Effect of the Stator Hub Configuration and Stage Design Parameters on Aerodynamic Loss in Axial Compressors

2014 ◽  
Author(s):  
Sungho Yoon ◽  
Rudolf Selmeier ◽  
Patricia Cargill ◽  
Peter Wood
Keyword(s):  
Pressure Loss ◽  
Axial Compressor ◽  
Flow Coefficient ◽  
Design Stage ◽  
Design Parameters ◽  
Leakage Flow ◽  
Design Decision ◽  
Leakage Loss ◽  
Stage Design ◽  
Degree Of Reaction

The choice of the stator hub configuration (i.e. cantilevered versus shrouded) is an important design decision in the preliminary design stage of an axial compressor. Therefore, it is important to understand the effect of the stator hub configuration on the aerodynamic performance. In particular, the stator hub configuration fundamentally affects the leakage flow across the stator. The effect of the stator hub configuration on the leakage flow and its consequent aerodynamic mixing loss with the main flow within the stator row is systematically investigated in this study. In the first part of the paper, a simple model is formulated to estimate the leakage loss across the stator hub as a function of fundamental stage design parameters, such as the flow coefficient, the degree of reaction and the work coefficient, in combination with some relevant geometric parameters including the clearance/span, the pitch-to-chord ratio and the number of seals for the shrouded geometry. The model is exercised in order to understand the effect of each of these design parameters on the leakage loss. It is found that, for a given flow coefficient and work coefficient, the leakage loss across the stator is substantially influenced by the degree of reaction. When a cantilevered stator is compared with a shrouded stator with a single seal at the same clearance, it is shown that a shrouded configuration is generally favored as a higher degree of reaction is selected, whereas a cantilevered configuration is desirable for a lower degree of reaction. Further to this, it is demonstrated that, for shrouded stators, an additional aerodynamic benefit can be achieved by using multiple seals. The second part of the paper investigates the effect of the rotating surfaces. Traditionally, only the pressure loss has been considered for stators. However, the current advanced CFD generally includes the leakage path with associated rotating surfaces, which impart energy to the flow. It is shown that the conventional loss coefficient, based on considering only the pressure loss, is misleading when hub leakage flows are modeled in detail, because there is energy addition due to the rotation of the hub or the shroud seals for the cantilevered stator and the shrouded stator, respectively. The calculation of the entropy generation across the stator is a better measure of relative performance when comparing two different stator hub configurations with detailed CFD.

Effect of the Stator Hub Configuration and Stage Design Parameters on Aerodynamic Loss in Axial Compressors

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Sungho Yoon ◽  
Rudolf Selmeier ◽  
Patricia Cargill ◽  
Peter Wood
Keyword(s):  
Pressure Loss ◽  
Axial Compressor ◽  
Flow Coefficient ◽  
Design Stage ◽  
Design Parameters ◽  
Leakage Flow ◽  
Design Decision ◽  
Leakage Loss ◽  
Stage Design ◽  
Degree Of Reaction

The choice of the stator hub configuration (i.e., cantilevered versus shrouded) is an important design decision in the preliminary design stage of an axial compressor. Therefore, it is important to understand the effect of the stator hub configuration on the aerodynamic performance. In particular, the stator hub configuration fundamentally affects the leakage flow across the stator. The effect of the stator hub configuration on the leakage flow and its consequent aerodynamic mixing loss with the main flow within the stator row is systematically investigated in this study. In the first part of the paper, a simple model is formulated to estimate the leakage loss across the stator hub as a function of fundamental stage design parameters, such as the flow coefficient, the degree of reaction, and the work coefficient, in combination with some relevant geometric parameters including the clearance/span, the pitch-to-chord ratio, and the number of seals for the shrouded geometry. The model is exercised in order to understand the effect of each of these design parameters on the leakage loss. It is found that, for a given flow coefficient and work coefficient, the leakage loss across the stator is substantially influenced by the degree of reaction. When a cantilevered stator is compared with a shrouded stator with a single seal at the same clearance, it is shown that a shrouded configuration is generally favored as a higher degree of reaction is selected, whereas a cantilevered configuration is desirable for a lower degree of reaction. Further to this, it is demonstrated that, for shrouded stators, an additional aerodynamic benefit can be achieved by using multiple seals. The second part of the paper investigates the effect of the rotating surfaces. Traditionally, only the pressure loss has been considered for stators. However, the current advanced computational fluid dynamics (CFD) generally includes the leakage path with associated rotating surfaces, which impart energy to the flow. It is shown that the conventional loss coefficient, based on considering only the pressure loss, is misleading when hub leakage flows are modeled in detail, because there is energy addition due to the rotation of the hub or the shroud seals for the cantilevered stator and the shrouded stator, respectively. The calculation of the entropy generation across the stator is a better measure of relative performance when comparing two different stator hub configurations with detailed CFD.

