Development and Validation of a Model for Centrifugal Compressors in Reversed Flow Regimes

Abstract

Turbochargers are widely used to help reduce the environmental impact of automotive engines. However, a limiting factor for turbochargers is compressor surge. Surge is an instability that induces pressure and flow oscillations that often damages the turbocharger and its installation. Most predictions of the surge limit are based on low-order models, such as the Moore-Greitzer model. These models tend to rely on a characteristic curve for the compressor created by extrapolating the constant speed lines of a steady-state compressor map into the negative mass flow region. However, there is little validation of these assumptions in the public literature. In this paper, we develop further the first-principles model for a compressor characteristic presented in Powers et al. [1], with a particular emphasis on reverse flow. We then perform experiments using a 58mm diameter centrifugal compressor provided by Cummins Turbo Technologies, where we feed air in the reverse direction though the compressor while the impeller is spinning in the forwards direction in order to obtain data in the negative mass flow region of the compressor map. This demonstrated experimentally that there is a stable operating region in the reverse flow regime. The recorded data showed a good match with the theoretical model developed in this paper We also identified a change in characteristic behaviour as the impeller speed is increased which, to the authors knowledge, has not been observed in any previously published experimental work.

A new first-principles model to predict mild and deep surge for a centrifugal compressor

“…In this case, air is travelling from the volute through to the impeller inlet but the impeller wheel is still rotating in the forward direction as this is controlled by the turbine. Therefore, the angle at which air enters from the volute into the diffuser has to be specified, and Powers et al [17] argued that this should be…”

“…The shear layer causes a loss in pressure due to viscous dissipation. Powers et al [17] decided to use an instantaneous loss at the interface,…”

“…Similarly, De Bellis and Bontempo [15] and Powers et al [16,17] developed models for the compressor characteristics from the 1D steady-state fundamental equations of fluid motion. De Bellis and Bontempo [15] also included multiple loss models with parameters tuned with experimental data, whereas Powers et al [16,17] developed their model with a minimal number of parameters and aimed to find universal relations for these so they wouldn't need tuning for individual compressors.…”

“…We will focus on improving their ability to qualitatively capture flow phenomena like mild surge. To do this, we will extend the work by Powers et al [16,17] and assess the resulting model via comparison to experiments.…”

“…The rest of the paper is structured as follows: In Section 2 we will improve on the model developed by Powers et al [16,17], mainly by including the effects of diffuser recirculation, to obtain new quintic-shaped compressor characteristics. In Section 3, we will develop a 1D model in space and time that can simulate the wave dynamics in the test facility pipework.…”