Detailed Heat Transfer Distributions of Narrow Impingement Channels for Cast-In Turbine Airfoils

Abstract

The current capabilities of the foundry industry allow the production of integrally cast turbine airfoils. Impingement cooling effectiveness can be then further increased due to the manufacturing feasibility of narrow impingement cavities in a double-wall configuration. This study examines experimentally, using the transient liquid crystal technique, the cooling performance of narrow cavities consisting of a single row of five impingement holes. Heat transfer coefficient distributions are obtained for all channel interior surfaces over a range of engine realistic Reynolds numbers varying between 10,900 and 85,900. Effects of streamwise jet-to-jet spacing (X/D), channel width (Y/D), jet-to-target plate distance (Z/D), and jet offset position (Δy∕D) from the channel centerline are investigated composing a test matrix of 22 different geometries. Additionally, the target plate and sidewalls heat transfer rates are successfully correlated within the experimental uncertainties providing an empirical heat transfer model for narrow impingement channels. The results indicate similarities with multijet impingement configurations; however, the achievable heat transfer level is about 20% lower compared to periodic multijet impingement correlations found in open literature.

Narrow impingement channels: recent advancements and future directions

“…This is due to the interaction with the lateral wall and the attempt of the crossflow to overcome the downstream jet(s) that results in higher local velocities. It should also be noted that similar effects of Y /D and Z/D variation were also observed for X/D=8 (Terzis, 2014). Figure 8(b) shows the complete area-averaged N u D of the target plate and the sidewalls as a function of the channel cross-section (Y /D×Z/D) for various Reynolds numbers.…”

“…Figure 3: (a) Crossflow development and (b) local jet massflow distributions for various channel geometries consisting of five impingement holes, according to Florschuetz 1D model (Florschuetz et al, 1981). Images are taken from Terzis (2014). Figure 4: Velocity vectors along the jet centerline and heat transfer coefficients on the plate for Re D = 27,500.…”

“…The most critical surface for a reliable thermal design of a narrow impingement channel is obviously the target plate since it is located closer to the external hot flow path, and hence, experiences the highest thermal loads. For this reason, although very nice comparisons for all channel interior walls have been obtained in the literature (Uysal et al, 2006;Llucià et al, 2015;Terzis et al, 2015Terzis et al, , 2014a, only the heat transfer characteristics of the target plate will be presented in detail. Figure 6 shows the local Nusselt number distributions at the target plate centerline at different Reynolds numbers for two different channel heights.…”

“…Figure 8: Effect of streamwise jet-to-jet spacing (X/D) on narrow impingement channels consisting of five impingement holes (N =5). Images are adopted from Terzis (2014) and Terzis et al (2014a) impingement literature (Chance, 1974;Hollworth & Berry, 1978;Andrews et al, 1987;San & Lai, 2001). However, this is true for upstream channel positions where the influence of the crossflow is small.…”

Basic Aspects of Gas Turbine Heat Transfer

“…For narrow channel impingement, it was recently highlighted in Ref. [28] that in addition to the high heat transfer from the target surface, the heat transfer from the impingement cavity side walls can also be significant. Figure 24 shows that for a narrow channel with in-line impingement holes, the heat transfer from the side walls can be up to 50% of that from the target plate.…”