The turbine blade tip clearances control in large aero-engines is currently performed by means of impinging fan air on the outer case flanges. The aim of the present study is to evaluate both the heat transfer coefficient and the adiabatic thermal effectiveness characteristics of an enginelike ACC system, and in particular, to comprehend the effects of the undercowl flow on the impingement jets. The considered geometry replicates the impingement tubes and the by-pass duct used in active control clearance systems. The tube's internal diameter is D = 12 mm, the cooling hole's diameter is d = 1 mm, and the span-wise pitch is Sy/d=12. In order to simulate the undercowl flow, the impingement arrays are inserted inside a tunnel that replicates the typical shape of a real engine by-pass duct. Tests were conducted varying both the mainstream Reynolds number and the jets Reynolds number in a range typical of real-engine operative conditions (Rej=2000-10000, β=1.05-1.15). Numerical calculations are finally proposed to point out if CFD is able to confidently reproduce the experimental evidences.

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