Dynamic Turbine Clearance Simulation Considering the Influence of Temperature on Mechanical Load-Induced Displacements

This paper addresses the problem of precise in-flight simulation of all dynamic engine operational modes, considering the specific features of the control in these modes. One of the dynamic processes that are most complex to simulate is "cold stabilization" - that is, acceleration with incomplete heating of engine elements. The principal peculiarity of this process is associated with a greater clearance between the blade tips and the casing facing them, which results in lower efficiency of the compressor or turbine. Hence, engine control programs that are developed for a heated engine tend to change the engine static performance (e.g., greater fuel consumption and higher gas turbine inlet temperature) and make the transients slower when applied to cold stabilization. The development of active clearance control systems makes evident the need for fast mathematical models that consider the clearance change at different dynamic operational conditions. Clearance is determined by the radial sizes of the disk, blades, and casing. Therefore, the main factors affecting it are thermal strains and strains generated by mechanical loads that change these sizes. Numerous studies have addressed thermal straining simulation, but only a few have considered straining due to mechanical loads. However, even these works do not consider the influence of disk temperature on the strains induced by mechanical loads. Indeed, these strains depend on temperature because the mechanical properties of the disk, especially the elasticity modulus, are temperature dependent. This paper describes a method to estimate the radial elongation of an engine heated element (HE) caused by heating and mechanical load, when the action of the latter takes into consideration the element temperature. The proposed method was experimentally validated for the radial clearance dynamics of a high-pressure turbine disk. Finite element analysis and real data proved that the accuracy of the method is high enough. Moreover, the method is relatively simple and can be integrated into an engine dynamic model; moreover, it does not significantly increase total time of the execution of the model program. In this way, this clearance evaluation method can be recommended for practical use.