Prediction Of Aircraft Surface Temperatures Based On The Onboard And Outboard Coupling

Commercial airplanes cruise at an altitude of 10,000 meters from the sea level, where the outdoor is at approximately-50 degrees Celsius but inside cabin it is still maintained at around 25 degrees Celsius. To ensure cabin comfort and also for evaluating aircraft wall insulation performance, it is necessary to accurately predict aircraft skin surface temperatures. The factors influencing aircraft surface temperatures can be generally divided into two categories, namely the outboard factors and the onboard factors. The outboard factors are cruising altitude, cruising speed, the solar, sky and ground radiation and heat convection between air and aircraft skin. The onboard factors are heat convection between air and inner surface of the cabin and the interior spatial radiation. However, most of the current practices omit coupling of the onboard and outboard environments and assume uniform wall surface temperature for simplicity when studying the internal cabin environment; or even with a simple coupling but including few outboard factors.This investigation establishes a computational fluid dynamics (CFD) model to predict aircraft surface temperatures with the solution domain covering the metallic shell, insulation, deck and the interior aircraft cabin. The outboard factors, such as the solar, ground and sky radiation, heat convection between air and the outer aircraft shell, and the onboard factors including heat convection between air and inner cabin surface and radiation of the interior cabin, are coupled for consideration. Inside the cabin space, the RNG k-ε turbulence model together with the enhanced wall function was utilized for turbulence modeling, and the S2S radiation model was activated for whole heat transfer modeling. Several case settings with differences in flight altitude, solar radiation considered or not, and cabin air-supply locations were designed for evaluating their impacts on aircraft surface temperatures. For validating the above modeling strategies, a section of a reduced-scale aircraft model was constructed in the laboratory for obtaining experimental data. The reduced-scale aircraft model was placed into an altitude pyschrometric chamber to create similar air conditions that are encountered by a cruising airplane. Several Pt100 resistance probes were used for measuring temperatures across aircraft walls. A digital barometer was adopted for cabin air pressure monitoring.This research finds that the coupled modeling based on the RNG k-ε turbulence model and the S2S radiation model is able to provide temperatures across aircraft walls in consisting with the measurement data. The simulation results reveal that the distribution of aircraft surface temperatures is not uniform, implying the necessity for coupling the onboard and outboard environments together. The outer aircraft shell skin surface temperature is the most sensitive to the flight altitude and then to the solar radiation. The cabin air-supply locations have nearly no impacts to the outer shell skin temperature. The inner aircraft cabin surface temperature is also more sensitive to the flight altitude than to the solar radiation and the cabin air-supply locations.