Aerodynamic Performance of an Axial Compressor Stage With Variable Rotor Blades and Variable Inlet Guide Vanes

1998 ◽  
Author(s):  
Václav Cyrus
Keyword(s):  
Volume Flow Rate ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Aerodynamic Performance ◽  
Rotating Stall ◽  
Rotor Blades ◽  
Flow Coefficient ◽  
Experimental Investigations ◽  
Compressor Stage ◽  
Flow Stage

Experimental investigations of flow fields and losses in an axial flow compressor stage were carried out. The stage has hub/tip ratio of 0.7. The design values of flow coefficient and pressure coefficient are 0.6 and 0.81, respectively. Aerodynamic performance was investigated for two principal configurations: i) axial flow stage with variable rotor blades, ii) axial flow stage with variable inlet guide and stator vanes. The most efficient volume flow rate regulation of the stage was with the application of variable rotor blades. On the basis of experimental data an analysis of the origin of flow separation on the suction and pressure surfaces of rotor and stator blades was made with the use of simple design criteria. The unsteady flow of rotating stall type in the tested stage appeared after simultaneous occurence of large stall regions in both rotor and stator blade rows. The existence of large stall regions in the IGV did not affect the rotating stall onset. At high values of the IGV stagger angle change (50 deg) pressure pulsations appeared due to the occurence of stall.

Reversing of Axial Flow Fans for Ventilation

2011 ◽  
Author(s):  
Vaclav Cyrus ◽  
Jiri Pelnar ◽  
Jan Cyrus
Keyword(s):  
Volume Flow Rate ◽  
Flow Direction ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Aerodynamic Performance ◽  
Flow Reversal ◽  
Design Flow ◽  
Flow Coefficient ◽  
Final Decision ◽  
Flow Mechanism

Changing the flow direction in fans is frequently required in emergency situations in traffic tunnels, chemical plants and mines ventilation. Reverse flow in axial flow fan is often achieved using two methods: a) Changing direction of fan rotation and turning the stator vanes (Method I). b) Turning / resetting rotor blades during fan rotation (Method II). The required volume flow rate at flow reversal is usually at least 60% valid for normal fan working point. The motivation of the present paper is to compare the aerodynamic performance and 3D flow mechanism in fan stage at flow reversal carried out by the two methods above. In our paper conditions of the flow reversal are discussed. Theoretical relations are derived for both methods using fundamental equations valid for internal aerodynamics of axial flow compressors and fans. Parameters of three fan axial stages were measured on a 600 diameter test rig at standard and reverse conditions. The investigated fan ventilation stages had a design flow coefficient of 0.35 to 0.40 and pressure coefficient of 0.30. Flow field measurements were carried out with the use of 5-hole pressure probes in the stage planes. The blade rows flow mechanism at the standard and reverse conditions is described using test data obtained for both flow reversal methods. The flow simulation results were also used. It has been found in our investigations that moderate aerodynamic loading of the ventilation fans has better aerodynamic performance during flow reversal if Method II is used. Fan designers and users making the final decision relating to the selection of the flow reversal method should also include the reliability and cost of the reverse fan design with blade turning mechanism.

Effect of Tip Vortex Reduction on Air-Cooled Condenser Axial Flow Fan Performance: An Experimental Investigation

2021 ◽  
Author(s):  
J. P. Pretorius ◽  
J. A. Erasmus
Keyword(s):  
Performance Test ◽  
Performance Enhancement ◽  
Large Diameter ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Tip Vortex ◽  
Experimental Investigations ◽  
Fan Performance

Abstract Large diameter axial flow fans are used in Air-cooled Condenser (ACC) systems of modern power stations. Efficiency improvements on these fans can significantly reduce the ACC power consumption and increase the net sent-out power to the grid. This study targets fan performance enhancement through blade tip vortex reduction. Experimental investigations are performed on a representative ACC scale fan, where tests consider the effects of tip clearance and two new tip endplate designs on fan performance. Test results confirm the findings of previous studies, showing the negative effect of increasing tip clearance on performance. Despite testing limitations, results from tests incorporating endplates show fan static pressure coefficient and efficiency increases over large ranges of flow coefficient compared to the datum fan. These outcomes agree with observations from literature and warrants further exploration. Future work is recommended to provide confirmation on the presented trends.

