Application of compact and multioperator schemes to the numerical simulation of acoustic fields generated by instability waves in supersonic jets

Acoustic fields generated by instability waves in supersonic jets were numerically simulated. A seventh-order multioperator scheme was used to solve the Euler equations linearized about the mean flow field in an axisymmetric turbulent jet. The mean field was computed using fifth-order compact approximations of the convective terms under conditions similar to experimental data. The numerical results were found to agree well with the experiment.     

超燃燃烧室气流参数诊断

基于可调谐二极管激光器吸收光谱技术, 利用7185.597cm^{-1}, 7444.35cm^{-1} + 7444.37cm^{-1}(重合吸收线)两条H_2O吸收线, 采用分时扫描-直接探测策略组建多光路吸收测量系统, 在4kHz的测量频率下, 定量测量了燃烧室气流的静温、水蒸气浓度和流向速度. 利用位移机构, 在以C_2H_4为燃料的超燃直连式试验台中, 在单次试验中同时诊断燃烧室内某截面和燃烧室出口的多气流参数的截面分布. 利用燃烧室出口截面的水蒸气浓度分布, 并结合壁面静压计算燃烧效率; 利用燃烧室出口截面的静温和速度分布, 获得出口气流马赫数分布; 利用凹腔后部某截面的温度和水蒸气浓度分布, 判读了凹腔附近流场特征.      

Temporal evolution of optical path difference of a supersonic turbulent boundary layer

The density distribution of a supersonic turbulent boundary layer is measured with the nanoparticle-based planar laser scattering technique, and the temporal evolution of its optical path difference (OPD) in a short time interval is characterized by proper orthogonal decomposition (POD). Based on the advantage of POD in capturing the energy of a signal, a temporal evolution model is suggested for the POD coefficients of OPD. In this model, the first few coefficients vary linearly with time, and the others are modeled by Gaussian statistics. As an application, this method is used to compute the short-exposure optical transfer function.     

基于混合网格的低声爆反设计方法研究

低声爆设计方法已成为新一代军民用超声速飞机研制过程中必须解决的关键难题之一。针对传统SGD低声爆外形反设计方法无法对声爆近场非线性效应进行描述和分析的缺点,提出了利用CFD方法求解得到的声爆近场压力分布代替F函数进行低声爆反设计的方法。声爆近场预测采用点-点对接的结构/非结构混合网格,充分利用非结构网格对复杂外形适应性强和结构化网格计算效率高的优点。结果分析表明,基于改进后的低声爆反设计方法得到的方案在声爆超压以及感觉噪声级等方面都比基于原始SGD方法得到的方案有较大改善。     

PIV技术在超及高超声速流场测量中的研究进展

本文分析了超声速流场对测量技术的特殊要求, 归纳了目前将粒子影像测速仪(particle image velocimetry, PIV)技术应用于超声速流场的测量时所面临的主要技术难点以及主要的解决方法, 分析了超声速流场中所用PIV粒子的主要要求、粒子特性、投放方法等, 介绍了PIV技术在超声速、高超声速流场测量中最新的国内外进展, 特别是给出了国内外关于高超声速流场中激波/附面层的相互干扰, 以及高超声速飞行器超燃冲压发动机主要部件内流场的PIV试验研究的最新进展.      

超声速钝体逆向喷流减阻的数值模拟研究

为研究逆向喷流技术对超声速钝体减阻的影响,采用标准k-ε湍流模型,通过求解二维Navier-Stokes方程对超声速球头体逆向冷喷流流场进行了数值模拟,并着重分析了喷口总压、喷口尺寸对流场模态和减阻效果的影响。计算结果显示:随着喷流总压的变化,流场可出现两种流动模态,即长射流穿透模态和短射流穿透模态;喷流能使球头体受到的阻力明显减小;存在最大减阻临界喷流总压值(在所研究参数范围内最大减阻可达51.1%);在其它喷流物理参数不变时,随着喷口尺寸的增大,同一流动模态下的减阻效果下降。本文的研究对超声速钝体减阻技术在工程上的应用具有一定的参考价值。     

基于三角波瓣混合器的超声速流场精细结构和掺混特性

在超声速吸气式混合层风洞中,采用基于纳米粒子的平面激光散射(NPLS)技术对平板混合层和三角波瓣混合器诱导的混合层流场精细结构进行了对比实验研究.上下两层来流的实测马赫数分别为1.98和2.84,对流马赫数为0.2.NPLS图像清晰地展示了Kelvin-Helmholtz涡、流向涡、波系结构以及大尺度涡结构的配对合并过程.通过对比分析时间相关的NPLS流场图像,发现了大尺度拟序结构随时间发展演化的非定常特性.基于流动显示结果,采用分形维数和间歇因子指标对流场结构和混合特性进行了定量分析.实验研究表明,三角波瓣混合器诱导的流向涡结构显著提高了上下两层来流的掺混效率,其流动远场的分形维数突破了平板混合层中完全湍流区的分形维数值,达到了1.88,流场结构表现出明显的破碎性,有利于流动在标量层面的扩散和掺混.流动间歇性分析表明,流向涡与展向涡的相互剪切作用主导着混合层的掺混特性,同时由于流向涡的卷吸作用,三角波瓣混合器诱导的混合层混合区域更大,更多的流质被卷入混合区完成混合.     

Panel flutter prediction in two dimensional flow with enhanced piston theory

Piston theory may be used in the high Mach number supersonic flow region and/or in very high frequency subsonic or supersonic flow. In this flow model, the pressure at a point on the fluid-solid interface only depends on the downwash at the same point. However the classical piston theory may not be sufficient for some phenomena in aeroelasticity and aeroacoustics (far field prediction). Dowell and Bliss have created an extension of piston theory that allows for higher order effects that take into account the effect the distribution of downwash on pressure at any point. For simple harmonic motion, expansions in reduced frequency, inverse reduced frequency and/or inverse (square of) Mach number have all been created; The effects of higher order terms in these several expansion in creating an enhanced piston theory was illustrated for plunge and pitch motion of an airfoil (discrete system) by Ganji and Dowell. In the present paper, flutter prediction for a flexible panel in two –dimensional flow is investigated using enhanced piston theory. The goal of the present paper is to demonstrate that an enhance version of piston theory can analyze single degree of freedom flutter of a panel as compared to the classical piston theory and quasi-steady aerodynamic models which can only treat coupled mode flutter.     

翼片扰动对COIL超音速平行流混合的影响

氧碘混合过程是化学氧碘激光器(COIL)中的一个重要步骤,氧碘混合质量直接决定着COIL的运行效率和光束质量。采用化学荧光法,研究了两种不同结构的扰动翼片组对COIL超音速平行流混合过程的影响。实验结果表明,1#扰动翼片组对氧碘超音速平行流的混合增强效果明显,其荧光区达到主气流中心线所经历的流向距离大幅缩短,碘解离区内的荧光区与测试区的面积比相对于无混合扰动时提高了4.2倍;采用2#翼片组扰动混合时,流向距离值进一步缩短了40%~60%,碘解离区内的面积比值又提高了20%~40%。氧发生器有/无主载气条件(2#翼片组)下的混合过程比较显示后者混合效果更好。