超声速压缩拐角激波/边界层干扰动力学模态分解

压缩拐角激波与边界层干扰问题广泛存在于高速飞行器的外部和内部流动中,其非定常复杂流场结构对飞行器气动性能影响显著。动力学模态分析将有助于进一步加深理解激波与边界层干扰流场不同特征频率对应的流动结构及动力学特性,为揭示其复杂流动机理提供参考。本文采用动态模态分解（DMD）方法对来流马赫数为2.9、24°压缩拐角内激波与超声速边界层干扰下的非定常流动进行了模态分析。评估了稀疏改进动态模态分解方法在压缩拐角流动中的适用性,研究了湍流干扰和转捩干扰下典型特征频率对应的动力学模态空间结构差异及其原因,分析了转捩边界层展向非均匀性对低频/高频模态动力学机制的影响规律。研究发现,湍流干扰与转捩干扰下拐角干扰区内均存在两类截然不同的动力学模态：低频模态和高频模态。低频模态结构集中在分离激波及分离泡剪切层的根部,表征为分离泡的大尺度膨胀和收缩运动;高频模态空间分布则以平均声速线附近正负交替结构为主,对应为边界层内不稳定波沿剪切层往下游的传播。转捩边界层的展向结构对低频模态运动特性影响明显,而对高频模态的影响则相对较小

压缩拐角激波与旁路转捩边界层干扰数值研究

为了研究激波与旁路转捩边界层的干扰机理,采用直接数值模拟(DNS)方法对来流马赫数Ma∞=2.9,24°压缩拐角内激波与转捩边界层的相互作用进行了系统的研究。考察了旁路转捩干扰下压缩拐角内分离区形态和激波波系结构的典型特征。比较了转捩干扰与湍流干扰流动结构的差异,并分析了造成差异的原因。研究了拐角内转捩边界层的演化特性,探讨了转捩干扰下脉动峰值压力和峰值摩阻的分布规律及形成机制。研究结果表明:相较于湍流干扰,两侧发卡涡串的展向挤压使得分离区起始点以V字型分布,且分离激波沿展向以破碎状态为主,激波脚呈现多层结构;拐角内的干扰作用急剧加速了边界层的转捩过程;转捩干扰下的拐角内峰值脉动压力以单峰结构出现在分离区的下游,同时干扰区内的强湍动能和高雷诺剪切应力使得其局部峰值摩阻系数要高于湍流干扰

大学における障害のある学生への支援システムに関する実験研究-ノートテイクへの報酬の影響-

Our last study (Ono et al., 2004) showed that some universities or colleges had campus-supporting systems for students with disabilities, and one of the systems was a reward system in which supporters to students with disabilities were paid some money for their help. The system was seemed to have positive effects, such as motivating supporters, and increasing responsibility of them etc., and also have negative effects, such as, decreasing intrinsic motivation of supporters, etc. So both of the effects of the reward system were studied by trial implementation of the system to supporters. Fourteen supporters participated with the implementation, and the total number of supporting time was 294 hours (210 hours for direct supporting, note-taking, and 84 hours for coordination between supporters and users). After the implementation, a questionnaire was carried out to participants. Statistical analysis of their responses to the questionnaire showed some positive effects, and no negative one, and could conclude that the system worked effectively

高精度软件OpenCFD开发及飞行器湍流直接数值模拟

超/高超声速湍流是飞行器关键气动问题，也是空气动力学学科前沿。由中国科学院力学研究所及中国空气动力研究与发展中心组成的项目团队近年来在该领域开展研究，提出了优化保单调格式、加权群速度控制格式等系列高精度数值方法，并在此基础上开发了一套高精度大规模数值模拟软件OpenCFD，该软件已得到国内外200余个科研团队使用，是当前最具影响力的飞行器湍流高分辨率模拟软件之一，大幅促进了飞行器湍流高分辨率模拟的进展。利用所发展的方法及软件，项目团队揭示了超/高超声速边界层转捩、充分发展湍流、激波/边界层干扰、激波/界面干扰、湍流燃烧以及螺旋湍流等关键流动机理，发展了螺旋度模型、尺度自适应模型及能流约束模型等系列新型大涡模拟模型，提升了对飞行器湍流的认知水平，为飞行器气动设计提供了理论基础，得到了业内的广泛认可及应用。该项成果获2022年度中国空气动力学会科学技术一等奖（自然科学类

Statistical analysis of temperature distribution on vortex surfaces in hypersonic turbulent boundary layer

The nonuniform temperature distribution (NUTD) on the coherent vortex surfaces of hypersonic turbulent boundary layer (TBL) is studied using the conditional sampling technique. The direct numerical simulation data of Mach 8 flat-plate TBL flows with different wall temperatures, T-w/T-infinity = 10.03 and 1.9, are used for this research, and the coherent vortex surface is identified by the O-criterion. Two characteristic sides of the vortex are defined, which are represented by the positive and negative streamwise velocity fluctuations (+/- u') of the vortex surfaces. The conditional sampling results between the mean temperature of the two sides show that there is a significant difference of up to 20% at the same wall-normal location. Furthermore, the velocity-temperature fluctuation correlations (R-u'T' and R-v'T') at the characteristic sides of vortex surfaces are studied. It is found that the temperature fluctuations are redistributed by the vortex rotational motion that has taken effect through R-u'T' and R-v'T' and then lead to the NUTD. The NUTD features are changed quantitatively by wall cooling but share the similar mechanism as that of the higher-temperature case. Published under license by AIP Publishing

