Abstract
► Correlation of whirling arm and water-jet erosion test rigs. ► Use of roughness measurements as a method to compare high velocity liquid impact tests. ► Development of a laboratory scale whirling arm rain erosion test rig. ► Inspection of eroded surfaces by scanning electron, confocal and optical microscopy. A laboratory-scale Whirling Arm Rain Erosion test Rig (WARER) has been designed, developed and commissioned at the University of Limerick. The facility is capable of impact speeds of 178 ms −1 and a rainfall rate of 25.4 mm h −1 . Circular samples of 27 mm diameter (nominal) and a maximum thickness of 2 mm can be accommodated. The facility was developed to test the resistance of leading edge aircraft materials to the repeated impact of rain droplets in flight. A challenging feature of the design was to enclose the whirling arm within a chamber so that it could be operated in an open-plan laboratory. A design problem that arose was the effect of aerodynamic heating of the air within the chamber. This led to a warming of the water and consequently a change in the droplet formation, which in turn caused problems relating to the repeatability of the tests. A cooling system was thus incorporated to keep the temperature of the water droplets below the established threshold of 20 °C. Calibration testing has been undertaken by conducting back-on-back testing of samples with a previously developed water-jet facility at EADS IW, Munich. This Pulsating Jet Erosion Test rig (PJET) is capable of 225 ms −1 droplet speed. Multiple impacts are produced on the sample at numerous locations, each location having an increased number of impacts. The impact frequency is equivalent of 25 mm h −1 rain fall. Clad aluminium alloy (AA2024-T3) was used with the soft AA1230 clad layer being removed during testing. Post impact evaluations were carried out using Confocal Laser Scanning Microscopy (CLSM) and surface roughness measurements. A cumulative erosion-time curve was produced from the WARER samples.
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