DIMPLE'S VORTEX ANALYSIS BASED ON EIGENVALUE OF VELOCITY GRADIENT TENSOR

As a new internal cooling technology for high performance turbine blades, dimple which belongs to vortex generator has the advantage of small flow resistance and high comprehensive heat transfer performance. The qualitative and quantitative analysis of the vortex is an important basis for the optimization design of the dimple, due to the fact that the stronger vortex cause greater heat transfer enhancement. Aiming at the problem that the vortex strength can not be quantitatively analyzed in different dimple models under the variation of the vortex structure, separation mode and background pressure, this paper proposes a method by using vortex core velocity and vortex core velocity gradient tensor eigenvalue. Using the velocity vector and velocity gradient tensor eigenvalue expressed by the local coordinate system at the vortex core, the axial velocity, radial velocity, swirling strength, axial acceleration and radial acceleration of the vortex core are obtained, and quantitative analysis method of vortex strength as a combination of maximum axial velocity, maximum axial acceleration, and maximum swirling strength is concluded. The vortex structure induced by different depth to print diameter ratio dimple is analyzed by this method. As the increase of the depth to print diameter ratio, the maximum axial velocity, maximum axial acceleration and maximum swirling strength all increased obviously, so the vortex strength increases. The research shows that this method has the advantages of simple data processing, wide application range, not limited by separation mode, not limited by background pressure, and the extracted data has clear physical meaning, thus this method is suitable for all kinds of vortex quantitative analysis.