Boundary layer ingesting(BLI)fans are required to operate under distorted inflow conditions,which significantly reduces their efficiency[1,2].Accurately predicting fan losses is crucial for designing high-performance,...Boundary layer ingesting(BLI)fans are required to operate under distorted inflow conditions,which significantly reduces their efficiency[1,2].Accurately predicting fan losses is crucial for designing high-performance,distortion-tolerant fans.展开更多
The complex 3D flow in a steam turbine exhaust hood model with different inlet swirl and inlet total pressure radial distributions has been simulated by employing CFX-5 and analyzed in this paper. It＇s found that the...The complex 3D flow in a steam turbine exhaust hood model with different inlet swirl and inlet total pressure radial distributions has been simulated by employing CFX-5 and analyzed in this paper. It＇s found that the inlet tangential flow angle at hub has a negative effect on the exhaust hood performance, while a negative gradient of inlet total pressure radial distribution has a positive impact on the hood performances. It＇s also numerically con- firmed that a proper distribution of total pressure at hood inlet can successfully eliminate the negative effects caused by the inappropriate inlet swirl distribution and improve the hood aerodynamic performance.展开更多
The inflow conditions for spatial direct numerical simulation(SDNS)of turbulent boundary layers should reflect the characteristics of upstream turbulence,which is a puzzle.In this paper a new method is suggested,in wh...The inflow conditions for spatial direct numerical simulation(SDNS)of turbulent boundary layers should reflect the characteristics of upstream turbulence,which is a puzzle.In this paper a new method is suggested,in which the flow field obtained by using temporal direct numerical simulation(TDNS)for fully developed turbulent flow(only flow field for a single moment is sufficient)can be used as the inflow of SDNS with a proper transformation.The calculation results confirm that this method is feasible and effective.It is also found that,under a proper time-space transformation,all statistics of the fully developed turbulence obtained by both temporal mode and spatial mode DNS are in excellent agreement with each other,not only qualitatively,but also quantitatively.The normal-wise distributions of mean flow profile,turbulent Mach number and the root mean square(RMS)of the fluctuations of various variables,as well as the Reynolds stresses of the fully developed turbulence obtained by using SDNS,bear similarity in nature.展开更多
For direct numerical simulation （DNS） of turbulent boundary layers, generation of an appropriate inflow condition needs to be considered. This paper proposes a method, with which the inflow condition for spatial-mod...For direct numerical simulation （DNS） of turbulent boundary layers, generation of an appropriate inflow condition needs to be considered. This paper proposes a method, with which the inflow condition for spatial-mode DNS of turbulent boundary layers on supersonic blunt cones with different Mach numbers, Reynolds numbers and wall temperature conditions can be generated. This is based only on a given instant flow field obtained by a temporal-mode DNS of a turbulent boundary layer on a flat plate. Effectiveness of the method is shown in three typical examples by comparing the results with those obtained by other methods.展开更多
The detailed flow structures and closely-related heat transfer characteristics are investigated along the wall of a cooling channel with rib tabulator by computation.Three typical Reynolds numbers defined by the rib h...The detailed flow structures and closely-related heat transfer characteristics are investigated along the wall of a cooling channel with rib tabulator by computation.Three typical Reynolds numbers defined by the rib height are set at 200,500,1300,and the Mach numbers is 0.2,respectively.Two inlet boundary conditions,including the uniform and the fully-developed turbulent conditions,are used to study the turbulence effects on the characteristics of heat transfer in the vicinity of rib and wall.Results show that the local Nusselt number increases when the Reynolds number rises from 200 to 1300.At lower Reynolds number,the turbulent inlet condition generates more tangible heat transfer enhancement.At higher Reynolds number,however,the uniform inlet condition contributes more to the convective heat transfer effects.The paper discovers that the high Nusselt number has a consistent correlation with the positive and negative sign alteration of the shear layer on the wall,which satisfactorily explains the mechanisms of heat transfer enhancement due to the flow.展开更多
