An Explanation for Flow Features of Spike-Type Stall Inception in an Axial Compressor Rotor

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Kazutoyo Yamada ◽  
Hiroaki Kikuta ◽  
Ken-ichiro Iwakiri ◽  
Masato Furukawa ◽  
Satoshi Gunjishima
Keyword(s):  
Flow Structure ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Leading Edge ◽  
Low Pressure ◽  
Stall Inception ◽  
Compressor Rotor ◽  
Pressure Region ◽  
Casing Pressure ◽  
Edge Separation

The unsteady behavior and three-dimensional flow structure of spike-type stall inception in an axial compressor rotor were investigated by experimental and numerical analyses. Previous studies revealed that the test compressor falls into a mild stall after emergence of a spike, in which multiple stall cells, each consisting of a tornado-like vortex, are rotating. However, the flow mechanism from the spike onset to the mild stall remains unexplained. The purpose of this study is to describe the flow mechanism of a spike stall inception in a compressor. In order to capture the transient phenomena of spike-type stall inception experimentally, an instantaneous casing pressure field measurement technique was developed, in which 30 pressure transducers measure an instantaneous casing pressure distribution inside the passage for one blade pitch at a rate of 25 samplings per blade passing period. This technique was applied to obtain the unsteady and transient pressure fields on the casing wall during the inception process of the spike stall. In addition, the details of the three-dimensional flow structure at the spike stall inception were analyzed by a numerical approach using the detached-eddy simulation (DES). The instantaneous casing pressure field measurement results at the stall inception show that a low-pressure region starts traveling near the leading edge in the circumferential direction just after the spiky wave was detected in the casing wall pressure trace measured near the rotor leading edge. The DES results reveal the vortical flow structure behind the low-pressure region on the casing wall at the stall inception, showing that the low-pressure region is caused by a tornado-like separation vortex resulting from a leading-edge separation near the rotor tip. A leading-edge separation occurs near the tip at the onset of the spike stall and grows to form the tornado-like vortex connecting the blade suction surface and the casing wall. The casing-side leg of the tornado-like vortex generating the low-pressure region circumferentially moves around the leading-edge line. When the vortex grows large enough to interact with the leading edge of the next blade, the leading-edge separation begins to propagate, and then the compressor falls into a stall with decreasing performance.

An Explanation for Flow Features of Spike-Type Stall Inception in an Axial Compressor Rotor

2012 ◽  
Author(s):  
Kazutoyo Yamada ◽  
Hiroaki Kikuta ◽  
Ken-ichiro Iwakiri ◽  
Masato Furukawa ◽  
Satoshi Gunjishima
Keyword(s):  
Flow Structure ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Leading Edge ◽  
Low Pressure ◽  
Stall Inception ◽  
Compressor Rotor ◽  
Pressure Region ◽  
Casing Pressure ◽  
Edge Separation

The unsteady behavior and three-dimensional flow structure of spike-type stall inception in an axial compressor rotor have been investigated by experimental and numerical analyses. Previous studies have revealed that the test compressor falls into a mild stall after emergence of a spike, in which multiple stall cells, each consisting of a tornado-like vortex, are rotating. However, the flow mechanism from the spike onset to the mild stall remains unexplained. The purpose of this study is to describe the flow mechanism of a spike stall inception in a compressor. In order to capture the transient phenomena of spike-type stall inception experimentally, an instantaneous casing pressure field measurement technique was developed, in which 30 pressure transducers measure an instantaneous casing pressure distribution inside the passage for one blade pitch at a rate of 25 samplings per blade passing period. This technique was applied to obtain the unsteady and transient pressure fields on the casing wall during the inception process of the spike stall. In addition, the details of the three-dimensional flow structure at the spike stall inception have been analyzed by a numerical approach using the detached-eddy simulation (DES). The instantaneous casing pressure field measurement results at the stall inception show that a low-pressure region starts traveling near the leading edge in the circumferential direction just after the spiky wave was detected in the casing wall pressure trace measured near the rotor leading edge. The DES results reveal the vortical flow structure behind the low-pressure region on the casing wall at the stall inception, showing that the low-pressure region is caused by a tornado-like separation vortex resulting from a leading-edge separation near the rotor tip. A leading-edge separation occurs near the tip at the onset of the spike stall and grows to form the tornado-like vortex connecting the blade suction surface and the casing wall. The casing-side leg of the tornado-like vortex generating the low-pressure region circumferentially moves around the leading-edge line. When the vortex grows large enough to interact with the leading edge of the next blade, the leading-edge separation begins to propagate, and then, the compressor falls into a stall with decreasing performance.

