Effect of wire mesh casing treatment on axial compressor performance and stability

In this paper,a kind of Wire Mesh Casing Treatment(WMCT)is proposed to improve the stable operating range of the compressor.In contrast to the traditional circumferential groove,as for WMCT,a layer of wire mesh is laid on the surface of the circumferential groove.Parametric studies were conducted on the low-speed axial flow compressor,including the groove width,axial location,and mesh count.The optimum axial location for WMCT is related to its groove width.A higher wire mesh count results in a smaller compressor stall margin improvement.Steady simulations were carried out to study the effect of WMCT on the flow structure of the compressor.The wire mesh in the WMCT has a certain flow resistance,which restricts the flow into and out of the groove.Due to the WMCT,the flow parameter in the tip region of the rotor is less sensitive to changes in the operating conditions of the compressor.The WMCT causes the rotor tip blade loading to shift backward,inhibiting the formation of spill forward of the leakage flow,and thus improving the stability of the compressor.The flow resistance on the groove surface is a new degree-of-freedom for the casing treatment designer.

Effect of fore/aft-loaded rotor on compressor stability under inlet circumferential distortion

A modified small perturbation stability prediction model for axial compressors with circumferential inlet distortions is established and applied to investigate the effect of fore/aft-loaded rotor on compressor stability under circumferentially distorted inlet conditions.The inlet total pressure distribution downstream of the distortion screen is measured in experiments and employed for simulations which are implemented via time-space spectral method.The stall inception prediction results via the stability model indicate that the compressor with aft-loaded rotor not only performs better in terms of stability under uniform inlet,but also maintains a larger stability margin under circumferentially distorted inlet.The experiments for compressors with fore-loaded and aft-loaded rotor are respectively carried out.The results validate the reliability of numerical simulations and the predicted conclusion that the aft-loaded rotor is beneficial for compressor stability.Besides,the ability of the developed theoretical model for compressor stability prediction under circumferential distortions is confirmed.In addition,dynamic pressure signals at rotor tip measured in experiments illustrate that the circumferential distortion has little effect on the compressor stall pattern.

Recent development of casing treatments for aeroengine compressors

Casing treatment is a mature stabilization technique which has been widely applied on aero-engines for modern aircrafts and turbo-chargers for automobiles. After the investigations of half century since the 1960 s, this technique has been well developed for various configurations with different effectiveness. From the perspective of stabilization mechanism, this paper roughly categorizes the configurations of casing treatment into two types: traditional ones which work by affecting the flow structure of blade tip region; a novel one named as Stall Precursor-Suppressed(SPS) casing treatment. The effectiveness of both types will be demonstrated for their applications on axial compressors and centrifugal compressors with uniform or distorted inlet. And the stabilization mechanism of casing treatments for regular types and SPS one will also be explained respectively. In addition, this review will summarize the methodologies of casing treatments with the numerical simulations for regular grooved configurations and the eigenvalue approach for SPS casing treatment.Looking forward to the future of compressor stabilization, casing treatment technique will still exist as a general and inexpensive option, and the exploration for its effectiveness and mechanism will be deeper with the development of computational fluid dynamics and advanced measurement techniques.

Response and stabilization of a two-stage axial flow compressor restricted by rotating inlet distortion

This paper considers effects of Rotating Inlet Distortion(RID)on a two-stage axial compressor and the stabilization effects of a casing treatment subjected to the considered RID.In multispool engines,the downstream compressor suffers a RID when the upstream fan/compressor is in rotating stall.A controlled rotating sectional screen upstream of the compressor was adopted to generate the RID in different intensities,and co-or counter spinning direction compared with the rotor.The response of the compressor to inlet distortion was interpreted as the changes of stall margin.Results show that there are two peaks for the stall margin degradation where the distortion screen rotates near 20%and 70%of the rotor’s rotational frequency,respectively.Based on the measurements taken during the pre-stall process,it is suggested that the two frequencies are associated with the eigen frequencies of the compressor.Specifically,the first is associated with a stall precursor that is suspected as an initial disturbance existing in compressor and the second is related to a spike-type stall precursor.At last,a kind of Stall Precursor-Suppressed(SPS)casing treatment was applied to enhance the compressor stability in RID conditions.The result indicates that the stall margin is improved by 6%at an average level and there is nearly no efficiency loss caused by the application of such casing treatment.