Active Stabilization of Rotating Stall in a Three-Stage Axial Compressor

1993 ◽  
Author(s):  
Joel M. Haynes ◽  
Gavin J. Hendricks ◽  
Alan H. Epstein
Keyword(s):  
High Speed ◽  
Travelling Waves ◽  
Axial Compressor ◽  
Open Loop ◽  
Rotating Stall ◽  
Forced Response ◽  
Flow Coefficient ◽  
Design Parameters ◽  
Time Lags ◽  
Active Stabilization

A three-stage, low speed axial research compressor has been actively stabilized by damping low amplitude circumferentially travelling waves which can grow into rotating stall. Using a circumferential array of hot wire sensors, and an array of high speed individually positioned control vanes as the actuator, the first and second spatial harmonics of the compressor were stabilized down to a characteristic slope of 0.9, yielding an 8% increase in operating flow range. Stabilization of the third spatial harmonic did not alter the stalling flow coefficient. The actuators were also used open loop to determine the forced response behavior of the compressor. A system identification procedure applied to the forced response data then yielded the compressor transfer function. The Moore-Greitzer, 2-D, stability model was modified as suggested by the measurements to include the effect of blade row time lags on the compressor dynamics. This modified Moore-Greitzer model was then used to predict both the open and closed loop dynamic response of the compressor. The model predictions agreed closely with the experimental results. In particular, the model predicted both the mass flow at stall without control and the design parameters needed by, and the range extension realized from, active control.

The Influence of Tip Clearance Momentum Flux on Stall Inception in a High-Speed Axial Compressor

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Joshua D. Cameron ◽  
Matthew A. Bennington ◽  
Mark H. Ross ◽  
Scott C. Morris ◽  
Juan Du ◽  
...  
Keyword(s):  
Momentum Flux ◽  
High Speed ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Axial Position ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage

Experimental and numerical studies were conducted to investigate tip-leakage flow and its relationship to stall in a transonic axial compressor. The computational fluid dynamics (CFD) results were used to identify the existence of an interface between the approach flow and the tip-leakage flow. The experiments used a surface-streaking visualization method to identify the time-averaged location of this interface as a line of zero axial shear stress at the casing. The axial position of this line, denoted xzs, moved upstream with decreasing flow coefficient in both the experiments and computations. The line was consistently located at the rotor leading edge plane at the stalling flow coefficient, regardless of inflow boundary condition. These results were successfully modeled using a control volume approach that balanced the reverse axial momentum flux of the tip-leakage flow with the momentum flux of the approach fluid. Nonuniform tip clearance measurements demonstrated that movement of the interface upstream of the rotor leading edge plane leads to the generation of short length scale rotating disturbances. Therefore, stall was interpreted as a critical point in the momentum flux balance of the approach flow and the reverse axial momentum flux of the tip-leakage flow.

An Analytical Model of Axial Compressor Off-Design Performance

1994 ◽  
Vol 116 (3) ◽  
pp. 425-434 ◽  
Author(s):  
T. R. Camp ◽  
J. H. Horlock
Keyword(s):  
Design Process ◽  
Axial Compressor ◽  
Axial Flow ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Design Stage ◽  
Turbine Engine ◽  
Design Performance ◽  
Design Value ◽  
Stage Matching

