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1
Hong, Shuli, Guoping Huang, Yuxuan Yang e Zepeng Liu. "Introduction of DMD Method to Study the Dynamic Structures of a Three-Dimensional Centrifugal Compressor with and without Flow Control". Energies 11, n. 11 (9 novembre 2018): 3098. http://dx.doi.org/10.3390/en11113098.
Testo completoAbstract (sommario):
The flow structures around the blade tip, mainly large-scale leakage vortex, exert a great influence on compressor performance. By applying unsteady jet control technology at the blade tip in this study, the performance of the compressor can be greatly improved. A numerical simulation is conducted to study the flow characteristics of a centrifugal compressor with and without a flow control. The complex flow structures cause great difficulties in the analysis of the dynamic behavior and flow control mechanism. Thus, we introduced a dynamic flow field analysis technology called dynamic mode decomposition (DMD). The global spectrums with different global energy norms and the coherent structures with different scales can be obtained through the DMD analysis of the three-dimensional controlled and uncontrolled compressors. The results show that the coherent structures are homogeneous in the controlled compressor. The leakage vortex is weakened, and its influence range of unsteady fluctuation is reduced in the controlled compressor. The effective flow control created uniform vortex structures and improved the overall order of the flow field in the compressor. This research provides a feasible direction for future flow control applications, such as transferring the energy of the dominant vortices to small-scale vortices.
2
Jiang, Bin, Xiangtong Shi, Qun Zheng, Qingfang Zhu, Zhongliang Chen e Zhitao Tian. "The Relationship of Spike Stall and Hub Corner Separation in Axial Compressor". International Journal of Turbo & Jet-Engines 37, n. 1 (26 marzo 2020): 1–16. http://dx.doi.org/10.1515/tjj-2016-0046.
Testo completoAbstract (sommario):
AbstractThe onset of spike stall induced by the interaction of hub corner separation flow with the tip leakage flow is investigated in detail by numerical method in this paper. The time resolved results indicate that the remarkable radial secondary flow from hub to tip near the trailing edge is formed when the compressor approaching rotating stall. The radial secondary flow is unstable and cross-passages propagates, which flows in and away out of the tip region periodically. The disturbance caused by radial secondary flow will influence the tip leakage flow directly by reforming the vortexes in blade tip region. A secondary vortex which comes from the radial migration of corner separation and is induced by the tip leakage vortex appears in the tip region. The simulation result demonstrates that the generation of the secondary vortex is an important symbol of blockage growth in the tip region at the stall inception phase. The disturbance produced by secondary vortex is an incentive of the leading edge overflow and the intensity of secondary vortex could be used as a criterion of rotating stall before leading edge spillage.
3
Schrapp, H., U. Stark e H. Saathoff. "Unsteady behaviour of the tip clearance vortex in a rotor equivalent compressor cascade". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 223, n. 6 (6 luglio 2009): 635–43. http://dx.doi.org/10.1243/09576509jpe816.
Testo completoAbstract (sommario):
From earlier experimental investigations in a single-stage axial-flow pump and different numerical calculations of the flow in single-stage axial-flow compressors, it is known that vortex breakdown of the tip clearance vortex can take place in turbomachines, although an experimental proof for subsonic compressors is lacking. Vortex breakdown, if existent, is a source of high instability in the sensitive tip region of axial-flow pumps and compressors and will also play an important role in the stall inception process. Therefore, the flow in a linear compressor cascade with a 3 per cent tip clearance to one side has been investigated at different flow angles from the design point up to the stability limit of the cascade. The cascade resembles the tip section of a single-stage, axial-flow, low-speed compressor that is also in use at the Technical University of Braunschweig. The measuring techniques used were (a) a commercial particle image velocimetry (PIV) system and (b) a pressure measuring system with several flush mounted high-response pressure transducers at selected locations where the vortex was expected. As the cascade approaches its stall limit, the analysis of the pressure signals in the frequency domain revealed a bump of increased amplitude at a certain non-dimensional frequency for some of the measuring positions. The measuring positions that exhibited the bump correlated very well with a paraboloid-shaped region of high standard deviation enveloping an area of very low momentum fluid. It is shown that the frequency of the striking bump corresponds to the rotational frequency of the vortex calculated from the PIV measurements.
