ASME Turbo Expo 2008

25 January 2008


PCA's policy is always to populate the expo with experienced engineers and methods development specialists who will be pleased to discuss any technical issues within our sphere of experience and to explain in more detail our products and services. You can find us in Booth #806, close to ANSYS Inc, with whom PCA enjoys a close working relationship in the development of preliminary aerodynamic design methods for turbomachinery applications.

Three papers have now been accepted for presentation during the technical program involving PCA staff:



A new streamline curvature throughflow code for radial turbomachinery

MV Casey (ITSM - Universität Stuttgart) and CJ Robinson (PCA)

This paper describes a newly developed streamline curvature throughflow code for the analysis of all types of turbomachinery, but designed specifically for single stage radial or mixed flow machines. The code includes curved planes and internal blade row calculating stations and a general method of specifying the empirical data which allows separate treatment of blockage, losses, and deviation. Incompressible and compressible fluids are allowed, including limited amounts of supersonic relative flow in blade rows. The paper describes in detail some new aspects of the code, in particular the models for spanwise mixing and for calculations with prescribed pressure ratio with choked compressor bladed rows. Examples are provided of the use and validation of the code for many types of radial turbomachinery.



The influence of lean and sweep in a low pressure steam turbine:

Throughflow modelling and experimental measurements

L Völker and MV Casey (ITSM - Universität Stuttgart)

J Dunham (PCA)  and H Stüer (Siemens AG, Mülheim)

This paper describes experimental and throughflow investigations on two configurations of a model three-stage steam turbine. Global performance measurements and detailed flow field measurements with pneumatic flow probes were carried out to quantify the changes in the design due to the introduction of sweep in the last stator nozzle. An existing 2D throughflow code was improved to enable the present calculations to be completed. The test results have been used in this paper to calibrate the 2D throughflow model, by adjustment of empirical correlation data to get good agreement with the experimental data on one of the configurations. This throughflow model was then used to examine the influence of lean and sweep on the design. The results identify that throughflow calculations can model the global effects of lean and sweep in the last stages of steam turbines and some insight is gained on the losses across the span for the different configurations and the benefits of lean and sweep in such stages.



A new optimisation technique for radial compressor impellers

MV Casey and F Gersbach (ITSM - Universität Stuttgart) and CJ Robinson (PCA)

A software tool has been created to aid in automated impeller design within an integrated design system for radial flow impellers. The design tool takes the results from the 1D preliminary design process and uses these to define a parameterised blade geometry, which incorporates features that are required for low mechanical stresses and simple manufacturing. This geometry is then adjusted to minimise a global objective function using a throughflow computation. The adjustment is based on selection with a breeder genetic algorithm. The initial population includes "elite" designs from a database of earlier well-proven experience, and the final design is honed to perfection with a hill-climbing method.

With the help of a suitable global objective function incorporating mechanical and aerodynamic criteria, and taking into account wide experience with the design of impellers, the tool provides a fast screening of various design possibilities to produce a geometrical input for more advanced computational fluid dynamic and mechanical analysis. This is demonstrated through the redesign of two impellers previously designed by conventional methods. Comparisons of the results of the CFD analysis and FEM mechanical analysis of the new impellers with those of the earlier designs demonstrate that the tool can rapidly produce nearly optimal designs as an excellent basis for further refinement by the more complex analysis methods.