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Cox G.D.,PCA Engineers Ltd | Fischer C.,University of Stuttgart | Casey M.V.,University of Stuttgart
9th International Conference on Turbochargers and Turbocharging - Institution of Mechanical Engineers, Combustion Engines and Fuels Group | Year: 2010

Radial and mixed flow turbines are important components of turbochargers in automotive engines. Their aerodynamic design is generally compromised by severe mechanical constraints, to deal with high temperature and unsteady operation, but also by the requirement of low inertia for rapid turbocharger response from low engine speed. Conventionally, the designer deals with these constraints in the preliminary design, using a high degree of empiricism, followed by extensive CFD analysis and geometry optimisation. This paper describes a new approach to the preliminary design using a quasi-3D throughflow method coupled to an optimiser, which allows a more rapid consideration of the design issues before moving on to 3D CFD analysis. The throughflow-based optimisation system was able to increase efficiency by over 3% at the same inertia or to reduce inertia by 20-30% at the same efficiency, compared to a baseline design. © Authors 2010. Source

Wu X.,PCA Engineers Ltd | Norster E.R.,Norster Combustion Research Ltd. | Xie G.,Dongfang Turbine Co.
Proceedings of the ASME Turbo Expo | Year: 2015

Many lean-burn combustors are prone to high levels of pressure oscillations resulting in early structural failure. These oscillations have their origins with the natural acoustic characteristics of the combustor flow/geometry and amplification and excitations factors associated with well-mixed flames. The coincidence of the frequency of these excitations with the mechanical vibration modes of the combustor may result in resonance and high cycle fatigue failure. Often with high levels of pressure oscillations the fuel system itself can become coupled driving the dynamics to higher levels. Thus detailed acoustic and mechanical vibration analysis of the combustor becomes important. This paper describes the numerically predicted transient flow characteristics of two configurations of DLN combustor double swirler in contra-and co-rotating arrangements with the sole difference being in the orientation of rotation of the inner nozzle airflow. Although much useful information has been obtained from the previous steady-state analysis, there remain many unresolved issues such as discrepancies of vortex breakdown and acoustic instabilities, which is also important for a final design selection. The transient analysis was performed for each configuration to compare flow instability and acoustic characteristics where the model includes the inlet air annulus, double swirler, main reaction zone and dilution duct. The studies indicate that there is a significant discrepancy in flow structures when the vortex breaks down between the two configurations. And there exists a strong interaction for the remaining swirl with the dilution jets, resulting in the hot core penetrating far downstream inside the transient duct in the co-rotating case. An FFT analysis indicates a significant discrepancy on main low acoustic frequencies and the magnitudes of oscillatory pressure. Copyright © 2015 by ASME. Source

Cox G.D.,PCA Engineers Ltd
Proceedings of the ASME Turbo Expo | Year: 2012

The modern trends in automotive turbocharger applications are towards the boosting of smaller internal combustion engines and more advanced systems including twostage, turbo-compounding and hybrid electric-motor assist. Off-the-shelf turbochargers will become a smaller share of the market and the choice of major parameters for the compressor and turbine, e.g. speed and diameter, will fall outside of the manufacturer's knowledge base. The selection of the compressor and turbine may even be independent. The only certainty is that the turbomachinery will have to be small, cheap and efficient. To provide some guidance to the turbine designer, this paper presents the results of a study in which practical designs have been generated to cover the range of conceivable parameters, presented in non-dimensional terms to provide general applicability. All the designs are generated using a throughflow-based optimisation system in which the candidate geometries are assessed against mechanical as well as aerodynamic and inertia targets. Analysis of the results gives clues to the form of the basic empiricism that would be of use in the preliminary design of automotive turbocharger turbines. Copyright © 2012 by ASME. Source

Casey M.,PCA Engineers Ltd | Casey M.,University of Stuttgart | Rusch D.,ABB
Journal of Turbomachinery | Year: 2014

The matching of a vaned diffuser with a centrifugal impeller is examined with a onedimensional (1D) analysis combined with extensive experimental data. A matching equation is derived to define the required throat area of the diffuser relative to the throat area of the impeller at different design speeds and validated by comparison with a wide range of compressor designs. The matching equation is then used to give design guidelines for the throat area of vaned diffusers operating with impellers at different tip-speed Mach numbers. An analysis of test data for a range of high pressure ratio turbocharger compressor stages is presented in which different matching between the diffuser and the impeller has been experimentally examined. The test data includes different impellers with different diffuser throat areas over a wide range of speeds. It is shown that the changes in performance with speed and diffuser throat area can be explained on the basis of the tip-speed Mach number which causes both the diffuser and impeller to choke at the same mass flow. Based on this understanding, a radial compressor map prediction method is extended to include this parameter, so that more accurate maps for matched and mismatched vaned diffusers can be predicted. © VC 2014 by ASME. Source

Casey M.,University of Stuttgart | Robinson C.,PCA Engineers Ltd
Proceedings of the ASME Turbo Expo | Year: 2011

A novel approach to calculate the performance map of a centrifugal compressor stage is presented. At the design point four non-dimensional parameters (the flow coefficient φ, the work coefficient λ, the tip-speed Mach number M and the efficiency η) characterize the performance. In the new method the performance of the whole map is also based on these four parameters through physically-based algebraic equations which require little prior knowledge of the detailed geometry. The variable empirical coefficients in the parameterized equations can be calibrated to match the performance maps of a wide range of stage types, including turbocharger and process compressor impellers with vaned and vaneless diffusers. The examples provided show that the efficiency and the pressure ratio performance maps of turbochargers with vaneless diffusers can be predicted to within ± 2% in this way. More uncertainty is present in the prediction of the surge line, as this is very variable from stage to stage. During the preliminary design the method provides a useful reference performance map based on earlier experience for comparison with objectives at different speeds and flows. Copyright © 2011 by ASME. Source

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