Dynamics and stability of lean-premixed swirl-stabilized combustion

Survey Constructive nonlinear control: a historical perspective

A computational study to define the phenomena that lead to the onset of short length-scale (spike) rotating stall disturbances has been carried out. Based on unsteady simulations, we hypothesize there are two conditions necessary for the formation of spike disturbances, both of which are linked to the tip clearance flow. One is that the interface between the tip clearance and oncoming flows becomes parallel to the leading-edge plane. The second is the initiation of backflow, stemming from the fluid in adjacent passages, at the trailing-edge plane. The two criteria also imply a circumferential length scale for spike disturbances. The hypothesis and scenario developed are consistent with numerical simulations and experimental observations of axial compressor stall inception. A comparison of calculations for multiple blades with those for single passages also allows statements to be made about the utility of single passage computations as a descriptor of compressor stall.

Criteria for Spike Initiated Rotating Stall

Bifurcation control deals with modification of bifurcation characteristics of a parameterized nonlinear system by a designed control input. Typical bifurcation control objectives include delaying t...

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Bifurcation control: theories, methods, and applications

Microfluidic devices are becoming increasingly common and are seen in applications ranging from biology to nanotechnology and manufacturing. Flow behavior in these small domains can often be counterintuitive because of the low Reynolds number or the relative importance of surface forces. Micro-particle image velocimetry (μPIV) is a quantitative method that can be used to characterize the performance of such microfluidic systems with spatial resolutions better than one micron. Illustrating the impact of this measurement technique, more than 100 journal articles are published per year that feature μPIV velocity measurements. This article discusses the fundamentals of the technique, its theoretical background, and several applications.

Recent Advances in Micro-Particle Image Velocimetry

Studies have been conducted on two laboratory test compressors to investigate the process leading to the formation of finite amplitude rotating stall cells. The measurements were obtained from circumferential arrays of hot wires and were spatially and temporarily analyzed to show that modal perturbations are not always present prior to stall, and when present, sometimes have little direct effect on the formation of the stall cells. The measurements lead to the conclusion that the occurrence of modal perturbations, and the formation of finite amplitude stall cells, are two separate phenomena, both occurring under roughly the same conditions at the peak of the pressure rise characteristic. The measurements also underline the hitherto unsuspected importance of short length scale disturbances in the process of stall inception. Examples are given of different ways in which stall cells can develop and the conclusions are backed up with a summary of current test data from various machines around the world.

Stall inception in axial flow compressors

This paper presents a study of stall inception mechanisms a in low-speed axial compressor. Previous work has identified two common flow breakdown sequences, the first associated with a short lengthscale disturbance known as a ‘spike’, and the second with a longer lengthscale disturbance known as a ‘modal oscillation’. In this paper the physical differences between these two mechanisms are illustrated with detailed measurements. Experimental results are also presented which relate the occurrence of the two stalling mechanisms to the operating conditions of the compressor. It is shown that the stability criteria for the two disturbances are different: long lengthscale disturbances are related to a two-dimensional instability of the whole compression system, while short lengthscale disturbances indicate a three-dimensional breakdown of the flow-field associated with high rotor incidence angles. Based on the experimental measurements, a simple model is proposed which explains the type of stall inception pattern observed in a particular compressor. Measurements from a single stage low-speed compressor and from a multistage high-speed compressor are presented in support of the model.Copyright © 1997 by ASME

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A Study of Spike and Modal Stall Phenomena in a Low-Speed Axial Compressor

This paper presents a study of stall inception mechanisms in a low-speed axial compressor. Previous work has identified two common flow breakdown sequences, the first associated with a short length-scale disturbance known as a “spike,” and the second with a longer length-scale disturbance known as a “modal oscillation.” In this paper the physical differences between these two mechanisms are illustrated with detailed measurements. Experimental results are also presented that relate the occurrence of the two stalling mechanisms to the operating conditions of the compressor. It is shown that the stability criteria for the two disturbances are different: Long length-scale disturbances are related to a two-dimensional instability of the whole compression system, while short length-scale disturbances indicate a three-dimensional breakdown of the flow-field associated with high rotor incidence angles. Based on the experimental measurements, a simple model is proposed that explains the type of stall inception pattern observed in a particular compressor. Measurements from a single-stage low-speed compressor and from a multistage high-speed compressor are presented in support of the model.

1997 Best Paper Award—Turbomachinery Committee: A Study of Spike and Modal Stall Phenomena in a Low-Speed Axial Compressor

Work on rotating stall and its related disturbances has been in progress since the Second World War. During this period, certain ‘hot topics’ have come to the fore — mostly in response to pressing problems associated with new engine designs. This paper will take a semi-historical look at some of these fields of study (stall, surge, active control, rotating instabilities etc.) and will examine the ideas which underpin each topic. Good progress can be reported, but the paper will not be an unrestricted celebration of our successes because, after 75 years of research, we are still unable to predict the stalling behaviour of a new compressor or to contribute much to the design a more stall resistant machine. Looking forward from where we are today, it is clear that future developments will come from CFD in the form of better performance predictions, better flow modelling and improved interpretation of experimental results. It is also clear that future experimental work will be most effective when focussed on real compressors with real problems — such as stage matching, large tip clearances, eccentricity and service life degradation. Today’s topics of interest are mostly associated with compressible effects and so further research will require more high speed testing.Copyright © 2015 by ASME

Stall, Surge, and 75 Years of Research

This paper reports on an experimental program in which active control was successfully applied to both rotating stall and surge in a multistage compressor. Two distinctly different methods were used to delay the onset of rotating stall in a four-stage compressor using fast-acting air injection valves. The amount of air injected was small compared to the machine mass flow, the maximum being less than 1.0 percent. In some compressor configurations modal perturbations were observed prior to stall. By using the air injection valves to damp out these perturbations, an improvement of about 4.0 percent in stall margin was achieved. The second method of stall suppression was to remove emerging stall cells by injecting air in their immediate vicinity. Doing this repeatedly delayed the onset of stall, giving a stall margin improvement of about 6.0 percent. Further studies were conducted using a large plenum downstream of the compressor to induce the system to surge rather than stall. The resulting surge cycles were all found to be initiated by rotating stall and therefore the stall suppression systems mentioned above could also be used to suppress surge. In addition, it was possible to arrest the cyclical pulsing of a compressor already in surge.

I. J. Day

Papers

Stall inception in axial flow compressors

A Study of Spike and Modal Stall Phenomena in a Low-Speed Axial Compressor

1997 Best Paper Award—Turbomachinery Committee: A Study of Spike and Modal Stall Phenomena in a Low-Speed Axial Compressor

Stall, Surge, and 75 Years of Research

Active suppression of rotating stall and surge in axial compressors