Heat transfer and pressure drop for a representative part of a turbine active cooling system were numerically investigated by means of an in-house code. This code has been developed in the framework of an internal research program and has been validated by experiments and CFD. The analysed system represents the classical open bird cage arrangement that consists of an air supply pipe with a control valve and the present system with a collector box and pipes, which distribute cooling air in circumferential direction of the casing. The cooling air leaves the ACC system through small holes at the bottom of the tubes. These tubes extend at about 180° around the casing and may involve a huge number of impinging holes; as a consequence, the impinging jets mass flow rate may vary considerably along the feeding manifold with a direct impact on the achievable heat transfer levels. This study focuses on the performance, in terms of heat transfer coefficient and pressure drop, of several impinging tube geometries. As a result of this analysis, several design solutions have been compared and discussed. 1. Introduction Impingement with high velocity jets has become an established method for surface cooling or heating in a wide variety of processes and thermal control applications. The use of impingement jets for the cooling of modern aeroengine components is widespread, especially within the hot stationary parts. Since the cooling performance of impinging jets is very high, this method provides an efficient way to manage a component heat load when a sufficient pressure head and geometrical characteristics are available for its implementation. The cooling jets are usually arranged as arrays [1]. Aero-engine casing temperature control is a very effective way to reduce aerodynamic losses and specific fuel consumption due to blade tip clearance. Because of the significant variations of centrifugal and thermal loads which occur at different engine operating conditions, the tip clearance can be extremely variable; such dimensional variation may worsen engine performance and reduce the components’ life span [2]. To overcome these issues, the Active thermal Clearance Control (ACC), generally based on impingement cooling, has been successfully introduced in several applications as described in Halila et al. [3], Beck and Fasching [4], and more recently by Justak and Doux [2]. In such systems, impinging jets are directed towards the external turbine casing by means of a series of circumferential feeding pipes with the final aim of keeping the clearance between blade tip and
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