Design features and efficiency of compact air-to-air heat exchangers installed in the turbofan engine's turbine cooling system

Аuthors

Nesterenko V. G.^*, Revanth R. A.^**

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: valerynesterenk@yandex.ru
**e-mail: revman16388@gmail.com

Abstract

The article presents the designs of the basic air-to-air heat exchanger (HE) installed in the turbofan engine bypass section and its modifications based on the computational studies results performed by the authors with ANSYS CFX software. This set of studies includes studies of HE blocks consisting of individual small-sized cylindrical or oval tubes, equal in area to cylindrical tubes, having a smooth or unsmooth inner surface, with circular projections being micro-intensifiers of heat exchange.

The purpose of the study consists in determining configuration and geometrical parameters of the HE tubes that provide a higher temperature drop of cooled air withdrawn from the high-pressure compressor in the turbofan engine, such as the AL-31f and RD 33, as well as lower pressure losses in its bypass section.

The second task was to obtain the dependences of ∆Т = f (d, l) and σ = ∆р/p for various configurations of tubes and tube bundles, with the cross-flow of cooling air.

All computations were performed with the ANSYS CFX software, which ensures the comparability of the obtained computational results. From the viewpoint of possible increase in the temperature drop of cooling air and minimum pressure losses in the bypass section of the turbofan engine, the best results were obtained from a HE with oval tubes with diagonal sizes of 6.3*4.0 mm and micro heat transfer intensifiers with protrusions on the smooth inner surface of the tube with a height of 0.30 mm, installed at intervals of 5.0 mm. These tubes are recommended for application in the HE of the turbofan engine.

The final part of the work presents a new constructive scheme of tubular HE. Its tube diameter was increased to 6.0 mm, compared to the previous HE with the tubes of d_o = 5.0 mm diameter. Here, in one block, one tube cools the air incoming from the intermediate stage of the high-pressure compressor, which is then employed to cool the low-pressure turbine. In the other two tubes of this HE, which diameter was also increased to d_o = 6.0 mm, the air drawn from the high-pressure compressor outlet is cooled and supplied to cool the high-pressure turbine rotor. This design allows reduce the mass characteristics of the HE, employed in the engines consisting of two different heat exchangers, and reduce the pressure loss in the bypass section of the turbofan engine as well.

Keywords:

air-to-air heat exchanger, heat transfer coefficient, air cooling system efficiency

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