Friction velocity vector probes have been designed for two-dimensional fluid flow based on a flush-mounted hot film operated in constant temperature mode. The magnitude of, was obtained with steady-state calibration curves in the reversing (separating) flow tested. The direction is determined from the result of an anti-coincidence correlation program with forward-backward discrimination of the thermal wake. Probe performance is evaluated for flow in an open channel with a submerged block atRe= 11,000 by measuring time-averaged vector values(x) in the longitudinal centerline. The reattachment position was found atx/h= 7.0. From the energy gradient of the channel flow and integration of the friction velocities along the transect theCDvalue of the block with a length/height ratio of 3.57 is found to be 3.1.