Effects of Tip Clearance on the Stall Inception Process in an Axial Compressor Rotor

2013 ◽  
Author(s):  
Kazutoyo Yamada ◽  
Hiroaki Kikuta ◽  
Masato Furukawa ◽  
Satoshi Gunjishima ◽  
Yasunori Hara
Keyword(s):  
Vortex Breakdown ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Tip Leakage Vortex ◽  
Stall Inception ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Flow Phenomena ◽  
Casing Pressure

The paper presents experimental and numerical studies on the effects of tip clearance on the stall inception process in a low-speed axial compressor rotor with a large tip clearance. It has been revealed that in the small tip clearance case, shortly after the spike disturbance which results from the leading-edge separation near the rotor tip appears, the tornado-like vortex is generated by the separation, and soon the compressor falls into stall. In the large tip clearance case, the experiment showed that the performance characteristic differs from that in the small tip clearance case at near-stall conditions. This implies that the stall inception process differs with the tip clearance size. The flow phenomenon in the stall inception leading to such difference has been investigated in this study. Pressure and velocity fields which were ensemble-averaged and phase-locked by the periodic multi-sampling technique were measured on the casing wall and downstream of the rotor, respectively. In addition, to capture the unsteady flow phenomena inside the rotor, “Instantaneous Casing Pressure Field Measurement” was carried out: instantaneous casing pressure fields in one rotor passage region were measured by 30 high response pressure transducers mounted on the casing wall. In order to investigate further details of near-stall flow field for the large tip clearance, DES (Detached Eddy Simulation) has been conducted using a computational mesh with 120 million points. The results are compared with those from previous studies for the small tip clearance. As expected, the measurement results show notable differences in the near-stall flow field between the two tip clearance cases. The results from the casing pressure measurement show that high pressure fluctuation appears on the pressure side near the rotor leading-edge in the large tip clearance case. In the result of the velocity field measurement downstream of the rotor, high turbulence intensity is found near the casing in the large tip clearance case. The numerical results reveal that the vortex breakdown occurs in the tip leakage vortex and induces the oscillation of the tip leakage vortex with its unsteady nature. The flow phenomena confirmed in the experimental results are clearly explained by considering the breakdown of the tip leakage vortex. The vortex breakdown gives rise to not only large blockage but also the rotating disturbance through the interaction of the fluctuating tip leakage vortex with the pressure surface of the adjacent blade, and governs the stall inception process.

Experimental and Numerical Investigation of Near-Tip Flow Field in an Axial Flow Compressor Rotor: Part II — Flow Characteristics at Stall Inception Condition

2013 ◽  
Author(s):  
Yanhui Wu ◽  
Junfeng Wu ◽  
Haoguang Zhang ◽  
Wuli Chu
Keyword(s):  
Flow Field ◽  
Flow Condition ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Current Investigation ◽  
Flow Mechanism ◽  
Stall Inception ◽  
Compressor Rotor ◽  
Casing Pressure ◽  
Stable Flow

Systematical casing pressure measurements were undertaken to supplement instantaneous experiment data to available database of a high-speed small-scale compressor rotor, which was crucial for understanding the flow mechanism of short-length scale stall inception. At the same time, improved full-annulus simulations were conducted to assist in interpretation of experimental observations. In Part II of current investigation, original instantaneous casing pressure signals and STFT (short time Fourier transformation) analyses were conducted to conclude flow characteristics near casing at stall inception operating condition, and reasonable explanation of experimental observations was given in combination with numerical results. The current experimental investigation showed the stall inception of the test rotor was triggered by a spike, propagating at about 66.7%, which evolved into a single fully-developed stall cell. STFF analysis of pressure signal detected by probe located at tip leading edge showed that frequency peaks with varied band, which already observed in near-stall stable flow condition in Part I, was still a dominant flow feature before spike emergence, though it was hardly perceived after spike emergence due to a sudden increase in the overall energy of pressure signal, which attributed to the interface of incoming and tip clearance flow beyond leading edge plane according to STFT results. Monitoring results of static pressures in the absolute frame from current simulation and the corresponding FFT and STFT analyses showed a similar flow field evolution process as those observed in experiment. The current investigation provided adequate experimental evidence to support the previous simulation results in which a viewpoint of formation and activity of tip secondary vortex (TSV) was proposed as the underlying flow mechanism of the origin of unsteadiness near casing at near-stall stable operating conditions, and emergence of spike during the transition of flow field into unstable state, and further verified that the unsteady flow phenomenon observed in near-stall stable flow condition was equivalent to rotating instability (RI), thus establishing the causal linkage between RI and stall inception for the test rotor.

