Angular Bias Errors in Three-Component Laser Velocimeter Measurements

Abstract

For three-component laser velocimeter systems, the change in projected area of the coincident measurement volume for different flow directions will introduce an “angular” bias in naturally sampled data. In this study, the effect of turbulence level and orientation of the measurement volumes on angular bias errors was examined. The operation of a typical three-component laser velocimeter was simulated using a Monte Carlo technique. Results for the specific configuration examined show that for turbulence levels less than 10 percent no significant bias errors in the mean velocities will occur and errors in the root-mean-square (r.m.s.) velocities will be less than 3 percent for all orientations. For turbulence levels less than 30 percent, component mean velocity bias errors less than 5 percent of the mean velocity vector magnitude can be attained with proper orientation of the measurement volume; however, the r.m.s. velocities may be in error as much as 10 percent. For turbulence levels above 50 percent, there is no orientation which will yield accurate estimates of all three mean velocities; component mean velocity errors as large as 15 percent of the mean velocity vector magnitude may be encountered.