In 1951 Ainley and Mathieson published a method of predicting the design and off-design performance of an axial turbine (British ARC, R & M 2974). The flow and hence the losses were calculated at a single “reference diameter” for each blade row. This method has been widely used ever since. A critical review of the method has been made, based on detailed comparisons between the measured and predicted performance of a wide range of modern turbines. As a result, improvements have been made in the formulas for secondary loss and tip clearance loss prediction. The accuracy of the improved method has been assessed. Despite its relatively simple approach, it is believed that it will remain of great value in project work and preliminary design work.
Centrifugal compressors are used in a wide range of applications in which performance and mechanical integrity are invariably among the paramount design objectives. There is therefore continuing interest in the development of a sound understanding of the relevant physical phenomena and in the systematic application of the knowledge base that is the forerunner of the established design procedures. The paper reviews centrifugal compressor design methods that are commonly used in industry and reviews the underlying engineering science supporting the design practices. The design process, starting with the preliminary design and its reliance on empirical rules through to state-of-the-art aerodynamic design using computational fluid dynamics (CFD), is presented. The essentials of impeller mechanical design are also included in the paper.
SYNOP s I sA computer-based c e n t r i f u g a l compressor design procedure developed a t t h e National Gas Turbine Establishment i s described. aerodynamic a n a l y s i s , stress a n a l y s i s , and t h e d i r e c t generation of d a t a f o r manufacture by numerical control. The method of d i f f u s e r design incorporates analyses of t h e flow i n t h e vaneless space and 'semi-vaneless' space adapted from a new performance p r e d i c t i o n technique; published d i f f u s e r pressure recovery d a t a a r e used i n t h e s e l e c t i o n of t h e d i f f u s e r channel geometry. The impeller design package includes a geometry modelling procedure, The a p p l i c a t i o n of t h e s e methods t o t h e design of a 6.5 p r e s s u r e r a t i o c e n t r i f u g a l compressor s t a g e is described. advantages o f f e r e d by t h e new design procedure. an earlier compressor designed w i t h less advanced techniques f o r t h e same aerodynamic duty, t h e advantages of t h e new design procedure a r e e s t a b l i s h e d . The experimental r i g t e s t i n g of t h i s compressor has been used t o evaluate t h e By comparing t h e measured performance with t h a t of 1.
By considering a many-bladed cascade, two simple theories are developed for secondary flow m cascades. Following the work of Hawthorne (1)#, three components of vorticity are identified at exit from the cascade. An expression is obtained for the difference in the time taken for fluid particles to travel over the two surfaces of the blade, and this is used to derive the governing equations for the distributed secondary, trailing fdament and trailing shed vorticities. It is shown that, for a many-bladed cascade, the total secondaly circulation in the downstream flow is zero. The calculation of secondary flow for a real cascade is discussed, and it is shown that earlier calculations of secondary flow at exit fromcascades are consistent with this new approach.
This paper is based mainly on theoretical and experimental work done as part of the research program on turbine blade cooling at the National Gas Turbine Establishment. After describing the effects of increased trailing edge thickness on turbine efficiency, the bulk of the paper is concerned with the losses caused by the cooling air. A simple theoretical method for calculating the pressure losses caused by discharging the spent coolant into the main gas stream is described and the available experimental results used for comparison. Reasonable agreement for the loss of efficiency is obtained. The results of some cascade tests on transportation cooled blades are also included.
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