A new multicolour laser two focus velocimeter for 3-dimensional flow analysis

The authors give an overview of the state of the art of laser-two-focus (L2F) velocimetry. New developments of laser velocimetry, with particular emphasis on turbomachinery applications, are also discussed. Two new L2F concepts based on optical fibers for two-dimensional and three-dimensional velocity component measurements are described. A multicolor two-dimensional system with selectable beam separation is presented which permits a considerable measuring-time reduction, particularly in flows of high turbulence intensities. A novel three-dimensional L2F method is introduced which is based on an axial displacement between start and stop beam centers. The effect of the main geometrical parameters on the system´s sensitivity has been studied theoretically using two methods of modeling the measuring procedure. The theoretical results are discussed and compared with experimental data.