4
Wu, T. T., e W. H. Hsieh. "Compression Processes and Performance Analysis of a High-Pressure Reciprocating Gas Compressor". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 210, n. 2 (marzo 1996): 153–65. http://dx.doi.org/10.1243/pime_proc_1996_210_182_02.
Testo completoAbstract (sommario):
Compression processes and compressor performance in a two-stage 41.34 MPa (6000 lb/in2) reciprocating gas compressor were investigated by transient multi-dimensional and transient global thermodynamic models. The transient multi-dimensional model was adopted to predict the two-dimensional compression processes in the second-stage cylinder of the high-pressure reciprocating gas compressor. Calculated results showed no significant temperature gradients anywhere in the compressor cylinder except near the wall, throughout one complete compressor cycle. On the other hand, the calculated velocity fields and streamline contours showed a convergent flow pattern during the process of compression with discharge and a large recirculation vortex during the process of expansion with suction. A parametric study based on the transient global thermodynamic model was conducted to investigate the effect of various parameters, that is clearance volume, wall temperature of cylinder head and stroke length, on the compressor performance. Among these parameters, it was found that the clearance volume had the strongest effect on the compressor performance. A reduced clearance volume increased volumetric efficiency. Also, it was found that decreasing the stroke length would not degrade the compressor performance, but it could reduce the compressor size and thereby the manufacturing cost significantly.
5
Mao, Xiaochen, Bo Liu e Tianquan Tang. "Effect of casing aspiration on the tip leakage flow in the axial flow compressor cascade". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 232, n. 3 (3 agosto 2017): 225–39. http://dx.doi.org/10.1177/0957650917724598.
Testo completoAbstract (sommario):
Tip leakage flow is usually responsible for the deterioration of compressor performance and stability. The current paper conducts numerical simulations on the impact of casing aspiration on the axial compressor cascade performance. Three aspiration schemes with different chordwise coverage are studied and analyzed. It is found that the cascade performance can be effectively improved by the appropriate casing aspiration, and the optimum aspiration scheme should cover the area including the onset point of tip leakage vortex and its vicinity. The control mechanisms are different for the aspiration schemes located at different blade chord ranges. For the aspiration scheme covering the onset point of tip leakage vortex, the improvement of the cascade performance is mainly due to that the starting point of the tip leakage vortex is shifted downstream. The original tip leakage vortex structure is divided into two parts if the aspiration scheme is located behind the onset point of tip leakage vortex and the final control effect is the combination of the influence from the two different parts of tip leakage vortex. Additionally, the casing aspiration redistributes the blade loading along the chord near blade tip. The results of these investigations may offer guidance for the appropriate design of aspiration scheme in the future updated compressors and the overall total pressure loss coefficient caused by aspiration slot should be considered in the design process.
6
Khalid, S. A. "Factors Affecting Measured Axial Compressor Tip Clearance Vortex Circulation". Journal of Turbomachinery 117, n. 3 (1 luglio 1995): 487–90. http://dx.doi.org/10.1115/1.2835685.
Testo completoAbstract (sommario):
The relationship between turbomachinery blade circulation and tip clearance vortex circulation measured experimentally is examined using three-dimensional viscous flow computations. It is shown that the clearance vortex circulation one would measure is dependent on the placement of the fluid contour around which the circulation measurement is taken. Radial transport of vorticity results in the magnitude of the measured clearance vortex circulation generally being less than the blade circulation. For compressors, radial transport of vorticity shed from the blade tip in proximity to the endwall is the principal contributor to the discrepancy between the measured vortex circulation and blade circulation. Further, diffusion of vorticity shed at the blade tip toward the endwall makes it impossible in most practical cases to construct a fluid contour around the vortex that encloses all, and only, the vorticity shed from the blade tip. One should thus not expect agreement between measured tip clearance vortex circulation and circulation around the blade.
