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The improvement of turbulence modeling for the aerothermal computation of hypersonic turbulent boundary layers

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Science china(Physics,mechanics & Astronomy) 2010年第2期53卷 369-379页

作者： DONG Ming & zhou heng department of mechanics,tianjin university,tianjin 300072.china 1. department of mechanics Tianjin University Tianjin 300072 China

The engineering computation of turbulent flows is mainly based on turbulence modeling,however,accurate aerothermal computation of hypersonic turbulent boundary layers is still a not well-solved problem. Aerothermal computation for turbulent boundary layers on a supersonic or hypersonic blunt cone with small bluntness is done firstly by using both direct numerical simulation and BL model,and seven different cases are investigated. Then the results obtained by the two methods are compared,and the reason causing the differences is found to be the incorrect assumption in the turbulence modeling that the ratio between eddy heat conductivity and eddy viscosity is constant throughout the whole boundary layer. Based on certain theoretical arguments,a method of modifying the expression of eddy heat conductivity in the region surrounding the peak location of the turbulent kinetic energy is proposed,which is verified to be effective,at least for the seven cases investigated.

关键词： hypersonic turbulent boundary layer aerothermal supersonic cone direct numerical simulation(DNS) BL model coefficient of eddy heat conductivity

The effect of high temperature induced variation of specific heat on the hypersonic turbulent boundary layer and its computation

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Science china(Physics,mechanics & Astronomy) 2010年第11期53卷 2103-2112页

作者： DONG Ming & zhou heng department of mechanics,tianjin university,tianjin 300072.china 1. department of mechanics Tianjin University Tianjin 300072 China

For hypersonic vehicles,as the temperature in its boundary layer usually exceeds 600 K,for which the molecular vibrational degree of freedom is excited,the perfect gas model is no longer *** this paper,the effect of high temperature induced variation of specific heat on the hypersonic turbulent boundary layer of flat plates is investigated by direct numerical simulations with the perfect gas model,*** constant specific heat,as well as with a variable specific heat gas *** comparison of the results from the two gas models has found that the effect of the variation of specific heat on the velocity of the turbulent boundary layers is relatively small,while its effect on temperature,such as the mean temperature,the temperature fluctuations,is *** is also found that the mean specific heat is quite close to the specific heat calculated by using the mean temperature,indicating that it is possible to do turbulence *** modeling is done under the variable specific heat gas model with the mean temperature as the *** feasibility of such consideration is verified by applying the SST model for variable specific heat turbulence computation.

关键词： hypersonic turbulent boundary layer specific heat direct numerical simulation SST model

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

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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 1. department of mechanics Tianjin University 300072 Tianjin China 2. Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University 300072 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

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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 1. department of mechanics Tianjin University 300072 Tianjin China 2. Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University 300072 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.

INSTABILITY WAVES IN THE WALL REGION OF A TURBULENT BOUNDARY LAYER ON A FLAT PLATE

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Acta Mechanica Sinica 1989年第1期5卷 11-19页

作者： zhou heng (department of mechanics,tianjin university,tianjin,china) 1. department of mechanics Tianjin University Tianjin China

Coherent structures and the bursting phenomena in the wall region of a turbulent boundary layer play a very important role in determining the characteristics of the boundary layer. Yet the nature and the origin of the coherent structures are unclear until *** this paper, nonlinear stability calculations for the wall region of a turbulent boundary layer have been *** was found that there do exist instability waves which may be responsible for the coherent structures.

关键词： coherent structures instability wave turbulent boundary layer

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

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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 1. department of mechanics Tianjin University Tianjin 300072 China 2. Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University Tianjin 300072 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

Transition prediction for supersonic and hypersonic boundary layers on a cone with angle of attack

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Science china(Physics,mechanics & Astronomy) 2009年第8期52卷 1223-1232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 300072 China Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University Tianjin 300072 China

Transition prediction for boundary layers has always been one of the urgent problems waiting for a solution for the development of aero-space technology,yet there is no reliable and effective method due to the complexity of the *** eN method has been regarded as an effective method for the transition prediction of boundary ***,it heavily relies on experiment or *** in cases with three-dimensional base flow,for instance,the boundary layer on a cone with angle of attack,the result of its application is not *** authors have found its cause and proposed the method for its improvement,which did yield the fairly satisfactory result for a given test case,and also did not rely so much on experiment or ***,before people can really apply this method to practical problems,more test cases have to be *** this paper,more test cases for the application of the improved eN method to problems of transition prediction of supersonic and hypersonic boundary layers on cones with angle of attack will be *** results are compared with those obtained by experiments and/or direct numerical simulations,confirming that the improved eN method is effective and *** also find that there may be more than one ZARF for each meridian plane,and which one should be chosen for the eN method has been clarified.

关键词： angle of attack cone boundary layer transition eN method

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

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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 300071 China Liu-Hui Center of Mathematics Nankai and Tianjin University Tianjin 300071 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.

The variation of transition location in response to the variation of the amplitudes of initial disturbances

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Science china(Physics,mechanics & Astronomy) 2010年第6期53卷 1109-1115页

作者： SU CaiHong & zhou heng department of mechanics,tianjin university,tianjin 300072.china 1. department of mechanics Tianjin University Tianjin 300072 China

The transition location of a boundary layer depends on the amplitude and characteristic of initial disturbances. The larger the amplitude and the amplification rate of the initial disturbances are,the more upstream the transition location is. However,the environment surrounding the flying vehicle is variable,so the amplitude and characteristic of the disturbances triggered in the boundary layer through receptivity are also variable. In this paper,how the transition location varies in response to the variation of the initial disturbance amplitudes is studied by using direct numerical simulation. The results show that if the initial disturbance amplitudes become smaller,the transition location moves downstream correspondingly,but there is a time delay compared to the time of arrival of the disturbances with reduced amplitudes. Moreover,the speed of moving downstream is appreciably lower than the propagation speed of the disturbances. On the other hand,if the amplitudes of the initial disturbances recover their original value,the transition would immediately take place whenever the disturbances reach the former transition location,but the laminar flow between the new and old transition locations would not become turbulent immediately. Theoretical explanations are provided based on the transition mechanism found by our group.

关键词： transition boundary layer stability modification of mean flow direct numerical simulation