Prediction of Wall Heat Fluxes in a Rocket Engine with Conjugate Heat Transfer Based on Large-Eddy Simulation

Although a lot of research and development has been done to understand and master the major physics involved in cryogenic rocket engines (combustion, feeding systems, heat transfer, stability, efficiency, etc.), the injection system and wall heat transfer remain critical issues due to complex physics, leading to atomization in the subcritical regime and the interactions of hot gases with walls. In such regimes, the fuel is usually injected through a coaxial annulus and triggers the atomization of the central liquid oxidizer jet. This type of injector is often referred to as air-assisted, or coaxial shear, injector, and has been extensively studied experimentally. Including such injection in numerical simulations requires specific models as simulating the atomization process is still out of reach in practical industrial systems. The effect of the injection model on the flame stabilization process and thus on wall heat fluxes is of critical importance when it comes to the design of wall-cooling systems. Indeed, maximizing the heat flux extracted from the chamber can lead to serious gain for the cooling and feeding systems for expander-type feeding cycles where the thermal energy absorbed by the coolant is converted into kinetic energy to drive the turbo-pumps of the feeding system. The methodology proposed in this work to numerically predict the flame topology and associated heat fluxes is based on state-of-the-art methods for turbulent reactive flow field predictions for rocket engines, including liquid injection, combustion model, and wall treatment. For this purpose, high-fidelity Large Eddy Simulation Conjugate Heat Transfer, along with a reduced kinetic mechanism for the prediction of H2/O2 chemistry, liquid injection model LOx sprays, and the use of a specific wall modeling to correctly predict heat flux for large temperature ratio between the bulk flow and the chamber walls, is used. A smooth and a longitudinally ribbed combustor configuration from JAXA are simulated. The coupling strategy ensures a rapid convergence for a limited additional cost compared to a fluid-only simulation, and the wall heat fluxes display a healthy trend compared to the experimental measurements. An increase of heat transfer coherent with the literature is observed when walls are equipped with ribs, compared to smooth walls. The heat transfer enhancement of the ribbed configuration with respect to the smooth walls is coherent with results from the literature, with an increase of around +80% of wall heat flux extracted for the same chamber diameter.     

高重复频率水冷Nd:YAG激活镜放大器的温度特性

为解决高重复频率大能量激光放大器的热管理问题,采用数值模拟与实验分析的方法,对背面水冷Nd:YAG激活镜放大器的流体散热进行了研究.基于低雷诺数k-e湍流模型,建立了流-固共轭传热多物理场耦合分析模型,对比分析了近壁面处理方法对流体流动、对流扩散和热传导过程及温度分布的影响,分析研究了不同冷却液流量和泵浦参数对流场特性...     

利用DISLab温度传感器测金属比热容

针对用冷却法测金属比热容实验的不足,对实验进行了改进。利用DISLab温度传感器测量金属样品在冷却过程中,温度随时间的变化速率,以解决传统的冷却法测金属比热容实验中,用热电偶和秒表测量时产生的误差较大问题。实验表明,该实验方法与传统实验相比,不仅操作简便,而且精度高,具有明显的优势。     

考虑热传递时有温度反馈的缓发超临界过程分析

对输入小阶跃反应性（ρ0〈β）、有热传递和温度反馈时反应堆缓发超临界过程进行了研究。提出了一个新的物理模型,由数值计算求出任意初始功率条件下反应堆反应性、功率随时间的变化规律,并进行分析讨论,给出了一些有益的新结果。The delayed supercritical process of nuclear reactor with temperature feedback and heat transfer while inserting small step reactivity（ρ0〈β）is analyzed. A new model is proposed. For an initial power, the variations of output power and reactivity with time are obtained by numerical method. The results are analyzed and discussed. Some useful new conclusions are drawn.     

Evaluation of Heat Transfer Coefficient During Drying of Typical Municipal Solid Waste Matrices with Significant Shrinkage at Medium Temperature

High-moisture municipal solid waste leads to lower heat value, lower combustion efficiency, and frequent and serious erosion during incinerating. Municipal solid waste should be dried before being efficiently incinerated. The purpose of this work is to carry out experimental study and simulation on characteristics of moisture migration of municipal solid waste matrices at medium temperature (100°C–200°C) in a muffle furnace. Obvious shrinkage during moisture migration of biological waste matrices with high initial moisture content was observed. The results showed the initial moisture content and framework mobility of waste matrices and the rate of moisture migration influence on shrinkage; and linear relationships between shrinkage and moisture content ratio of waste matrices during the first falling-rate period at certain drying temperature were established. Certain experimental results of drying characteristics of moisture migration of biological waste matrices, such as potato slices and watermelon peels, under medium temperature were simulated using the shrinkage model with introducing a shrinkage term in the governing equations. The model was numerically solved by applying the finite-differences method. The results show good agreement with experiment data. The shrinkage of biological waste matrices can enhance surface heat transfer of matrices. Thus, shrinkage plays an important role in the drying behavior of high-moisture biological municipal solid waste matrices.