Natural convection cooling of aircraft wingbox structures during turnaround period

Modern commercial aircraft can experience significant solar loading during turnaround when the aircraft is stationary on the tarmac. With the increased usage of composite materials, a change in the aircraft thermal environment results due to the substantial difference in metal and composite thermal properties. In this paper, an experimental study is undertaken to compare the thermal environment established in a CFRP and aluminium wingbox compartment due to solar loading for levels of 81 W/m2, 396 W/m2, 700 W/m2 and two further cases with a constant wing skin temperature of 100 °C. It was found that conduction through the vertical front and rear spars established a complex but stable flow environment comprising of four counter-rotating circulations which interact strongly with the spar walls, a criterion using scale analysis was also established to determine whether the induced flow would persist. Nusselt number measurements were carried out for each circulation and compared to existing correlations from the literature for differentially heated and top wall heated cavities. The measurements provide aircraft thermal designers with representative values for the heat transfer coefficient which can be used in the thermal modeling of aircraft wing structures.