Summary

Drag caused by separated flow behind the hub of a helicopter has an adverse effect on aerodynamic perfor-mance of the aircraft. To determine the effect of sepa-rated flow on a configuration used extensively for helicopter aerodynamic investigations, an experiment was conducted using a laser velocimeter to measure velocities in the wake of a model helicopter hub operat-ing at Mach-scaled conditions in forward flight. Velocity measurements were taken using a laser velocimeter with components in the vertical and down-stream directions. Measurements were taken at 13 sta-tions downstream from the rotor hub. At each station, measurements were taken in both a horizontal and verti-cal row of locations. These measurements were analyzed for harmonic content based on the rotor period of revolu-tion. After accounting for these periodic velocities, the remaining unsteady velocities were treated as turbulence. Turbulence intensity distributions are presented. Aver-age turbulent intensities ranged from approximately 2 percent of free stream to over 15 percent of free stream at specific locations and azimuths. The maximum aver-age value of turbulence was located near the rear-facing region of the fuselage