报告题目：Influence of Surface Roughness on the Flat-Plate Boundary Layer Transition under a Low Pressure Turbine Pressure Gradient
报告时间：2021年6月25日（周五） 上午10:00
报告人： Prof. Seung Jin SONG（韩国首尔大学）
报告地点：明故宫校区A8-605会议室
主办单位：多功能轻量化材料与结构研究中心、航空学院
报告内容简介：
This talk will cover an experimental study which has been conducted to investigate the effects of surface roughness on the profile loss of a flat-plate with a contoured wall. The time-resolved streamwise and wall-normal velocity fields for three different surface roughness values of Ra/C·10^5=0.065,4.417 and 7.428 have been measured with a 2D hot-wire probe. At the take-off condition (Rec=5.2·10^5), attached flow transition occurs, and increased surface roughness increases the loss. For all of the surfaces, momentum deficitsin the laminar to early transition region (y≈0.05) are similar. For the intermediate transition (y≈0.5), increased roughness reduces the Reynolds stress and accelerates the breakdown of large-scaleturbulent spots into small-scale turbulent eddies. Therefore, turbulent energy and momentum deficit are decreased for rough surfaces. For the late transition (y>0.9), transitional boundary layers become similar to turbulent boundary layers, and increased surface roughness increases turbulent mixing, boundary layer thickness, and, hence, the momentum deficit. On the other hand, at the cruise condition(Rec=1.2·10^5), separated flow transition occurs and increased surface roughness decreases loss. Since the portion of turbulent flow is relatively small, the overall profile loss is mainly determined by the momentum deficit generated during transition. Increased roughness decreases the maximum height and length of the separation bubble but does not affect the separation bubble onset location. The beneficial effects of increased surface roughness on the profile loss appear in the separated shear layer and reattachment. Increased surface roughness increases turbulent mixing in the separated shear layer, reducing the shear layer thickness and momentum deficit. In addition, increased surface roughness reduces the length scale and turbulence intensity of the shed vortices.Consequently, turbulent mixing and momentum deficit during the reattachment of boundary layers are decreased, resulting in a lower profile loss.
报告人简介：
Professor Seung Jin Song received his BS in Mechanical Engineering and Materials Science from Duke University, and SM and ScD in Aeronautics and Astronautics from MIT. He was Assistant Professor of Aerospace Engineering at Inha University in Incheon, Korea, before moving to the Department of Mechanical Engineering at Seoul National University in 1999.
He received Best Paper Awards from the International Gas Turbine Institute(IGTI) of the American Society of Mechanical Engineers (ASME). In 2003, he received the Melville Medal, the highest academic honor bestowed by ASME. He has also received the Best Teacher Award from the College of Engineering at Seoul National University.
He has served as Member of the Board of the Directors (2010-2016) and Chair of lGTI(2015). He has also served as the Associate Editor of ASME Journal of Turbomachinery (2013-2019). He currently serves on the International Advisory Committee of the Gas Turbine Society of Japan (GTSJ).