RANS simulations on combustion and emission characteristics of a premixed NH_(3)/H_(2) swirling flame with reduced chemical kinetic model

Ammonia(NH_(3))is considered as a potential alternative carbon free fuel to reduce greenhouse gas emission to meet the increasingly stringent emission requirements.Co-burning NH_(3) and H_(2) is an effective way to overcome ammonia’s relative low burning velocity.In this work,3D Reynolds Averaged Navier-Stokes(RANS)numerical simulations are conducted on a premixed NH_(3)/H_(2) swirling flame with reduced chemical kinetic mechanism.The effects of(A)overall equivalence ratio Φ and(B)hydrogen blended molar fraction XH2 on combustion and emission characteristics are examined.The present results show that when 100%NH_(3)-0%H_(2)-air are burnt,the NO emission and unburned NH3 of at the swirling combustor outlet has the opposite varying trends.With the increase of Φ,NO emission is found to be decreased,while the unburnt ammonia emission is increased.NH_(2)→HNO,NH→HNO and HNO→NO sub-paths are found to play a critical role in NO formation.Normalized reaction rate of all these three sub-paths is shown to be decreased with increased Φ.Hydrogen addition is shown to significantly increase the laminar burning velocity of the mixed fuel.However,adding H_(2) does not affect the critical equivalence ratio corresponding to the maximum burning velocity.The emission trend of NO and unburnt NH_(3) with increased Φ is unchanged by blending H_(2).NO emission with increased X_(H2) is increased slightly less at a larger Φ than that at a smaller Φ.In addition,reaction rates of NH_(2)→HNO and HNO→NO sub-paths are decreased with increased X_(H2),when Φ is larger.Under all tested cases,blending H_(2) with NH_(3) reduces the unburned NH_(3) emission,especially for rich combustion conditions.In summary,the present work provides research finding on supporting applying ammonia with hydrogen blended in low-emission gas turbine engines.

Effect of system response on partial surge initiated instability in a transonic axial flow compressor

Partial surge is a type of instability inception in transonic compressors and occurs in the form of axisymmetric low-frequency disturbances localized in the hub region.Previous studies illustrate that the frequency of partial surge is set by the Helmholtz frequency of the entire system,which motivates to propose a hypothesis that the system response performs an important role in the formation of partial surge.For further verification,a series of experiments are conducted to explore the link between the propagating of the partial surge and the system feedback in this study.In the first case,an additional test point is set on the wall of the plenum to detect the system response.Combining the flow behaviors inside the plenum with the disturbances in the rotor tip and stator hub/tip regions,the effects of the system feedback on the occurrence of the continuous disturbances and the rotating stall cells are illustrated.In the second case,a screen is mounted at the compressor outlet to prevent positive feedback from the plenum.The experimental results demonstrate that in the absence of system feedback,it is the occurrence of spike-type stall inception that leads to the flow instability instead of that of partial surge.In addition,three flow phenomena in the second case are discussed,including the occurrence of the single pulse,the unstable process during the stall evolution and the switch of instability inception.

Experimental and model investigations of SPS casing treatment on a two-stage compressor

This paper will first carry out experimental investigations on a test compressor which is a large-scale,two-stage and low-speed axial one to evaluate the participation of a novel casing treatment(stall precursor-suppressed casing treatment,SPS CT).The compressor performance for its pressure rise characteristics and efficiency are tested and illustrated.Besides,the time-averaged steady and the time-resolved unsteady measurement in this paper finally lead to some further analyses about the stall evolution of this compressor tending to uncover the process of the stall evolution and the mechanism of the SPS CT.The overall performance results indicate that the SPS CT can extend the compressor stall margin by 3%e11%with very limited efficiency loss.And the mechanism for such casing treatment has also been revealed as stall-precursor suppression by observing the evolution of the inception waves.In addition,modeling work have been conducted subject to the effects of SPS CT on the test two-stage axial compressor.The compressor stability model is able to investigate the effects of different geometrical parameters on the compressor stability and then make an optimal design for the SPS CT when it is applied on the test compressor.