scholarly journals Unsteady Flow and Whirl-Inducing Forces in Axial-Flow Compressors: Part I—Experiment

2000 ◽  
Vol 123 (3) ◽  
pp. 433-445 ◽  
Author(s):  
A. F. Storace ◽  
D. C. Wisler ◽  
H.-W. Shin ◽  
B. F. Beacher ◽  
F. F. Ehrich ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Theoretical Investigation ◽  
Computational Models ◽  
Aerodynamic Force ◽  
Axial Flow ◽  
Pressure Rise ◽  
Static Structure ◽  
Stall Margin ◽  
First Time ◽  
Axial Flow Compressors

An experimental and theoretical investigation has been conducted to evaluate the effects seen in axial-flow compressors when the centerline of the rotor is displaced from the centerline of the static structure of the engine. This creates circumferentially nonuniform rotor-tip clearances, unsteady flow, and potentially increased clearances if the rotating and stationary parts come in contact. The result not only adversely affects compressor stall margin, pressure rise capability, and efficiency, but also generates an unsteady, destabilizing, aerodynamic force, called the Thomas/Alford force, which contributes significantly to rotor whirl instabilities in turbomachinery. Determining both the direction and magnitude of this force in compressors, relative to those in turbines, is especially important for the design of mechanically stable turbomachinery components. Part I of this two-part paper addresses these issues experimentally and Part II presents analyses from relevant computational models. Our results clearly show that the Thomas/Alford force can promote significant backward rotor whirl over much of the operating range of modern compressors, although some regions of zero and forward whirl were found near the design point. This is the first time that definitive measurements, coupled with compelling analyses, have been reported in the literature to resolve the long-standing disparity in findings concerning the direction and magnitude of whirl-inducing forces important in the design of modern axial-flow compressors.

scholarly journals Unsteady Flow and Whirl-Inducing Forces in Axial-Flow Compressors: Part I — Experiment

2000 ◽  
Author(s):  
A. F. Storace ◽  
D. C. Wisler ◽  
H.-W. Shin ◽  
B. F. Beacher ◽  
F. F. Ehrich ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Theoretical Investigation ◽  
Computational Models ◽  
Aerodynamic Force ◽  
Axial Flow ◽  
Pressure Rise ◽  
Static Structure ◽  
Stall Margin ◽  
First Time ◽  
Axial Flow Compressors

An experimental and theoretical investigation has been conducted to evaluate the effects seen in axial-flow compressors when the centerline of the rotor is displaced from the centerline of the static structure of the engine. This creates circumferentially non-uniform rotor-tip clearances, unsteady flow, and potentially increased clearances if the rotating and stationary parts come in contact. The result not only adversely affects compressor stall margin, pressure rise capability and efficiency but also generates an unsteady, destabilizing, aerodynamic force, called the Thomas/Alford force, which contributes significantly to rotor whirl instabilities in turbomachinery. Determining both the direction and magnitude of this force in compressors, relative to those in turbines, is especially important for the design of mechanically-stable turbomachinery components. Part I of this two-part paper addresses these issues experimentally and Part II presents analyses from relevant computational models. Our results clearly show that the Thomas/Alford force can promote significant backward rotor whirl over much of the operating range of modern compressors, although some regions of zero and forward whirl were found near the design point. This is the first time that definitive measurements, coupled with compelling analyses, have been reported in the literature to resolve the long-standing disparity in findings concerning the direction and magnitude of whirl-inducing forces important in the design of modern axial-flow compressors.

scholarly journals Unsteady Flow and Whirl-Inducing Forces in Axial-Flow Compressors: Part II—Analysis

2000 ◽  
Vol 123 (3) ◽  
pp. 446-452 ◽  
Author(s):  
F. F. Ehrich ◽  
Z. S. Spakovszky ◽  
M. Martinez-Sanchez ◽  
S. J. Song ◽  
D. C. Wisler ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Axial Flow ◽  
Turbine Engines ◽  
Jet Engines ◽  
Static Structure ◽  
Static Pressure Distribution ◽  
Eccentric Rotor ◽  
Unsteady Effects ◽  
Analytic Models ◽  
Axial Flow Compressors

