An Experimental and Computational Study of Pulsating Flow within a Double Entry Turbine with Different Nozzle Settings

Abstract

This thesis presents a detailed study of the performance of a nozzled, double entry turbine. This configuration is primarily found in the turbocharger application and encompasses two different entries, each feeding 180° of a single turbine wheel. The primary motives for this research are to enhance the knowledge and understanding of the behaviour of such a device under steady and pulsating flows including the effect of three different nozzle vane geometries. The work incorporates both experimental and computational analyses. Experimental results show that with unequal admission between the two volute entries the performance of the turbine is greatly affected compared to when both entries are flowing equally. A methodology was developed which successfully linked the unequal admission performance of the turbine to the full admission maps which are more readily available. Pulsating flow was found to affect the average performance of the turbine compared to the steady state characteristics. Examination of the instantaneous mass flow showed a large degree of mass storage in the turbine domain for all conditions of pulsating flow. A new parameter was developed based upon the conservation of mass in order to quantify unsteadiness taking into account both pulse amplitude and frequency. Steady and unsteady computational simulations were undertaken for one of the different nozzle configurations. Entropy generation rate was used to establish the distribution of loss within the turbine. In partial admission the loss distribution within the rotor wheel was found to be different to any case during full admission operation. Under pulsed flow conditions the computational analysis showed that the loss distribution changes throughout a pulse cycle showing that the flow regime will also undergo a large change. The loss distribution within the rotor wheel at one point within the pulse cycle was found to be very similar the equivalent steady state condition.