Modeling and Computation of Flow in a Passage With 360-Degree Turning and Multiple Airfoils

Abstract

The spiral casing of a hydraulic turbine is a complex flow device which contains a passage of 360-degree turning and multiple elements of airfoils (the so-called distributor). A three-dimensional flow analysis has been made to predict the flow behavior inside the casing and distributor. The physical model employs a two-level approach, comprising of (1) a global model that adequately accounts for the geometry of the spiral casing but smears out the details of the distributor, and represents the multiple airfoils by a porous medium treatment, and (2) a local model that performs detailed analysis of flow in the distributor region. The global analysis supplies the inlet flow condition for the individual cascade of distributor airfoils, while the distributor analysis yields the information needed for modeling the characteristics of the porous medium. Comparisons of pressure and velocity profiles between measurement and prediction have been made to assess the validity of the present approach. Flow characteristics in the spiral casing are also discussed.