7
Mailach, R., I. Lehmann e K. Vogeler. "Rotating Instabilities in an Axial Compressor Originating From the Fluctuating Blade Tip Vortex". Journal of Turbomachinery 123, n. 3 (1 febbraio 2000): 453–60. http://dx.doi.org/10.1115/1.1370160.
Testo completoAbstract (sommario):
Rotating instabilities (RIs) have been observed in axial flow fans and centrifugal compressors as well as in low-speed and high-speed axial compressors. They are responsible for the excitation of high amplitude rotor blade vibrations and noise generation. This flow phenomenon moves relative to the rotor blades and causes periodic vortex separations at the blade tips and an axial reversed flow through the tip clearance of the rotor blades. The paper describes experimental investigations of RIs in the Dresden Low-Speed Research Compressor (LSRC). The objective is to show that the fluctuation of the blade tip vortex is responsible for the origination of this flow phenomenon. RIs have been found at operating points near the stability limit of the compressor with relatively large tip clearance of the rotor blades. The application of time-resolving sensors in both fixed and rotating frame of reference enables a detailed description of the circumferential structure and the spatial development of this unsteady flow phenomenon, which is limited to the blade tip region. Laser-Doppler-anemometry (LDA) within the rotor blade passages and within the tip clearance as well as unsteady pressure measurements on the rotor blades show the structure of the blade tip vortex. It will be shown that the periodical interaction of the blade tip vortex of one blade with the flow at the adjacent blade is responsible for the generation of a rotating structure with high mode orders, termed a rotating instability.
8
Hah, C., e J. Loellbach. "Development of Hub Corner Stall and Its Influence on the Performance of Axial Compressor Blade Rows". Journal of Turbomachinery 121, n. 1 (1 gennaio 1999): 67–77. http://dx.doi.org/10.1115/1.2841235.
Testo completoAbstract (sommario):
A detailed investigation has been performed to study hub corner stall phenomena in compressor blade rows. Three-dimensional flows in a subsonic annular compressor stator and in a transonic compressor rotor have been analyzed numerically by solving the Reynolds-averaged Navier–Stokes equations. The numerical results and the existing experimental data are interrogated to understand the mechanism of compressor hub corner stall. Both the measurements and the numerical solutions for the stator indicate that a strong twisterlike vortex is formed near the rear part of the blade suction surface. Low-momentum fluid inside the hub boundary layer is transported toward the suction side of the blade by this vortex. On the blade suction surface near the hub, this vortex forces fluid to move against the main flow direction and a limiting stream surface is formed near the hub. The formation of this vortex is the main mechanism of hub corner stall. When the aerodynamic loading is increased, the vortex initiates further upstream, which results in a larger corner stall region. For the transonic compressor rotor studied in this paper, the numerical solution indicates that a mild hub corner stall exists at 100 percent rotor speed. The hub corner stall, however, disappears at the reduced blade loading, which occurs at 60 percent rotor design speed. The present study demonstrates that hub corner stall is caused by a three-dimensional vortex system and that it does not seem to be correlated with a simple diffusion factor for the blade row.
9
Zhang, Mingming, e Anping Hou. "Numerical Investigation on Unsteady Separation Flow Control in an Axial Compressor Using Detached-Eddy Simulation". Applied Sciences 9, n. 16 (12 agosto 2019): 3298. http://dx.doi.org/10.3390/app9163298.
