Validation experiment on the transition of three-dimensional boundary layers on wings with spanwise varying flow conditions

过渡段预报对未来运输机层流机翼的发展具有重要意义。目前，用于边界层稳定性分析的工业设计工具使用局部数据，并假定沿展向的流动条件不变。这些假设一般不适用于真实的机翼构型，并且限制了过渡预测的准确性。直到今天，还没有实验数据来量化预期的不准确性。该研究项目的目的是设计和进行具有展宽变化平均流的后掠翼上的转弯验证实验。用红外热像仪测量了整个机翼区域的过渡位置，并用来监测横流涡流及其展向发展。研究了机翼后掠变区可能存在的弥散效应。用热膜阵列测量了频率谱和边界层不稳定模式的放大。在第一个项目阶段，这些测量是在一个中等大小的大学风洞中进行的，雷诺数为275万，采用常规水平的自由流湍流。在第二阶段，过渡研究将特别集中在具有展向变化的横流不稳定性的机翼区域。通过在更大的DNW-NWB风洞中进行这些测量，获得了明显更大的雷诺数和更低的自由流湍流水平。这将为生成的数据库增加价值。

Transition prediction is important for future laminar wing development for transport aircraft. Nowadays industrial design tools for stability analysis of the boundary layer use local data with the assumption of invariant flow conditions in spanwise direction. These assumptions are not generally valid on real wing configurations, and limit the accuracy of transition prediction. Until today there exist no experimental data to quantify the expected inaccuracy. The aim of the research project is to design and to conduct validation experiments on the transition on a swept wing with spanwise varying mean flow. The transition location is measured with infrared thermography over the whole area of the wing and is used to monitor crossflow vortices and their spanwise development. Possible dispersion effects in the area of wing sweep variations are investigated. Frequency spectra and the amplification of boundary layer instability modes are measured with hotfilm arrays.During the first project phase these measurements were performed in a medium size university wind tunnel, at Reynoldsnumbers of 2.75 million and with conventional levels of freestream turbulence. In the second phase the transition investigations will be particularly focussed at wing areas with spanwise varying crossflow instabilities. By performing these measurements in the larger DNW-NWB wind tunnel, significantly larger Reynoldsnumbers and lower freestream turbulence levels are obtained. This will add value to the resulting data base.