Thermal and Structural Insight into Lightweight Lattice Channels for Active Cooling Technology

The active cooling technology that can reduce the combustor temperature is commonly used to protect the scramjet.In order to further improve the performance of active cooling,the structural weight reduction,cooling efficiency and stress level of the cooling channel must be considered simultaneously.In this paper,new types of lattice channels for active cooling were designed and compared with the conventional cooling channel in terms of weight reduction,thermal and structural performance.The results showed that,at the same channel height,the cooling channel with staggered lattice arrays has the optimal comprehensive performance:the weight reduction effect reaches 39.93%;the wall temperature drops significantly,and the maximum Nu number is 2.155times of the conventional channel.The flow field analysis showed that horseshoe vortices formed by the impact effect and hairpin vortices near the trailing edge are the main factors of heat transfer enhancement.The disturbed boundary layer and the excited turbulent kinetic energy also contribute much to enhance the heat transfer.In addition,due to the HTE-induced increment of metal tensile strength,the system reliability of lattice channel is better than the conventional one.

Lessons from construction and health condition evaluation of high-grade highway in permafrost regions

Located in the eastern margin of the Tibetan Plateau,the Gonghe-Yushu high-grade highway was the first of its kind in plateau permafrost regions.Most of the road sections along the high-grade highway are unstable or extremely unstable warm permafrost with an average annual ground temperature above −1℃,which is vulnerable to global warming and human engineering activities.This paper describes permafrost characteristics,roadbed design,and operation of the Gonghe-Yushu high-grade highway in detail.It is found that thaw settlement of warm and ice-rich permafrost is the main cause of subgrade subsidence in permafrost sections of this highway due to insufficient permafrost survey and drainage design.It is recommended that the interception and drainage system's design be optimized,and the permafrost upper limit and the variation of ground temperature be further investigated to provide essential data for the treatment of highway distress.It should be emphasized that protecting permafrost soil environment and optimized engineering design are crucial to successful high-grade highway engineering in permafrost regions.

Turbulence Statistics of Thermo-Buoyancy Supercritical Fuel Flow in a Regenerative Cooling Channel

Active regenerative cooling with supercritical hydrocarbon fuel is considered as the most promising thermal protection method.The existence of buoyancy force would lead to strongly anisotropic flow and thermal transport characteristics.It is closely related to the cooling performance of the engine.To elucidate the mechanisms of turbulent transport,the large eddy simulation(LES) was performed to assess turbulence statistics within different turbulence scales.The results indicated that the buoyancy and inertial force together dominated the change of turbulent structure.Moreover,the spatial thermal buoyancy effect significantly suppressed the vertical velocity fluctuation.This is due to the laminar motion caused by the buoyancy force,thereby weakening the thermal transport.For the statistics of velocity fluctuation,it was found that the buoyancy force and inertial force greatly weaken the vertical and streamwise velocity fluctuation,respectively.For the statistics of thermal transport,the results pointed out that the near-wall heat transport characteristics need to be paid more attention.The thickness of the temperature mixing boundary layer led to the attenuation of vertical heat flux,which inhibited vertical temperature diffusion and predisposed to extreme conditions of heat transfer deterioration.The results can enhance the academic understanding of the heat transfer mechanism of supercritical fluids,and give guidance for further applications of thermal protection.

Analytic estimation and numerical modeling of actively cooled thermal protection systems with nickel alloys

Actively cooled thermal protection system has great influence on the engine of a hypersonic vehicle, and it is significant to obtain the thermal and stress distribution in the system. So an analytic estimation and numerical modeling are performed in this paper to investigate the behavior of an actively cooled thermal protection system. The analytic estimation is based on the electric analogy method and finite element analysis（FEA） is applied to the numerical simulation. Temperature and stress distributions are obtained for the actively cooled channel walls with three kinds of nickel alloys with or with no thermal barrier coating（TBC）. The temperature of the channel wall with coating has no obvious difference from the one with no coating, but the stress with coating on the channel wall is much smaller than that with no coating. Inconel X-750 has the best characteristics among the three Ni-based materials due to its higher thermal conductivity, lower elasticity module and greater allowable stress. Analytic estimation and numerical modeling results are compared with each other and a reasonable agreement is obtained.

主动冷却平板型结构件的最高温度及温度分布解析模型

主动冷却平板型结构件应用广泛,快速评估其温度性能具有重要意义.本文提出了一种用于预测主动冷却平板型结构件的最高温度和温度分布的解析模型.解析模型有三种输入参数,包括热边界条件、材料特性和几何参数.分别讨论了两种热边界条件下的求解过程,包括热流密度边界和对流传热边界.根据能量守恒原理,建立了热流密度边界模型(MHF).采用二次函数拟合真实热流密度分布的方法,建立了对流传热边界模型(MCHT).结构件的材料有铝合金和钛合金.结果表明,与数值模型结果相比,该解析模型能够预测最高温度,误差小于4%.该模型能够快速、准确地评估主动冷却平板型结构件的热防护性能.

Treatment of Severe Cholestatic Hepatitis by Integrating Traditional Chinese and Western Medicines

Objective: To study the curative effect of Chinese medicines in treating severe cholestatic hepatitis (SCH).Methods: Three hundred and fifty patients of SCH with total bilirubin level 171 μmol/L were treated with Chinese medicines. Those with Blood Stasis Syndrome were treated with the recipe mainly consisting of Radix Paeoniae Rubra, and those accompanied by blood Heat, fluid retention in the epigastric region, dampness disseminated in Sanjiao ( ) or Yang deficiency of both Spleen and Kidney were treated with recipe modified according to the symptoms and signs.Results: The treatment was markedly effective in 288 cases and effective in 26 cases, the total effective rate being 89.7%.Conclusion: It is difficult to treat severe cholestatic hepatitis, es pecially the chronic cholestatic good effect of Chinese herbal medicine in eliminating jaundice.