Nozzled Turbine Research Articles

Study on a flow-field-based meanline model of nozzled twin-entry mix-flow turbine

Variable geometry twin-entry turbine has advantages in fuel economy, low-end torque, emission and turbo-engine matching of internal combustion engine. The reliability of performance prediction method for nozzled twin-entry turbine is heavily dependent on the understanding of flow mechanism of the turbine which is always confronted by time-dependent unequal admissions. This paper establishes a new meanline model of a nozzled twin-entry turbine based on the internal flow features. Firstly, flow mechanism of the twin-entry turbine with a vaned nozzle under different admissions is investigated via an experimentally validated CFD method. Results clearly demonstrate that the flow distortion in spanwise direction caused by unequal admissions notably influences the turbine efficiency discrepancy between symmetric unequal admissions, especially the two partial admissions. The evolution of flow distortion in the nozzle passage is the key to the performance discrepancy, which is impossible to be considered by a conventional performance model of a nozzled twin-entry turbine. Inspired by this, a newly-designed meanline model, named ‘parallel nozzle’ is proposed. Specifically, a nozzle passage is divided into two parallel sub-passages in spanwise direction to consider the flow distortion in nozzle passage. The model is validated against the detailed CFD results in terms of both overall performance and detailed flow parameters over different admissions. Results prove that turbine performance and flow parameters are well predicted by the model. Specifically, the influence of admissions on nozzled twin-entry turbine performance and flow parameters can be predicted by the method in satisfying accuracy.

Unsteady performance analysis of a twin-entry variable geometry turbocharger turbine

This paper discusses the details of unsteady experimentation and analysis of a twin-entry variable geometry turbine for an automotive turbocharger. The turbine in this study is the product of design progression from a commercial nozzleless unit to a single-entry variable geometry and consequently to a twin-entry unit. The main features of the turbine were kept similar across all configurations for equivalent comparison basis. The unsteady curves of the twin-entry turbine exhibited the conventional looping characteristics representing filling and emptying effects, which was also the case for the nozzleless and single-entry nozzled turbine. The swallowing capacity of the twin-entry turbine, during full admission testing, was recorded to be inconsistent between the two entries, in particular they were at different pressure ratio levels – the shroud end entry was in most cases more pressurized compared to the hub end entry, as much as 13%. Contrarily, during out-of-phase testing the swallowing capacity of both the turbine entries was found to be similar. The cycle-averaged efficiency of the nozzled turbine either twin or single-entry was found to depart significantly from the equivalent quasi-steady, in comparison to the nozzleless single-entry turbine, this was as much as 32%.

Unsteady Effect in a Nozzled Turbocharger Turbine

The unsteady behavior of a nozzled turbocharger turbine under pulsating flow conditions has been studied experimentally in a cold flow test facility that replicates engine pulses. The results presented are obtained at a turbine speed of 48,000 rpm for pulsating frequencies of 40 Hz and 60 Hz (which correspond to 1600 rpm and 2400 rpm in a twin turbocharger six cylinder internal combustion engine). The turbine unsteady behavior is compared for nozzle vane angles ranging between 40 deg and 70 deg. A nozzled turbocharger turbine is found to behave differently from a nozzleless turbine under pulsating flow. The existence of a nozzle ring “damps” the unsteady flow leading to a reduced level of flow dynamics affecting the turbine wheel for all vane angles. The bigger volume in the nozzled turbine is also another contributing factor to the observed characteristics. The results are more pronounced in the higher frequency and maximum vane opening condition. Given this “damping” behavior, the concept of unsteady efficiency is questioned. The level of unsteadiness in the flow is characterized by the relevant nondimensional parameters, and the onset of the unsteadiness in the flow and its effect on a nozzled turbocharger turbine is discussed. The onset of the unsteady effect is suggested to be at 40 Hz flow condition. However, the nozzled turbine exhibits more of filling and emptying characteristics for both the frequency conditions, especially at close nozzle position cases. The effect of unsteadiness on the instantaneous efficiency calculation is more pronounced in the nozzled turbine compared with a nozzleless turbine.

Experimental performance evaluation of a 99.0 mm radial inflow nozzled turbine with varying shroud profiles

In addition to the experimental data already presented by Spence, Doran and Art in 1999, further comprehensive performance tests were carried out on the same 99.0 mm radial turbine using four different shroud profiles with three nozzles of varying sizes. Efficiency maps are presented for each of 12 different turbine configurations tested. For the largest stator size giving the highest flowrate the turbine efficiency is shown to vary by over 3.5 per cent with different shroud profiles. An examination of the effect of shroud profile with respect to rotor incidence angle revealed that a larger radius of shroud curvature was better for positive incidence while a smaller shroud radius was most efficient for negative incidence.

Experimental performance evaluation of a 99.0 mm radial inflow nozzled turbine at larger stator-rotor throat area ratios

Following on from experimental data already presented by Spence and Artt in 1997, further comprehensive performance tests were carried out on a 99.0 mm radial turbine with three larger vaned stators. The results have helped to confirm some of the trends noted in the earlier tests. Measurements of the efficiency, mass flowrate and rotor pressure ratio are presented together with the results of a simple loss analysis. For smaller stator sizes the turbine mass flowrate is shown to be proportional to the stator throat area. The significance of the stator-rotor throat area ratio is examined and its dependence on the stage pressure ratio is noted.

A loss analysis based on experimental data for a 99.0 mm radial inflow nozzled turbine with different stator throat areas

The results of experimental performance tests on a 99.0 mm radial inflow turbine with seven different nozzle throat areas were reported by the same authors in a previous publication (1). In order to perform a loss analysis, dividing the turbine losses between the stator and the rotor, a theoretical model of the stator loss was required. Several stator loss models were evaluated and the model described by Rohlik (9) was used as the basis for a loss analysis. Plots are given for the breakdown of losses at two operating speeds for each nozzle size. Both the stator and the rotor losses decreased markedly as the stator throat area increased towards a stator-rotor throat area ratio of 0.5. A significant step change in the magnitude of the rotor loss was evident at every stator size and appeared to correlate with the volumetric flowrate in the turbine exducer. Therefore a transition to a more efficient flow pattern in the exducer seemed to occur at higher flow-rates.

Experimental performance evaluation of a 99.0 mm radial inflow nozzled turbine with different stator throat areas

The performance of a single-stage, radial inflow turbine was measured with seven vaned stators of different throat areas. The turbine test facility is described and details of the turbine rotor and stator geometry are provided. Efficiency, mass flowrates and rotor static pressure ratios are presented for each turbine configuration at a range of speeds and pressure ratios. The experimental data clearly shows the turbine mass flowrate increasing approximately in proportion to the stator throat area, while the maximum attainable efficiency decreased as the stator throat area decreased.