This paper presents the velocity and turbulence characteristics of the flow in an annular diffuser, which is a model of a gas turbine exhaust diffuser with six struts. The diffuser where the measurements were made is a scaled down model of a 10 MW gas turbine, built by GE/Nuovo Pignone.

In a previous paper (Desideri and Manfrida, 1995) 2-D turbulence and velocity measurements were presented with axial inlet velocity conditions.

In this paper a more detailed 3-D analysis of the design and off design behavior of the diffuser is presented. Turbulence characteristics were determined by means of two hot split-film probes, which allowed measuring axial, radial and tangential components of the mean velocity and their fluctuating components. The measuring point is moved inside the diffuser by means of two step-motors, which allow the rotation of the hub and the radial displacement of the probe.

Off-design behavior of the annular diffuser was determined by changing the inlet velocity angle of 10° from axial direction. The effect of swirl on the performance of the diffuser will be presented.

Turbulence microscales were also calculated in regions of interest inside the diffuser, with particular attention to the strut wake.

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