Experimental analysis of friction drag above moving surfaces

该研究小组的目标是分析湍流摩擦阻力的机制，并开发一种现代模型预测闭环控制系统，该系统能够使用展向横向表面波控制湍流摩擦阻力。在第一个供资期间，主要问题是在稳定流入条件下对紊流边界层进行研究。在第二个供资期，重点将是在多大程度上不稳定，因此，更实际的来流条件对减阻机制以及如何利用展向横向表面波补偿这些时间扰动具有影响。子项目1的目的是确定周期性非定常来流条件和正压梯度对湍流边界层的影响，具有和不具有展向横向表面波的光滑和结构化平板。热线风速仪，粒子图像测速仪，壁面剪切应力和压力测量将被用来确定重要的机制，负责在这些边界条件下的湍流摩擦，并获得控制变量，可用于开发一个模型预测的闭环控制系统，能够减少阻力，即使在不稳定的流入条件。

It is the objective of this research group to analyze the mechanisms that are responsible for turbulent friction drag and to develop a modern model-predictive closed-loop control system that is able to control turbulent friction drag using spanwise transversal surface waves. The investigation of turbulent boundary layers at steady inflow conditions was the major issue during the first funding period. In the second funding period, the focus will be on the question, to what extent unsteady and, hence, more realistic inflow conditions possess an influence on the drag reduction mechanisms and how these temporal perturbations can be compensated using spanwise transversal surface waves.The objective of subproject 1 is to determine the effect of periodic unsteady inflow conditions and of a positive pressure gradient on the turbulent boundary layer of smooth and structured flat plates with and without spanwise transversal surface waves. Hot-wire anemometry, particle-image velocimetry, wall-shear stress, and pressure measurements will be used to determine the significant mechanisms that are responsible for turbulent friction under these boundary conditions and to derive control variables that can be used to develop a model-predictive closed-loop control system that is able to reduce drag even at unsteady inflow conditions.