Reexamination of the self-preservation state in the planar mixing layer with Joint PDF

• Main Authors: Jheng-Jhen Tsai, 蔡政臻
• Other Authors: Keh-Chin Chang
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/20535513687670425858

碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 97 === Traditionally, achievement of the self-preserving state in a planar turbulent mixing layer is justified by the invariant sectional profiles of some turbulent flow quantities. However, this is not a precise approach to justify the achievement of self-preserving state in turbulent mixing layer. It is observed the joint probability function (JPDF) of the fluctuating velocities of streamwise and transverse components exhibits an inclined elliptic shape at the position of η=0 which denotes the transverse position of the half of the values of high-speed and low-speed stream velocities (i.e.y0.5 ). The inclined angle (β) at η=0 (i.e. β︱η=0 ) is mathematically a function of Reynolds stress and two root-mean-squared fluctuating velocities of streamwise and transverse components. The value of β︱η=0 will approach an asymptotic level as the flow state moves into the self-preserving. Thus, the evolution of β︱η=0 , which is a single parameter in the turbulent mixing layer, is suggested to monitor the achievement of self-preserving state. As β︱η=0 reaches its asymptotic value, it indicates the achievement of self-preserving state. In addition, the transition from the shear layer to the two other free stream regions can be monitored through the transverse variation of the roundness of JPDF, which is better than the conventional approach distinguished by y0.95 and y0.05.