PCA will be manning Booth #507 at the ASME Turbo Expo in Orlando, June 8th to 12th 2009. Graham Cox, John Calvert and Mick Casey will be attending the conference and exposition and would be pleased to welcome visitors to the booth. There is a wealth of experience in compressor and turbine aerodynamic design between these engineers, covering both radial and axial machines from a wide range of applications.
PCA staff will present two technical papers: Mick Casey will present a paper entitled 'On the Efficency of Compressors with Diabatic Flows' in session 7-1 Education Strategies and Tools I, at 0945 on Monday June 8th. Graham Cox will present 'The Development of a Deviation Model for Radial and Mixed-Flow Turbines for use in Throughflow Calculations' in session Turbomachinery: Radial Turbine Aerodynamics at 2:30pm on Wednesday June 10th. Further details of the papers are below.
ASME GT2009-59921 The development of a deviation model for radial and mixed-flow turbines for use in throughflow calculations
GD Cox, A Roberts and MV Casey
Radial and mixed-flow turbine stages are an important component of turbochargers in automotive engines. The aerodynamic design of such turbines is generally compromised by the severe mechanical and manufacturing constraints to withstand the harsh motor environment with high stresses, high temperatures and unsteady operation. Conventionally, the designer deals with these constraints in the preliminary design stage by using a high degree of empiricism. This is then followed in the detailed design by extensive and time-consuming 3D CFD analysis and geometry optimisation.
This paper describes a new approach to the preliminary design of radial turbine impellers using a quasi-3D throughflow method, which allows a more rapid consideration of the design issues before moving on to a full 3D CFD analysis. The paper describes the development of deviation models suitable for radial and mixed-flow turbines out of a range of CFD solutions in which a number of important features have been varied: aerodynamic loading, tip clearance and blade root thickness. The features of the deviation model are related to predicted features of the flow. The results of throughflow calculations including the deviation model are compared against the CFD predictions.
ASME GT2009-59015 On the Efficiency of Compressors with Diabatic Flows
MV Casey and TM Fesich (University of Stuttgart)
In most compressors the flow is adiabatic, but in micro-compressors, and in turbochargers at low speeds, the compression process has both heat transfer and work input. The classical adiabatic efficiency definition found in most text books is then incorrect. This paper extends the text book definitions of compressor efficiency to diabatic flows.
The paper explains different compressor efficiency definitions in a logical way and identifies fundamental flaws in the use of isentropic efficiency for a diabatic flow. It shows that the polytropic efficiency can be used with or without heat transfer without ambiguities. Other significant advantages of the polytropic efficiency are also summarised, as they are not fully covered in any turbomachinery text books.
The advantages of the polytropic approach for a practical application are demonstrated by analysing the heat transfer in a turbocharger compressor. A simple model of the heat transfer allows a correction for this effect on the polytropic efficiency at low speed to be derived.
Compressor characteristics that have been corrected for this surprisingly large effect maintain a much higher efficiency down to low speeds.