Influence of tip clearance on flow behavior and noise generation of centrifugal compressors in near-surge conditions

CFD has become an essential tool for researchers to analyze centrifugal compressors. Tip leakage flow is usually considered one of the main mechanisms that dictate compressor flow field and stability. However, it is a common practice to rely on CAD tip clearance, even though the gap between blades and shroud changes when compressor is running. In this paper, sensitivity of centrifugal compressor flow field and noise prediction to tip clearance ratio is investigated. 3D CFD simulations are performed with three different tip clearance ratios in accordance to expected operating values, extracted from shaft motion measurements and FEM predictions of temperature and rotational deformation. Near-surge operating conditions are simulated with URANS and DES. DES shows superior performance for acoustic predictions. Cases with reduced tip clearance present higher pressure ratio and isentropic efficiency, but no significant changes in compressor acoustic signature are found when varying clearance. In this working point, tip clearance is immersed in a region of strongly swirling backflow. Therefore, tip leakage cannot establish any coherent noise source mechanism.The equipment used in this work has been partially supported by FEDER project funds "Dotacion de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energetica y Medioambiental de Sistemas de Transporte (CiMeT), (FEDER-ICTS-2012-06)", framed in the operational program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain. The authors wish to thank Mr. Pau Raga for his worthy assistance during the meshing process.Galindo, J.; Tiseira Izaguirre, AO.; Navarro García, R.; López Hidalgo, MA. (2015). Influence of tip clearance on flow behavior and noise generation of centrifugal compressors in near-surge conditions. International Journal of Heat and Fluid Flow. 52:129-139. https://doi.org/10.1016/j.ijheatfluidflow.2014.12.004S1291395

Connecting research and professionalism in teacher education

© 2020 Association for Teacher Education in Europe. The three main themes of this Special Issue of European Journal of Teacher Education are brought together and considered in the light of what has been said in the articles included. These themes of teacher education, professionalism and research are all dynamic in the way they have been developing over time and also demonstrate considerable geographical diversity in their manifestations. This paper considers the extent to which these temporal and spatial differences indicate a series of tensions, difficulties and paradoxes as the processes of globalisation continue to influence educational policies and practices around the world. The extent to which the outcomes represent increasing convergence or divergence is discussed and the paper concludes by suggesting a number of key questions that may be asked within a particular context in order to make an assessment of the state of health of the teaching profession within that setting

The same but different? Post-devolution regulation and control in education in Scotland and England

When 'New Labour' came to power in the United Kingdom in 1997, one of their first major initiatives was to establish new devolved political institutions in Scotland, Wales and Northern Ireland. Drawing upon developments in education in Scotland and England, this article explores some aspects of 'regulation', 'autonomy' and 'control' in the post-devolution context. The purpose of the article is to assess the ways in which New Public Management have influenced education policy in the two countries. Aspects of the governance of education are examined in the two national contexts. The 'modernisation' of the teaching profession is examined as a particular case, as well as more general aspects of governance. A number of similarities and differences in the two countries are identified. The themes that best demonstrate these similarities and differences are privatisation, performativity and the policy process. The conclusion seeks to identify the extent to which developments in either or both countries can be attributed to the global neo-liberal agenda