Surface flow visualization using thermal tufts produced by an encapsulated phase change material

A new thermal tuft method for flow visualization similar to the laser thermal tuft method is described. The earlier laser thermal tuft method involved heating a spot on a surface with a laser, producing a teardrop temperature distribution on a surface coated with thermochromic liquid crystals. In the present study, thermal tufts are produced by embedding small thermal masses in a low thermal conductivity substrate. When a model is exposed to wind tunnel flow, the embedded thermal masses remain (nearly) isothermal while the thermal tufts appear downstream. The advantage of using embedded thermal masses over previous methods is that no laser or heated base is needed. Multiple tufts can easily be achieved. By using an encapsulated phase change material the phase change between solid and liquid (ice) produces isothermal spots. Images of the surface temperature distributions associated with these thermal tufts were obtained using both liquid crystal and infrared thermography. Flow visualization using these thermal tufts is demonstrated for an impinging jet and on a flat surface in a wind tunnel with crossflow.