Small and micro unmanned aircraft are the focus of scientific interest due to their wide range of applications.They often operate in a highly unstable flight environment where the application of new morphing wing tech...Small and micro unmanned aircraft are the focus of scientific interest due to their wide range of applications.They often operate in a highly unstable flight environment where the application of new morphing wing technologies offers the opportunity to improve flight characteristics.The investigated concept comprises port and starboard adjustable wings,and an adaptive elastoflexible membrane serves as the lifting surface.The focus is on the benefits of the deforming membrane during the impact of a one-minus-cosine type gust.At a low Reynolds number of Re=264000,the morphing wing model is investigated numerically by unsteady fluid-structure interaction simulations.First,the numerical results are validated by experimental data from force and moment,flow field,and deformation measurements.Second,with the rigid wing as the baseline,the flexible case is investigated,focusing on the advantages of the elastic membrane.For all configurations studied,the maximum amplitude of the lift coefficient under gust load shows good agreement between the experimental and numerical results.During the decay of the gust,they differ more the higher the aspect ratio of the wing.When considering the flow field,the main differences are due to the separation behavior on the upper side of the wing.The flow reattaches earlier in the experiments than in the simulations,which explains the higher lift values observed in the former.Only at one intermediate configuration does the lift amplitude of the rigid configuration exceeds that of the flexible by about 12%,with the elastic membrane resulting in a smaller and more uniform peak load,which is also evident in the wing loading and hence in the root bending moment.展开更多
We study the stationary Wigner equation on a bounded, one- dimensional spatial domain with inflow boundary conditions by using the parity decomposition of L. Barletti and P. F. Zweifel [Transport Theory Statist. Phys....We study the stationary Wigner equation on a bounded, one- dimensional spatial domain with inflow boundary conditions by using the parity decomposition of L. Barletti and P. F. Zweifel [Transport Theory Statist. Phys., 2001, 30（4-6）： 507-520]. The decomposition reduces the half-range, two-point boundary value problem into two decoupled initial value problems of the even part and the odd part. Without using a cutoff approximation around zero velocity, we prove that the initial value problem for the even part is well-posed. For the odd part, we prove the uniqueness of the solution in the odd L2-spaee by analyzing the moment system. An example is provided to show that how to use the analysis to obtain the solution of the stationary Wigner equation with inflow boundary conditions.展开更多
基金supported by the National Key Research and Development Program(Grant No.2022YFF0708903)the Ningbo Key Technology Re-search and Development Program(Grant No.2023Z018)+3 种基金the National Natural Science Foundation of China(Grant No.52275043)the Youth Fund of National Natural Science Foundation of China(Grant Nos.72301015,52105046)the Young Elite Scientist Sponsorship Program by China Association for Science and Technology(Grant Nos.2022QNRC001,YESS20220292)the Liupanshan Laboratory Basic Research Program(Grant No.LPS-2024-KY-D-JC-0009)。
文摘Boundary layer ingesting(BLI)fans are required to operate under distorted inflow conditions,which significantly reduces their efficiency[1,2].Accurately predicting fan losses is crucial for designing high-performance,distortion-tolerant fans.
基金the National Natural Science Foundation of China (grant No.50336050)
文摘The complex 3D flow in a steam turbine exhaust hood model with different inlet swirl and inlet total pressure radial distributions has been simulated by employing CFX-5 and analyzed in this paper. It＇s found that the inlet tangential flow angle at hub has a negative effect on the exhaust hood performance, while a negative gradient of inlet total pressure radial distribution has a positive impact on the hood performances. It＇s also numerically con- firmed that a proper distribution of total pressure at hood inlet can successfully eliminate the negative effects caused by the inappropriate inlet swirl distribution and improve the hood aerodynamic performance.
基金the National Natural Science Foundation of China(Grant No.90205021)the China Postdoctoral Science Foundation(Grant No.20060400707)the Foundation for the Author of National Excellent Doctoral Dissertation of China(Grant No.200328)
文摘The inflow conditions for spatial direct numerical simulation(SDNS)of turbulent boundary layers should reflect the characteristics of upstream turbulence,which is a puzzle.In this paper a new method is suggested,in which the flow field obtained by using temporal direct numerical simulation(TDNS)for fully developed turbulent flow(only flow field for a single moment is sufficient)can be used as the inflow of SDNS with a proper transformation.The calculation results confirm that this method is feasible and effective.It is also found that,under a proper time-space transformation,all statistics of the fully developed turbulence obtained by both temporal mode and spatial mode DNS are in excellent agreement with each other,not only qualitatively,but also quantitatively.The normal-wise distributions of mean flow profile,turbulent Mach number and the root mean square(RMS)of the fluctuations of various variables,as well as the Reynolds stresses of the fully developed turbulence obtained by using SDNS,bear similarity in nature.
