An experimental investigation of the performance of extended fin surfaces for the forced convective cooling of a range of engine component geometries in crossflow is reported. The experiments were undertaken to measure the surface heat transfer coefficient distributions of external finning around non-cylindrical geometries for use in aviation gas turbines in which the cooling performance/mass ratio must be maximised. The geometries examined were a box (square with rounded corners), a flute (rectangle with circular ends) and a 30° wedge. These models were sized to have equivalent cross sectional area to allow a direct comparison of performance. Perspex models coated with thermochromic liquid crystal were tested at a range of Reynolds numbers in a heat transfer wind tunnel in which a step change in flow temperature was used to measure the transient thermal behaviour of the fins. This technique enables the full surface mapping of local heat transfer coefficients on the surface of the fins.
These measurements are compared with those for the equivalent smooth geometries and also with empirical calculations from the literature where available. A comparison with previous cylindrical measurements is also made. Knowledge of the distributions of local heat transfer coefficients enables the optimisation of the geometry through strategies such as baffling of the fins. Some examples of these strategies have been implemented and the results are reported.
The finned geometries are seen to outperform the unfinned geometries (by factors greater than 3) though by factors less than simply the increase in area. The enhancement in h results because the increased surface area of the fins more than outweighs the decrease in local h on the fin surface as compared to the smooth geometries.