An experimental and theoretical investigation was conducted to evaluate the effects seen in axial-flow compressors when the centerline of the rotor becomes displaced from the centerline of the static structure of the engine, thus creating circumferentially nonuniform rotor-tip clearances. This displacement produces unsteady flow and creates a system of destabilizing forces, which contribute significantly to rotor whirl instability in turbomachinery. These forces were first identified by Thomas (1958. Bull. AIM, 71, No. 11/12, pp. 1039–1063.) for turbines and by Alford (1965. J. Eng. Power, Oct., pp. 333–334) for jet engines. In Part I, the results from an experimental investigation of these phenomena were presented. In this Part II, three analytic models were used to predict both the magnitude and direction of the Thomas/Alford force in its normalized form, known as the β coefficient, and the unsteady effects for the compressors tested in Part I. In addition, the effects of a whirling shaft were simulated to evaluate differences between a rotor with static offset and an actual whirling eccentric rotor. The models were also used to assess the influence of the nonaxisymmetric static pressure distribution on the rotor spool, which was not measured in the experiment. The models evaluated were (1) the two-sector parallel compressor (2SPC) model, (2) the infinite-segment-parallel-compressor (ISPC) model, and (3) the two-coupled actuator disk (2CAD) model. The results of these analyses were found to be in agreement with the experimental data in both sign and trend. Thus, the validated models provide a general means to predict the aerodynamic destabilizing forces for axial flow compressors in turbine engines. These tools have the potential to improve the design of rotordynamically stable turbomachinery.

scholarly journals Unsteady Flow and Whirl-Inducing Forces in Axial-Flow Compressors: Part II — Analysis

2000 ◽  
Author(s):  
F. F. Ehrich ◽  
Z. S. Spakovszky ◽  
M. Martinez-Sanchez ◽  
S. J. Song ◽  
D. C. Wisler ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Axial Flow ◽  
Jet Engines ◽  
Static Structure ◽  
Static Pressure Distribution ◽  
Eccentric Rotor ◽  
Actuator Disc ◽  
Unsteady Effects ◽  
Analytic Models ◽  
Axial Flow Compressors

An experimental and theoretical investigation was conducted to evaluate the effects seen in axial-flow compressors when the centerline of the rotor becomes displaced from the centerline of the static structure of the engine, thus creating circumferentially non-uniform, rotor-tip clearances. This displacement produces unsteady flow and creates a system of destabilizing forces, which contribute significantly to rotor whirl instability in turbomachinery. These forces were first identified by Thomas (1958) for turbines and by Alford (1965) for jet engines. In Part I, the results from an experimental investigation of these phenomena were presented. In this Part II, three analytic models were used to predict both the magnitude and direction of the Thomas/Alford force in its normalized form, known as the β coefficient, and the unsteady effects for the compressors tested in Part I. In addition, the effects of a whirling shaft were simulated to evaluate differences between a rotor with static off-set and an actual whirling eccentric rotor. The models were also used to assess the influence of the non-axisymmetric static pressure distribution on the rotor spool, which was not measured in the experiment. The models evaluated were: (1) the Two-Sector Parallel Compressor (2SPC) model (Ehrich, 1993), (2) the Infinite-Segment-Parallel-Compressor (ISPC) model (Spakovszky, 2000), and (3) the Two-Coupled Actuator Disc (2CAD) model (Song and Cho, 2000). The results of these analyses were found to be in agreement with the experimental data in both sign and trend. Thus, the validated models provide the general means to predict the aerodynamic destabilizing forces for axial flow compressors in turbine engines. These tools have the potential to improve the design of rotordynamically stable turbomachinery.

Aerodynamics of Contra-Rotating Fans With Swept Blades

2015 ◽  
Author(s):  
K. Vijayraj ◽  
M. Govardhan
Keyword(s):  
Rotational Speed ◽  
Axial Flow ◽  
Pressure Rise ◽  
Aerodynamic Performance ◽  
The Other ◽  
Flow Structures ◽  
Current Investigation ◽  
Rotating System ◽  
Stall Margin ◽  
Static Head

A Counter-Rotating System (CRS) is composed of a front rotor and a rear rotor which rotates in the opposite direction. Compared with traditional rotor-stator system, the rear rotor is used not only to recover the static head but also to supply energy to the fluid. Therefore, to achieve the same performance, the use of a CRS may lead to a reduction of the rotational speed and may generate better homogeneous flow downstream of the stage. On the other hand, the mixing area in between the two rotors induces complicated interacting flow structures. Blade sweep has attracted the turbomachinery blade designers owing to a variety of performance benefits it offers. However, the effect of blade sweep on the performance, stall margin improvements whether it is advantageous/disadvantageous to sweep one or both rotors has not been studied till now. In the current investigation blade sweep on the performance characteristics of contra rotating axial flow fans are studied. Two sweep schemes (axial sweeping and tip chord line sweeping) are studied for two sweep angles (20° and 30°). Effect of blade sweep on front rotor and rear rotor are dealt separately by sweeping one at a time. Both rotors are swept together and effect of such sweep scheme on the aerodynamic performance of the stage is also reported here. The performance of contra rotating fan is significantly affected by all these parameters. Blade sweep improved the pressure rise and stall margin of front rotors. Axially swept rotors are found to have higher pressure rise with reduced incidence losses near the tip for front rotors. Sweeping the rear rotor is not effective since the pressure rise is less than that of unswept rotor and also has less stall margin.

