Two‐Dimensional Rotating Stall Analysis in a Wide Vaneless Diffuser

Abstract

We report a numerical study on the vaneless diffuser core flow instability in centrifugal compressors. The analysis is performed for the purpose of better understanding of the rotating stall flow mechanism in radial vaneless diffusers. Since the analysis is restricted to the two-dimensional core flow, the effect of the wall boundary layers is neglected. A commercial code with the standard incompressible viscous flow solver is applied to model the vaneless diffuser core flow in the plane parallel to the diffuser walls. At the diffuser inlet, rotating jet-wake velocity pattern is prescribed and at the diffuser outlet constant static pressure is assumed. Under these circumstances, two-dimensional rotating flow instability similar to rotating stall is found to exist. Performed parameter analysis reveals that this instability is strongly influenced by the diffuser geometry and the inlet and outlet flow conditions.

Rotating instability in the vaneless diffuser of a radial flow pump

“…The development of PIV allows for such a better understanding [7]. Levjar et al [8] have conducted numerical calculations using a two dimensional viscous incompressible flow model to decide if 2D instabilities in the diffuser can contribute to rotating stall. They have compared [9] their results to already published [10][11] PIV measurements performed in the vaneless diffuser of a centrifugal pump.…”

Experimental Study and Theoretical Analysis of the Rotating Stall in a Vaneless Diffuser of Radial Flow Pump

“…A synthesis of the unstable modes that can be evidenced for each flow rates is proposed in table 3, in which n is the number of rotating cells that could be identified through the analysis of the phase difference of the pressure signals of the two microphones. [11]). Based on the rotating stall frequency, the propagation velocity of the stall cell-ω, can be estimated as follow:…”

“…For two dimensional analysis, it was suggested the 2D core flow instability might be responsible for rotating stall. Generally, it is admitted that the effect of [11], Dazin et al [1,12], Dodds and Vahdati [13,14], Ferrara et al [15,16], Abdelhamid et al [17][18][19], Abidogun [20], Nishida and Kobayshi [21,22], Cellai et al [23], Tsurusaki et al [24], Suzuki et al [25], Caignaert et al [26]. The main research contents of these experimental studies were focused on several aspects: i.…”

Analysis of Vaneless Diffuser Stall Instability in a Centrifugal Compressor

“…For the actual evolution of the dynamic character and thus prediction of the number of rotating stall cells and their propagation speed around the annulus, different research groups have considered a time-evolving calculation assuming 2D-unsteady, inviscid and incompressible flow, see e.g., [5][6][7]. The effect of the blades on the flow is fed at the diffuser inlet boundary and a Dirichlet condition with static pressure is considered on the outlet surface.…”