Abstract: Aiming at the application of stratospheric aerostats filled with gas helium, the natural convection of a low pressure gas inside a huge ellipsoidal enclosure is simulated numerically. The natural convection is induced by the combined thermal conditions of the airflow and radiative heat transfer outside the wall of the enclosure. Using the user-define feture (UDF), the combined thermal conditions are introduced into the numerical simulation by the Fluent, and the dependence of gas density on its pressure and temperature is considered. Thermal and dynamic characteristics are analyzed, such as the temperature field, the heat transfer coefficient distribution as well as the velocity field, the pressure field and the centroid. A correlation is presented for the local heat transfer coefficient by analyzing the numerical results. The investigation demonstrates that the varying non-uniform thermal conditions of stratospheric surroundings exert significant influences on both the thermal and dynamic characteristics of the natural convection of a low pressure gas inside an enclosure.

Key words: natural convection, ellipsoidal enclosure, low pressure, combined thermal conditions