Active stabilization of compressor surge

A novel approach to model unsteady fluid dynamics in compressors network by using bond graph is presented. The model is intended in particular for compressor control system development. First, we develop a bond graph model of a single compression system. Bond graph modeling offers a different perspective to previous work by modeling the compression system based on energy flow instead of fluid dynamics. Analysing the bond graph model explains the energy flow during compressor surge. Two principal solutions for compressor surge problem are identified: upstream energy injection and downstream energy dissipation. Both principal solutions are verified in bond graph modelings of single compression system equipped with surge avoidance system (SAS) and single compression system equipped with active control system. Moreover, the bond graph model of single compressor equipped with SAS is able to show the effect of recycling flow to the compressor upstream states which improves the current available model. The bond graph model of single compression system is then used as the base model and combined to build compressors network models. Two compressor networks are modeled: serial compressors and parallel compressors. Simulation results show the surge conditions in both compressor networks.Keywords: bond graph, compressor modeling, compressor surge, surge avoidance system, active surge control system, serial compressors, parallel compressors. IntroductionA centrifugal compressor is basically used to increase gas pressures. The compressor operating area is described by a plot of the compressor pressure against the flow for different compressor speeds known as a compressor map. Figure 1 shows an example of a compressor map. The stable compressor operating area is limited by a surge line for lower flow. Operating the compressor at a flow lower than the surge line would cause the compressor to go into an unstable condition known as surge. It is an axisymmetric oscillation of the compressor flow and the compressor produced pressure followed by severe vibrations. The vibrations may reduce the reliability of the compression system and large amplitude vibrations may lead to compressor damage in particularly to the compressor blades and bearings, and also damages on pipe connections.Surge phenomena is of interest as higher compressor efficiency operating points are located near the surge line and some processes are requiring low mass flow at high pressure. However, operating in such points may endanger the compressor because a disturbance could bring the compressor into the surge area. There is a trade-off between operating the compressor at a higher efficiency and the stability. Two methods have been developed to overcome the surge problem:

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“…The implementations of R u can be found in by movable plenum wall [30,31], piston-actuation [4], and blow off valve [32].…”

Section: Upstream Energy Injectionmentioning

confidence: 99%

Bond graph modeling of centrifugal compression systems

Uddin

Gravdahl

2015

SIMULATION

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“…Active flow control has been used for various applications in order to enhance stability of unsteady flow, such as for stabilization of compressor surge in jet engines [15,39]. Small disturbances in the incoming flow can have large repercussions on the system stability.…”

Section: Motivationmentioning

confidence: 99%

Reduced-Order, Trajectory Piecewise-Linear Models for Nonlinear Computational Fluid Dynamics

Gratton

Willcox

2004

34th AIAA Fluid Dynamics Conference and Exhibit

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Computational fluid dynamics (CFD) is now widely used throughout the fluid dynamics community and yields accurate models for problems of interest. However, due to its high computational cost, CFD is limited for some applications. Therefore, model reduction has been used to derive low-order models that replicate CFD behavior over a restricted range of inputs, and various frameworks have been developed. Unfortunately, the majority of those methods are limited to linear cases and do not properly handle reduction of nonlinear systems.In order to overcome restrictions of weak nonlinearity and the costly representation of the system's nonlinearity found in other nonlinear reduction approaches, a trajectory piecewise-linear (TPWL) scheme is developed for a CFD model of the twodimensional Euler equations. The approach uses a weighted combination of linearized models to represent the nonlinear CFD system. Using a set of training trajectories obtained via a simulation of the nonlinear CFD model, algorithms are presented for linearization point selection and weighting of the models. Using the same training trajectories to provide a snapshot ensemble, the proper orthogonal decomposition (POD) is used to create a reduced-space basis, onto which the TPWL model is projected. This projection yields an efficient reduced-order model of the nonlinear system, which does not require the evaluation of any full-order system residuals, while capturing a large portion of the nonlinear space.The method is applied to the case of flow through an actively controlled supersonic diffuser. Convergence of the TPWL approach is presented for both full-order and reduced-order cases. The TPWL approach and the POD combine naturally to form an efficient reduction procedure and the methodology is found to yield accurate results, including cases with significant shock motion. Reduced-order PWL models are shown to be three orders of magnitude more efficient than the nonlinear CFD for simulation of a representative test case. AcknowledgmentsA number of peoples contributed in various ways to the last two years of my life here, in Boston, and made them more than enjoyable and memorable.Foremost on my list is my advisor, Karen, who helped me more than anything else in getting through MIT. Even though a communication problem initially restricted the flow of information between us, and despite the fact that I thought for a long time that she was English, she has always shown me a great deal of patience. Also, the availability, guidance and responsiveness she provided during all that time went beyond any expectations I possibly could have had for a research advisor. I will never thank her enough for the opportunities to go to Rotterdam and Singapore.Thanks to Jim Paduano and all the member of the supersonic project for their initial interest toward me and allowing me such an easy switch to model order reduction. Thanks to Mark Drela who provided me with precious hints in debugging mtflow. I must also acknowledge Michal Rewienski and Alexandre Megretsk...

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“…, all the roots have negative real parts, if and only if [27] (for details see, e.g., [9,Chapter 51):…”

Section: Stability Of Compression Systemsmentioning

confidence: 99%

“…[23]. For example, in [37, 561, 25% decrease in mass flow at the surge point is reported in a radial compressor whereas Ffowcs Williams and Huang [27] achieve approximately 20% reduction in mass flow using a loud- …”

Section: Surge Controlmentioning

confidence: 99%

Modeling and control of compressor flow instabilities

1999

IEEE Control Syst.

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Stable operation of both axial and radial compressors is constrained by the occurence of aerodynamic flow instabilities: rotating stall and surge. Developments in the understanding of the physics behind these instabilities and ideas of how t o stabilize the compressor system, have opened the door t o a new era in the field of compressor control.This study gives an overview of the current state in modeling and control of surge and rotating stall in axial and radial compressors. It summarizes different types of aerodynamic flow instabilities that can occur in these machines. Compressor performance is discussed on the basis of compressor maps and important features of these instabilities are treated. But, this work focuses on active control systems applied in experimental systems. Compressor models that are used frequently in controller designs are described and the effect of assumptions on the prediction capability of these models is discussed. Furthermore, this report deals with control concepts t o guarantee stable operation and an outline is given of sensors, actuators and controllers applied in laboratory set-ups.The main contribution of this study is the comparison of aerodynamical flow instabilities found in axial and radial compressors, of several models, and of controllers implemented on experimental set-ups. It appeared that the behavior of a compressor system subsequent to instability onset is reasonably grasped but the considered models can not describe all types of instabilities encountered. Nevertheless, the Moore-Greitzer model seems an useful starting point for further research since it describes the compressor behavior subsequent t o the onset of rotating stall and surge. A better understanding of the mechanism(s) behind the onset of these instabilities may allow refinements to existing models and may give insights into new control methods. Currently, apart from a few exceptions, only complex-valued proportional feedback controllers are used. More advanced, nonlinear controllers are expected to improve the performance of the compressor system.

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Active stabilization of compressor surge

Cited by 121 publications

References 7 publications

Bond graph modeling of centrifugal compression systems

Bond graph modeling of centrifugal compression systems

Reduced-Order, Trajectory Piecewise-Linear Models for Nonlinear Computational Fluid Dynamics

Modeling and control of compressor flow instabilities

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