Testo completoAbstract (sommario):
Unsteady excitation has proved its effectiveness in separation flow control and has been extensively studied. It is observed that disordered shedding vortices in compressors can be controlled by unsteady excitation, especially when the excitation frequency coincides with the frequency of the shedding vortex. Furthermore, former experimental results indicated that unsteady excitation at other frequencies also had an impact on the structure of shedding vortices. To investigate the impact of excitation frequency on vortex shedding structure, the Detached-Eddy Simulation (DES) method was applied in the simulation of shedding vortex structure under unsteady excitations at different frequencies in an axial compressor. Effectiveness of the DES method was proved by comparison with URANS results. The simulation results showed a good agreement with the former experiment. The numerical results indicated that the separation flow can be partly controlled when the excitation frequency coincided with the unsteady flow inherent frequency. It showed an increase in stage performance under the less-studied separation flow control by excitation at a certain frequency of pressure side shedding vortex. Compared with other frequencies of shedding vortices, the frequency of pressure side shedding vortex was less sensitive to mass-flow variation. Therefore, it has potential for easier application on flow control in industrial compressors.
10
Rattanongphisat, Waraporn. "Efficiency of Vortex Tube Enclosure Cooling". Applied Mechanics and Materials 666 (ottobre 2014): 154–58. http://dx.doi.org/10.4028/www.scientific.net/amm.666.154.
Testo completoAbstract (sommario):
A vortex tube offers an alternative cooling with advantages of simplicity and compact. Using a natural refrigerant, a vortex tube enclosure cooling is environmentally benign. In this paper, the performance of a vortex tube enclosure cooling, VTEC, is investigated experimentally. The VTEC system comprises of the vortex tube cooling, an enclosure with a volume space of 0.045 m3, an air compressor, a compressed air storage tank and a compressed air line. The VTEC system is tested for its efficiency and cooling potential in the laboratory. An operating condition is controlled by a pressure regulator for an inlet air pressure of 3 bars, for energy saving, and a cold flow rate is adjusted by a needle valve near the hot exit of a vortex tube for the cold fraction between 0 and 1. Accordingly, the analysis of experimental data shows the maximum isentropic efficiency of the vortex tube enclosure cooling is 0.37 at the cold mass fraction of 0.45. Air temperature in the enclosure is about 13°C in average.
11
Estevadeordal, J., S. Gogineni, L. Goss, W. Copenhaver e S. Gorrell. "4. Vortex-shedding in a transonic compressor". Journal of Visualization 3, n. 4 (dicembre 2001): 310. http://dx.doi.org/10.1007/bf03181722.
Testo completo
12
Inoue, M., e M. Kuroumaru. "Structure of Tip Clearance Flow in an Isolated Axial Compressor Rotor". Journal of Turbomachinery 111, n. 3 (1 luglio 1989): 250–56. http://dx.doi.org/10.1115/1.3262263.
Testo completoAbstract (sommario):
Ensemble-averaged and phase-locked flow patterns in various tip clearances of two axial compressor rotors were obtained by aperiodic multisampling technique with a hot wire in the clearance and with a high-response pressure sensor on the casing wall. A leakage flow region distinct from a throughflow region exists at every clearance. In the case of a small tip clearance, the leakage jet flow interacts violently with the throughflow near the leading edge, and a rolling-up leakage vortex decays downstream. As the clearance increases, a stronger leakage vortex comes into existence at a more downstream location, and a reverse flow due to the vortex grows noticeably. A scraping vortex is recognized at the pressure side near the trailing edge only for the small clearance. A horseshoe vortex appears in the upstream half of the through flow region for every tip clearance. The solidity does not affect the flow pattern substantially except for the interaction of the leakage vortex with the adjacent blade and wake.
13
Hou, Jieuxuan, Yangwei Liu, Luyang Zhong, Weibo Zhong e Yumeng Tang. "Effect of vorticity transport on flow structure in the tip region of axial compressors". Physics of Fluids 34, n. 5 (maggio 2022): 055102. http://dx.doi.org/10.1063/5.0087833.
