Turbulence measurements with a Laser Doppler Velocimeter (LDV) using the dual scatter or differential Doppler mode have been made in a subsonic, fully developed channel flow. The measurements were made using only those light scattering particles occurring naturally in air. Results include mean velocity profiles, turbulence intensities, Reynolds stress distributions and a skewness measurement of the velocity distribution function across the channel. Statistical techniques were used to obtain the various turbulence parameters. Guidelines have been established for the amount of data needed to obtain results with a specified accuracy and confidence level. Measurements have also been made to determine the particle-size distribution. An aerodynamic means was used to determine the size distribution, in contrast to the usual optical procedures. (Modified author abstract).

Turbulence measurements with a Laser Doppler Velocimeter (LDV) using the dual scatter or differential Doppler mode have been made in a subsonic, fully developed channel flow. The measurements were made using only those light scattering particles occurring naturally in air. Results include mean velocity profiles, turbulence intensities, Reynolds stress distributions and a skewness measurement of the velocity distribution function across the channel. Statistical techniques were used to obtain the various turbulence parameters. Guidelines have been established for the amount of data needed to obtain results with a specified accuracy and confidence level. Measurements have also been made to determine the particle-size distribution. An aerodynamic means was used to determine the size distribution, in contrast to the usual optical procedures. (Modified author abstract).

A numerical model for evaluating seed requirements for accurate turbulence measurements with the LV has been developed. A Monte Carlo turbulence model was developed which included an elementary description of the internal structure of an eddy. The model was applied to two simple turbulent flows, grid generated turbulence and a subsonic axisymmetric jet, to evaluate particle response and to establish particle size requirements for accurate LV measurements in these flows. Large monodisperse particles were found to cause the turbulence quantities to be underestimated, leading to a requirement for very small particles for meaningful turbulence measurements with the L.V. Rule of thumb criteria for particle size selection are developed. Keywords: Velocity data; Computer code; Turbulence measurements; laser velocimeter.