Extensive Experimental Study of Circumferential Single Groove in an Axial Flow Compressor

2014 ◽  
Author(s):  
Jichao Li ◽  
Feng Lin ◽  
Sichen Wang ◽  
Juan Du ◽  
Chaoqun Nie ◽  
...  
Keyword(s):  
Experimental Study ◽  
Unsteady Flow ◽  
Axial Compressor ◽  
Axial Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Good Tool ◽  
Stall Margin ◽  
Casing Treatment ◽  
Tip Leakage

Circumferential single-groove casing treatment becomes an interesting topic in recent few years, because it is a good tool to explore the interaction between the groove and the flow in blade tip region. The stall margin improvement (SMI) as a function of the axial groove location has been found for some compressors, such a trend cannot be predicted by steady high-fidelity CFD simulations. Recent efforts show that to catch such a trend, multi-passage, unsteady flow simulations are needed as the stalling mechanism itself involves cross-passage flows and unsteady dynamics. This indicates a need to validate unsteady numerical simulation results. In this paper, an extensive experimental study of a total of fifteen single casing grooves in a low-speed axial compressor rotor is presented, the groove location varies from 0.4% to 98.3% of axial tip chord are tested. The unsteady pressure data both at casing and at the blade wake with different groove locations are measured and processed, including the movement of trajectory of tip leakage flow, the evolution of unsteadiness of tip leakage flow (UTLF), the unsteady spectrum signature during the stall process, and the outlet unsteady flow characteristic along the span. These data provide a case study for validation of the unsteady CFD results, and may be helpful for further interpretation on the stalling mechanism affected by circumferential casing grooves.

Influence of Rain Ingestion on the Endwall Treatment in an Axial Flow Compressor

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Jichao Li ◽  
Juan Du ◽  
Mingzhen Li ◽  
Feng Lin ◽  
Hongwu Zhang ◽  
...  
Keyword(s):  
Rotor Blade ◽  
Axial Flow ◽  
Pressure Rise ◽  
Water Film ◽  
Stall Margin ◽  
Axial Flow Compressor ◽  
Water Ingestion ◽  
Blade Row ◽  
Flow Compressor ◽  
The Stability

The effects of water ingestion on the performance of an axial flow compressor are experimentally studied with and without endwall treatment. The background to the work is derived from the assessment of airworthiness for an aero-engine. The stability-enhancing effects with endwall treatments under rain ingestion are not previously known. Moreover, all the endwall treatments are designed under dry air conditions in the compressor. Water ingestion at 3% and 5% relative to the design mass flow proposed in the airworthiness standard are applied to initially investigate the effects on the performance under smooth casing (SC). Results show that the water ingestions are mainly located near the casing wall after they move through the rotor blade row. The pressure rise coefficient increases, efficiency declines, and torque increases under the proposed water ingestion. The increase of the inlet water increases the thickness of the water film downstream the rotor blade row and aggravates the adverse effects on the performances. Subsequently, three endwall treatments, namely circumferential grooves, axial slots, and hybrid slots–grooves, are tested with and without water ingestion. Compared with no water ingestion, the circumferential grooves basically have no resistance to the water ingestion. The axial slots best prevent the drop of the pressure rise coefficient induced by water ingestion, and hybrid slots–grooves are the second-best place owing to the contribution of the front axial slots. Therefore, the hybrid slots–grooves can not only extend the stall margin with less efficiency penalty compared with axial slots, but also prevent rain ingestion from worsening the compressor performance.

Compressibility Effects on the Two Generations of Unsteady Flow Types in Axial Flow Compressors

2005 ◽  
Author(s):  
Xinqian Zhen ◽  
Sheng Zhou ◽  
Anping Hou ◽  
Jinsong Xiong
Keyword(s):  
Unsteady Flow ◽  
Axial Flow ◽  
Separated Flows ◽  
Design System ◽  
Relative Reduction ◽  
Positive Effects ◽  
Flow Type ◽  
Wide Range ◽  
Two Generations ◽  
Axial Flow Compressors