Analysis of Axial Compressor Stall Inception Using Unsteady Casing Pressure Measurements

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Joshua D. Cameron ◽  
Scott C. Morris
Keyword(s):  
Pressure Sensors ◽  
Axial Compressor ◽  
Leading Edge ◽  
Scalar Function ◽  
Pressure Measurements ◽  
Time Resolved ◽  
Fourier Decomposition ◽  
Stall Inception ◽  
Axial Compressors ◽  
Casing Pressure

The unsteady flow in axial compressors during pre-stall and stall inception is often studied using circumferentially distributed pressure sensors. The present investigation utilized a transonic axial compressor facility to acquire time resolved casing static pressure measurements at an axial location upstream of the rotor leading edge. These measurements were processed using a variety of analysis techniques in order to provide insight into the fluid dynamics and compression system dynamics prior to and during stall inception. Specifically, visual inspection of the time series, spatial Fourier decomposition, traveling wave energy, and wavelet transform results will be described and compared for two representative stall inception events. Additionally, a new method was developed based on a windowed, two-point correlation function between adjacent sensors. The intent was to provide a scalar function that was nonzero only when disturbances that rotated around the compressor annulus in the direction of the rotor’s rotation were present. The results indicated that this method highlights many detailed features of the rotating disturbances with both spatial and temporal resolution during both pre-stall and stall inception.

Unsteady Three-Dimensional Flow Phenomena Due to Breakdown of Tip Leakage Vortex in a Transonic Axial Compressor Rotor

2004 ◽  
Author(s):  
K. Yamada ◽  
M. Furukawa ◽  
T. Nakano ◽  
M. Inoue ◽  
K. Funazaki
Keyword(s):  
Shock Wave ◽  
Flow Field ◽  
Vortex Breakdown ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Compressor Rotor

Unsteady three-dimensional flow fields in a transonic axial compressor rotor (NASA Rotor 37) have been investigated by unsteady Reynolds-averaged Navier-Stokes simulations. The simulations show that the breakdown of the tip leakage vortex occurs in the compressor rotor because of the interaction of the vortex with the shock wave. At near-peak efficiency condition small bubble-type breakdown of the tip leakage vortex happens periodically and causes the loading of the adjacent blade to fluctuate periodically near the leading edge. Since the blade loading near the leading edge is closely linked to the swirl intensity of the tip leakage vortex, the periodic fluctuation of the blade loading leads to the periodic breakdown of the tip leakage vortex, resulting in self-sustained flow oscillation in the tip leakage flow field. However, the tip leakage vortex breakdown is so weak and small that it is not observed in the time-averaged flow field at near-peak efficiency condition. On the other hand, spiral-type breakdown of the tip leakage vortex is caused by the interaction between the vortex and the shock wave at near-stall operating condition. The vortex breakdown is found continuously since the swirl intensity of tip leakage vortex keeps strong at near-stall condition. The spiral-type vortex breakdown has the nature of self-sustained flow oscillation and gives rise to the large fluctuation of the tip leakage flow field, in terms of shock wave location, blockage near the rotor tip and three-dimensional separation structure on the suction surface. It is found that the breakdown of the tip leakage vortex leads to the unsteady flow phenomena near the rotor tip, accompanying large blockage effect in the transonic compressor rotor at the near-stall condition.

Hydrodynamics of swimming in stingrays: numerical simulations and the role of the leading-edge vortex

2016 ◽  
Vol 788 ◽  
pp. 407-443 ◽  
Author(s):  
R. G. Bottom II ◽  
I. Borazjani ◽  
E. L. Blevins ◽  
G. V. Lauder
Keyword(s):  
Three Dimensional ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Low Pressure ◽  
Body Motion ◽  
Vortical Structures ◽  
Leading Edge Vortex ◽  
Large Eddy ◽  
Pressure Region ◽  
Edge Vortex