Effect of Tip Vortex Reduction on Air-Cooled Condenser Axial Flow Fan Performance: an Experimental Investigation

2021 ◽  
pp. 1-28
Author(s):  
J.P. Pretorius ◽  
Johan A Erasmus
Keyword(s):  
Performance Test ◽  
Performance Enhancement ◽  
Large Diameter ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Tip Vortex ◽  
Experimental Investigations ◽  
Fan Performance

Abstract Large diameter axial flow fans are used in Air-cooled Condenser (ACC) systems of modern power stations. Efficiency improvements on these fans can significantly reduce the ACC power consumption and increase the net sent-out power to the grid. This study targets fan performance enhancement through blade tip vortex reduction. Experimental investigations are performed on a representative ACC scale fan, where tests consider the effects of tip clearance and two new tip endplate designs on fan performance. Test results confirm the findings of previous studies, showing the negative effect of increasing tip clearance on performance. Despite testing limitations, results from tests incorporating endplates show fan static pressure coefficient and efficiency increases over large ranges of flow coefficient compared to the datum fan. These outcomes agree with observations from literature and warrants further exploration. Future work is recommended to provide confirmation on the presented trends.

Performance Improvement of a Centrifugal Compressor Stage by Increasing Degree of Reaction and Optimizing Blade Loading of a 3D Impeller

2010 ◽  
Vol 133 (2) ◽  
Author(s):  
Takanori Shibata ◽  
Manabu Yagi ◽  
Hideo Nishida ◽  
Hiromi Kobayashi ◽  
Masanori Tanaka
Keyword(s):  
Performance Improvement ◽  
Relative Velocity ◽  
High Efficiency ◽  
Pressure Coefficient ◽  
Flow Coefficient ◽  
Compressor Stage ◽  
Blade Loading ◽  
Surge Margin ◽  
Velocity Diffusion ◽  
Stage Efficiency

Performance improvement of 3D impellers in a high specific speed range was investigated using computational fluid dynamics analyses and experimental tests. In order to reduce the loss production within the stator passages, the backsweep angle of the impellers was increased. At the same time, the inlet-to-exit relative velocity diffusion ratio was also increased by increasing the impeller exit width to prevent the reduction in the pressure ratio. Moreover, the blade loading distribution at the impeller shroud side was optimized to suppress the surge margin reduction caused by the increased relative velocity diffusion ratio. Five types of unshrouded impellers were designed, manufactured, and tested to evaluate the effects of blade loading, backsweep angle, and relative velocity diffusion ratio on the compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that the compressor stage efficiency was increased by 5% compared with the base design without reducing the pressure coefficient and surge margin. It was concluded that an increased relative velocity diffusion ratio coupled with large backsweep angle was a very effective way to improve the compressor stage efficiency. An appropriate blade loading distribution was also important in order to achieve a wide operating range as well as high efficiency.

Experimental investigations on instability evolution in a transonic compressor at different rotor speeds

2015 ◽  
Vol 229 (18) ◽  
pp. 3378-3391 ◽  
Author(s):  
Qiushi Li ◽  
Tianyu Pan ◽  
Tailu Sun ◽  
Zhiping Li ◽  
Yifang Gong
Keyword(s):  
Low Frequency ◽  
Axial Flow ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Rotor Speed ◽  
Axial Flow Compressor ◽  
Transonic Compressor ◽  
New Type ◽  
Flow Compressor

Experimental investigations are conducted to study the instability evolution in a transonic axial flow compressor at four specific rotor speeds covering both subsonic and transonic operating conditions. Two routes of evolution to final instability are observed in the test compressor: at low rotor speeds, a disturbance in the rotor tip region occurs and then leads to rotating stall, while at high rotor speeds, a low-frequency disturbance in the hub region leads the compressor into instability. Different from stall and surge, this new type of compressor instability at high rotor speed is initiated through the development of a low-frequency axisymmetric disturbance at the hub, and we name it “partial surge”. The frequency of this low-frequency disturbance is approximately the Helmholtz frequency of the system and remains constant during instability inception. Finally, a possible mechanism for the occurrence of different instability evolutions and the formation of partial surge are also discussed.

