The Flow Structure During Onset and Developed States of Rotating Stall Within a Vaned Diffuser of a Centrifugal Pump

Abstract

Particle Image Velocimetry (PIV) and pressure fluctuation measurements are used for investigating the onset and development of rotating stall within a centrifugal pump having a vaned diffuser. The experiments are performed in a facility that enables measurements between the diffuser vanes, within part of the impeller, in the gap between them and in the volute. The diffuser is also instrumented with pressure transducers that track the circumferential motion of rotating stall in the stator. The timing of low-pass-filtered pressure signals are also used for triggering the acquisition of PIV images. The data include detailed velocity distributions, instantaneous and phase-averaged, at different blade orientations and stall phases, as well as auto-and cross-spectra of pressure fluctuations measured simultaneously in neighboring vane passages. The cross-spectra show that the stall propagation rate is 0.93 Hz, 6.2 percent of the impeller speed, and that the stall travels from the passages located on the exit side of the volute toward the beginning side, crossing the tongue region in the same direction as the impeller, where it diminishes. Under stall conditions the flow in the diffuser passage alternates between outward jetting, when the low-pass-filtered pressure is high, to a reverse flow, when the filtered pressure is low. Being below design conditions, there is a consistent high-speed leakage flow in the gap between the impeller and the diffuser from the exit side to the beginning of the volute. Separation of this leakage flow from the diffuser vane causes the onset of the stall. The magnitude of the leakage and the velocity distribution in the gap depend on the orientation of the impeller blade. Conversely, the flow in a stalled diffuser passage and the occurrence of stall do not vary significantly with blade orientation. With decreasing flow-rate the magnitudes of leakage and reverse flow within a stalled diffuser passage increase, and the stall-cell size extends from one to two diffuser passages.

Experimental Investigation of Flow Instabilities and Rotating Stall in a High-Energy Centrifugal Pump Stage

“…Resulting from the simulation, diffuser rotating stall rotating with 10% of the rotational speed has been found. The simulated flow pattern was in accordance with the measurements of Hergt and Benner [5], Sinha et al [10] and Wang and Tsukamoto [11]. While in the case studied by Sinha the gap between diffuser and impeller vanes was relatively large (20% of impeller radius), in Wang's analysis the gap was only 3% of the impeller outer radius.…”

The application of laser measurement techniques to aerospace flows

“…In-board vortices were found to interact with the tip vortex, having a signi®cant effect on its roll-up. Finally, in work by Sinha et al [105],¯ow structure within a centrifugual pump diffuser was studied with a 4 Mpixel DPIV system which was triggered by diffuser pressure measurements. Results showed the¯ow structure at stall to be highly complex and transient with signi®cant leakage between the impeller and the diffuser.…”

A Behavior of the Diffuser Rotating Stall in a Low Specific Speed Mixed-Flow Pump

“…They concluded that the flow instabilities in the vaned diffuser occur in the range with negative slope of the diffuser pressure performance. Hergt et al [5], Eisele et al [6] and Sinha et al [7] made experimental observations of the internal flow in vaned diffusers at a low flow rate, but those investigations are not enough in spatial or temporal resolution. There are even few studies on rotating stall in mixed flow diffuser pumps.…”