An analysis is presented of the off-design performance of multistage axial-flow compressors. It is based on an analytical solution, valid for small perturbations in operating conditions from the design point, and provides an insight into the effects of choices made during the compressor design process on performance and off-design stage matching. It is shown that the mean design value of stage loading coefficient (ψ = Δh0/U2) has a dominant effect on off-design performance, whereas the stage-wise distribution of stage loading coefficient and the design value of flow coefficient have little influence. The powerful effects of variable stator vanes on stage-matching are also demonstrated and these results are shown to agree well with previous work. The slope of the working line of a gas turbine engine, overlaid on overall compressor characteristics, is shown to have a strong effect on the off-design stage-matching through the compressor. The model is also used to analyze design changes to the compressor geometry and to show how errors in estimates of annulus blockage, decided during the design process, have less effect on compressor performance than has previously been thought.

scholarly journals An Analytical Model of Axial Compressor Off-Design Performance

1993 ◽  
Author(s):  
T. R. Camp ◽  
J. H. Horlock
Keyword(s):  
Design Process ◽  
Axial Compressor ◽  
Axial Flow ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Design Stage ◽  
Turbine Engine ◽  
Design Performance ◽  
Design Value ◽  
Stage Matching

An analysis is presented of the off-design performance of multistage axial-flow compressors. It is based on an analytical solution, valid for small perturbations in operating conditions from the design point, and provides an insight into the effects of choices made during the compressor design process on performance and off-design stage matching. It is shown that the mean design value of stage loading coefficient (ψ = Δho/U2) has a dominant effect on off-design performance, whereas the stage-wise distribution of stage loading coefficient and the design value of flow coefficient have little influence. The powerful effects of variable stator vanes on stage-matching are also demonstrated and these results are shown to agree well with previous work. The slope of the working line of a gas turbine engine, overlaid on overall compressor characteristics, is shown to have a strong effect on the off-design stage-matching through the compressor. The model is also used to analyse design changes to the compressor geometry and to show how errors in estimates of annulus blockage, decided during the design process, have less effect of compressor performance than has previously been thought.

Numerical Investigation of Effects of Different Hub Tip Diameter Ratios on Aerodynamic Performance of Single Shaft Multistage Centrifugal Compression Systems

2012 ◽  
Author(s):  
Thomas Ceyrowsky ◽  
Andre Hildebrandt
Keyword(s):  
Characteristic Curve ◽  
Design Flow ◽  
Flow Coefficient ◽  
Low Flow ◽  
Design Stage ◽  
Daily Routine ◽  
Stage Design ◽  
Design Point ◽  
Thermodynamic Behaviour ◽  
The Impact

Regarding industrial centrifugal compressors in single shaft design, different configurations with e.g. varying numbers of stages or diverse circumferential speeds, necessitate different shaft diameters. Thus the application of impellers with different hub/tip ratios (dh/d2) is daily routine in industrial practice. Increasing hub/tip ratio leads to higher radii and therefore higher relative speeds, to a reduction in the impeller’s meridional length and hence more rapid diffusion, and to a sharper bending from axial to radial direction. In this paper the impact of hub/tip ratio on stage performance is investigated for three different centrifugal compressor stages, by steady state CFD-calculations. The hub/tip ratio is varied between 0.325 < dh/d2 < 0.45. The relation between design stage flow coefficient and hub/tip ratio is also analysed, both at design and off-design. Thermodynamic behaviour is assessed by 1D-data and also by the investigation of secondary flow features. The current analysis shows, that hub/tip ratio’s influence on characteristics is strongly dependent on the particular stage’s design flow coefficient and circumferential Mach-Number. Increasing a high flow stage’s hub/tip ratio is shown to decrease peak efficiency as well, as to limit the operating range. On the contrary, in case of a low flow stage, design point efficiency is hardly affected, but the characteristic curve is tilted around design point, by applying a different hub/tip ratio. However severity of hub/tip ratio’s impact on thermodynamic behaviour shows to decrease together with stage design flow coefficient.

scholarly journals Performance Limits of Axial Compressor Stages

2012 ◽  
Author(s):  
D. K. Hall ◽  
E. M. Greitzer ◽  
C. S. Tan
Keyword(s):  
Axial Compressor ◽  
Cycle Performance ◽  
Design Parameters ◽  
Compressor Stage ◽  
Performance Limits ◽  
Stage Design ◽  
Design Variables ◽  
Gas Turbine Cycle ◽  
The Impact ◽  
Stage Efficiency

