PCA will be manning Booth #318 at the ASME Turbo Expp in Vancouver BC, June 6th to 10th 2011. Chris Robinson and Mick Casey will be attending the conference and will be pleased to welcome visitors to the booth. Both have extensive experience in the aerodynamic optimisation of axial and centrifugal compressors for a wide range of applications covering fans, multistage compressors for gas turbine application, turbochargers and industrial centrifugal compressor stages. In addition, over recent years PCA has been developing new methods to improve the accuracy of preliminary designs and in automated optimisation of components. Please do visit Booth #318 to learn more.
PCA staff are involved in a number of technical papers as lead and supporting authors:-
A method to calculate the performance map of a centrifugal compressor stage
Mick Casey and Chris Robinson GT2011-45502
Abstract: A new approach to calculate an approximate performance map during the preliminary design of a centrifugal compressor stage is presented. Measured characteristic curves of several well-designed stages have been analysed to produce a generic set of analytic equations with empirical coefficients that approximate the variation of efficiency and work input with flow coefficient and tip-speed Mach number away from the design point. The empirical coefficients can be adjusted to match the performance maps of a wide range of stage types, including subsonic and supersonic impellers, stages with vaned and vaneless diffusers, and turbocharger and process compressor stages. Some considerable uncertainty remains with the estimate of the surge line as this is found to be very variable from stage to stage, but an optimistic, a realistic and a pessimistic estimate can be made. The method allows a reliable stage performance map for centrifugal compressor stages to be obtained quickly at an early point in the preliminary design process as an excellent guide to subsequent design decisions.
[To be presented by Mick Casey on Tuesday 7th June at 4:30pm in Room 210]
Evaluation of heat transfer effects on turbocharger performance
Borislav Sirakov and Mick Casey GT2011-45887
[To be presented by Borislav Sirakov of Honeywell Turbo Technologies on Thursday 9th June at 10:15am Room 211]
A comparison of advanced numerical techniques to model transient flow in turbomachinery blade rows
A joint paper between GE Global Research and ANSYS Inc. Graham Cox of PCA is a co-author, the turbine stage analysed in the paper was designed by PCA specifically for this purpose, to give a design representative or modern highly loaded turbomachinery without the problems of proprietary data.
Abstract: Computational predictions of the transient flow in multiple blade row turbomachinery configurations are considered. For cases with unequal numbers of blades/vanes in adjacent rows ("unequal pitch") a computation over multiple passages is required to ensure that simple periodic boundary conditions can be applied. For typical geometries, a time accurate solution requires computation over a significant portion of the wheel.
A number of methods are now available that address the issue of unequal pitch while significantly reducing the required computation time. Considered here are a family of related methods ("Transformation Methods") which transform the equations, the solution or the boundary conditions in a manner that appropriately recognises the periodicity of the flow, yet do not require solution of all or a large number of the blades in a given row. This paper will concentrate on comparing and contrasting these numerical treatments.
The first method, known as "Profile Transformation", overcomes the unequal pitch problem by simply scaling the flow profile that is communicated between neighboring blade rows, yet maintains the correct blade geometry and pitch ratio. The next method, known as the "Fourier Transformation" method applies phase shifted boundary conditions. To avoid storing the time history on the periodic boundary, a Fourier series method is used to store information at the blade passing frequency (BPF) and its harmonics. In the final method, a pitch-wise time transformation is performed that ensures that the boundary is truly periodic in the transformed space. This method is referred to as "Time Transformation".
The three methods have recently been added to a commercially-available CFD solver which is pressure based and implicit in formulation. The results are compared and contrasted on two turbine cases of engineering significance: a high pressure power turbine stage and a low pressure aircraft engine turbine stage. The relative convergence rates and solution times are examined together with the effect of non blade passing frequencies in the flow field. Transient solution times are compared with more conventional steady stage analyses, and in addition detailed flow physics such as boundary layer transition location are examined and reported.
The following are papers involving Professor Casey and his former colleagues at ISTM, Stuttgart University:
Experimental investigation of geometrical parameters on the pressure recovery of low pressure steam turbine exhaust hoods
Impact of mistuning on the vibration behaviour of the last stage in a model 3-stage low pressure steam turbine
Modelling and validation of wet steam flow in a low pressure steam turbine
Innovative variable turbine concept for turbochargers