基金the National Natural Science Foundation of China(Nos.10632050,90716007)the Special Foundation for the Authors of National Excellent Doctoral Dissertations(No.200328)
文摘For direct numerical simulation （DNS） of turbulent boundary layers, generation of an appropriate inflow condition needs to be considered. This paper proposes a method, with which the inflow condition for spatial-mode DNS of turbulent boundary layers on supersonic blunt cones with different Mach numbers, Reynolds numbers and wall temperature conditions can be generated. This is based only on a given instant flow field obtained by a temporal-mode DNS of a turbulent boundary layer on a flat plate. Effectiveness of the method is shown in three typical examples by comparing the results with those obtained by other methods.
基金financially supported by the United Innovation Program of Shanghai Commercial Aircraft Engine (No. AR908)
文摘The detailed flow structures and closely-related heat transfer characteristics are investigated along the wall of a cooling channel with rib tabulator by computation.Three typical Reynolds numbers defined by the rib height are set at 200,500,1300,and the Mach numbers is 0.2,respectively.Two inlet boundary conditions,including the uniform and the fully-developed turbulent conditions,are used to study the turbulence effects on the characteristics of heat transfer in the vicinity of rib and wall.Results show that the local Nusselt number increases when the Reynolds number rises from 200 to 1300.At lower Reynolds number,the turbulent inlet condition generates more tangible heat transfer enhancement.At higher Reynolds number,however,the uniform inlet condition contributes more to the convective heat transfer effects.The paper discovers that the high Nusselt number has a consistent correlation with the positive and negative sign alteration of the shear layer on the wall,which satisfactorily explains the mechanisms of heat transfer enhancement due to the flow.
基金funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)(No.BR 1511/12-1)。
文摘Small and micro unmanned aircraft are the focus of scientific interest due to their wide range of applications.They often operate in a highly unstable flight environment where the application of new morphing wing technologies offers the opportunity to improve flight characteristics.The investigated concept comprises port and starboard adjustable wings,and an adaptive elastoflexible membrane serves as the lifting surface.The focus is on the benefits of the deforming membrane during the impact of a one-minus-cosine type gust.At a low Reynolds number of Re=264000,the morphing wing model is investigated numerically by unsteady fluid-structure interaction simulations.First,the numerical results are validated by experimental data from force and moment,flow field,and deformation measurements.Second,with the rigid wing as the baseline,the flexible case is investigated,focusing on the advantages of the elastic membrane.For all configurations studied,the maximum amplitude of the lift coefficient under gust load shows good agreement between the experimental and numerical results.During the decay of the gust,they differ more the higher the aspect ratio of the wing.When considering the flow field,the main differences are due to the separation behavior on the upper side of the wing.The flow reattaches earlier in the experiments than in the simulations,which explains the higher lift values observed in the former.Only at one intermediate configuration does the lift amplitude of the rigid configuration exceeds that of the flexible by about 12%,with the elastic membrane resulting in a smaller and more uniform peak load,which is also evident in the wing loading and hence in the root bending moment.
文摘We study the stationary Wigner equation on a bounded, one- dimensional spatial domain with inflow boundary conditions by using the parity decomposition of L. Barletti and P. F. Zweifel [Transport Theory Statist. Phys., 2001, 30（4-6）： 507-520]. The decomposition reduces the half-range, two-point boundary value problem into two decoupled initial value problems of the even part and the odd part. Without using a cutoff approximation around zero velocity, we prove that the initial value problem for the even part is well-posed. For the odd part, we prove the uniqueness of the solution in the odd L2-spaee by analyzing the moment system. An example is provided to show that how to use the analysis to obtain the solution of the stationary Wigner equation with inflow boundary conditions.