This paper presents a framework for estimating the upper limit of compressor stage efficiency. Using a compressor stage model with a representative design velocity distribution with turbulent boundary layers, losses are calculated as the sum of selected local irreversibilities, rather than from correlations based on data from existing machines. By considering only losses that cannot be eliminated and optimizing stage design variables for minimum loss, an upper bound on stage efficiency can be determined as a function of a small number of stage design parameters. The impact of the stage analysis results are evaluated in the context of gas turbine cycle performance. The implication from the results of the stage level and cycle analyses is that compressor efficiency improvements that result in substantial increases in cycle thermal efficiency are still to be realized.

Optimizing a Suction Channel to Improve Performance of a Centrifugal Compressor Stage

2010 ◽  
Author(s):  
Manabu Yagi ◽  
Takanori Shibata ◽  
Hideo Nishida ◽  
Hiromi Kobayashi ◽  
Masanori Tanaka ◽  
...  
Keyword(s):  
Pressure Loss ◽  
Flow Coefficient ◽  
Design Parameters ◽  
Compressor Stage ◽  
Flow Distortion ◽  
Dominant Design ◽  
Improvement Effect ◽  
Computational Fluid Dynamics Cfd ◽  
Suction Flow ◽  
Stage Efficiency

Design parameters for a suction channel of process centrifugal compressors were investigated, and an optimizing method to improve efficiency by using the new design parameters was proposed. Both pressure loss and circumferential flow distortion in the suction channel were evaluated by using computational fluid dynamics (CFD). The main dimensions, which had a large influence on pressure loss and circumferential flow distortion, were identified by using design of experiments (DOE). Next, the passage sectional area ratios Ac/Ae, Ae/As, and Ac/As were found to be the dominant design parameters for the pressure loss and circumferential flow distortion, where Ac, Ae and As are passage sectional areas for the casing upstream side, casing entrance and impeller eye, respectively. Then the shape of the suction channel was optimized using Ac/Ae, Ae/As, and Ac/As. Finally, to evaluate the improvement effect of optimizing the values of Ac/Ae, Ae/As, and Ac/As on compressor stage performance, a base suction channel and an optimized type of suction channel were manufactured and tested. The design suction flow coefficient was 0.1 and the peripheral Mach number was 0.78. Test results showed that the optimized suction channel achieved 3.8% higher stage efficiency than the base one while maintaining the overall operating range from surge to choke. The method for optimizing suction channels by using the three described design parameters was concluded to be very effective for improving the stage efficiency.

Active Stabilization of Rotating Stall in a Three-Stage Axial Compressor

1994 ◽  
Vol 116 (2) ◽  
pp. 226-239 ◽  
Author(s):  
J. M. Haynes ◽  
G. J. Hendricks ◽  
A. H. Epstein
Keyword(s):  
Axial Compressor ◽  
Open Loop ◽  
Rotating Stall ◽  
Forced Response ◽  
Flow Coefficient ◽  
Design Parameters ◽  
Time Lags ◽  
Response Data ◽  
Active Stabilization ◽  
Low Amplitude

A three-stage, low-speed axial research compressor has been actively stabilized by damping low-amplitude circumferentially traveling waves, which can grow into rotating stall. Using a circumferential array of hot-wire sensors, and an array of highspeed individually positioned control vanes as the actuator, the first and second spatial harmonics of the compressor were stabilized down to a characteristic slope of 0.9, yielding an 8 percent increase in operating flow range. Stabilization of the third spatial harmonic did not alter the stalling flow coefficient. The actuators were also used open loop to determine the forced response behavior of the compressor. A system identification procedure applied to the forced response data then yielded the compressor transfer function. The Moore-Greitzer two-dimensional stability model was modified as suggested by the measurements to include the effect of blade row time lags on the compressor dynamics. This modified Moore-Greitzer model was then used to predict both the open and closed-loop dynamic response of the compressor. The model predictions agreed closely with the experimental results. In particular, the model predicted both the mass flow at stall without control and the design parameters needed by, and the range extension realized from, active control.

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