Teng Cao

Radial Turbine Rotor Response to Pulsating Inlet Flows

The performances of automotive turbocharger turbines have long been realized to be quite different under pulsating flow conditions compared to that under the equivalent steady and quasi-steady conditions on which the conventional design concept is based. However, the mechanisms of this phenomenon are still intensively investigated nowadays. This paper presents an investigation of the response of a stand-alone rotor to inlet pulsating flow conditions by using validated unsteady Reynolds Averaged Navier-Stokes solver (URANS). The effects of the frequency, the amplitude and the temporal gradient of pulse waves on the instantaneous and cycle integrated performances of a radial turbine rotor in isolation were studied, decoupled from the upstream turbine volute. Numerical method was used to help gaining the physical understandings of these effects. A validation of the numerical method against the experiments on a full configuration of the turbine has been performed prior to the numerical tool being used in the investigation. The rotor is then taken out to be studied in isolation. The results show that the turbine rotor alone can be treated as a quasi-steady device only in terms of cycle integrated performance; however, instantaneously, the rotor behaves unsteadily which increasingly deviates from the quasisteady performance as the local Strouhal number of the pulsating wave is increased. This deviation is dominated by the effect of quasi-steady time-lag; at higher local Strouhal number, the transient effects also become significant. Based on this study, an interpretation and a model of estimating the quasisteady time lag have been proposed; a criterion for unsteadiness based on the temporal local Strouhal number concept is developed, which reduces to the Λcriterion proposed in the published literature when cycle averaged; this in turn emphasizes the importance of the pressure wave gradient in time. Copyright

A Low Order Model for Predicting Turbocharger Turbine Unsteady Performance

In this paper, a low order model for predicting performance of radial turbocharger turbines is presented. The model combines an unsteady quasi-three dimensional CFD method with multiple one-dimensional meanline impeller solvers. The new model preserves the critical volute geometry features, which is crucial for the accurate prediction of the wave dynamics and retains effects of the rotor inlet circumferential non-uniformity. It also still maintains the desirable properties of being easy to set up and fast to run.The model has been validated against a experimentally validated full three-dimensional URANS solver. The loss model in the meanline model is calibrated by the full 3D RANS solver under the steady flow states. The unsteady turbine performance under different inlet pulsating flow conditions predicted by the model was compared with the results of the full 3D URANS solver. Good agreement between the two was obtained with a speed up ratio of about four orders of magnitude (∼104) for the low order model.The low order model was then used to investigate the effect of different pulse wave amplitudes and frequencies on the turbine cycle averaged performance. For the cases tested, it was found that compared with quasi-steady performance, the unsteady effect of the pulsating flow has a relatively small impact on the cycle averaged turbine power output and the cycle averaged mass flow capacity while it has a large influence on the cycle averaged ideal power output and cycle averaged efficiency. This is related to the wave dynamics inside the volute and the detailed mechanisms responsible are discussed in this paper.Copyright

Improved Hierarchical Modelling for Aerodynamically Coupled Systems

© 2017 ASME. Strong aerodynamic coupling can make the high fidelity simulation of a number of critical aero-engine components prohibitively expensive - particularly within the timeframes of industrial design cycles. This paper develops a body force based hierarchy of approaches to modelling the effects of blade rows. These are envisaged as allowing the computationally expensive parts of coupled systems to be resolved much more cheaply, rendering the cost of the overall simulation as more manageable. Simulation of the coupling that exists between the flow around an aero-engine intake and its fan is particularly emphasised, as this is becoming stronger and more performance critical with the modern trends towards the reduction of the relative diffuser length. The use of the viscous smeared geometry level of fidelity is initially shown to be an effective model over a number of cases a simple compressor blade row, a modern high bypass fan, and the Darmstadt rotor. After this, it is shown working as part of a coupled system in an intake experiencing crossflow. Higher fidelity geometry representations are then considered, which mimic the effect of struts. Finally, a mix of various fidelity geometry representations and turbulence modelling approaches is shown to bring otherwise hugely expensive calculations within the realm of practical computation, in the form of a full fan-to-flap calculation.

A Low-Order Model for Predicting Turbocharger Turbine Unsteady Performance

In this paper, a low-order model for predicting performance of radial turbocharger turbines is presented. The model combines an unsteady quasi-three-dimensional (Q3D) computational fluid dynamics (CFD) method with multiple one-dimensional (1D) meanline impeller solvers. The new model preserves the critical volute geometry features, which is crucial for the accurate prediction of the wave dynamics and retains effects of the rotor inlet circumferential nonuniformity. It also still maintains the desirable properties of being easy to set-up and fast to run. The model has been validated against a experimentally validated full 3D unsteady Reynolds-averaged Navier–Stokes (URANS) solver. The loss model in the meanline model is calibrated by the full 3D RANS solver under the steady flow states. The unsteady turbine performance under different inlet pulsating flow conditions predicted by the model was compared with the results of the full 3D URANS solver. Good agreement between the two was obtained with a speed-up ratio of about 4 orders of magnitude (~10E4) for the low-order model. The low-order model was then used to investigate the effect of different pulse wave amplitudes and frequencies on the turbine cycle averaged performance. For the cases tested, it was found that compared with quasi-steady performance, the unsteady effect of the pulsating flow has a relatively small impact on the cycle-averaged turbine power output and the cycle-averaged mass flow capacity, while it has a large influence on the cycle-averaged ideal power output and cycle-averaged efficiency. This is related to the wave dynamics inside the volute, and the detailed mechanisms responsible are discussed in this paper.