激波-湍流边界层干扰的直接数值模拟研究

激波-湍流边界层干扰是飞行器设计中的关键气动问题,也是近年来流体力学研究的前沿热点问题。报告介绍了本课题组近年来利用直接数值模拟(DNS)进行激波-湍流边界层干扰问题的研究进展。包括如下方面:1.壁温对压缩折角激波-湍流边界层干扰影响规律研究运用自主开发的OpenCFD软件,通过直接数值模拟(DNS)探讨了壁面及转

激波与转捩边界层干扰非定常特性数值分析

激波与边界层干扰的非定常问题是高速飞行器气动设计中基础研究内容之一.以往研究主要针对层流和湍流干扰，在分离激波低频振荡及其内在机理方面存在着上游机制和下游机制两类截然不同的理论解释.分析激波与转捩边界层干扰下非定常运动现象有助于进一步加深理解边界层状态以及分离泡结构对低频振荡特性的影响规律，为揭示其产生机理指出新的方向.采用直接数值模拟方法对来流马赫数2.9，24 压缩拐角内激波与转捩边界层干扰下激波的非定常运动特性进行了数值分析.通过在拐角上游平板特定的流向位置添加吹吸扰动激发流动转捩，使得进入拐角的边界层处于转捩初期阶段.在验证了计算程序可靠性的基础上，详细分析了转捩干扰下激波运动的间歇性和振荡特征，着重研究了分离泡展向三维结构对激波振荡特性的影响规律，最后还初步探索了转捩干扰下激波低频振荡产生的物理机制.研究结果表明：分离激波的非定常运动仍存在强间歇性和低频振荡特征，其时间尺度约为上游无干扰区内脉动信号特征尺度的10倍量级；分离泡展向三维结构不会对分离激波的低频振荡特征产生实质影响.依据瞬态脉动流场的低通滤波结果，转捩干扰下激波低频振荡的诱因来源于拐角干扰区下游，与流场中分离泡的收缩/膨胀运动存在一定的关联

Shock wave and turbulent boundary layer interaction in a double compression ramp

Direct numerical simulations of shock wave and supersonic turbulent boundary layer interaction in a double compression ramp with fixed ramp angles of 12 degrees and 24 degrees at Mach 2.9 are conducted. The characteristics of the shock interactions are investigated for four different length between the two ramp kinks, corresponding to L-c = 0.9 delta(ref), 1.8 delta(ref), 2.7 delta(ref), and 3.6 delta(ref) (delta(ref) being the upstream turbulent boundary layer thickness). The influence of increasing L-c on flow structures, unsteadiness, Reynolds stress, turbulence kinetic energy, and Reynolds stress anisotropy tensor is assessed. The size of the separation region is significantly decreased and reattached flow appears between the two ramp kinks. Streamwise vorticity contours and streamline curvature show the decreased spanwise width and increased spanwise coherency of Gortler-like vortices. Analysis of fluctuating wall pressure indicates that the low-frequency unsteadiness is strongly suppressed in the interaction region. Profiles of Reynolds stress components and turbulence kinetic energy exhibit different turbulence evolution across the interaction, leading to substantial differences observed in the anisotropy invariant map. It is found that the near wall region is characterized by decreased anisotropy, becoming closer to the axisymmetric compression state, while a significant increase of turbulence is identified in the outer region, following the axisymmetric expansion limit. Moreover, downstream of the interaction, turbulence in the near-wall region experiences a faster recovery and the influence of L-c is found to be marginal. The main effect of L-c is observed in the outer region, an increase of L-c resulting in a monotonic decay of turbulence intensities and an inward movement of turbulent structures

Characteristics of wall-shear stress fluctuations in shock wave and turbulent boundary layer interaction

The wall-shear stress (WSS) fluctuations in the interaction of an oblique shock wave with a flat-plate turbulent boundary layer are investigated by means of direct numerical simulation (DNS) at Mach 2.25. The numerical results agree very well with previous experiments and DNS data in terms of turbulence statistics, wall pressure, and skin friction. The fluctuating WSS characteristics, including probability density function (PDF), frequency spectrum, space-time correlation, and convection velocity, are analysed systematically. It is found that the positively skewed PDF shape of the streamwise WSS fluctuations is significantly changed due to the presence of a separation bubble, while the PDF shape of the spanwise component is slightly affected, exhibiting a symmetric behaviour across the interaction. The weighted power-spectrum density map indicates that the low-frequency unsteadiness associated with the separated shock - exhibits little influence on the spectrum for either component, and no enhancement of the low-frequency energy is observed. A significant reduction in the spatial extent of the two-point correlation is observed, causing spanwise elongated coherence for the streamwise WSS fluctuations in the separation region. Moreover, the elliptic behaviour of the space-time correlations is essentially preserved throughout the interaction, and this is accompanied by a sudden reduction of the convection velocity in the separation bubble

Wall-shear stress fluctuations in a supersonic turbulent boundary layer over an expansion corner

The effect of wall expansion on the structural and statistical characteristics of wall-shear stress (WSS) fluctuations was investigated by direct numerical simulations of a supersonic turbulent boundary layer over a sharp expansion corner with various deflection angles (beta = 0(0), 2(0), 5(0)and 10(0)). It is found that the two-dimensional fields of WSS are characterised as streamwise-elongated streaky structures being aligned in the spanwise direction, resembling low- and high-speed streaks in the buffer region of the flow. Due to the relaminarization effect, these WSS steaks experience a sudden weakening shortly after the expansion corner, but present gradual regrowth with their length scales even exceeding those of the flat-plate case in the far downstream. A strong streamwise-alignment of the instantaneous WSS vector is evident in the case of the largest deflection angle, suggesting a distinct reduction of the intermittency in the relaminarization process. Furthermore, the characteristic time scale of the spanwise component of WSS is quasi-invariant to the expansion effect, while the peak frequency of the streamwise component increases with the increase of the deflection angle