Ryoji Imai

Non-linear calculation of separated flow in centrifugal impellers and its application to filing problems.

Separated flows in a centrifugal impeller are analyzed by using a singularity method on the assumption that the absolute flow is two-dimensional, steady, imcompressible, inviscid, and irrotational. By using an iterative method, the boundary conditions on the surface of separated region is applied exactly on the surface; a non-linear theory. From the angular momentum relations, it is shown that the most reasonable flow is obtained in the case when the separated region terminates with a cusped form. The velocity field and the pressure distributions are given for various flow rated and assumed separation points. The decrease in head is larger for upstream separation. Over/under filing effects are discussed by applying the present method on the assumption that the flow is separated at the trailing corners of thick vanes.

A free streamline analysis of separated flow in a centrifugal impeller.

The flow in a logarithmic impeller with trailing edge separation is analysed by using a conformal mapping method. The problem is linearised by assuming that the thickness of the separated region is small. The flow can be determined by specifying the location of the separation point, and by the application of the condition that there should be no singularity at the closure point. The latter condition results in the location of the closure point shortly downstream of the trailing edge. It is shown that the head is significantly reduced by the separation. Discussions are made about the angular momentum conservation relations for a few models and it is found that the conservation relation is better satisfied for those cases with a thinner separated region, without much dependence on the model used.