Influence of External Heat Transfer on the Thermo-Structural Stress of a Radial Turbine Wheel

Structural simulations are key for designing the wheel of a turbocharger’s turbine. These simulations enable the assessment of components’ durability and performance in demanding conditions such as extreme exhaust gas temperatures, facilitate the development of the cooling strategies that essential for managing excessive heat, and allow enhancing turbocharger efficiency and preventing catastrophic failures in high-temperature environments. External heat transfer plays a crucial role, since the housing temperature can reach values in the order of 103 K and the contribution of convective heat to ambient air is one of the major sources of loss. The present paper aims to assess the influence of natural or forced convection between the turbine’s housing and the external ambient on the temperature and stress distributions of the turbine’s wheel. The methodology adopted for the analysis is based on a two-step approach. First, a three-dimensional steady-state conjugate heat transfer (CHT) simulation of the entire turbine stage (including volute, outlet duct, and wastegate valve) is performed to evaluate the temperature field on the metal body of the turbine. Then, the temperature distribution of the body is imported as a load for the thermo-structural simulation of the rotor wheel. The numerical setup was validated against experimental measurements of the temperature of the rotor blade. For the evaluation of the structural behavior of the component, the most critical regions in terms of stresses were identified in the backdisc part of the wheel. The results show the variation of the structural response as the external convection is increased from an ideal adiabatic condition to a forced external cooling condition. The impact of the same on the overall performance limits of the turbine are discussed.