scholarly journals Effects of Non-Axisymmetric Tip Clearance on Axial Compressor Performance and Stability

1997 ◽  
Author(s):  
M. B. Graf ◽  
T. S. Wong ◽  
E. M. Greitzer ◽  
F. E. Marble ◽  
C. S. Tan ◽  
...  
Keyword(s):  
Steady State ◽  
Theoretical Model ◽  
Peak Pressure ◽  
Good Description ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Tip Clearance ◽  
Maximum Efficiency ◽  
Stall Margin ◽  
Compressor Performance

The effects of circumferentially non-uniform lip clearance on axial compressor performance and stability have been investigated experimentally and analytically. A theoretical model for compressor behavior with non-axisymmetric tip clearance has been developed and used to design a series of first-of-a-kind experiments on a four-stage, low speed compressor. The experiments and computational results together show clearly the central physical features and controlling parameters of compressor response to non-axisymmetric lip clearance. It was found that the loss in stall margin was more severe than that estimated based on average clearance. The stall point was, in fact, closer to that obtained with uniform clearance at the maximum clearance level. The circumferential length scale of the tip clearance (and accompanying flow asymmetry) was an important factor in determining the stall margin reduction. For the same average clearance, the loss in peak pressure rise was 50% higher for an asymmetry with fundamental wavelength equal to the compressor circumference than with wavelength equal to one-half the circumference. The clearance asymmetry had much less of an effect on peak efficiency; the measured maximum efficiency decrease obtained was less than 0.4 percent compared to the 8% decrease in peak pressure rise due to the asymmetric clearance. The efficiency penalty due to non-axisymmetric tip clearance was thus close to that obtained with a uniform clearance at the circumferentially-averaged level. The theoretical model accurately captured the decreases in both steady-state pressure rise and stable operating range which are associated with clearance asymmetry. It also gave a good description of the observed trends of (i) increasing velocity asymmetry with decreasing compressor flow, and (ii) decreasing effect of clearance asymmetry with decreasing dominant wavelength of the clearance distribution. The time resolved data showed that the spatial structure of the pre-stall propagating disturbances in the compressor annulus was well represented and that the stability limiting process could be linked to the unsteady structure of these disturbance modes. The model was also utilized for parametric studies to define how compressor performance and stability is affected by the circumferential distribution of clearance, steady-state compressor pressure-rise characteristic, and system dynamic parameters. Sensitivity to clearance asymmetry was found to fall off strongly with the (asymmetry-related) reduced frequency and to increase with peak pressure rise and increasing curvature of the characteristic near the peak.

scholarly journals Effects of Nonaxisymmetric Tip Clearance on Axial Compressor Performance and Stability

1998 ◽  
Vol 120 (4) ◽  
pp. 648-661 ◽  
Author(s):  
M. B. Graf ◽  
T. S. Wong ◽  
E. M. Greitzer ◽  
F. E. Marble ◽  
C. S. Tan ◽  
...  
Keyword(s):  
Steady State ◽  
Theoretical Model ◽  
Peak Pressure ◽  
Good Description ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Tip Clearance ◽  
Maximum Efficiency ◽  
Stall Margin ◽  
Compressor Performance

