圆形湍流喷射速度梯度张量不变量的层析PIV研究
Turbulence of the round jet has been assessed using invariantsof the velocity gradient tensor. Experimental data, obtainedusing Tomographic Particle Image Velocimetry (Tomo-PIV),using four PCO-4000 cameras with 11 megapixel resolution,is presented for a seeded free air jet, operating in the turbulentregime and the Re number based on the diameter of the nozzleis 10000. Using the acquired 3-D velocity fields, the localstatistical and geometrical structure of three-dimensionalturbulent flow can be described by properties of the velocitygradient tensor. The invariants of the velocity gradient (R andQ), rate-of-strain ( Rs andQs ), and rate-of-rotation (Qw )tensors are analyzed across the turbulent expanding regions atdifferent distances from the nozzle outlet. More specifically,the JPDF of invariants is computed, which allows a detailedstatistical characterization of the dynamics, geometry andtopology of the flow during the entrainment process. It shouldbe noted that the results obtained are indicative of thepreliminary work in this area.