A Study of the Behaviour of Flow in a Diagonal-Flow Turbomachine

1996 ◽  
Author(s):  
Arjun Sarathi Ray
Keyword(s):  
Fluid Dynamic ◽  
Characteristic Curve ◽  
Axial Flow ◽  
Time History ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Flow Measurements ◽  
Flow Rates ◽  
Rotor Losses ◽  
Reduced Flow

Experiments were conducted on a diagonal-flow machine to study the behaviour of flow. Measurements showed that at reduced flow rates, reversal of flow occurs near the tip upstream of the rotor and near the hub downstream. At high flow rates, the flow reverses near tip at downstream only. In fact, there is only a limited regime of operation where the flow is not reversed before or after the impeller. The best fluid-dynamic efficiency was observed to be midway of this non-reversed flow regime. Through-flow solutions of the mean hub-to-tip streamsurface were carried out by streamline curvature computation and compared with experimental results. The comparison showed good agreement of the predicted values with the experimental data. However, attempts to compare theoretical estimates of rotor losses with experimental measurements showed that the existing loss models are inadequate for loss prediction and further work is required in this direction. The head-flow characteristic of the machine showed a droop at reduced flow rates, typical of what one usually notices in an axial-flow machine with the onset of blade stall. Study of the time history of velocity downstream of rotor illustrated that unlike rotating ‘stall-cells’ in axial-flow machines, the blade stall in the present case did not possess any regular pattern nor any unique speed of propagation. Near the hub at downstream of rotor, where the flow finally reverses upon reduction of flow rate, the stall appeared as patches of ‘blockage’ type disturbance over an otherwise systematic train of blade wakes when the flow coefficient reaches a value where the droop in the characteristic curve starts.

scholarly journals Investigation on Unsteady Flow Characteristics in an Axial-Flow Fan under Stall Conditions

Processes ◽  
2020 ◽  
Vol 8 (8) ◽  
pp. 958
Author(s):  
Chenlong Jiang ◽  
Mengjiao Li ◽  
Enda Li ◽  
Xingye Zhu
Keyword(s):  
Unsteady Flow ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Rotating Stall ◽  
Air Separation ◽  
Flow Coefficient ◽  
Tip Leakage Flow ◽  
Axial Flow Fan ◽  
Time Frequency ◽  
Flow Capacity

Based on Shear Stress Transport (SST) turbulence model for unsteady simulation of an axial-flow fan, this paper studies the time-frequency information in the hump region, and investigates the disturbance information of spike and modal wave under different flow coefficients based on continuous wavelet transform (CWT). The results show that before the hump point, the low-frequency modal wave occupies the main disturbance form and circularly propagates at 1/10 of the rotor speed, and the axial-flow fan does not enter the stall stage; while after the flow coefficient reduces to the hump point, the spike wave with higher frequency replaces the modal wave as the main disturbance mode while the axial-flow fan enters the stall stage. Through in-depth investigation of unsteady flow characteristics under the hump point, it is found that after experiencing the emerging spike, with the sharp increase of incidence angle, some flow distortions appear on the intake surface, and further induce some flow paths to form stall vortices. When a path goes into stall stage, the airflow state is greatly affected, the inverse flow and air separation phenomenon in the rim region increase significantly, and the flow capacity decreases significantly, so the flow capacity in the hub region increases correspondingly. The flow path distortion of tip leakage flow (TLF) and leading edge (LE) spillage caused by the stall vortices are the main inducements of rotating stall.

Separated Flows in Axial Flow Compressor With Variable Stator Vanes at Positive Incidence Angles

1994 ◽  
Author(s):  
Vaclav Cyrus
Keyword(s):  
Three Dimensional ◽  
Axial Compressor ◽  
Axial Flow ◽  
Separated Flow ◽  
Rotating Stall ◽  
Compressor Stage ◽  
Diffusion Factor ◽  
Stator Blade ◽  
Flow Compressor ◽  
End Wall

A detailed investigation of three-dimensional flow was carried out in a low speed rear axial compressor stage with the change of the stator blade row setting. The stator blade stagger change was in the range of (−14) – (23) degree. Measurements were performed by means of both stationary and rotating pressure probes at seven working points. The origin of large regions of separated flow in blade rows at positive incidence angles was analysed with the use of the spanwise diffusion factor distribution. These areas in the rotor and stator rows originated as the diffusion factor exceeded the critial value D = 0.6 within (1/4 – 1/3) of the blade height near one end-wall. The rotating stall in compressor stage arised when large regions of separated flow occured simultaneously in both rotor and stator blade rows.

