Plenary Lecture

Analysis of separated flows in hydro machines

Prof. Arpad A. Fay
Mechanical engineer, PhD, retired from GANZ Co.
(the only Hungarian hydro turbine manufacturer),
and from the Department of Fluid and Heat Machinery,
University of Miskolc,
Hungary
E-mail: arpad.fay@t-online.hu
 

Abstract: Starting point of the discussion is a paper by the author ″Analysis of separated 2D flows″ shown in the WSEAS Conference FMA’07 (Vouliagmeni Beach, Athens, August 25-27, 2007, Paper 565-373). From this paper, statements about the flows around circular cylinders, the Coanda effect, the Knapp’s cycle, and the alternate jet theory of Karman vortices are recalled to mind. These are then applied to flows around single airfoils, cascades of airfoils, Francis and Kaplan turbine runners, and axial-flow pump impellers.
For single airfoils experiences obtained with circular cylinders are generalized. Adherence or reattachment of the boundary layer is discussed. Stall is defined as flow separation without reattachment. For non-stalled flows around profiles the Kutta-Joukowskij condition (equal velocities on suction and pressure sides near exit) is explained by the von Karman vortex row.
For cascades of vanes the onset of stall is moving from vane to vane as learned from the theory of rotating stall. The nature and effects of rotating stall are well known from the blower and compressor practice. However, they are more general, valid also for incompressible flows. For axial-flow pumps the shape of the pump characteristics is explained by single and multiple rotating stall on the suction sides of the blades. The merits and limitations of using 3D Euler solvers in the computations of hydro turbine or pump characteristics are discussed from practical point of view.
For Francis turbine runners part-load instabilities (limiting the allowed operating range), which are generally associated with spiraling cavitation ropes in the draft tubes, are explained by rotating stall on the suction sides of the runner vanes. Full-load instabilities obtained in a few Francis turbines (60 MW surges for 315 MW turbines) are also understandable based on rotating stall at the pressure sides of the vanes and the model turbine tests by the author. The vain of such instabilities in Kaplan turbines is also explained. At the end a summary is attempted and open questions are listed.
 

Brief Biography of the Speaker:
Arpad A. Fay, M. Math & Mech. Eng. PhD, retired from Fluid and Heat Machinery Department of Miskolc University, Hungary. He has been engaged in experimental and theoretical research on hydroturbines and pumps, field work, guarantee tests on models and prototypes, calculation of forces on large parts of hydromachines, computing, consultancy and teaching for the past 50 years at GANZ Company the largest hydroturbine and pump manufacturer in Hungary. He worked in Egypt, South Africa, Universities of Budapest, Southampton and Miskolc, UNESCO & UNDP projects at NIT Bhopal and CWPRS Pune India etc., He was a member of IEC Working Group on Scale effects of Technical Committee on Hydraulic Turbines and IAHR Section on Hydraulic Machinery, Equipment and Cavitation, Working Group on Scale effects. He has over 50 papers published. As a member of the Society of the Hungarian Mechanical Engineers, he organized several international Conferences on Fluid Machinery in Budapest.