Testo completoAbstract (sommario):
Numerical simulations are carried out to investigate the flow structure in the blade tip region of axial compressors. Various tip clearance heights and end wall motion conditions in a linear compressor cascade are studied to assess the effect of vorticity transport on the tip leakage flow (TLF). Moreover, the effect of vorticity transport on the TLF in a compressor rotor at different operating conditions is studied using delayed detached eddy simulation. The results show that the vorticity transport at both the blade tip and the end wall plays an important role in the roll-up and evolution of the tip leakage vortex (TLV), resulting in great impacts on the loss and stability of the TLV. It is found that the TLV is composed of a two-layer structure. The inner vortex core region formed by the vorticity transport from the blade tip shear layer to the TLV has a great effect on the strength and loss of the vortex, and the structure of the outer shear layer is altered by the secondary vortex formed by the vorticity transport from the end wall shear layer and thus affects the stability of the TLV. By the mechanism of the vorticity transport, the effects of the clearance height, the end wall motion, and the non-uniform clearance as a control method can be explained uniformly. The new understanding of the TLF structure and the vorticity transport mechanism helps to improve the performance of axial compressors by controlling the vorticity transport of the TLF.
14
Kang, Qiang, Shuguang Zuo e Kaijun Wei. "Study on the aerodynamic noise of internal flow of regenerative flow compressors for a fuel-cell car". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 228, n. 7 (30 agosto 2013): 1155–74. http://dx.doi.org/10.1177/0954406213500746.
Testo completoAbstract (sommario):
The regenerative flow compressor used in fuel-cell cars generates high aerodynamic noise, which is the main source of noise. Compared with the research on centrifugal or axial turbomachinery, research on the noise of regenerative flow compressors is far from adequate. This paper presents the on-going work on it at Tongji University based on both experimental and computational works. In this study, a three-dimensional unsteady computational fluid dynamic model of the compressor was constructed with the large eddy approach. The pressure fluctuation, vortex noise source and Ffowcs William-Hawkings (FW-H) method were used to analyze the characteristics of the aerodynamic noise sources. Additionally, the far-field aerodynamic noise generated by the internal flow of the compressor was predicted using the aeroacoustic finite element method. The simulation results were validated with the experimental data. It was found that combining the fluid dynamic model and aeroacoustic finite element analysis promising results for aerodynamic noise prediction of compressors could be produced. The effects of the impeller parameters on the aerodynamic noise of the compressor were also studied.
15
Inoue, M., M. Kuroumaru e M. Fukuhara. "Behavior of Tip Leakage Flow Behind an Axial Compressor Rotor". Journal of Engineering for Gas Turbines and Power 108, n. 1 (1 gennaio 1986): 7–14. http://dx.doi.org/10.1115/1.3239889.
Testo completoAbstract (sommario):
Performance testing and detailed flow measurements were made in an axial compressor rotor with various tip clearances. The experiments were conducted on the condition of the same incidence angle at midspan. Thus, the effect of tip clearance distinguished from that of incidence angle was investigated on the overall performance, work-done factor, blockage factor, and increases in displacement, momentum, and blade-force-deficit thicknesses of the casing wall boundary layer, The phase-locked flow patterns obtained by the multisampling technique show clear evidence of a leakage vortex core behind the rotor. Behavior of the leakage vortex was clarified for various tip clearances by examining loci of the vortex center, decay characteristics of the vorticity at the center, and the total amount of vorticity shed from the blade tip. These results were compared with the leakage vortex model presented by Lakshminarayana.
16
Stauter, R. C. "Measurement of the Three-Dimensional Tip Region Flow Field in an Axial Compressor". Journal of Turbomachinery 115, n. 3 (1 luglio 1993): 468–76. http://dx.doi.org/10.1115/1.2929275.
Testo completoAbstract (sommario):
A two-color, five-beam LDV system has been configured to make simultaneous three-component velocity measurements of the flow field in a two-stage axial compressor model. The system has been used to make time-resolved measurements both between compressor blade rows and within the rotating blade passages in an axial compressor. The data show the nature and behavior of the complex, three-dimensional flow phenomena present in the tip region of a compressor as they convect downstream. In particular, the nature of the tip leakage vortex is apparent, being manifested by high blockage as well as the expected vortical motion. The data indicate that the radial flows associated with the tip leakage vortex begin to decrease while within the rotor passage, and that they temporarily increase aft of the passage.
