Laser Doppler Velocimetry Characterization of Unsteady Vaned Diffuser Flow in a Centrifugal Compressor

Abstract

Modern turbomachinery faces increased performance demands in terms of efficiency, compactness, and pressure-rise. Advancements in computational technology have allowed numerical methods to become the backbone of design development efforts. However, the unique complexities of centrifugal compressor flow-fields pose difficult computational problems. As such, advanced experimental methods must be used to obtain high-quality data sets to further inform, improve, and validate computational methods in complex flow regimes. A recent experimental work on a high-speed centrifugal compressor has provided detailed, unsteady, three-component velocity data using laser Doppler velocimetry. A passage vortex is present, and its nascent tied to the increased incidence at mid-span associated with impeller wake flow. This vortex begins in the hub-pressure side corner and grows to fill the passage and become temporally stable. The vortex development is unsteady in nature, and the unsteady effects persist 40% downstream of the throat. Distinct jet and wake flow patterns from the impeller also do not agglomerate until 40% downstream of the throat. Additionally, the critical impact of the unsteady flow development on the time-averaged flow-field is explained.

Numerical study of wake and potential interactions in a two-stage centrifugal refrigeration compressor

“…Ziegler et al (2003aZiegler et al ( , 2003b) measured unsteady and time-averaged flow fields in the region between the impeller outlet and diffuser inlet and investigated the CONTACT Yijun Mao maoyijun@hust.edu.cn effect of impeller-diffuser gap on the compressor performance. Gooding et al (2020) measured unsteady, threedimensional velocity fields in the vaned diffuser of a centrifugal compressor using a three-component laser Doppler velocimetry system, and illustrated that it is important to resolve the spanwise flow component for better capturing evolution of secondary flow structures.…”

The Impact of Various Modeling Decisions on Flow Field Predictions in a Centrifugal Compressor

“…However, unsteadiness is one such flow driver that can significantly impact the measured flow field. Recent experimental measurements of the unsteady velocity field through the diffuser show that unsteadiness persists further into the diffuser passage than typically assumed [21], suggesting a strong influence of unsteady effects on the flow field. The methodology used for model selection here-always stepping toward a more physically realistic model-was done to minimize the impact of omitted flow drivers.…”