摘要
高超声速边界层流动转捩是近期空气动力学研究的热点问题。对于环境扰动较小的自然转捩过程,稳定性分析已被证明是研究扰动演化的重要手段。另一方面,高超声速边界层内的温度会随着马赫数的升高而快速上升,极高的温度会引起所谓的高温真实气体效应,使得量热完全气体假设失效,从而对边界层稳定性和转捩产生影响。本文针对高温热化学非平衡气体,利用空气5组分模型开展了平板边界层的线性稳定性分析,重点研究了热化学过程对模态稳定性的影响,并探究了边界层离散谱模态的演化和同步过程。研究表明,对于由第二模态主导的高超声速二维边界层:(1)扰动相比基本流更趋向于热化学冻结态;(2)扰动方程中新出现的非平衡源项的扰动项对稳定性影响很小,非平衡过程主要是通过改变基本流剖面来间接影响稳定性;(3)声速是影响第二及更高模态的重要参数,热化学平衡态假设引起的声速计算式的变化能够解释边界层温度和厚度降低时第二模态频率反而降低的非常规趋势。
The research on hypersonic boundary layer transition is a recent focal point in aerodynamics.For the so-called‘natural transition’,where the level of environment disturbance is low,stability analysis has been proved to be a helpful technique in studying evolution of disturbances.On the other hand,temperatures in hypersonic boundary layer increase dramatically with Mach number.Extremely high-temperature causes the so-called‘real-gas effects’,or more exactly,‘thermal-chemical non-equilibrium effects’,which invalidates the calorically perfect gas assumption,and inevitably influences the stability and transition process.The flow treated in this paper is a hypersonic boundary layer on a flat-plate with thermal-chemical non-equilibrium effects.Linear stability theory(LST)is applied to study the effects thermal-chemical process take on modal instability.Meanwhile,the evolution and synchronization process between discrete and continuous spectrum are explored.Results for the 2-D hypersonic boundary layer where the 2nd mode dominates are concluded as follows.Firstly,disturbances are more thermal-chemical frozen than the basic flow.Secondly,the new term in the disturbance equation introduced by the non-equilibrium source term has little effects on stability.The differences in stability behaviors between non-equilibrium and calorically perfect gas mainly attribute to different basic flow profiles.Thirdly,speed of sound is crucial to Mack modes.The different evaluation of the speed of sound for thermal-chemical equilibrium flow is the answer to the unconventional trend that a cooler and thinner boundary layer has lower 2nd-mode frequency.
作者
陈贤亮
符松
CHEN Xianliang;FU Song(School of Aerospace Engineering,Tsinghua University,Beijing 100084,China)
出处
《空气动力学学报》
CSCD
北大核心
2020年第2期316-325,共10页
Acta Aerodynamica Sinica
基金
国家重点研发计划资助项目(2019YFA0405201)
国家数值风洞工程(2018-ZT1B03)。
关键词
高超声速流动
边界层转捩
热化学非平衡效应
hypersonic flow
boundary layer transition
thermal-chemical non-equilibrium effects