Stingrays, in contrast with many other aquatic animals, have flattened disk-shaped bodies with expanded pectoral ‘wings’, which are used for locomotion in water. To discover the key features of stingray locomotion, large-eddy simulations of a self-propelled stingray, modelled closely after the freshwater stingray, Potamotrygon orbignyi, are performed. The stingray’s body motion was prescribed based on three-dimensional experimental measurement of wing and body kinematics in live stingrays at two different swimming speeds of 1.5 and $2.5L~\text{s}^{-1}$ ($L$ is the disk length of the stingray). The swimming speeds predicted by the self-propelled simulations were within 12 % of the nominal swimming speeds in the experiments. It was found that the fast-swimming stingray (Reynolds number $Re=23\,000$ and Strouhal number $St=0.27$) is approximately 12 % more efficient than the slow-swimming one ($Re=13\,500$, $St=0.34$). This is related to the wake of the fast- and slow-swimming stingrays, which was visualized along with the pressure on the stingray’s body. A horseshoe vortex was discovered to be present at the anterior margin of the stingray, creating a low-pressure region that enhances thrust for both fast and slow swimming speeds. Furthermore, it was found that a leading-edge vortex (LEV) on the pectoral disk of swimming stingrays generates a low-pressure region in the fast-swimming stingray, whereas the low- and high-pressure regions in the slow-swimming one are in the back half of the wing and not close to any vortical structures. The undulatory motion creates thrust by accelerating the adjacent fluid (the added-mass mechanism), which is maximized in the back of the wing because of higher undulations and velocities in the back. However, the thrust enhancement by the LEV occurs in the front portion of the wing. By computing the forces on the front half and the back half of the wing, it was found that the contribution of the back half of the wing to thrust in a slow-swimming stingray is several-fold higher than in the fast-swimming one. This indicates that the LEV enhances thrust in fast-swimming stingrays and improves the efficiency of swimming.

Effect of Inflow Circumferential Distortion on a Transonic Axial Compressor

2017 ◽  
Author(s):  
Yuyun Li ◽  
Zhiheng Wang ◽  
Guang Xi
Keyword(s):  
Total Pressure ◽  
Rotor Blade ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Leading Edge ◽  
Inlet Distortion ◽  
Compressor Rotor ◽  
Structure Changes ◽  
Transonic Axial Compressor

The Inlet distortion, which may lead to the stability reduction or structure failure, is often non-ignorable in an axial compressor. In the paper, the three-dimensional unsteady numerical simulations on the flow in NASA rotor 67 are carried out to investigate the effect of inlet distortion on the performance and flow structure in a transonic axial compressor rotor. A sinusoidal circumferential total pressure distortion with eleven periods per revolution is adopted to study the interaction between the transonic rotor and inlet circumferential distortion. Concerning the computational expense, the flow in two rotor blade passages is calculated. Various intensities of the total pressure distortion are discussed, and the detailed flow structures under different rotating speeds near the peak efficiency condition are analyzed. It is found that the distortion has a positive effect on the flow near the hub. Even though there is no apparent decrease in the rotor efficiency or total pressure ratio, an obvious periodic loading exists over the whole blade. The blade loadings are concentrated in the region near the leading edge of the rotor blade or regions affected by the oscillating shocks near the pressure side. The time averaged location of shock structure changes little with the distortion, and the motion of shocks and the interactions between the shock and the boundary layer make a great contribution to the instability of the blade structure.

Numerical Study on Three-Dimensional Optimization of a Low-Speed Axial Compressor Rotor

2014 ◽  
Author(s):  
Chenkai Zhang ◽  
Jun Hu ◽  
Zhiqiang Wang ◽  
Chao Yin ◽  
Wei Yan
Keyword(s):  
Numerical Optimization ◽  
Large Scale ◽  
Numerical Study ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Trailing Edge ◽  
Compressor Rotor ◽  
Flow Loss

This paper presents numerical optimization of a compressor rotor, to deepen the knowledge of endwall flow in the large-scale axial subsonic compressor, accordingly reduce its endwall loss and improve its aerodynamic performance. With numerical simulation and numerical optimization tools, three-dimensional stacking principle is optimized to improve the design operation point performance for the rotor. Results show that, hub region of the rotor cannot undertake large blade loading; compared to the prototype rotor, obvious aerodynamic performance improvements locate near the hub area, and a certain degree of positive dihedral in this region effectively helps to reduce its flow loss. The effect of “loaded leading edge and unloaded trailing edge” due to positive dihedral was shown, which suppresses flow separation near the trailing edge, consequently obviously reduces the flow loss and largely improves the rotor aerodynamic performance.

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