The effects of circumferentially nonuniform tip clearance on axial compressor performance and stability have been investigated experimentally and analytically. A theoretical model for compressor behavior with nonaxisymmetric tip clearance has been developed and used to design a series of first-of-a-kind experiments on a four-stage, low-speed compressor. The experiments and computational results together show clearly the central physical features and controlling parameters of compressor response to nonaxisymmetric tip clearance. It was found that the loss in stall margin was more severe than that estimated based on average clearance. The stall point was, in fact, closer to that obtained with uniform clearance at the maximum clearance level. The circumferential length scale of the tip clearance (and accompanying flow asymmetry) was an important factor in determining the stall margin reduction. For the same average clearance, the loss in peak pressure rise was 50 percent higher for an asymmetry with fundamental wavelength equal to the compressor circumference than with wavelength equal to one-half the circumference. The clearance asymmetry had much less of an effect on peak efficiency; the measured maximum efficiency decrease obtained was less than 0.4 percent compared to the 8 percent decrease in peak pressure rise due to the asymmetric clearance. The efficiency penalty due to nonaxisymmetric tip clearance was thus close to that obtained with a uniform clearance at the circumferentially averaged level. The theoretical model accurately captured the decreases in both steady-state pressure rise and stable operating range which are associated with clearance asymmetry. It also gave a good description of the observed trends of: (i) increasing velocity asymmetry with decreasing compressor flow, and (ii) decreasing effect of clearance asymmetry with decreasing dominant wavelength of the clearance distribution. The time-resolved data showed that the spatial structure of the prestall propagating disturbances in the compressor annulus was well represented and that the stability limiting process could be linked to the unsteady structure of these disturbance modes. The model was also utilized for parametric studies to define how compressor performance and stability are affected by the circumferential distribution of clearance, steady-state compressor pressure-rise characteristic, and system dynamic parameters. Sensitivity to clearance asymmetry was found to fall off strongly with the (asymmetry-related) reduced frequency and to increase with peak pressure rise and increasing curvature of the characteristic near the peak.

Impact of Rotor Wakes on Steady-State Axial Compressor Performance

1996 ◽  
Author(s):  
P. Deregel ◽  
C. S. Tan
Keyword(s):  
Steady State ◽  
Static Pressure ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Initial Step ◽  
Inviscid Flow ◽  
Causal Link ◽  
Design Parameters ◽  
Compressor Design ◽  
Compressor Performance

This paper addresses the causal link first described by Smith between the unsteady flow induced by the rotor wakes and the compressor steady-state performance. As an initial step, inviscid flow in a compressor stage is examined. First of a kind numerical simulations are carried out to show that if the rotor wakes are mixed out after (as opposed to before) the stator passage, the time-averaged overall static pressure rise is increased and the mixing loss is reduced. An analytical model is also presented and shown to agree with the numerical results; the model is then used to examine the parametric trends associated with compressor design parameters.

Design and Test of a Novel Highly-Loaded Compressor

2019 ◽  
Author(s):  
Chengwu Yang ◽  
Ge Han ◽  
Shengfeng Zhao ◽  
Xingen Lu ◽  
Yanfeng Zhang ◽  
...  
Keyword(s):  
Pressure Ratio ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Flow Angle ◽  
Stall Margin ◽  
High Pressure Ratio ◽  
Numerical Predictions ◽  
Highly Loaded

Abstract The blades of rear stages in small size core compressors are reduced to shorter than 20 mm or even less due to overall high pressure ratio. The growing of tip clearance-to-blade height ratio of the rear stages enhance the leakage flow and increase the possibility of a strong clearance sensitivity, thus limiting the compressor efficiency and stability. A new concept of compressor, namely diffuser passage compressor (DP), for small size core compressors was introduced. The design aims at making the compressors robust to tip clearance leakage flow by reducing pressure difference between pressure and suction surfaces. To validate the concept, the second stage of a two-stage highly loaded axial compressor was designed with DP rotor according to a diffuser map. The diffuser passage stage has the same inlet condition and loading as the conventional compressor (CNV) stage, of which the work coefficient is around 0.37. The predicted performance and flow field of the DP were compared with the conventional axial compressor in detail. The rig testing was supplemented with the numerical predictions. Results reveal that the throttle characteristic of DP indicates higher pressure rise and the loss reduction in tip clearance is mainly responsible for the performance improvement. For the compressor with DP, the pressure and flow angle are more uniform on exit plane. What’s more, the rotor with diffused passage reveals more robust than the conventional rotor at double clearance gap. Furthermore, the experimental data indicate that DP presents higher pressure rise at design and part speeds. At design speed, the stall margin was extended by 7.25%. Moreover, peak adiabatic efficiency of DP is also higher than that of CNV by about 0.7%.

