Extensive Studies on Internal and External Heat Transfer Characteristics of Integrated Impingement Cooling Structures for HP Turbines

Abstract

This paper deals with experimental and computational studies on internal and external heat transfer characteristics of advanced impingement cooling units combined with pin-fin cooling as well as film cooling, which is called integrated impingement cooling structure. This integrated cooling structure can be employed in the not too distant future as a simple model of quasi-transpiration cooling system for ultra high TIT (Turbine Inlet Temperature) aeroengines or gas turbines. The present study is motivated by the study of Nakamata et al. (2005) who carried out a series of studies on the integrated impingement cooling system. They found that several arrangements of impingement holes and film cooling holes mutually staggered with respect to pins yielded better cooling performance than other non-staggered configurations, although there was no evidence-based explanations shown in their study on the flow physics happening in the cooling models. Therefore, two large-scaled acrylic-resin test models with different arrangements of the impingement and film cooling holes around the pins are made in the present study, emulating the specimens used by Nakamata et al., to evaluate internal and external heat transfer coefficients as well as film effectiveness of the test models. This study accordingly aims at clarification of the reason for the clear distinction in cooling efficiency observed by Nakamata et al. between those two different cooling configurations. The measurement technique employed is a transient method using thermochromic liquid crystal to determine not only heat transfer coefficient but also film effectiveness at the same time. Steady RANS simulation is also executed using ANSYS CFX-10 to acquire detailed information on the flow behaviors and heat transfer characteristics inside and outside the cooling systems. The experimental data, along with the numerical information, reveal that the observed difference in cooling efficiency is can be explained mainly by the difference in internal heat transfer coefficient over the target plate, indicating that the pin arrangement around the impingement jet is an important factor in order to attain higher cooling performance of the proposed integrated impingement cooling system.

Numerical Simulation of Integrated Impingements Cooling Structure: Heat Removal at the Impingement and Pin Surfaces

“…Fig. 3 shows good agreement between the present numerical results and the experimental data of Funazaki and Hamidon [5]. x is the axial distance from origin and D is the diameter of the film hole.…”

“…Cooling performance of four newly proposed IIC configurations along with two configurations by Funazaki and Hamidon (2008) have been investigated using k-ε turbulence model via commercial CFD package, Ansys Fluent. The simulations were validated against the experimental data of Funazaki and Hamidon (2008) and good agreement between the numerical results and the experimental data was observed. Pin configuration of STAG1 and STAG3 gave the highest heat transfer coefficient at the target plate and pin surfaces respectively.…”

“…Computational Domain and Boundary Conditions. The computational domain and boundary conditions of the IIC structure in the present study followed that by Funazaki and Hamidon [5] which is shown in Fig. 1 The only different is that, periodic boundary condition replaces symmetrical boundary condition so that the present simulation models the experimental conditions more accurately.…”

“…Six configurations was studied. STAG1 and STAG2 were originally proposed by Funazaki and Hamidon [5]. STAG3, STAG4, STAG5 and STAG6, are added to find out the possibilities of better cooling performance.…”

“…It is suggested that the interaction between the pins and the impingement jet on the target plate could be a prime cause of disparity. Funazaki and Hamidon [5] then carried an extensive study on internal and external heat transfer characteristics of IIC. The aim of the work was to investigate the effect of pin arrangements on internal and external heat transfer characteristics.…”