A Three-Dimensional Computational Study of Pulsating Flow Inside a Double Entry Turbine

Abstract

The double entry turbine contains two different gas entries, each feeding 180 deg of a single rotor wheel. This geometry can be beneficial for use in turbocharging and is uniquely found in this application. The nature of the turbocharging process means that the double entry turbine will be fed by a highly pulsating flow from the exhaust of an internal combustion engine, most often with out-of-phase pulsations in each of the two entries. Until now research on the double entry turbine under pulsating flow conditions has been limited to experimental work. Although this is of great value in showing how pulsating flow will affect the performance of the double entry turbine, the level of detail with which this can be studied is limited. This paper is the first to use a three-dimensional computational analysis to study the flow structures within a double entry turbine under conditions of pulsating flow. The analysis looks at one condition of pulsating flow with out-of-phase pulsations. The computational results are validated against experimental data taken from the turbocharger test facility at Imperial College and a good agreement is found. The analysis first looks at the degree of mass flow storage within different components of the turbine and discusses the effect on the performance of the turbine. Each of the volute limbs is found to be subject to a large degree of mass storage throughout a pulse cycle demonstrating a definite impact of the unsteady flow. The rotor wheel shows a much smaller degree of mass flow storage overall due to the pulsating flow; however, each rotor passage is subject to a much larger degree of mass flow storage due to the instantaneous flow inequality between the two volute inlets. This is a direct consequence of the double entry geometry. The following part of the analysis studies the loss profile within the turbine under pulsating flow using the concept of entropy generation rate. A significant change in the loss profile of the turbine is found throughout the period of a pulse cycle showing a highly changing flow regime. The major areas of loss are found to be due to tip leakage flow and mixing within the blade passage.

Unsteady Flow Loss Mechanism and Aerodynamic Improvement of Two-Stage Turbine under Pulsating Conditions

“…Based on the understanding of the unsteady turbine characteristics, a number of models were developed to capture the unsteady effects. These models are helpful in turbine preliminary design and performance evaluation [14][15][16][17][18][19][20][21]. Also, the performance of engines matched with different turbines can be predicted before the experiment.…”

Radial Gradient Pressure Effects on Flow Behavior in a Dual Volute Turbocharger Turbine

“…Cases 6, 7, and 8, respectively, have higher MFR, so the efficiency gain is decreased from cases 6 to 8. Interspace losses in the non-flowing sector contribute a significant portion to the overall losses in the turbine, but in the full admission case, the entropy generation in the Interspace regions is minimal throughout the whole operating range of the turbine [25]. So, in the case 9 which is almost an equal admission (MFR = 0.9) isolating in tongue region has no significant impact.…”

Simulation of entropy generation during the evolution of rotating stall in a two-stage variable-pitch axial fan

“…The volute also has a large effect on the entropy of the centrifugal fan. Newton et al 8 analysed the capacities of different components with respect to the mass flow storage of a turbine and discussed the impact on turbine performance. Butt and Ali 9 studied the entropy effects due to the flow of a viscous fluid in a rotating channel.…”