Experimental analysis of friction drag above moving surfaces

本课题组的目标是分析产生湍流摩擦阻力的机理，并开发一种能够利用横向表面波控制湍流摩擦阻力的现代模型预测闭环控制系统。在第一个供资期间，对稳定流入条件下的湍流边界层的调查是主要问题。在第二个资助期，重点将放在以下问题上：非定常和更接近实际的流入条件对减阻机制的影响有多大，以及如何利用横向横向表面波补偿这些时间扰动。子项目1的目标是确定周期性非定常流入条件和正压力梯度对有和没有横向横向表面波的光滑和结构化平板的湍流边界层的影响。热线风速仪、粒子图像测速仪、壁面剪切力和压力测量将被用来确定在这些边界条件下导致湍流摩擦的重要机制，并得出可用于开发即使在非稳定流入条件下也能够减少阻力的模型预测闭环系统的控制变量。

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.