17
Wu, Yanhui, Guangyao An, Zhiyang Chen e Bo Wang. "Computational analysis of vortices near casing in a transonic axial compressor rotor". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, n. 2 (5 dicembre 2017): 710–24. http://dx.doi.org/10.1177/0954410017740922.
Testo completoAbstract (sommario):
Complicated flowfields near casing in a transonic axial flow compressor rotor have been numerically investigated in this paper. Two vortex identification methods, namely the Eigenvector Method and Lambda 2 Method, are introduced as important tools for the graphical representation of the concentrated vortices arising from tip leakage flow and blade boundary layer separation. The analysis of the numerical results reveals that multiple tip vortices whose development are dependent on the variation of shock wave configuration are observed at conditions around the peak efficiency point. However, with the decrease of the massflow rate, only the well-known tip leakage vortex and the second tip vortex are left in the tip region due to the disappearance of the second shock wave. Then when the massflow rate further decreases to the stall limit, an deceleration flow region emerges downstream of the shock wave due to an increasing interaction between the first shock wave and the well-known tip leakage vortex. The tip leakage vortex further experiences a bubble-type and then spiral-type breakdown at near stall flow conditions. In addition, the validity of the two vortex identification methods is also discussed in this paper. It is found that both methods are able to identify and accentuate the concentrated streamwise vortices near casing when a vortex is not disrupted. However, if the vortex breakdown occurs, only Eigenvector Method can describe the breakdown region in a deep view.
18
Beheshti, Behnam H., Joao A. Teixeira, Paul C. Ivey, Kaveh Ghorbanian e Bijan Farhanieh. "Parametric Study of Tip Clearance—Casing Treatment on Performance and Stability of a Transonic Axial Compressor". Journal of Turbomachinery 126, n. 4 (1 ottobre 2004): 527–35. http://dx.doi.org/10.1115/1.1791643.
Testo completoAbstract (sommario):
The control of tip leakage flow through the clearance gap between the moving and stationary components of rotating machines is still a high-leverage area for improvement of stability and performance of aircraft engines. Losses in the form of flow separation, stall, and reduced rotor work efficiency are results of the tip leakage vortex (TLV) generated by interaction of the main flow and the tip leakage jet induced by the blade pressure difference. The effects are more detrimental in transonic compressors due to the interaction of shock TLV. It has been previously shown that the use of slots and grooves in the casing over tip of the compressor blades, known as casing treatment, can substantially increase the stable flow range and therefore the safety of the system but generally with some efficiency penalties. This paper presents a numerical parametric study of tip clearance coupled with casing treatment for a transonic axial-flow compressor NASA Rotor 37. Compressor characteristics have been compared to the experimental results for smooth casing with a 0.356 mm tip clearance and show fairly good agreement. Casing treatments were found to be an effective means of reducing the negative effects of tip gap flow and vortex, resulting in improved performance and stability. The present work provides guidelines for improvement of steady-state performance of the transonic axial-flow compressors and improvement of the stable operating range of the system.
19
Qin, Yong, Yanping Song, Ruoyu Wang e Huaping Liu. "Numerical Investigation of Three-dimensional Separation Control on a High-speed Compressor Stator Vane with Tailored Synthetic Jet". International Journal of Turbo & Jet-Engines 37, n. 4 (18 novembre 2020): 383–97. http://dx.doi.org/10.1515/tjj-2017-0036.
