检索结果-南通市图书馆

Transition prediction of a hypersonic boundary layer over a cone at small angle of attack——with the improvement of e^N method

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2009年第1期52卷 115-123页

作者： SU CaiHong1 & ZHOU Heng1,2 1 Department of Mechanics, tianjin university, tianjin 300072, china 2 liu-hui center of applied mathematics, nankai university and tianjin university, tianjin 300072, china Department of Mechanics Tianjin University Tianjin China liu-hui center of applied mathematics Nankai University and Tianjin University Tianjin China

The problem of transition prediction for hypersonic boundary layers over a sharp cone has been studied in this work. The Mach number of the oncoming flow is 6, the cone half-angle is 5°, and the angle of attack is 1°. The conventional e N method is used, but the transition location so obtained is obviously incorrect. The reason is that in the conventional method, only the amplifying waves are taken into account, while in fact, for different meridians the decay processes of the disturbances before they begin to grow are different. Based on our own previous work, new interpretation and essential improvement for the e N method are proposed. Not only the amplification process but also the decay process is considered. The location, where by linear stability theory, the amplitude of disturbance wave is amplified from its initial small value to 1%, is considered to be the transition location. The new result for transition prediction thus obtained is found to be fairly satisfactory. It is also indicated that for the calculation of base flow, boundary layer equations can be used for a small angle of attack. Its computational cost is much smaller than those for DNS.

关键词： angle of attack cone transition eN method

The mechanism of breakdown in laminar-turbulent transition of a supersonic boundary layer on a flat plate-temporal mode

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2005年第5期48卷 614-625页

作者： HUANG Zhangfeng 1, CAO Wei 1,2 & ZHOU Heng 1,2 1. Department of Mechanics, tianjin university, tianjin 300072, china 2. liu-hui center of applied mathematics, nankai university and tianjin university, tianjin 300072, china Department of Mechanics Tianjin University Tianjin China liu-hui center of applied mathematics Nankai University and Tianjin University Tianjin China

Temporal mode direction numerical simulation has been done for the transition of a supersonic boundary layer on a flat plate with Mach number 4.5. Analysis of the result showed that during the breakdown process in laminar-turbulent transition, the mechanism causing the mean flow profile to evolve swiftly from laminar to turbulent was that the modification of mean flow profile by the disturbances,when they became larger,led to a remarkable change of its stability characteristics. Though the most unstable T-S wave was of second mode for laminar flow, the first mode waves played the key role in the breakdown process in laminar-turbulent transition.

关键词： supersonic boundary layer, transition, breakdown.

Direct numerical simulation of a supersonic turbulent boundary layer on a flat plate and its analysis

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2005年第5期48卷 626-640页

作者： HUANG Zhangfeng1, ZHOU Heng1,2 & LUO Jisheng1,2 1. Department of Mechanics, tianjin university, tianjin 300072, china 2. liu-hui center of applied mathematics, nankai university and tianjin university, tianjin 300072, china Department of Mechanics Tianjin University Tianjin China liu-hui center of applied mathematics Nankai University and Tianjin University Tianjin China

Temporal mode direct numerical simulation (DNS) has been done for a supersonic turbulent boundary layer on a flat plate with Mach number 4.5. It was found that the mean flow profile, the normal-wise distribution of turbulent Mach number and the root mean square (RMS) of the fluctuations of various variables, as well as the Reynolds stresses, bore similarity in nature, when the turbulence reached a fully developed state. But the compressibility effect was strong and must be considered. The strong Reynolds analogy (SRA) and the Morkovin hypothesis were no longer valid. From the end of transition to the fully developed state of turbulence, it was in the transient period, for which the similarity did not hold.

关键词： turbulence, similarity, compressibility effect, supersonic boundary layer, direct numerical simulation.

On the composition operators on the Bloch space of several complex variables

在线全文

学校读者我要写书评

暂无评论

Science china mathematics 2005年第Z1期48卷 392-399页

作者： ZHOU Zehua & CHE Renyu Department of mathematics, tianjin university, tianjin 300072, china liuhui center for applied mathematics, nankai university & tianjin university,tianjin 300072, china Department of mathematics Tianjin University Tianjin China liuhui center for applied mathematics Nankai University & Tianjin University Tianjin China

In this paper we first look upon some known results on the composition operator as bounded or compact on the Bloch-type space in polydisk and ball, and then give a sufficient and necessary condition for the compositio... 详细信息

关键词： Bloch space, bounded symmetric domains, composition operator, bergman metric.

Inflow conditions for spatial direct numerical simulation of turbulent boundary layers

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2008年第8期51卷 1106-1115页

作者： HUANG ZhangFeng & ZHOU Heng Department of Mechanics,tianjin university,tianjin 300072,china liu-hui center of applied mathematics,nankai university and tianjin university,tianjin 300072,china Department of Mechanics Tianjin University Tianjin China liu-hui center of applied mathematics Nankai University and Tianjin University Tianjin China

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.

