Experimental and Numerical Investigation of Tip Clearance and Bleed Effects in a Centrifugal Compressor Stage With Pipe Diffuser

Abstract

The subject of this paper is the experimental and numerical investigation of a state-of-the-art high pressure centrifugal compressor stage with pipe diffuser for a jet engine application. This study shows the impact of impeller tip clearance- and bleed-variation on the centrifugal stage. The purpose of this paper is threefold. In the first place, it investigates the effects on the stage performance. Secondly, it seeks to explain local flow-phenomena, especially in the diffuser. Finally, it shows that steady CFD simulations are capable of predicting these phenomena. Experimental data were gathered using conventional pitot and three-hole-probes as well as particle-image-velocimetry. Numerical simulations with the CFD solver TRACE were conducted to get fundamental insight into the flow. Thus, this study contributes greatly towards understanding the principle of the flow phenomena in the pipe diffuser of a centrifugal compressor.

Investigation of two pipe diffuser configurations for a compact centrifugal compressor

“…Similarly, when the reverse flow caused by the impeller passes through the ridge of the pipe diffuser near the shroud, a vortex is formed at the shroud/suction side region. This is different from the results shown in the previous studies, [1][2][3] where just two vortices were found induced by scallop leading edge of pipe diffuser. As the fluid convects along the pipe passage, these three vortices are enhanced until the throat at Plane III.…”

“…This configuration is normally employed by General Electric. [1][2][3][4][5]10 As shown in Figure 2, at the throat of the pipe diffuser, the cross section is circular, and then the cross section becomes oblong with semi-circular ends attached by straight lines, like an oval along a straight centerline. The long axis of the cross section gradually increases, whereas the short axis and semicircular radius are equal to the diffuser throat diameter along a straight centerline.…”

“…Many researchers have focused on investigating both the particularly little understood flow mechanisms between the impeller exit and pipe diffuser throat and the diffusing passages behind the throat. Zachau and Buescher, 1 Zachau and Niehuis, 2 and Kunte et al 3,4 performed flow investigations in diffusers using a nonintrusive measurement technique and numerical simulations. A comparison of predicted and measured flow fields was conducted in detail and strong agreement was found.…”

“…Furthermore, altering the flow from the radial to axial direction in a pipe diffuser is a difficult challenge for pipe diffuser design. In previous publications, two main configurations, which will be discussed in more detail later, have been presented: The first is a radial pipe diffuser connected to a dump followed by a deswirler, which is mainly used by General Electric, [1][2][3][4][5]10 and the second is a fishtail diffuser, which is employed by Pratt & Whitney Canada. [11][12][13][14] Despite the extensive studies on pipe diffusers, few comprehensive results have been published addressing the complex flow characteristics in fishtail diffusers.…”

Miniature gas turbines : numerical study of the effects of miniaturization on the performance of compressor

“…The impeller deformation and adjusted tip clearance was claimed to influence the aerodynamic performance and structure reliability of the compressor system. Kunte and Schwarz [35] have investigated the tip clearance and bleed effect, based on a centrifugal compressor stage. Experimental data were gathered and compared with CFD results from TRACE, which was developed by DLR.…”