Abstract
Forced convection heat transfer is a significant factor for the thermal control of a stratospheric airship. However, most of researches were conducted without considering the influence of flight state causing serious errors. In order to accurately predict the forced convection heat transfer of the stratospheric airship at an angle of attack, firstly, an empirical correlation of Nusselt number (Nu) as function of Reynolds number (Re) andlength to diameter ratio (e) is developedunder horizontal state based on a validated computational fluid dynamic (CFD) method. Then, a correction factor K, considering its angle of attack (α), is proposed to modify this correlation. The results show that: (1) Nusselt number increases with the increase of Reynolds number, decreases as the length to diameter ratio changes from 2 ~ 6, and increases as the angle of attack changes from 0° ~ 20°. (2) At higher Reynolds number, the calculated results are 30 percent higher than those of previous studies with α = 20°. (3) Compared with α and e, the effect of Re on correction factor K can be ignored, and K is a strong equation of α and e. The efficiency of heat transfer is increased by 6 percent with α = 20°. The findings of this paper provide a technical reference for the thermal control of a stratospheric airship.
Highlights
A stratospheric airship is a type of aircraft that takes off by buoyancy
No specific correlation is available on the external forced convection heat transfer of an ellipsoidal airship flying with a certain angle of attack, the literature has pointed out that the efficiency of heat transfer is increased by 7 percent considering the angle of attack [24]
Existing studies have shown that the main factors affecting forced convection heat transfer around an ellipsoidal airship are the length to diameter ratio and the Reynolds number under a horizontal state [20,28,32,33,34]
Summary
A stratospheric airship is a type of aircraft that takes off by buoyancy. Thermal performance is one of the most important factors affecting the flight state of a stratospheric airship. The stratospheric airship is filled with a large amount of gas, and it experiences a rough external environment during flight, as the change in temperature affects the buoyancy to a large extent [23]. Many research activities have been held on the forced convection heat transfer of a stratospheric airship. In their researches, Kreith and Kreider [11] established a simple numerical model to simulate the average temperature of balloon envelope and lifting gas
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