Toward a wall-stress model for LES over rough boundaries ; contributions to experimental and simulation technology

为了促进壁面湍流模拟的研究，本课题发展了相应的测量技术，提出了LES-RANS混合壁面应力模拟技术和模拟高浓度弥散颗粒湍流的虚拟域方法，并在此基础上发展了适用于明渠的立体PIV（Particle Image Velocimetry）测量技术。首先，我们指出了摄像机标定的一些简单但新的方面。接下来，我们提出了一种新的图像处理技术来直接测量壁的剪切速率，既可以通过单个相机看到，也可以从两个相机视图进行3D重建。这种“PIV/界面测量”技术成功地应用于正弦曲线壁的实验图像。这种基本的贡献将有利于应用（立体）PIV可能复杂boundaries.To允许附近的沉积物beds. To固液两相流的数值模拟区域附近，我们扩展了Kajishima的虚拟域技术来处理高颗粒浓度的情况下。对部分填充玻璃珠的“封闭式”和“开放式”转鼓进行的试验，在床层角度和其他重要参数上取得了良好的一致性。在这些测试之后，我们考虑了包含1500个球形珠的双周期“最小”湍流通道。参数进行了调整，以产生颗粒雷诺数约15，和无量纲剪切应力（盾牌参数）在0.06 - 1.1的范围内。在此范围内，泥沙通量的结果同意在20%以内的Meyer-Peter Mueller equation.To有助于复杂形状的边界上的LES相关的未解决的理论问题的预测，PI还导出了一个方程的压力阻力的“补丁”的壁附近的涡度平流。

To contribute to research on simulation of wall turbulence, the present research project has developed relevant measurement technology, and has proposed a hybrid LES-RANS wall-stress modeling technique and a new fictitious-domain method for simulating turbulent flow with highly concentrated dispersed particles.Concerning measurement technique, we have developed Stereo PIV (Particle Image Velocimetry) as applied to an open water-channel. First, we pointed out some simple but new aspects of camera calibration. Next, we proposed a new image-processing Technique to directly measure the rate of shear at a wall, both as seen by a single camera, and as reconstructed in 3D from two camera views. This "PIV/Interface Gradiometry" technique was successfully applied to experimental images from a sinusoidal wall. Such basic contributions will facilitate application of (stereo) PIV to regions near possibly complex boundaries.To allow numerical simulation of solid-liquid two-phase flow near a sediment bed, we extended Kajishima's fictitious-domain technique to handle cases of high particle concentration. Tests on "closed" and "open" rotating drums, partially filled with glass beads, gave good agreements on bed angles and other important parameters. Following these tests, we considered a biperiodic "minimal" turbulent channel containing 1500 spherical beads. Parameters were adjusted to yield particle Reynolds number around 15, and nondimensional shear stress (Shields parameter) in the range 0.06 1.1. Over this range, results for sediment flux agreed to within 20% with the prediction of the Meyer-Peter Mueller equation.To contribute to the unresolved theoretical issues related to LES over a boundary of complex shape, the PI has also derived an equation for the pressure drag on a "patch" of wall in terms of the advection of vorticity nearby.