Revisiting Compressibility Effects in Free Shear Layers Using Advanced Optical Diagnostics

项目简介：CTS-0306266 PRINCIPAL研究员：Mohammad SAMIMYINSTUTION：俄亥俄州立大学使用先进的光学诊断技术重新研究自由剪切层中的可压缩效应可压缩喷嘴在大量工程应用中被使用，尺寸从乘客尺寸的汽车喷油器的一毫米到商用飞机喷气发动机的一米不等，并且几乎总是高雷诺数和湍流。在该团队最近进行的一项工作中，一种新型的MHz速率平面成像系统被用来生成超音速轴对称喷流中大规模结构的实时电影。一个关键的结果是，对于相对较高的可压缩性水平(对流马赫数为0.87)，对流速度呈双峰分布，结构比理论预测的快或慢约33%。这种偏离理论的现象以前已经在平面剪切层中发现过，但从来没有观察到在同一流动中同时存在快模和慢模的偏离。一项全面的研究将系统地探索流动几何、流动可视化方法和可压缩程度等变量矩阵对湍流结构的动力学及其测量的对流速度的影响。这项工作将通过研究生和本科生的参与，将开发的测量技术纳入研究生课程，并通过保持活跃的网站以及学生和个人参与国家和国际会议，迅速传播主要调查结果，从而促进“发现和理解”。

ABSTRACTPROPOSAL NO.: CTS-0306266PRINCIPAL INVESTIGATORS: MOHAMMAD SAMIMYINSTITUTION: OHIO STATE UNIVERSITY REVISITING COMPRESSIBILITY EFFECTS IN FREE SHEAR LAYERS USING ADVANCED OPTICAL DIAGNOSTICSCompressible jets are utilized in a myriad of engineering applications, vary in size from one millimeter in passenger size automobile fuel injectors to one meter in commercial airplane jet engines, and are almost always high Reynolds number and turbulent. In a recent work conducted by this team, a novel MHz rate planar imaging system was used to generate real-time movies of large-scale structures within supersonic axisymmetric jets. A key result was that for relatively high compressibility level (convective Mach number of 0.87), the convective velocity exhibited a bimodal distribution where structures were either approximately 33% faster or slower than theory predicted. Such deviation from theory has been found previously in planar shear layers, but has never been observed to deviate with both a fast and a slow mode in the same flow. A comprehensive study will systematically explore the effects of a matrix of variables such as flow geometry, flow visualization method, and compressibility level, on the dynamics of turbulence structures and their measured convective velocity. The work will advance "discovery and understanding" by involvement of graduate and undergraduate students, incorporation of the measurement techniques developed into the graduate curriculum, and rapidly disseminating the principal findings by maintaining an active web site and by participation of students and PIs in national and international meetings.