variavel0=<b>Waldir de Oliveira</b> - waldir@iem.efei.br Universidade Federal de Itajubá
<b>Nelson Manzanares Filho</b> - nelson@iem.efei.br Universidade Federal de Itajubá
<b>Euclides Carvalho Fernandes</b> - euclides@mec.ita.cta.br Instituto Tecnológico de Aeronáutica
<b>Abstract.</b> In the initial design phase of a new centrifugal impeller, the blade number is usually estimated by means of empirical formulae available in the literature. These formulae are always established by considering some geometrical parameters of the impellers, as the inlet and outlet angles and diameters. Depending on the adopted empirical coefficients, the calculated blade number can vary in a broad range for the same design situation, which makes the choice of an adequate blade number a difficult task. The principal aim of this paper is to present a criterion based on local flow characteristics, taking into account the whole impeller geometry. These characteristics can be obtained with a potential flow calculation, by means of an integral formulation based on the singularity method. Using the relative velocity and pressure distributions, one defines a dimensionless parameter called Richardson number. With basis on sound physical arguments, one shows that the maximum value of this parameter indicates the optimum blade number of turbomachinery impellers leading to good aerodynamic performance. Some numerical results are compared with experimental data, validating the effectiveness of the proposed criterion.
<b>Keywords.</b> turbomachinery, centrifugal impeller, singularity method, Richardson number, blade number.