Laser velocimeter measurements and analysis in turbulent flows with combustion. Part 3: A correction lens for laser Doppler measurements in a cylindrical tube

A lens was designed using analytical ray tracing techniques to correct aberrations caused by a cylindrical tube wall when measurements are made off the plane of symmetry with a Laser Doppler Velocimeter. The single element correction lens was found to work well and good results were obtained out to a normalized tube radius of r/R = 0.83. LDV measurements were made in three axisymmetric flow geometries: a turbulent flow in a straight pipe, a sudden expansion with diameter ratio 1.90:1, and a second sudden explosion with diameter ratio 2.70:1. Mean velocity and turbulence intensity were measured as well as Reynolds stress and turbulence kinetic energy. Numerical predictions of the flow field using the k-epsilon turbulence model were compared to the experimental measurements in the 1:90:1 sudden expansion. In the 2.70:1 sudden expansion, the presence of a secondary recirculation zone in the corner of the step was confirmed and velocity measurements were made in this region.