Accounting for Eccentricity in Compressor Performance Predictions

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Anna M. Young ◽  
Teng Cao ◽  
Ivor J. Day ◽  
John P. Longley
Keyword(s):  
Axial Velocity ◽  
Pressure Rise ◽  
Two Dimensions ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Three Dimensional Model ◽  
Stall Margin ◽  
Rule Of Thumb ◽  
Compressor Performance ◽  
Flow Gradients

In this paper, experiments and numerical modeling are used to quantify the effects of clearance and eccentricity on compressor performance and to examine the influence of each on flow distribution and stall margin. A change in the size of the tip-clearance gap influences the pressure rise and the stall margin of a compressor. Eccentricity of the tip-clearance gap then further exacerbates the negative effects of increasing tip-clearance. There are few studies in the literature dealing with the combined effect of clearance and eccentricity. There is also little guidance for engine designers, who have traditionally used rules of thumb to quantify these effects. One such rule states that the stall margin of an eccentric machine will be equal to that of a concentric machine with uniform clearance equal to the maximum eccentric clearance. In this paper, this rule of thumb is checked using experimental data and found to be overly pessimistic. In addition, eccentric clearance causes a variation in axial velocity around the circumference of the compressor. The current study uses a three-dimensional model which demonstrates the importance of radial flow gradients in capturing this redistribution. Flow redistribution has been treated analytically in the past, and for this reason, previous modeling has been restricted to two dimensions. The circumferential variation in axial velocity is also examined in terms of the local stability of the flow by considering the stalling flow coefficient of an equivalent axisymmetric compressor with the same local tip-clearance. The large clearance sector of the annulus is found to operate beyond its equivalent axisymmetric stall limit, which means that the small clearance sector of the annulus must be stabilizing the large clearance sector. An improved rule of thumb dealing with the effects of eccentricity is presented.

The Effects of Tip Leakage Flow on the Performance of Multistage Compressors Used in Small Core Engine Applications

2015 ◽  
Vol 138 (5) ◽  
Author(s):  
Reid A. Berdanier ◽  
Nicole L. Key
Keyword(s):  
Experimental Data ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Tip Leakage ◽  
Small Core ◽  
Thermal Growth

Large rotor tip clearances and the associated tip leakage flows are known to have a significant effect on overall compressor performance. However, detailed experimental data reflecting these effects for a multistage compressor are limited in the open literature. As design trends lead to increased overall compressor pressure ratio for thermal efficiency benefits and increased bypass ratios for propulsive benefits, the rear stages of the high-pressure compressor will become physically small. Because rotor tip clearances cannot scale exactly with blade size due to the margin needed for thermal growth considerations, relatively large tip clearances will be a reality for these rear stages. Experimental data have been collected from a three-stage axial compressor to assess performance with three-tip clearance heights representative of current and future small core machines. Trends of overall pressure rise, stall margin, and efficiency are evaluated using clearance derivatives, and the summarized data presented here begin to narrow the margin of tip clearance sensitivities outlined by previous studies in an effort to inform future compressor designs. Furthermore, interstage measurements show stage matching changes and highlight specific differences in the performance of rotor 1 and stator 2 compared to other blade rows in the machine.

scholarly journals Effects of Upstream Wake Phasing on Transonic Axial Compressor Performance

2009 ◽  
Author(s):  
S. P. R. Nolan ◽  
B. B. Botros ◽  
C. S. Tan ◽  
J. J. Adamczyk ◽  
E. M. Greitzer ◽  
...  
Keyword(s):  
Axial Compressor ◽  
Pressure Rise ◽  
Stagnation Pressure ◽  
Tip Clearance ◽  
Model Calculations ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
Work Input ◽  
Compressor Performance ◽  
Stability Limits

