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Journal ArticleDOI

Rotating Instabilities in an Axial Compressor Originating From the Fluctuating Blade Tip Vortex

08 May 2000-Journal of Turbomachinery-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 123, Iss: 3, pp 453-460
TL;DR: In this article, the rotational instability (RI) is observed in axial flow fans, centrifugal compressors as well as in low-speed and high-speed axial compressors.
Abstract: Rotating instabilities (RI) have been observed in axial flow fans, centrifugal compressors as well as in low-speed and high-speed axial compressors. They are responsible for the excitation of high amplitude rotor blade vibrations and noise generation. This flow phenomenon moves relative to the rotor blades and causes periodic vortex separations at the blade tips and an axial reversed flow through the tip clearance of the rotor blades.The paper describes experimental investigations of RI in the Dresden Low-Speed Research Compressor (LSRC). The objective is to show that the fluctuation of the blade tip vortex is responsible for the origination of this flow phenomenon.RI have been found at operating points near the stability limit of the compressor with relatively large tip clearance of the rotor blades. The application of time-resolving sensors in both fixed and rotating frame of reference enables a detailed description of the circumferential structure and the spatial development of this unsteady flow phenomenon, which is limited to the blade tip region.Laser-Doppler-Anemometry (LDA) within the rotor blade passages and within the tip clearance as well as unsteady pressure measurements on the rotor blades show the structure of the blade tip vortex.It will be shown that the periodical interaction of the blade tip vortex of one blade with the flow at the adjacent blade is responsible for the generation of a rotating structure with high mode orders, termed as rotating instability (RI).Copyright © 2000 by ASME
Citations
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Journal ArticleDOI
TL;DR: In this paper, 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.
Abstract: 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.

393 citations

Journal ArticleDOI
TL;DR: In this article, a semi-historical look at some of these fields of study (stall, surge, active control, rotating instabilities etc.) and examine the ideas which underpin each topic are presented.
Abstract: 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

238 citations

Journal ArticleDOI
TL;DR: In this article, an experimental and numerical investigation aimed at understanding the mechanisms of rotating instabilities in a low speed axial flow compressor was carried out with high-resolution pressure measurements at different clearances.
Abstract: This paper reports on an experimental and numerical investigation aimed at understanding the mechanisms of rotating instabilities in a low speed axial flow compressor. The phenomena of rotating instabilities in the current compressor were first identified with an experimental study. Then, an unsteady numerical method was applied to confirm the phenomena and to interrogate the physical mechanisms behind them. The experimental study was conducted with high-resolution pressure measurements at different clearances, employing a double phase-averaging technique. The numerical investigation was performed with an unsteady 3-D Navier-Stokes method that solves for the entire blade row. The current study reveals that a vortex structure forms near the leading edge plane. This vortex is the result of interactions among the classical tip-clearance flow, axially reversed endwall flow, and the incoming flow. The vortex travels from the suction side to the pressure side of the passage at roughly half of the rotor speed. The formation and movement of this vortex seem to be the main causes of unsteadiness when rotating instability develops. Due to the nature of this vortex, the classical tip-clearance flow does not spill over into the following blade passage. This behavior of the tip-clearance flow is why the compressor operates in a stable mode even with the rotating instability, unlike traditional rotating stall phenomena.Copyright © 2001 by ASME

214 citations

Journal ArticleDOI
TL;DR: In this paper, the tip-leakage flow in a turbomachinery cascade is studied using large-eddy simulation with particular emphasis on understanding the underlying mechanisms for viscous losses in the vicinity of the tip gap.
Abstract: The tip-leakage flow in a turbomachinery cascade is studied using large-eddy simulation with particular emphasis on understanding the underlying mechanisms for viscous losses in the vicinity of the tip gap. Systematic and detailed analysis of the mean flow field and turbulence statistics has been made in a linear cascade with a moving endwall. Gross features of the tip-leakage vortex, tip-separation vortices, and blade wake have been revealed by investigating their revolutionary trajectories and mean velocity fields. The tip-leakage vortex is identified by regions of significant streamwise velocity deficit and high streamwise and pitchwise vorticity magnitudes. The tip-leakage vortex and the tip-leakage jet which is generated by the pressure difference between the pressure and suction sides of the blade tip are found to produce significant mean velocity gradients along the spanwise direction, leading to the production of vorticity and turbulent kinetic energy. The velocity gradients are the major causes for viscous losses in the cascade endwall region. The present analysis suggests that the endwall viscous losses can be alleviated by changing the direction of the tip-leakage flow such that the associated spanwise derivatives of the mean streamwise and pitchwise velocity components are reduced.

