Effects of thermal conductivity of airframe substrate on the dynamic ice accretion process pertinent to UAS inflight icing phenomena. (March 2019)

• Record Type: Journal Article
• Authors: Li, Linkai; Liu, Yang; Zhang, Zichen; Hu, Hui
• Is Part Of: International journal of heat and mass transfer. Volume 131(2019)
• Page Start: 1184
• Page End: 1195
• Publication Date: 2019-03
• Subjects: UAS inflight icing -- Icing physics -- Dynamic ice accretion process -- Unsteady heat transfer -- Release of the latent heat of fusion due to phase changing; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2018.11.132
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Icing on composite-based UAS airframes is compared with that on metal-based airframes. The effects of thermal conductivity of airframe substrate on the ice accretion were studied. An analytical model was deduced to assess the effects of substrate thermal conductivity. A high-speed imaging system was used to quantify the dynamic ice accretion process. An infrared imaging system is used to map temperature distributions over the airfoil surface. Abstract: An experimental investigation was conducted to quantify the dynamic ice accretion and the unsteady heat transfer process over the ice accreting surfaces of composite-based airframes widely used for light-weight, Unmanned-Aerial-Systems (UAS), in comparison to those over the surfaces of metal-based airframes used by conventional manned aircraft, in order to elucidate the underlying icing physics specifically pertinent to UAS inflight icing phenomena. Two airfoil/wing models with the same airfoil shape, but made of different materials (i.e., thermoplastic material with the thermal conductivity being only ∼0.2 W/m⋅ K to represent typical UAS airframe substrates vs. Aluminum with the thermal conductivity being ∼200 W/m⋅ K widely used for conventional manned aircraft). The two test models were mounted side-by-side inside an Icing Research Tunnel available at Iowa State University (i.e., ISU-IRT) under the same wet glaze or dry rime icing condition. During the icing experiment, while a high-speed imaging system was used to record the dynamic ice accretion process over the surfaces of the test models, an infrared thermal imaging system was also used to map the corresponding surface temperature distributions over the ice accreting airfoil surfaces. It was found that, upon the impacting of the airborne, super-cooled water droplets in ISU-IRT, ice would start to accrete rapidly on the surfaces of the test models with a significant amount of the latent heat of fusion being released associated with the phase changing of the impacted super-cooled water mass over the airfoil surfaces. The thermal conductivity of the airframe substrate was found to affect the dynamic ice accretion and unsteady heat transfer processes over the ice accreting surfaces significantly. With the two test models being exposed under the same icing conditions, the released latent heat of fusion was found to be dissipated much slower over the surface of the thermoplastic model, due to the much lower thermal conductivity of the thermoplastic substrate. In comparison with those on the surface of the Aluminum model, the slower dissipation of the released latent heat of fusion on the surface of the thermoplastic model was found to cause higher surface temperatures and greater "heated" regions near the airfoil leading edge, more obvious surface water runback over the airfoil surface, and formation of more complex rivulet-shaped ice structures at further downstream locations beyond the direct impinging zone of the super-cooled water droplets.