Effect of Misalignment at the Flat and Profiled Endwall of Nozzle Guide Vane on Heat Transfer

Misalignment of gas turbine engines is caused by the difference in thermal expansion from the design point when starting or stopping the engine, or when operating at partial load. This study evaluated the differences in heat transfer characteristics between a flat endwall and a profiled endwall with misalignment. To ensure consistency with the flow conditions, experiments were conducted at an outlet Reynolds number of 300,000 for both geometries. The experiment was performed under three different conditions: a case without step, a case with a forward-facing step (h/C_x= -0.1), and a case with a backward-facing step (h/C_x= 0.1). In the flat endwall, the thermal load of the upstream region increases significantly with both step circumstances compared to the case without a step. The misalignment causes a recirculation flow to occur between the interface of the combustor and turbine. This leads to the mainstream reattaching upstream of the endwall. Nevertheless, the heat transfer characteristics of the profiled endwall differ from those of the flat endwall under step conditions. Most locations do not experience significant changes, with only a slight increase observed in the upstream region. The recirculation flow is crucially reduced due to the intensity of the secondary vortex in the profiled shape. Hence, the increase in the thermal load on the profiled endwall with step is considerably lower than that on the flat endwall. As a result, the thermal load on the profiled endwall has decreased by 25 % for the forward-facing step and 20.7 % for the backward-facing step compared to the flat endwall.