Radial and Axial Turbulent Flow Measurements With an LDV in an Axisymmetric Sudden Expansion Air Flow

Radial velocity component measurements in cylindrical tubes have been difficult to make because of optical aberrations introduced by the curved tube wall. This is particularly troublesome in gas flows where refractive index matching techniques cannot be employed. The present investigation utilized a specially designed correction lens system to overcome this problem. As a result it was possible to map the axial and radial velocity behavior in detail for the air flow downstream of a sudden expansion in a cylindrical duct. Quantities measured and derived included mean velocities, turbulence intensities, turbulent kinetic energy and Reynolds stress. The weak secondary recirculation zone existing just below the sudden expansion was clearly identified and mapped. Where possible the measurements were compared with numerical predictions based on a k-ε model.