at cell interfaces,the present DUGKS has the nice unified preserving properties such that the cell size is not limited by the photon mean free path even in the optical thick regime.Several one-and two-dimensional numerical tests are conducted to validate the performance of the present DUGKS,and the numerical results demonstrate that the scheme is a reliable method for anisotropic radiative heat transfer problems.