关键词： inflow conditions spatial direct numerical simulation turbulent boundary layer similarity

Inherent mechanism of breakdown in laminar-turbulent transition of plane channel flows

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2005年第2期48卷 228-236页

作者： LUO Jisheng, WANG Xinjun & ZHOU Heng Department of Mechanics, tianjin university liu-hui center of mathematics, nankai and tianjin university, tianjin 300071, china Department of Mechanics Tianjin University Tianjin China liu-hui center of mathematics Nankai and Tianjin University Tianjin China

Laminar-turbulent transition is an old yet unsolved problem. Notwithstanding the great effort made, there is an important question that seems not to have been addressed yet, that is, what is the inherent mechanism of breakdown that eventually leads to transition? The conventional idea is that the transition starts from the amplification of disturbances, and when the disturbances become larger, higher harmonics will be generated due to nonlinear effect, making the flow more and more complicated, and finally turbulent. Though the scenario seems clear, yet there is a missing link, that is, what happens in the breakdown process. Here we show by analyzing the results from direct numerical simulations that the change of stability characteristics of the mean flow profile plays a key role in the breakdown process.

关键词： laminar-turbulent transition, breakdown, plane channel flow.

A numerical investigation of the evolution of 2-D disturbances in hypersonic boundary layers and the effect on the flow structure due to the existence of shocklets

在线全文

学校读者我要写书评

暂无评论

Science china(Physics,Mechanics & Astronomy) 2004年第2期47卷 244-255页

作者： CAO Wei & ZHOU Heng Department of Mechanics,tianjin university liu hui center of applied mathematics,nankai and tianjin university,tianjin 300072,china Correspondence should be addressed to Zhou Heng(email:hzhou 1 @ ***) Department of Mechanics Tianjin University China liu hui center of applied mathematics Nankai China tianjin university Tianjin China

The evolution of 2-D disturbances in hypersonic boundary layer with Mach number 6,8, and 10 was investigated numerically by three different numerical schemes. At the entrance, second mode T-S waves with different amplitudes were introduced, and the relation between the Mach number and the amplitude of the disturbance when shocklets started to appear was investigated. By comparing the disturbance velocity profiles with those provided by linear stability theory, the effects of shocklets on flow structures were also investigated.

关键词： hypersonic boundary layers, T-S wave, shocklet, direct numerical simulation.

Mechanism of Breakdown in Laminar-Turbulent Transition of Incompressible Boundary Layer on a Flat Plate

在线全文

学校读者我要写书评

暂无评论

Transactions of tianjin university 2007年第2期13卷 79-87页

作者：唐洪涛罗纪生周恒 School of Mechanical Engineering Tianjin University

Temporal mode direct numerical simulation was done for the process of laminar-turbulent transition in an incompressible boundary layer on a flat plate. The analysis of the results showed that during the breakdown process of laminar-turbulent transition, the modification of the mean flow profile by the disturbances led to a remarkable change in its stability characteristics, manifested in the significant enlargement of the linear unstable zone and the maximum amplification rate, and led to that many more disturbances were excited and enhanced rapidly, correspondingly the turbulent energy also increased rapidly, and the mean flow profiles evolved swiftly from laminar to turbulent. It was also found that if the oblique waves in the initial disturbances did not form symmetrical pairs, the subsequent span-wise mean velocities would, in general, be nonzero due to nonlinear interaction, which would have a great effect on the stability characteristics and also implied that the turbulence obtained by direct numerical simulation might not be fully a random process.

关键词： boundary layer transition direct numerical simulation breakdown

Enlarged interlayer of separator coating enabling high-performance lithiumsulfur batteries

在线全文

学校读者我要写书评

暂无评论

Frontiers of Chemical Science and Engineering 2024年第2期18卷 103-112页

作者： Yanqi Feng hui liu Xiaoting liu Qiongqiong Lu School of Materials&Environment Engineering Chengdu Technological UniversityChengdu 611730China School of Materials Science and Engineering Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic MaterialsShaanxi University of Science and TechnologyXi’an 710021China Green Catalysis center and College of ChemistryZhengzhou UniversityZhengzhou 450001China Institute of Materials Henan Key Laboratory of Advanced Conductor MaterialsHenan Academy of SciencesZhengzhou 450046China Leibniz Institute for Solid State and Materials Research(IFW) Dresden e.V.Dresden 01069Germany

Lithiumsulfur batteries have been intensively studied due to their high theoretical energy density and abundant sulfur resources. However, their commercial application is hindered by the low redox kinetics and high sulfur losses. In principle, in the design of cathodes and separators, the adsorption toward lithium-polysulfides should be enhanced and the conversion of soluble high-order lithium-polysulfides should be catalyzed. Herein, a KV_(3)O_(8)·0.75H_(2)O separator is designed as an effective lithium-polysulfides mediator in lithiumsulfur batteries. The intercalated K+ would enlarge the interlayer spacing of vanadium oxides, preventing the collapse of the layer structure and improving the electrical/ion conductivity of the interface. Moreover, the KV_(3)O_(8)·0.75H_(2)O modified separator possess a prior adsorption and high redox kinetics toward lithium-polysulfides due to the enhanced diffusion kinetics, which guarantees the high-rate capability and efficient utilization of sulfur. As a result, lithiumsulfur batteries exhibit a high capacity of 1362 mAh·g^(-1) and a long lifespan with a low capacity loss of 0.073% per cycle. This work may provide an alternative way to establish a functional separator to balance the adsorption and conversion of polysulfides during the redox back and forth.

关键词： lithium kinetics adsorption