Low frequency turbulence and energy dissipation in the Solar Wind

The possibility to perform in-situ measurements of velocity, magnetic field, density and temperature fluctuations in the Solar Wind has greatly improved our knoweledge of MHD turbulence not only from the point of view of space physics but also from the more general point of view of plasma physics.These fluctuations on the one hand extend over a wide range of frequencies (about 5 decades), a fact which seems to be the signature of turbulent non-linear energy cascade, on the other hand display, mainly in the trailing edge of high speed streams, a number of striking features: (i) a high degree of correlation between magnetic and velocity field fluctuations, (ii) a very low level of fluctuations in mass density and magnetic field intensity, (iii) a considerable anisotropy revealed by minimum variance analysis of the magnetic field correlation tensor. More recently it has been stressed that MHD turbulence in the Solar Wind displays a clear intermittent character.The picture which emerges from the most recent analytical theories and numerical simulations is presented. In particular the observations which give us informations about the dissipation mechanism, which remains yet largely unknown, are discussed.     

二维超音速湍流混合特性研究

着重讨论顺流喷射情况下的超音速混合的流场特征及影响因素。简要介绍了顺流喷射混合的研究现状。同时，探讨了不同的来流参数对流场特征的影响及混合机理。计算采用了一种二阶ＴＶＤ格式有限体积法及Ｂ－Ｌ湍流模型求解二维湍流Ｎ－Ｓ方程。结果表明：所采用的计算方法能成功地抑制非物理振荡，适用于二维超音速内流的湍流混合特性研究。     

高湍流度对平板边界层传的热影响

在雷诺数为１０６—１０７之间对０．１％—２５％湍流度的自由来流流过平板边界层传热问题进行了实验与数值研究。实验是在吸入式风洞内进行，用自由来流冷却加热平板，自由来流的湍流度可高达３０％。计算模型针对二维定常流，采用代数应力（热流）湍流模型，用ＳＩＭＰＬＥ算法进行计算。结果表明：高湍流度自由来流可使平板的平均Ｓｔａｎｔｏｎ数增加８５％。     

低速大尺寸传热风洞的研制

为进行航空发动机内特别是叶轮机械内的边界层、传热和气膜冷却研究，设计、建造了大尺寸低速回流式风洞。描述了风洞结构和设计中考虑的主要问题。风洞性能测试结果表明，试验段中的气流达到很高的均匀度，不用紊流发生器时可达到很低的紊流度，试验板上的边界层参数和换热系数都和公认的关系式符合良好。     

Experimental investigation of the full coverage film cooling effectiveness of a turbine blade with shaped holes

The film cooling effectiveness of two turbine blades at different turbulence intensities(0.62% and 16.00%) and mass flux ratios(2.91%, 5.82%, 8.73% and 11.63%) is studied by using the Pressure-Sensitive Paint(PSP) measurement technique. There are a baseline and an improved turbine blade in current work, and their film cooling hole position distribution is the same. But the hole shape on suction surface and pressure surface is changed from cylindrical hole(baseline)to laid-back fan-shaped hole(im...     

扇形与平面叶栅内高负荷叶片的换热特性实验研究

为了探究扇形与平面叶栅条件下,高负荷叶片的外换热特性,采用瞬态液晶测量技术,测量了雷诺数(Re)、湍流强度(Tu)对扇形叶栅(曲端壁)的小展弦比高负荷涡轮叶片表面努塞尔数(Nu)的影响,并与平面叶栅(直端壁)进行了对比。结果表明,曲端壁相较于直端壁增加了21.5°的径向进气角以及上下端壁曲率不同,从而导致换热沿叶高的不对称分布。雷诺数增大,叶片各位置的换热明显增强,吸力面边界层转捩点位置不断向前缘靠近,雷诺数对直端壁的影响大于曲端壁。随湍流强度增大,努塞尔数整体有所升高,吸力面转捩点位置前移,压力面过渡现象明显增强,中弦部分努塞尔数一维特性更为明显,湍流强度对两类端壁的叶片影响类似。在研究低雷诺数或湍流强度对高负荷叶片的换热影响时,可采用直端壁进行简化,而在高雷诺数时,为了保证结果准确性,需在发动机实际扇形叶栅中进行实验。     

数值模拟侧向超声速单喷流干扰流场特性

采用数值方法研究了平板上超/高超声速来流与超声速横向喷流相撞引起的复杂干扰流场特性。所建立的单介质冷喷流数值模拟方法,经过了表面多方位压力分布测量结果、纹影显示的激波结构以及表面油流图谱表现的表面分离范围的实验验证。根据数值模拟与实验对比的结果,合理地描述了喷流干扰流场压力分布以及表面、空间结构特性,并分析了压力比对流场结构和特性的影响。     

Improvement of Baldwin-Lomax turbulence model for supersonic complex flows

Entropy represents the dissipation rate of energy. Through direct numerical simulation (DNS) of supersonic compression ramp flow, we find the value of entropy is monotonously decreasing along the wall-normal direction no matter in the attached or the separated region. Based on this feature, a new version of Baldwin-Lomax turbulence model (BL-entropy) is proposed in this paper. The supersonic compression ramp and cavity-ramp flows in which the original Baldwin-Lomax model fails to get convergent solutions are chosen to evaluate the performance of this model. Results from one-equation Spalart-Allmaras model (SA) and two-equation Wilcox k-x model are also included to compare with available experimental and DNS data. It is shown that BLentropy could conquer the essential deficiency of the original version by providing a more physically meaningful length scale in the complex flows. Moreover, this method is simple, computationally efficient and general, making it applicable to other models related with the supersonic boundary layer.     

Fluctuations of cosmic rays and IMF in the vicinity of interplanetary shocks

Fluctuations of cosmic rays and interplanetary magnetic field upstream of interplanetary shocks are studied using data of ground-based polar neutron monitors as well as measurements of energetic particles and solar wind plasma parameters aboard the ACE spacecraft. It is shown that coherent cosmic ray fluctuations in the energy range from 10 keV to 1 GeV are often observed at the Earth’s orbit before the arrival of interplanetary shocks. This corresponds to an increase of solar wind turbulence level by more than the order of magnitude upstream of the shock. We suggest a scenario where the cosmic ray fluctuation spectrum is modulated by fast magnetosonic waves generated by flux of low-energy cosmic rays which are reflected and/or accelerated by an interplanetary shock.