A Simplified Thermal Model and Comparison Analysis for a Stratospheric Lighter-Than-Air Vehicle

Abstract

Transient thermal behavior modeling and simulation is a key issue in predicting flight performance of stratospheric lighter-than-air (LTA) vehicles, such as airships or balloons. To reduce computational load of the transient thermal model without significant loss of accuracy, first this paper adopted an analytical model of view factor from the element surfaces to the Earth and constructed a full distributed parameter transient thermal model. Then, the full model was validated by comparing the predictions obtained from the full model with the flight experimental data. The comparison results show that the divergence of the predicted average internal gas temperatures from the flight data is about 0.4%, and the divergence of the predicted envelop temperatures from the flight data is less than 2.4%. Furthermore, considering that the effect of the net radiation heat transfer among the inner surface enclosure on average internal gas temperature is far less than radiation heat transfer of the outer surfaces, the full model was simplified by omitting radiant heat exchange within the inner surface enclosure. The accuracy of the simplified model was investigated by comparing the predictions of average internal gas temperature and skin temperature distribution between the simplified model and full model under various conditions, such as flight time, altitude, and different external skin thermal properties. The comparison results indicate that the simplified model agrees well with the full model. The discrepancies of the predicted average internal gas temperature between the two models are less than 0.3% under most conditions, and the discrepancies of the predicted temperature distribution between the two models are also acceptable when the LTA vehicle, especially with low absorptivity/emissivity ratio coatings, operates at about 20 km altitude.