Design and optimization study of discrete inclined ribs enhanced bend tube based on “Diamond” active cooling thermal protection systems of hypersonic aircraft

Abstract

When the hypersonic aircraft cruises, the surface will generate huge aerodynamic heating. Aiming at the thermal protection of hypersonic aircraft, this paper presented a study on the thermal–hydraulic and thermodynamic performance of discrete inclined ribs enhanced bend tube based on the designed “Diamond” channel. Meanwhile, a comprehensive numerical investigation was carried out for different models. The fluid velocity was found to vary in the range of 0.1–3.5 m·s−1, with the corresponding Reynolds number ranging from 3600 to 127000. The inlet temperature of heat transfer fluid was set to 253 K. It was visible that double–symmetrical longitudinal swirl was generated under a single upper and lower arrangement (Model D), which led to the best cooling performance on the inner wall. The performance evaluation criteria (PEC) and efficiency evaluation criterion (EEC) reached 0.99–1.18 and 0.66–1.00, respectively. The effect of four geometrical parameters (height–width ratio(H/d), length–width ratio (L/d), group number of ribs (n), and tilt angle (α)) of which the ranges are 0.5–2.5, 1.0–4.0,6–15 and 0°–90°, separately, was explored. The results showed that the inner wall temperature decreased up to 4.4 K when the Reynolds number was 72000. The Nusselt number and friction factor increased about 9.9 %–28.8 % and 16.5 %–111.5 %. Efficiency evaluation criterion reached 0.43–0.96. It was found that the combination of parameters would significantly affect the distribution of longitudinal swirls under the influence of secondary circulation in the bend tube. Moreover, many pairs of small vortices near the wall could improve active thermal protection performance. After obtaining the fitting function through the artificial neural network (ANN), the genetic algorithm (GA) was applied to obtain the Pareto front. The design variable for the L/d = 3.19, n = 11, and α = 14.3° was selected as the optimal solution by the TOPSIS method. When Reynolds number is 72000, the corresponding Tin and ΔP were 261.86 K and 2471.2 Pa. The performance evaluation criteria and efficiency evaluation criterion reached 1.02 and 1.09, respectively. Furthermore, a design variable for the L/d = 3.0, n = 11, and α = 15° was given for ease of engineering. The present work verified the feasibility of realizing heat transfer enhancement by combining the secondary circulation with longitudinal swirls formed by bend tube and discrete inclined ribs and proposed a new design scheme of active cooling thermal protection systems (ACTPS).