Numerical Predictions of Enhanced Impingement Jet Cooling with Ribs and Pins in Co-Flow and Cross-Flow Configurations

Abstract

Numerical calculations relevant to gas turbine internal wall heat transfer cooling were conducted using conjugate heat transfer (CHT) computational Fluid Dynamics (CFD) commercial codes. The CHT CFD predictions were carried out for impingement heat transfer with different types of obstacle walls (fins) on the target surfaces. A 10 × 10 row of impingement air jet holes (or hole density n of 4306 m-2) was used, which gives ten rows of holes in the cross-flow direction and only one heat transfer enhancement obstacle per impingement jet was investigated. Previously, four different shaped obstacles were investigated experimentally and were used to validate the present predictions. The obstacle walls, which were equally spaced on the centreline between each impingement jet are of the co-flow and cross-flow configurations. The impingement jet pitch X to diameter D, X/D and gap Z to diameter, Z/D ratios were kept constant at 4.66 and 3.06 for X, Z and D of 15.24, 10.00 and 3.27 mm, respectively. The obstacles investigated were ribs and rectangular pin-fins shapes, using two obstacles height H to diameter, H/D ratio of 1.38 and 2.45. Computations were carried out for three different mass flux G of 1.08, 1.48 and 1.94 kg/sm2. Relative pressure loss ∆P/P and surface average heat transfer coefficient (HTC) h predictions for the range of G, showed good agreement with the experimental results. The prediction also reveals that obstacles not only increases the turbulent flows, but also takes away most of the cooling heat transfer that produces the regions with highest thermal gradients. It also reduces the impingement gap downstream cross-flow.