Surface flow visualization using the thermal wakes of small heated spots

 This note describes a surface flow visualization technique which uses the thermal wakes of an array of small heated spots to infer the local flow direction. The thermal wake is made visible using wide band thermochromic liquid crystals. The technique is illustrated using the endwall flow under a horseshoe vortex at the base of a right circular cylinder in a turbulent boundary layer. Comparisons to results generated using the oil of wintergreen technique were in good agreement. In addition to surface flow direction, the technique has the potential to be used to measure the heat transfer coefficient at each spot. Data are presented in terms of photographs of the actual visualization surface. The techniques is suitable for low speed flows.