Heat transfer and friction in trapezoidal channels with X-shaped ribs

Rib turbulators are widely applied in internal cooling channels of gas turbine blades to improve cooling performance. In this study, heat transfer and friction factor were investigated in internal cooling channels with V-shaped, X-shaped, and cutback X-shaped ribs. Infrared thermography was used to measure heat transfer distribution on the ribbed surface, and the Reynolds number ranged from 10 000 to 40 000. Ribs were applied on two opposite walls of the trapezoidal channel, namely the vertical wall and inclined wall. The cross-section of the internal cooling channel was a right-angle trapezoid, and the rib height-to-channel hydraulic diameter ratio (e/Dh) was 0.128. Numerical simulations were conducted using ANSYS-Fluent to capture the complex flow phenomena caused by the ribs, which were used to interpret the experimental data. The results indicated that the flow was accelerated near the short base of the trapezoidal channel and caused higher heat transfer. The regular X-shaped rib produced higher heat transfer as a result of augmented secondary flow, particularly in the midsection and immediately downstream of the rib. However, the X-shaped rib also caused a larger pressure drop. To reduce the frictional losses, cutback X-shaped ribs were proposed by reducing the rib length at either the upstream or downstream portion. The full X-shaped ribs and downstream cutback X-shaped ribs attained higher thermal performance than did traditional V-shaped ribs. The full X-shaped ribs contributed to the highest thermal performance of 1.65, which was approximately 20%–25% higher than that of V-shaped ribs.