Experimental and Computational Studies on Flow structure of Turbulent Separated Regions and Their Manipulation

1. 对钝板和钝圆柱前缘形成的分离区域进行了实验研究，得到了(1)脉动速度与表面压力的时均特性、雷诺应力、湍流能谱、相关性等；(2)非定常流动特性，如逆流动间断性、局部流动方向切换频率、相干结构对流速度等；(3)分离剪切层再附着区相干结构的速度、涡度和表面的相位平均时空分布特性；(4)名义二维分离区域与轴对称分离区域的相似性。通过周期性地将分离边分割成等腰三角形，可以有效地实现对二维分离区域的操作。自由流湍流可以作为一种有效的手段，以减少分离区域的纵向长度，更多的二维和轴对称的情况。建立了一种二维离散涡方法来模拟离心叶轮内的分离非定常流动。分离区产生的非定常流对叶轮总压的上升起主导作用。采用三维离散涡模型模拟了不同形状涡丝之间的相互作用。这些模拟为我们了解分离剪切层的展向或周向变形以及在再连接区域最终形成三维相干结构提供了线索。本研究获得的相干结构的结构和运动成功地模拟了分离区域的湍流特性和非定常流动特性。分离区相干结构的伪周期性脱落是由一种反馈机制引起的，在这种反馈机制中，撞击相干结构产生的扰动向上游传播，激发了分离边缘附近的剪切层。少

1. Separated regions formed at the leading edge of a blunt plate and a blunt circular cylinder were experimentally studied to obtain (1) time-mean properties, Reynolds stresses, turbulence-energy spectra, correlations, etc. of fluctuating velocities and surface pressure; (2) unsteady-flow properties such as the reverse-flow intermittency, the frequency of switching of the local-flow direction, the convection velocity of coherent structures; (3) properties of the coherent structures in the reattaching regin of the separated shear layer in terms of the phase-averaged space-time distributions of the velocity, vorticity and surface; (4) similarity of the nominally two-dimensional and axisymmetric separated regions.2. Manipulation of the two-dimensional separated region can be effectively achieved by periodically segmenting the separation edge into isosceles triangle. The free-stream turbulence can serve as an effective means to reduce the longitudinal length of the separated region for the … More two-demensional and axisymmetric cases.3. A two-dimensional discrete-vortex method was obtained to simulate separated unsteady flows in centrifugal impellers, which appear when the flow eate is off the value at the design point. The unsteady flow due to the separated region was found to have a dominant effect on the total pressure rise through the impeller.4. A three-dimensional discrete-vortex model was employed to simulate interaction vetween vortex filaments of various shapes. These simulations gave us a clue to understand the spanwise or circumferential deformation of the separated shear layer and the eventual formation of the three-dimensional coherent structures in the reattaching region.5. The structure and motion of the coherent structures obtained in the present study successfully modelled the turbulent properteis and unsteady-flow properties in the separated regions. The pseudo periodic shedding of the coherent structures from the separated regions was suggested to be prodeced by a feedback mechanism in which disturbances produced by the impinging coherent structures propagate upstream to excite the shear layer near the separation edge. Less