Experimental Study of the Scallop Formation on Swept Cylinder

Two-dimensional models have been developed to predict and reproduce ice accretion shapes on airfoil profiles. These simulated shapes mostly are similar to experimental forms. However, in some conditions, the ice shapes could present some discontinuity along span showing some ice deposit separated by air inclusion: this deposit is called “lobster tail” or “scallop icing”. The classical 2D approaches fail to predict this kind of ice shapes. The 3D simulation requires to take into account a fully detailed heat and mass balance parameters which scallop accretion is sensitive. For that, the scallop formation was experimentally led on the swept cylinders.

An experiment in the icing wind tunnel PAG of the CEPr (The French Engine Test Center) was conducted in order to characterize the phenomenon and find the most relevant criteria. The ice accretions were obtained at different conditions. Influence of velocity, temperature, liquid water content (LWC) and median volume diameter (MVD) was studied for varying sweep angle from 0° to 60°. All the ice accretion sequences were documented with video and digital camera. Additionally, wax molds were made and then plaster castings were produced allowing measurement of scallop spacing and height. The results of the test are presented and analyzed. The experimental investigation showed that for high air velocity, the scallops are not formed because of an important droplet spreading. On the other hand, low velocity values caused some incomplete scallop and had the same effect on the ice shape than colder temperature. For higher MVD, the ice accretion is rougher and more compact. Finally, the scallop formation is found to be strongly influenced by the local sweep angle and occurs only in a limited range of temperature.