Unsteady Effects in the Heat Load Predictions for a Two-Stage Compressor Turbine

Abstract

Heat load analysis play an important role in the estimation of hot gas components’ lifetime. To achieve a high level of accuracy in heat load analysis, predicting the temperature distribution on the vane and blades is one area where further development is needed. Due to strong flow unsteadiness and mixing effects from blade row interactions and cooling injections, accurate heat load predictions have become an engineering challenge. This study uses both steady and time-accurate computational fluid dynamics (CFD) simulations to investigate the unsteady and mixing effects in a two-stage compressor turbine. The commercial code ANSYS CFX-15 is utilized to evaluate the performance of the steady state, mixing plane (MP) method, versus time-accurate, profile transformation (PT) and time transformation (TT) methods. The presence or absence of the rotor-stator cavities from which purge or cooling air is entering the main flowpath can also play an important role in the unsteadiness and mixing properties. Therefore the unsteady effects have been examined for two cases; a simplified model without any cavity and a detailed geometry with all the cavities included. In the simplified case, the cooling has been implemented as local patches. The results are then compared with gas temperature measurements from the real engine tests using thermo-crystals. The measurements include temperature profiles in front of the leading edge of each stator and rotor for both stages. The findings suggest that including cooling cavities may not improve the results in steady state simulations, however their presence in transient simulations can lead to mixing prediction improvements. Moreover, the results indicate that the transient simulations will improve the mixing predictions mainly in the second stage of the turbine. The results also indicate that in transient simulations, number of passages and pitch ratio between the stators of consecutive stages directly affect the results regardless of which transient method is used.