On Annulus Flow Characteristics and Performance of Dilution Holes in a Gas Turbine Combustor

Experimental investigations on discharge coefficient (Cd) of a row of plunged dilution holes of a reverse-flow gas turbine combustor were carried out using water as the working fluid. Studies were carried in a wide range of inlet Re (0.5 × 104 – 1.65 × 104) on an individual row of dilution holes (Dd = 7 mm; 1/Dd = 0.428; s/Dd = ∞ − 2) as well as in combinations with two rows of skirted cooling holes (Dc = 2 mm; 1/Dc = 0.67) and a row of plain primary holes (Dp = 3 mm; 1/Dp = 1) using a plane annulus model. The model represented narrow outer annulus, a passage between outer casing and liner of a combustor. The downstream end of the annulus was closed, as is the case in all combustors, to establish its impact on the pressure distribution and discharge coefficient of plunged dilution holes. It is observed that presence of the other liner holes (cooling and primary), when operating together, and formation of recirculation zones towards the closed end significantly diminish pressure values at the row of dilution holes and reduce its Cd to a lower range as compared to its performance when operating individually. In this case, static pressure at all the four rows of liner holes increased parabolically up to a magnitude of Re = 1.35 × 104 and decreased thereafter with further increase in the Re. The Cd of the row of dilution holes, when operating alone, remained in the range of 0.95 to 0.81 for s/Dd = 2. For a single hole Cd varied from 0.96–98, which compares well with the data present in the literature. These values reduced in the presence of first cooling holes (by ≈ 19–23%) and primary holes (by ≈ 16–18%), while with second row of cooling holes no significant change was observed. Similarly, in combination with a pair of other rows of holes also Cd values were affected, while with all the four rows of the liner holes operating together reduced the range of Cd values to ≈ 0.88–0.85 (K = 25–27).