Testo completoAbstract (sommario):
AbstractA numerical study on the performance of synthetic jet for flow separation control on a high-speed compressor stator vane is performed. Four control schemes including full-span and part-span configurations are investigated at both design and off-design conditions. Results indicate that both full-span and part-span schemes could effectively delay flow separation and reduce total pressure loss for the compressor stator vane, the adaptability of the flow control under off-design conditions is also validated. Within the investigated incidence range, the full-span configuration is able to gain the most significant performance improvement, by which a maximum loss reduction of 23.8 % is obtained at i=2 deg. The part-span configuration could reorganize the vortex structures more efficiently and cut off the interaction between the ring-like vortex and the passage vortex, thus improving its performance in the corner region. In terms of flow control efficiency, the part-span configurations turn out to be more superior, where the highest control efficiency of 614.0 % is achieved at i=0 deg with the total height of the actuator being 40 %H. The flow control efficiency for all the schemes is higher than 100 % within the whole operating range, demonstrating a promising prospect for the application of synthetic jet in axial compressors.
20
Вараксин, A. Varaksin, Протасов e M. Protasov. "Analysis of Particle Motion in Wall-Free Concentrated Vortexes in Relation to Flight Safety Problem". Safety in Technosphere 3, n. 6 (23 dicembre 2014): 31–36. http://dx.doi.org/10.12737/6633.
Testo completoAbstract (sommario):
The ingestion in aircraft engines is one of the actual problems related to the flight safety. One of possible reasons of ingestion
in the gas-air flow duct of compressor is a formation of vortex core under an air intake on a runway surface during engine
working on a stop. Calculations of the solid particles’ motion in wall-free concentrated vortexes, being the analogues of vortex
core have been made in this paper. The numerical results have allowed to find peculiarities of behavior for particles with
different inertia (different density and sizes) in vortexes of various intensity. Based on calculations and available experimental
data a dimensionless criterion had been supposed, which determines the particles’ behavior in concentrated vortex structures.
Estimations for maximal time of dynamic relaxation for particles involved in the air intake by vortex cores of different
intensities have been made with use of this criterion. The knowledge of particles’ dynamics in the vortex cores formed near
the air intake of aircraft engines is necessary to develop the methods to protect them from possible ingestion from the
runway to ensure the flight safety.
21
Epstein, A. H., J. B. Gertz, P. R. Owen e M. B. Giles. "Vortex shedding in high-speed compressor blade wakes". Journal of Propulsion and Power 4, n. 3 (maggio 1988): 236–44. http://dx.doi.org/10.2514/3.23054.
Testo completo
22
Chen, Cong, Huaping Liu e Fu Chen. "Effect of the end-wall vortex generator jets on the performance of a high subsonic compressor cascade". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 233, n. 3 (1 agosto 2018): 324–36. http://dx.doi.org/10.1177/0957650918789507.
Testo completoAbstract (sommario):
This paper presents a numerical and experimental result of the end-wall vortex generator jets for controlling corner separation and enhancing the aerodynamic performance in a high subsonic (Ma = 0.7) compressor cascade. The experiments were carried out on a compressor cascade at design point ( i = 0°) and off-design points ( i = −2°, 2°, and 4°). At design point, the total pressure loss coefficient could be reduced up to 12.1%.With the increase in the incidence, the control effect is enhanced first and then reduced. The maximum total pressure loss reduction is up to 14.6% when the incidence is 2°. The numerical study is further conducted to analyze the flow pattern and the vortex structure. The jet vortex is formed downstream of the jet hole using the vortex generator jets, the cross flow on the end wall is also suppressed.
23
Furukawa, M., M. Inoue, K. Saiki e K. Yamada. "The Role of Tip Leakage Vortex Breakdown in Compressor Rotor Aerodynamics". Journal of Turbomachinery 121, n. 3 (1 luglio 1999): 469–80. http://dx.doi.org/10.1115/1.2841339.
