DIRECT NUMERICAL-SIMULATION OF TURBULENT-FLOW OVER A MODELED RIBLET COVERED SURFACE
DIRECT NUMERICAL-SIMULATION OF TURBULENT-FLOW OVER A MODELED RIBLET COVERED SURFACE
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DOI：
10.1017/s0022112095004125
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发表时间：
1995-11-10
影响因子：
3.7
通讯作者：
SIROVICH, L
中科院分区：
文献类型：
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作者：
GOLDSTEIN, D;HANDLER, R;SIROVICH, L
浸没边界技术被用来模拟一个沟槽覆盖表面上的一个壁的通道边界充分发展的湍流。的猜想，有益的减阻效果的沟槽是横向流动速度波动的阻尼的结果，然后检查。其他人也讨论过这种可能性，但未经证实。阻尼效果是明确建模通过应用横流阻尼力场在细长的流向区域的高度和间距对应的脊波峰。在沟槽和阻尼表面上方的湍流剖面中观察到相同的趋势，从而支持横流阻尼作为一种有益的机制。结果表明，沟槽对平均流场参数（平均速度分布、速度脉动、雷诺切应力和低速条纹间距）的影响很小。沟槽引起约4%的相对较小的阻力减小，该数字与实验和其他计算大致一致。模拟还提出了一种机制，所观察到的位移的湍流量远离wall.The浸没边界技术用于建模的riblets包括创建一个外部施加的空间局部体积力，反对的流速，并创建一个riblet样的表面。对于非定常粘性流，力的计算是用反馈方案完成的，其中速度用于迭代地确定期望值。特别地，表面体积力由关系f（x（s），t）= α积分（0）（t）U（x（s），t'）dt' + β U（x（s），t）确定，对于表面点x（s），速度U，时间t和负常数α和β。所有的模拟都是在一个单一的计算域没有任何映射的网格与频谱代码。浸没边界和光谱技术的组合可以潜在地用于解决具有复杂几何形状和流动物理的其他问题。
An immersed boundary technique is used to model a riblet covered surface on one wall of a channel bounding fully developed turbulent flow. The conjecture that the beneficial drag reduction effect of riblets is a result of the damping of cross-flow velocity fluctuations is then examined. This possibility has been discussed by others but is unverified. The damping effect is explicitly modelled by applying a crossflow damping force field in elongated streamwise zones with a height and spacing corresponding to the riblet crests. The same trends are observed in the turbulence profiles above both riblet and damped surfaces, thus supporting cross-flow damping as a beneficial mechanism. It is found in the examples presented that the effect of the riblets on the mean flow field quantities (mean velocity profile, velocity fluctuations, Reynolds shear stress, and low-speed streak spacing) is small. The riblets cause a relatively small drag reduction of about 4%, a figure that is in rough agreement with experiments and other computations. The simulations also suggest a mechanism for the observed displacement of the turbulence quantities away from the wall.The immersed boundary technique used to model the riblets consists of creating an externally imposed spatially localized body force which opposes the flow velocity and creates a riblet-like surface. For unsteady viscous flow the calculation of the force is done with a feedback scheme in which the velocity is used to iteratively determine the desired value. In particular, the surface body force is determined by the relation f(x(s),t) = alpha integral(0)(t)U(x(s),t')dt' + beta U(x(s),t) for surface points x(s), velocity U, time t and negative constants alpha and beta. All simulations are done with a spectral code in a single computational domain without any mapping of the mesh. The combination of the immersed boundary and spectral techniques can potentially be used to solve other problems having complex geometry and flow physics.