Combined Effect of Slot Injection, Effusion Array and Dilution Hole on the Cooling Performance of a Real Combustor Liner

Abstract

Due to the higher cooling requirements of novel combustor liners a comprehensive understanding of the phenomena concerning the interaction of hot gases with different coolant flows plays a major role in the definition of a well performing liner. An experimental analysis of a real engine cooling scheme was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. Test section consists of a rectangular cross-section duct and a flat perforated plate with 272 holes arranged in 29 staggered rows (d = 1.65 mm, Sx/d = 7.6, Sy/d = 6, L/d = 5.5, α = 30 deg); a dilution hole (D = 18.75 mm) is located at the 14th row. Both effusion and dilution holes are fed by a channel replicating combustor annulus, that allows to control cold gas side cross-flow parameters. Upstream the first effusion row, a 6.0 mm high slot ensure the protection of the very first region of the liner. Final aim was the measurement of adiabatic effectiveness of the cooling scheme by means of a steady-state Thermochromic Liquid Crystals (TLC) technique, considering the combined effects of slot, effusion and dilution holes. Experiments were carried out imposing three different effusion velocity ratios typical of modern engine working conditions (VReff = 3, 5, 7) and keeping constant slot flow parameters (VRsl = 1.1). CFD RANS calculations were also performed with the aim of better understanding interactions between coolant exiting from the slot and injected by effusion cooling rows. Numerical analysis revealed a large dependency on effusion velocity ratio. An in-house one-dimensional fluid network solver was finally used to compare experimental and numerical results with the ones predicted by correlations and then quantify the possibility of giving predictions. Both CFD and experimental results reveal that slot protection is reduced in the first rows by coolant injected with such high velocity ratios; nevertheless effusion, though in penetration regime, guarantees a significant effectiveness level in the more downstream region. Dilution hole alters the effectiveness growth rate, moreover leading to local protection lowering just after its injection.

Impact of Swirl Flow on the Cooling Performance of an Effusion Cooled Combustor Liner

“…Ceccherini et al [12] conducted studies on the combined effect of a slot injection, comparable to a starter film, effusion array and dilution hole on the cooling performance of a combustor liner. An increasing blowing ratio leads to a decrease in cooling effectiveness due to penetration of cooling air into the main flow.…”

Investigation on the Effect of a Realistic Flow Field on the Adiabatic Effectiveness of an Effusion-Cooled Combustor

“…An interesting attempt to characterize the effects of the swirled flow on combustor heat transfer is conducted by Patil et al [11] which, studying an air spray nozzle with a swirl number of 0.7, pointed out how increasing Reynolds number does not change the position of the peak in heat flux due to the impingement of the swirl flow on the liner, whereas the intensity of the peak is reduced. However, as already mentioned, most studies devoted to effusion cooling deal with flat plates which have been quite exten sively studied both singularly and with additional cooling features such as impingement jets [12,13], slot cooling [14], and dilution holes [15,16]. Focusing on effusion systems only, Behrendt et al [4] showed that shallow angles promote cooling effectiveness due to reduced jet penetration and increased heat removal within the perforations.…”

Density Ratio Effects on the Cooling Performances of a Combustor Liner Cooled by a Combined Slot/Effusion System

“…In the following rows the effectiveness slightly decreases due to the wake of the dilution jet, and finally reaches an asymptotic value at the end of the plate. The presence of the slot coolant strongly enhances the adiabatic effectiveness: according to Andreini et al [9], after the first three rows, where the η aw remains nearly constant, there is a lower effectiveness area due to the interaction of the slot coolant and the effusion jets; after the dilution hole, η aw reaches an asymptotic value. Finally Figure 9 shows the averaged adiabatic effectiveness results for the whole test matrix, plotted versus BR e f f and V R e f f .…”

“…T aw was evaluated through a post-processing procedure which takes into account the thermal fluxes across the plate due to conduction and due to the coolant inside the annulus and the holes. This procedure is based on a 1D approach and considers the following equation: (9) where T w is the wall temperature measured with TLC. Heat flux across the plate (q) is evaluated through TLC wall temperature, coolant temperature and using the Colburn correlation Nu = 0.023Re 0.8 Pr 1/3 to estimate heat transfer coefficients inside the holes and on the annulus side of the plate; Reynolds and Nusselt numbers were evaluated with the hole diameter and with the annulus cross section hydraulic diameter respectively.…”

“…As reported by Kelly and Bogard [8], increases in heat transfer coefficient due to high blowing ratios could potentially be replaced by an increase in heat transfer coefficient due to high mainstream turbulence. More recently Facchini et al [9,10] measured the overall effectiveness and the heat transfer coefficient at variable blowing ratios on a real engine cooling scheme to evaluate the combined effects of slot, effusion and a large dilution hole; they found that an increase in BR leads to lower values of effectiveness. On the other hand, they found that high BR values enhance the heat transfer phenomena.…”