There occurred unsteady separated flows inside axial flow compressors, which was however not taken into consideration in the present aerodynamic design system. This discrepancy indicates that the potential underlying unsteady separated flows is yet to be explored, hence the present research team proposes the concept of two generations of unsteady flow types, i.e. Unsteady Natural Flow Type (UNFT) and Unsteady Cooperative Flow Type (UCFT). Numerical simulations are carried out in the present paper to study the compressibility effect on the unsteady cooperative flow type in axial flow compressors. The studies show that aerodynamic performances are remarkably enhanced by means of transforming the flow type from UNFT into UCFT by imposing unsteady excitations. In the case of 2D subsonic cascade, performances are greatly improved in a wide range of Ma number (Ma < 0.8) and the maximum relative reduction of the loss coefficient reaches 40.2%. In the case of 2D trans-supersonic cascade, positive effects can’t be captured. However, in the case of a 3D trans-supersonic single rotor, the adiabatic efficiency is increased from 87.0% to 90.2%.

scholarly journals Recessed Casing Treatment Effects on Fan Performance and Flow Field

1995 ◽  
Author(s):  
C. S. Kang ◽  
A. B. McKenzie ◽  
R. L. Elder
Keyword(s):  
Flow Field ◽  
Axial Flow ◽  
Pressure Rise ◽  
Operating Efficiency ◽  
Flow Measurements ◽  
Blade Loading ◽  
Stall Margin ◽  
Casing Treatment ◽  
Stall Margin Improvement ◽  
Blade Tip

An experimental investigation to examine the influence of the vaned recess casing treatment on stall margin, operating efficiency and the flow field of a low speed axial flow fan with aerospace type blade loading is presented. Different geometrical designs of the vaned passages were examined. The best configuration resulted in a stall margin improvement of 67%, a significantly higher pressure rise in the stall region and insignificant change in peak efficiency. Detailed 3-D flow measurements in the endwall region and in the casing recess were carried out with a slanted hot-wire, providing some insight to the operation of the device. The results revealed that the stall margin improvement was largely due to the removal of flow from the blade tip to the recess, and the elimination of the growth of the stall region at the tip, which occurs at stall in the solid casing build.

scholarly journals Application of Recess Vaned Casing Treatment to Axial Flow Fans

1989 ◽  
Author(s):  
A. R. Azimian ◽  
R. L. Elder ◽  
A. B. McKenzie
Keyword(s):  
Unsteady Flow ◽  
Frequency Response ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Axial Position ◽  
Flow Conditions ◽  
Peak Efficiency ◽  
Stall Margin ◽  
Casing Treatment

The effect of applying a vaned recessed casing treatment to a single stage axial flow fan has been investigated. The influence of the axial position of the recess relative to the rotor leading edge and other geometrical modifications of the vane passage have been examined. Significant improvements in stall margin were observed without (in some builds) loss in peak efficiency. Slow and fast frequency response yawmeter probes have been used in the study to examine both the steady flow conditions and the unsteady flow caused by rotating stall.

Improving Stall Margin by Using an Air-Separator for a Variable-Pitch Axial-Flow Fan

2004 ◽  
Author(s):  
Takahiro Nishioka ◽  
Shuuji Kuroda ◽  
Tadashi Kozu
Keyword(s):  
Axial Flow ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Axial Flow Fan ◽  
Clearance Ratio ◽  
Variable Pitch ◽  
Stall Margin ◽  
Operating Range ◽  
Exposure Ratio ◽  
Air Separator

An air-separator for extending the operating range of a variable-pitch axial-flow fan has been developed. It has a circular-are outer casing, a part of which forms the guide vane at the inlet of the air-separator. To obtain a wide operating range and to minimize penalties in terms of efficiency and noise, the influence of exposure and clearance ratios at various stagger-angle settings for rotor blades in low-speed and high-speed axial flow fans was experimentally investigated. Flow distributions and pressure fluctuations downstream of the rotor were also measured in order to investigate the influence of the air-separator on rotating stall. The distributions and fluctuations suggested that the air-separator decreased the blockage effect near the rotor tip and suppressed the rotating stall. Moreover, stall-margin and pressure-rise improvements were independent of the clearance ratio. These improvements depended on the exposure ratio and stagger-angle settings for the rotor blades. The fan efficiency for the air-separator also depended on the exposure ratio. In addition, the efficiency had the opposite tendency to the stall-margin and pressure-rise improvements. In contrast, the noise for the air-separator was independent of the exposure ratio and decreased as the clearance ratio increased. For the optimum combination of the exposure and clearance ratios, the stall-margin and pressure-rise were improved by over 20% with minimized penalties in terms of efficiency and noise. It is concluded from these results that the developed air-separator can provide a wide operating range for a variable-pitch axial-flow fan.

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