Impact of Manufacturing Variability on the Aerodynamic Performance of a Centrifugal Compressor Stage With Curvilinear Blades

2016 ◽  
Author(s):  
A. Panizza ◽  
R. Valente ◽  
D. Rubino ◽  
L. Tapinassi
Keyword(s):  
Centrifugal Compressor ◽  
Sampling Methods ◽  
Aerodynamic Performance ◽  
High Flow ◽  
Flow Coefficient ◽  
Design Parameters ◽  
Compressor Stage ◽  
Centrifugal Compressor Stage ◽  
Performance Variability ◽  
The Impact

The goal of the present study is to quantify the uncertainty in the aerodynamic performance of a centrifugal compressor stage with curvilinear impeller blades, due to impeller manufacturing variability. Impellers with curvilinear element blades allow a greater control of secondary flows with respect to impellers having ruled blades. High flow coefficient impellers for centrifugal compressors exhibit larger secondary flow than medium or low flow coefficient impellers, due to the stronger curvature of the flow path and the larger blade height for the same external diameter. Thus curvilinear blade impellers allow to improve the efficiency and range of high flow coefficient centrifugal compressor stages. As the design of these impellers is more complex than the design of ruled blade impellers, it is important to estimate the impact of the impeller manufacturing variability on the performance of the full stage. Sampling methods are often used in uncertainty propagation studies. However, sampling based approaches require a very large number of samples to have an accurate estimate of the performance uncertainty. 3D steady RANS computations are necessary to capture the impact of the geometric variability of the curvilinear blade impeller, on the stage performance. Thus, sampling methods would require an excessive computational time. In this work, the Polynomial Chaos Expansion (PCE) method with arbitrary probability distributions, implemented in DAKOTA, is used to reduce the number of runs required for the uncertainty quantification study. Manufacturing measurement data are been used to derive the histograms of the main impeller design parameters. From these histograms, numerically-generated orthogonal polynomials are computed for each parameter using a discretized Stieltjes procedure. Stochastic expansion methods such as PCE suffer from the curse of dimensionality, i.e., an exponential increase in the number of runs as the number of uncertain parameters increases. To mitigate the curse of dimensionality, sparse grids are used, which allow a drastic reduction of the number of runs. The results of the study show that the performance variability is small, thus our design with curvilinear element blades is robust with respect to impeller manufacturing variability. Using Sobol indices, we also rank the design parameters according to their impact on the performance variability.

Wake–Boundary Layer Interactions in an Axial Flow Turbine Rotor at Off-Design Conditions

1989 ◽  
Vol 111 (2) ◽  
pp. 181-192 ◽  
Author(s):  
H. P. Hodson ◽  
J. S. Addison
Keyword(s):  
Rotor Blade ◽  
Axial Flow ◽  
Leading Edge ◽  
Surface Flow ◽  
Design Flow ◽  
Flow Coefficient ◽  
Experimental Investigations ◽  
Pressure Side ◽  
Suction Surface ◽  
Edge Separation

A series of experimental investigations has been undertaken in a single-stage low-speed turbine. The measurements involved rotor blade surface flow visualization, surface-mounted hot-film anemometry, and exit pitot traverses. The effects of varying the flow coefficient and Reynolds number upon the performance of the rotor blade at midspan are described. At the design flow coefficient (φ = 0.495), the rotor pressure surface flow may be regarded as laminar, while on the suction surface, laminar flow gives way to unsteady stator wake-induced transition and then to turbulent flow. Over the range of Reynolds numbers investigated (1.8×105–3.3×105), the rotor midspan performance is dominated by the suction surface transition process; suction surface separation is prevented and the rotor midspan loss coefficient remains approximately constant throughout the range. At positive incidence, suction surface leading edge separation and transition are caused by a velocity overspeed. Reattachment occurs as the flow begins to accelerate toward the throat. The loss associated with the separation becomes significant with increasing incidence. At negative incidence, a velocity overspeed causes leading edge separation of the pressure side boundary layers. Reattachment generally occurs without full transition. The suction surface flow is virtually unaffected. Therefore, the rotor midspan profile loss remains unchanged from the zero incidence value until pressure side stall occurs.

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