Error Evaluation in Metal Surface Temperature Prediction Due to Non-Simulation of the Effect of Water Impingement and Runback Water on an Anti-Iced Turboprop Engine Inlet Guide Vane Structure

During the optimization of the TP400D6 engine (powering the A400M military transport aircraft), the mechanical design of the Front Bearing Structure has proven to be one of the most challenging topics in the engine development programme. One of the leading technical subjects has been the design and optimization of the thermal anti-icing system of the component. When non-specific icing simulation software tools are available, the effect of the water impingement and runback water is difficult to simulate. The objective of this paper is to show one particular aspect learnt during the design and development phase of the project: the evaluation of the error obtained in the calculation of metal temperatures on an antiiced airfoil surface due to the effect of water impingement and runback water. TP400D6 engine front end arrangement consists of a single radial structure after the engine air intake performing both the structural and aerodynamic function, transmitting bearing and high propeller loads and being the compressor IGVs. The anti-icing system employs hot compressor bleed air circulating internally in the component through a series of internal channels and passages and exiting the airfoil through trailing edge holes. Due to airfoil aerodynamic constraints and material selection, it was realised in the earlier stages of the project that it was not possible to heat the whole vane profile up to the trailing edge. In consequence, the effects of the impingement water and runback of non-evaporated water from the intake and the IGV leading edge itself, play a key role on the determination of the airfoil surface temperature and potential ice accretion. Because of not having a specific icing simulation software, water impingement and runback water effects cannot be predicted with sufficient accuracy. During the engine programme’s development phase, a dedicated component antiicing rig test was conducted in order to evaluate and obtain a closer approximation of the real behaviour of the system. The scope of this paper is to go through the details of the aforementioned effect of icing water on airfoil surface temperature, focusing on the discrepancies between predicted temperatures and test rig measured temperatures. Typical thermal modelling is used, which incorporates the best possible understanding of the water particle impingement pattern onto the airfoils and flow lines distribution around the IGV profiles. Results from the rig test have been applied to the traditional thermal model in order to improve the thermal prediction simulation and understanding of the component.