Turbulent wake measurements with a laser velocimeter

An investigation has been conducted in the Langley V/STOL tunnel with a laser velocimeter to demonstrate the capabilities of this technique through measurements of airflow velocities in the wake region of a NACA 0012 wing in stall and cruise angles of attack (19.4 deg and 4.75 deg). A direction-sensitive, two-component, fringe-type laser velocimeter with a focal length of 3.86 m to reach center span was used with high-speed burst counter and minicomputer data acquisition and processing. The size of the seeding particles was measured and the velocity lag error determined along with errors due to the instrumentation. The measured velocities were found to have a bias uncertainty of -1.33 percent to 0.91 percent and a random uncertainty of + or - 0.47 percent.