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

湍流分离区域流动结构及其调控的实验和计算研究

基本信息

批准号：
60420026
负责人：
KIYA Masaru
金额：
$ 24.38万
依托单位：
Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (A)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1988
项目状态：
已结题

项目摘要

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

1. 对钝板和钝圆柱体前缘形成的分离区域进行实验研究，获得（1）脉动速度和表面压力的时间平均特性、雷诺应力、湍流能谱、相关性等； (2) 非定常流特性，如逆流间歇性、局部流向切换频率、相干结构的对流速度等； (3) 分离剪切层再附着区域的相干结构在速度、涡度和表面的相位平均时空分布方面的性质； (4)名义上二维轴对称分离区域的相似性。2．通过周期性地将分离边缘分割成等腰三角形，可以有效地实现对二维分离区域的操纵。对于二维和轴对称的情况，自由流湍流可以作为减少分离区域纵向长度的有效手段。 3．采用二维离散涡流方法来模拟离心叶轮中的分离非定常流动，这种分离非定常流动是在流量偏离设计点时出现的。研究发现，由于分离区域引起的不稳定流动对通过叶轮的总压升具有主导影响。4．采用三维离散涡流模型来模拟各种形状的涡流丝之间的相互作用。这些模拟为我们理解分离剪切层的展向或周向变形以及重新附着区域三维相干结构的最终形成提供了线索。5．本研究中获得的相干结构的结构和运动成功地模拟了分离区域中的湍流特性和非定常流特性。相干结构从分离区域的伪周期性脱落被认为是由反馈机制引起的，其中撞击相干结构产生的扰动向上游传播以激发分离边缘附近的剪切层。较少的