156 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe the structures that produce a spike-type route to rotating stall and explain the physical mechanism for their formation based on numerical simulations, complemented and corroborated by experiments.
Abstract: In this paper we describe the structures that produce a spike-type route to rotating stall and explain the physical mechanism for their formation. The descriptions and explanations are based on numerical simulations, complemented and corroborated by experiments. It is found that spikes are caused by a loss of pressure rise capability in the rotor tip region, due to flow separation resulting from high incidence. The separation gives rise to shedding of vorticity from the leading edge and the consequent formation of vortices that span between the suction surface and the casing. As seen in the rotor frame of reference, near the casing the vortex convects toward the pressure surface of the adjacent blade. The approach of the vortex to the adjacent blade triggers a separation on that blade so the structure propagates. The above sequence of events constitutes a spike. The simulations show shed vortices over a range of tip clearances including zero. The implication is that they are not part of the tip clearance vortex, in accord with recent experimental findings. Evidence is presented for the existence of these vortex structures immediately prior to spike-type stall and, more strongly, for their causal connection with spike-type stall inception. Data from several compressors are shown to reproduce the pressure and velocity signature of the spike-type stall inception seen in the simulations.Copyright © 2012 by ASME

155 citations


Cites result from "Rotating Instabilities in an Axial ..."

  • ...It is also found that the tip clearance flow is highly unsteady, as has been observed by others [20,21]....

    [...]

References
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Proceedings ArticleDOI
TL;DR: In this article, a study of stall inception mechanisms in low-speed axial compressors is presented, where the authors show 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 length-scale disturbances indicate a three-dimensional breakdown of the flow field associated with high rotor incidence angles.
Abstract: 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

306 citations

Journal ArticleDOI
TL;DR: In this article, a study of stall inception mechanisms in a low-speed axial compressor is presented, where the authors show 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.
Abstract: 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.

277 citations

Journal ArticleDOI
TL;DR: In this paper, aperiodic multisampling technique with a hot wire in the clearance and with a high-response pressure sensor on the casing wall was used to obtain ensemble-averaged and phase-locked flow patterns in various tip clearances of two axial compressor rotors.
Abstract: Ensemble-averaged and phase-locked flow patterns in various tip clearances of two axial compressor rotors were obtained by aperiodic multisampling technique with a hot wire in the clearance and with a high-response pressure sensor on the casing wall. A leakage flow region distinct from a throughflow region exists at every clearance. In the case of a small tip clearance, the leakage jet flow interacts violently with the throughflow near the leading edge, and a rolling-up leakage vortex decays downstream. As the clearance increases, a stronger leakage vortex comes into existence at a more downstream location, and a reverse flow due to the vortex grows noticeably. A scraping vortex is recognized at the pressure side near the trailing edge only for the small clearance. A horseshoe vortex appears in the upstream half of the through flow region for every tip clearance. The solidity does not affect the flow pattern substantially except for the interaction of the leakage vortex with the adjacent blade and wake.

190 citations

Journal ArticleDOI
TL;DR: In this article, the negative effects of the tip clearance gap on the aerodynamic and acoustic performance of axial turbomachines were investigated and a turbulence generator was used to eliminate the noise and improve aerodynamic performance.
Abstract: An experimental study is described to investigate the negative effects of the tip clearance gap on the aerodynamic and acoustic performance of axial turbomachines. In addition to the increased broadband levels reported in the literature when the tip clearance is enlarged, significant level increases were observed within narrow frequency bands below the blade passing frequency. Measurements of the pressure and velocity fluctuations in the vicinity of the blade tips reveal that the tip clearance noise is associated with a rotating flow instability at the blade tip, which in turn is only present under reversed flow conditions in the tip clearance gap. A turbulence generator inserted into the tip clearance gap is found to be effective in eliminating the tip clearance noise and in improving the aerodynamic performance.

165 citations

Proceedings ArticleDOI
02 Jun 1998
TL;DR: In this paper, the influence of three-dimensional flow structures within a compressor blade passage has been examined computationally to determine their role in rotating stall inception, and it was concluded that the flow structure within the blade passages must be addressed to explain the stability of an axial compression system which exhibits such short length-scale disturbances.
Abstract: The influence of three-dimensional flow structures within a compressor blade passage has been examined computationally to determine their role in rotating stall inception. The computations displayed a short length-scale (or spike) type of stall inception similar to that seen in experiments; to the authors’ knowledge this is the first time such a feature has been simulated. A central feature observed during the rotating stall inception was the tip clearance vortex moving forward of the blade row leading edge. Vortex kinematic arguments are used to provide a physical explanation of this motion as well as to motivate the conditions for its occurrence. The resulting criterion for this type of stall inception (which appears generic for axial compressors with tip-critical flow fields) depends upon local flow phenomena related to the tip clearance and it is thus concluded that the flow structure within the blade passages must be addressed to explain the stability of an axial compression system which exhibits such short length-scale disturbances.© 1998 ASME

102 citations