Heat transfer from a dimple-imprint downstream of boundary-layer trip-wire

Dimples are widely known to increase heat transfer coefficients in internal passages with a minimal pressure drop. The naphthalene sublimation method was used to measure local heat transfer coefficient variations of single dimple imprint channel with the analogy between heat and mass transfers. The effect of a boundary layer trip-wire with different diameters was compared under different flow conditions (1000 < Re < 5000), which is expected to cover different flow regimes from laminar flow to turbulent flow. With the installation of a trip-wire upstream of the dimple, the flow with the Reynolds number greater than 3000 transitioned to turbulence as shown from the measured Sherwood number ratio (Sh/Sh₀). However, under the laminar flow (Re ~ 1000), the flow was re-laminarized, resulting in a negligible effect of the trip-wire. Without a trip-wire, the heat and mass transfer increase was limited to the downstream of dimple cavity. With installation of a trip-wire, even the upstream of dimple cavity exhibited increased heat and mass transfer variations with enhanced turbulent intensity. As the diameter of a trip-wire increased, the area-averaged Sherwood number ratio (Sh¯¯/Sh₀) under the transitional and turbulent flow conditions (3000 < Re < 5000) increased by 24%. The heat transfer of trip-wire imprint channel can be augmented as much as 38% for the Reynolds number range from 3000 to 5000. Therefore, installing trip-wire is recommended when designing a dimple-cooling passage for gas turbine blades and vanes.