Numerical studies on the effect of the key parameter to hypersonic “pitch-up anomaly”

高温真实气体效应所引起气体比热比γ的降低被认为是导致航天飞机"上仰异常"的主要原因.为详细研究此问题,本文数值求解了Euler方程,化学反应源项采用有限速率模型,考虑了5个组分、17个基元反应.研究结果表明采用低比热比气体CF4作为实验气体会导致膨胀区的压力分布与真实气体效应的影响规律不一致,并不能反映出"上仰异常"现象的本质.在高温真实气体效应的影响下,化学反应所带来的影响大于振动激发的影响,对于y方向半模压力积分Cay来说是3.8倍,而对于半模力矩积分系数Cam来说是1.7倍.对比分析表明,热化学反应导致的比热比分布不均衡是导致"上仰异常"现象出现的根本原因

Numerical simulation of deflagration to detonation transition in a straight duct: Effects of energy release and detonation stability

Numerical simulation based on the Euler equation and one-step reaction model is carried out to investigate the process of deflagration to detonation transition (DDT) occurring in a straight duct. The numerical method used includes a high resolution fifth-order weighted essentially non-oscillatory (WENO) scheme for spatial discretization, coupled with a third order total variation diminishing Runge-Kutta time stepping method. In particular, effect of energy release on the DDT process is studied. The model parameters used are the heat release at q = 50,30,25,20,15,10 and 5, the specific heat ratio at 1.2, and the activation temperature at Ti = 15, respectively. For all the cases, the initial energy in the spark is about the same compared to the detonation energy at the Chapman-Jouguet (CJ) state. It is found from the simulation that the DDT occurrence strongly depends on the magnitude of the energy release. The run-up distance of DDT occurrence decreases with the increase of the energy release for q = 50 similar to 20, and increases with the increase of the energy release for q = 20 similar to 5. This phenomenon is found to be in agreement with the analysis of mathematical stability theory. It is suggested that the factors to strengthen the DDT would make the detonation more stable, and vice versa. Finally, it is concluded from the simulations that the interaction of the shock wave and the flame front is the main reason for leading to DDT.</font

壁面催化效应数值研究

高超声速飞行器壁面催化效应会导致激波层中原子在壁面处复合释热,加剧周围气动热环境。针对高超声速流动壁面催化特性,选择不同飞行马赫数及高度条件,采用完全催化和非催化两种条件对球锥模型壁面热流率进行数值模拟计算,研究壁面催化效应对气动热的影响规律。结果表明,固定飞行高度时,壁面催化效应对气动热的影响随马赫数增加而加强,Ma 25条件下驻点处完全催化与非催化热流比值高达1.92。壁面催化效应不仅会影响壁面附近的流场特性及组分分布状态,而且对整个激波层都有一定的影响作用

Numerical study of inflow equivalence ratio inhomogeneity on oblique detonation formation in hydrogen-air mixtures

In this study, numerical simulations using Euler equations with detailed chemistry are performed to investigate the effect of fuel-air composition inhomogeneity on the oblique detonation wave (ODW) initiation in hydrogen-air mixtures. This study aims for a better understanding of oblique detonation wave engine performance under practical operating conditions, among those is the inhomogeneous mixing of fuel and air giving rise to a variation of the equivalence ratio (ER) in the incoming combustible flow. This work focuses primarily on how a variable equivalence ratio in the inflow mixture affects both the formation and characteristic parameters of the oblique detonation wave. In this regard, the present simulation imposes initially a lateral linear distribution of the mixture equivalence ratio within the initiation region. The variation is either from fuel-lean or fuel-rich to the uniform stoichiometric mixture condition above the oblique shock wave. The obtained numerical results illustrate that the reaction surface is distorted in the cases of low mixture equivalence ratio. The so-called &quot;V-shaped&quot; flame is observed but differed from previous results that it is not coupled with any compression or shock wave. Analyzing the temperature and species density evolution also shows that the fuel-lean and fuel-rich inhomogeneity have different effects on the combustion features in the initiation region behind the oblique shock wave. Two characteristic quantities, namely the initiation length and the ODW surface position, are defined to describe quantitatively the effects of mixture equivalence ratio inhomogeneity. The results show that the initiation length is mainly determined by the mixture equivalence ratio in the initiation region. Additional computations are performed by reversing ER distribution, i.e., with the linear variation above the initiation region of uniform stoichiometric condition and results also demonstrate that the ODW position is effectively determined by the ER variation before the ODW, which has in turn only negligible effect on the initiation length. (C) 2017 Elsevier Masson SAS. All rights reserved.</p

超高速试验气流的建立与分析

激波风洞是高超声速地面试验设备的主力,包括反射型激波风洞和激波-膨胀管(风洞)。然而,对于超高速(>5km/s)流动来说,试验气流在前者的喷管喉道上游驻止,高总温高总焓条件给试验设备带来严重挑战,如驻室材料毁、试验气流污染热/化学非平衡的激发与冻结等现象,引起试验条件的不确定。激波-膨胀管的工作原理不同于反射型激波风洞,它不需要试验气流驻止,可以在一定程度上缓解上述问题,提供相对稳定和洁净的高总

超高速流动研究进展

中国科学院力学研究所高温气体动力学国家重点实验室(LHD)激波与爆轰物理课题组,应用正向爆轰驱动技术,建成了国内首座可实现8公里/秒超高速试验气流的爆轰驱动激波—膨胀管(JF-16)。应用流场测量与显示技术,开展了楔、尖锥、双锥等典型模型试验。针对激波—膨胀管超高速试验气流的建立过程进行数值研究也遇到了挑战,由于强激波、强间断面等流场结构的存在,非物理振荡出现,改进了相关数值格式,抑制了数值振荡

超高速流动实验设备和相关数值研究

超高速流动是指速度超过5 公里/秒的流动，由于流动具有高速高焓的特点，模拟超高速流动的地面试验设备面临极大挑战，目前，激波-膨胀管（风洞）是少数具备超高速流动复现能力的地面试验设备之一。中国科学院力学研究所高温气体动力学国家重点实验室（LHD），通过将正向爆轰驱动技术和膨胀管结合在一起，建成了可实现8 公里/秒高品质超高速试验气流的爆轰驱动激波-膨胀管（JF-16），并成功开展了典型模型试验。同时，本文介绍了针对激波-膨胀管的相关数值方法，对超高速流动条件下的尖锥模型进行了数值模拟，数值模拟结果提供了一些试验结果难以获取的流场信息，并很好的解释了试验中获取的流场结构照片，体现了数值方法在高超声速流动中的辅助分析作用。关键字 超高速，激波-膨胀管，数值方

钝锥模型高焓流动的再压缩效应研究

在钝体高焓流动中,热化学非平衡效应使膨胀区壁面压力显著低于冻结流动,相关研究表明,再压缩效应可以消除上述差异.为详细分析此问题,数值求解了Euler方程,化学反应源项采用有限速率模型并考虑了5个组分,17个基元反应.结果表明,随着再压缩角的增大,热化学非平衡效应引起锥面压力先降后增非单调变化,这是由于再压缩流场中放热复合反应与吸热分解反应的强度变化决定的,其宏观表现为比热比的空间不均衡分布