The effect on rotor work, of the phase of an upstream wake relative to the rotor, is examined computationally and analytically for a transonic blade row. There can be an important impact on time-mean performance when the time-dependent circulation of the shed vortices in the wake is phase-locked to the rotor position, as occurs when there is strong interaction between rotor static pressure field and upstream vanes. The rotor work is found to depend on the path of the wake vortices as they travel through the blade passage; for configurations examined, the calculated change in time-mean rotor work was approximately three percent. It is shown that the effect on work input can be analyzed in terms of the influence of the time-mean relative stagnation pressure nonuniformity associated with the unsteady (but phase-locked) wake vortex flow field, in that changes in vortex path alter the location of the nonuniformity relative to the rotor. Lower pressure rise and work input occurs when the rotor blade is embedded in a region of low time-mean relative stagnation pressure than when immersed in a region of high relative stagnation pressure. In addition to the work changes, which are an essentially two-dimensional effect, it is demonstrated that the location of the wake may affect the tip clearance flow, implying a potential impact on pressure rise capability and rotor stability limits. Model calculations are presented to give estimates of the magnitude and nature of this phenomenon.

scholarly journals Effects of Upstream Wake Phasing on Transonic Axial Compressor Performance

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
S. P. R. Nolan ◽  
B. B. Botros ◽  
C. S. Tan ◽  
J. J. Adamczyk ◽  
E. M. Greitzer ◽  
...  
Keyword(s):  
Axial Compressor ◽  
Pressure Rise ◽  
Stagnation Pressure ◽  
Tip Clearance ◽  
Model Calculations ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
Work Input ◽  
Compressor Performance ◽  
Stability Limits

The effect on rotor work of the phase of an upstream wake relative to the rotor is examined computationally and analytically for a transonic blade row. There can be an important impact on the time-mean performance when the time-dependent circulation of the shed vortices in the wake is phase-locked to the rotor position, as it occurs when there is strong interaction between the rotor static pressure field and the upstream vanes. The rotor work is found to depend on the path of the wake vortices as they travel through the blade passage; for the configurations examined, the calculated change in time-mean rotor work was approximately 3%. It is shown that the effect on work input can be analyzed in terms of the influence of the time-mean relative stagnation pressure nonuniformity associated with the unsteady (but phase-locked) wake vortex flow field, in that the changes in vortex path alter the location of the nonuniformity relative to the rotor. Lower pressure rise and work input occurs when the rotor blade is embedded in a region of low time-mean relative stagnation pressure than when immersed in a region of high relative stagnation pressure. In addition to the work changes, which are essentially two-dimensional effects, it is demonstrated that the location of the wake may affect the tip clearance flow, implying a potential impact on the pressure rise capability and rotor stability limits. Model calculations are presented to give estimates of the magnitude and nature of this phenomenon.

Accounting for Eccentricity in Compressor Performance Predictions

2016 ◽  
Author(s):  
Anna M. Young ◽  
Teng Cao ◽  
Ivor J. Day ◽  
John P. Longley
Keyword(s):  
Three Dimensional ◽  
Computational Modelling ◽  
Pressure Rise ◽  
Single Stage ◽  
Tip Clearance ◽  
Engine Operation ◽  
Stall Margin ◽  
Starting Point ◽  
Compressor Performance ◽  
Exact Effect

It is known that the tip-clearance gap plays a pivotal role in determining the performance of an aero-engine compressor, both in terms of stability and pressure rise. However, the exact effect of tip-clearance size on stall margin over the range of clearances experienced during engine operation is not known, and most designers substitute rules of thumb for real knowledge when developing new compressors. Eccentricity in the tip-clearance is also known to affect compressor performance, though again little work has been done to quantify the penalties. It is generally assumed that the stall margin of an eccentric machine will be approximately equal to that of a concentric machine with a clearance equal to the maximum eccentric clearance. Results given in this paper show a stabilising effect of the small tip-clearance sector of an eccentric compressor on the large tip-clearance sector, so the penalty on stall margin is not as large as commonly assumed. It is shown that the stall margin penalty in a single-stage eccentric machine is only 50–60% of that which a concentric compressor with clearance equal to the maximum clearance would exhibit. In addition, the effect of eccentricity is shown to diminish as the average clearance is increased. In this paper, experiments and computational modelling are used to examine the effects of eccentric tip-clearance on flowfield redistribution and compressor performance. In particular, the three-dimensional nature of the flowfield generated by an eccentric gap is shown for the first time. The purpose of this work is not to provide ‘hard-and-fast’ design rules for eccentric compressors (this cannot be done on the basis of single-stage measurements), but to provide a starting point for a better physical understanding of the problem.

