Heat Transfer in a Coupled Impingement-Effusion Cooling System

Abstract

Modern research on gas turbine cooling continues to focus on the optimization of different cooling designs, and better understanding of the underlying flow physics so that cooling schemes can be coupled together. The current study focuses on one particular coupled cooling design: an impingement-effusion cooling system, which combines impingement cooling on the backside of the cooled component and full coverage effusion cooling on the exposed surface. The goal of this study is to explore a wide range of geometrical parameters outside the ranges normally reported in the available literature. Particular attention is given to the total coolant spent per unit surface area cooled. Through determination of impingement heat transfer, film cooling effectiveness, and film cooling heat transfer on the target wall, a simplified heat transfer model of the cooled component is developed to show the relative impact of each parameter on the overall cooling effectiveness. The use of Temperature Sensitive Paint (TSP) for data acquisition allows for high resolution local heat transfer and effectiveness results. Impingement arrays with local extraction of coolant via effusion are able to produce higher overall heat transfer, as no significant cross flow is present to deflect the impinging jets. Low jet-to-target-plate spacing produces the highest yet most non-uniform heat transfer distribution; at high spacing the heat transfer rate is much less sensitive to impingement height. Arrays with high hole-to-hole spacing and high jet Reynold’s number are more effective (per mass of coolant used) than tightly spaced holes at low jet Reynold’s number. On the effusion side, staggered hole arrangements provide significantly higher film cooling effectiveness than their in-line counterparts as the staggered arrangement minimizes jet interactions and promotes a more even lateral distribution of coolant.

Secondary flows and extra heat transfer enhancement of ribbed surfaces with jet impingement

“…[1][2][3][4][5]. To achieve the maximum cooling performance, combinations of different techniques are often applied to the components which experience extremely high thermal loadings, such as those associated with combustor liners and with high-pressure turbine blades and associated apparatus [2,4,6]. The general design philosophy is to promote the turbulent mixing and break the local thermal boundary layer.…”