ABSTRACT
The pressing need for continuous improvements in turbine efficiencies has promoted in recent years an intense research activity on secondary flows aimed at achieving a deeper knowledge of such complex fluid dynamic phenomena and to reduce the secondary losses. The knowledge of blade row performance, in terms of spanwise loss and flow angle distribution, is in fact of utmost importance in the aerodynamic development of multistage turbines, both for optimizing the design and for predicting the overall efficiency at partial loads. This is true especially in high pressure stages, where the secondary effects are often dominant because of the low aspect ratio of the bladings. A very large amount of experimental work on secondary flows in turbine cascades at design conditions has been carried out in the recent past. These investigations aimed at clarifying the details of three-dimensional flow development (e.g., Langston et al. [1], Marchal and Sieverding [2], Sieverding [3], Sharma and Butler [4], Hodson and Dominy [5], and Yamamoto [6]), at analyzing the loss production mechanism (e.g., Moore and Adhye [7], and Gregory-Smith et al. [8]), and at determining the development of turbulence quantities (e.g., Moore et al. [9], Zunino et al. [10], Gregory-Smith 126et al. [11], and Gregory-Smith and Cleak [12]). Other papers, but not so many in the published literature, reported on secondary flows at off-design conditions. Yamamoto and Nouse [13] have shown the influence of the incidence angle on the three-dimensional flow inside a linear cascade. Hodson and Dominy [14] have reported on secondary flows downstream of a high speed linear cascade under off-design conditions, including incidence angle, pitch-chord ratio, and Reynolds number and inlet boundary layer thickness variations.