Numerically Understanding the Steady State Response of Single Stage Transonic Axial Flow Compressor to Axial Locations of Step for Stepped Tip Clearance

2014 ◽  
Author(s):  
Hardik K. Vashi ◽  
Dilipkumar Bhanudasji Alone ◽  
Harish S. Choksi
Keyword(s):  
Steady State ◽  
Peak Pressure ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Single Stage ◽  
Tip Clearance ◽  
Peak Efficiency ◽  
Stall Margin ◽  
Axial Location ◽  
Stall Margin Improvement

This paper describes the steady state numerical work carried out to study the influence of providing stepped tip clearances at various axial locations along the rotor chord on the performance of the single stage transonic axial compressor. Uniform tip clearance study on compressor under consideration showed performance deterioration of compressor at higher tip clearance of 2mm [3.4% of rotor axial chord] therefore in order to improve performance of compressor, stepped tip clearance method was introduced. Commercially available Ansys Fluent 12.0 software was used to perform steady state RANS simulations with three dimensional implicit pressure based solver and SST K-ω as turbulence model. Stepped tip clearance concept is based on providing smaller tip clearance in front portion and providing higher tip clearance after step above the rotor. In present case, study was carried out for stepped tip clearance with steps at four different axial locations [i.e. 10, 20, 40 & 60 % of rotor chord from leading edge of rotor] and results were compared with baseline model of 0.5 mm [0.9% of rotor axial chord] uniform tip clearance at 100% speed. The stepped tip clearance combinations used for the analysis was 0.5–2mm. It was observed that there was increase in compressor peak efficiency & peak pressure ratio for all stepped clearance cases. A trend was noticed where there was relative increase in peak efficiency as well as peak pressure ratio when step was moved downstream along rotor chord [i.e. moving from 10% to 60% axial location]for one of the combinations stepped tip clearance. Stall margin improvement was observed for all cases of stepped tip clearance. Stall margin gain obtained was higher when step was provided in front portion above rotor [i.e. 10 & 20 % axial location] compared to stall margin improvement when step was provided in rear portion above rotor [i.e. 40 & 60% axial location]. It can be concluded that stepped tip clearance provided near leading edge shows potential in improving performance for compressor under consideration. Numerical analysis of single stage has been carried out but data has been presented for rotor only to study the flow changes occurring in rotor vicinity created by implementation of stepped tip clearance method.

scholarly journals Effects of Endwall Suction and Blowing on Compressor Stability Enhancement

1989 ◽  
Author(s):  
N. K. W. Lee ◽  
E. M. Greitzer
Keyword(s):  
Flow Injection ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Primary Objective ◽  
Stall Margin ◽  
Casing Treatment ◽  
Blade Row ◽  
Stall Margin Improvement ◽  
Stability Enhancement ◽  
Suction And Blowing

An experimental investigation was carried out to examine the effects on stall margin of flow injection into, and flow removal out of, the endwall region of an axial compressor blade row. A primary objective of the investigation was clarification of the mechanism by which casing treatment (which involves both removal and injection) suppresses stall in turbomachines. To simulate the relative motion between blade and treatment, the injection and removal took place through a slotted hub rotating beneath a cantilevered stator row. Overall performance data and detailed (time-averaged) flowfield measurements were obtained. Flow injection and removal both increased the stalling pressure rise, but neither was as effective as the wall treatment. Removal of high blockage flow is thus not the sole reason for the observed stall margin improvement in casing or hub treatment, as injection can also contribute significantly to stall suppression. The results also indicate that the increase in stall pressure rise with injection is linked to the streamwise momentum of the injected flow, and it is suggested that this should be the focus of further studies.

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