Comparison of the influence of unsteadiness between nozzled and nozzleless mixed flow turbocharger turbine

Nozzled and nozzleless volutes are the most commonly used stator configurations for the turbocharger turbine. In this paper detailed experimental investigation was carried out to compare the performance of a mixed flow turbine with nozzled and nozzleless stator under steady and pulsating conditions which replicates the pulsating exhaust flow from the internal combustion engine. The results show that the turbine with nozzled volute has higher efficiency at low load conditions in both steady and unsteady conditions. The steady peak efficiency is nearly the same as the nozzleless one but it shifts to higher velocity ratio. The improvement of the cycle average efficiency for the nozzled volute under pulsating conditions is influenced on the pulse frequency. The hysteresis loops of the swallowing capacity, reflecting the filling and emptying as well as the wave action effect in the turbine, are similar for two configurations. The comparison shows that the volute configuration has no direct influence on the ‘unsteady’ behaviour in the turbine. Instead, the results of the 1-D model show that the swallowing capacity curve has an evident influence on the unsteadiness in the turbine. Furthermore, the unsteadiness of a turbine is enhanced by reducing the swallowing capacity or increasing the turbine loading.