Testo completoAbstract (sommario):
The breakdown of tip leakage vortex has been investigated on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics are elucidated by Navier–Stokes flow simulations and visualization techniques for identifying the breakdown. The simulations show that the leakage vortex breakdown occurs inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown is characterized by the existence of the stagnation point followed by a bubblelike recirculation region. The onset of breakdown causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex. The expansion has an extremely large blockage effect extending upstream of the leading edge. The disappearance of the concentrated vorticity results in no rolling-up of the vortex downstream of the rotor and the disappearance of the pressure trough on the casing. The leakage flow field downstream of the rotor is dominated by the outward radial flow, resulting from the contraction of the bubblelike structure of the breakdown region. It is found that the leakage vortex breakdown plays a major role in characteristic of rotor performance at near-stall conditions. As the flow rate is decreased from the peak pressure rise operating condition, the breakdown region grows rapidly in the streamwise, spanwise, and pitchwise directions. The growth of the breakdown causes the blockage and the loss to increase drastically. Then, the interaction of the breakdown region with the blade suction surface gives rise to the three-dimensional separation of the suction surface boundary layer, thus leading to a sudden drop in the total pressure rise across the rotor.
24
Ma¨rz, Joachim, Chunill Hah e Wolfgang Neise. "An Experimental and Numerical Investigation into the Mechanisms of Rotating Instability". Journal of Turbomachinery 124, n. 3 (1 luglio 2002): 367–74. http://dx.doi.org/10.1115/1.1460915.
Testo completoAbstract (sommario):
This paper reports on an experimental and numerical investigation aimed at understanding the mechanisms of rotating instabilities in a low speed axial flow compressor. The phenomena of rotating instabilities in the current compressor were first identified with an experimental study. Then, an unsteady numerical method was applied to confirm the phenomena and to interrogate the physical mechanisms behind them. The experimental study was conducted with high-resolution pressure measurements at different clearances, employing a double phase-averaging technique. The numerical investigation was performed with an unsteady 3-D Navier-Stokes method that solves for the entire blade row. The current study reveals that a vortex structure forms near the leading edge plane. This vortex is the result of interactions among the classical tip-clearance flow, axially reversed endwall flow, and the incoming flow. The vortex travels from the suction side to the pressure side of the passage at roughly half of the rotor speed. The formation and movement of this vortex seem to be the main causes of unsteadiness when rotating instability develops. Due to the nature of this vortex, the classical tip clearance flow does not spill over into the following blade passage. This behavior of the tip clearance flow is why the compressor operates in a stable mode even with the rotating instability, unlike traditional rotating stall phenomena.
25
Furukawa, M., K. Saiki, K. Nagayoshi, M. Kuroumaru e M. Inoue. "Effects of Stream Surface Inclination on Tip Leakage Flow Fields in Compressor Rotors". Journal of Turbomachinery 120, n. 4 (1 ottobre 1998): 683–92. http://dx.doi.org/10.1115/1.2841777.
Testo completoAbstract (sommario):
Experimental and computational results of tip leakage flow fields in a diagonal flow rotor at the design flow rate are compared with those in an axial flow rotor. In the diagonal flow rotor, the casing and hub walls are inclined at 25 deg and 45 deg, respectively, to the axis of rotation, and the blade has airfoil sections with almost the same tip solidity as that of the axial flow rotor. It is found out that “breakdown” of the tip leakage vortex occurs at the aft part of the passage in the diagonal flow rotor. The “vortex breakdown” causes significant changes in the nature of the tip leakage vortex: disappearance of the vortex core, large expansion of the vortex, and appearance of low relative velocity region in the vortex. These changes result in a behavior of the tip leakage flow that is substantially different from that in the axial flow rotor: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing pressure trough at the aft part of the rotor passage, large spread of the low-energy fluid due to the leakage flow, much larger growth of the casing wall boundary layer, and considerable increase in the absolute tangential velocity in the casing wall boundary layer. The vortex breakdown influences the overall performance, also: large reduction of efficiency with the tip clearance, and low level of noise.
26
Chen, G. T., E. M. Greitzer, C. S. Tan e F. E. Marble. "Similarity Analysis of Compressor Tip Clearance Flow Structure". Journal of Turbomachinery 113, n. 2 (1 aprile 1991): 260–69. http://dx.doi.org/10.1115/1.2929098.
Testo completoAbstract (sommario):
A new approach is presented for analyzing compressor tip clearance flow. The basic idea is that the clearance velocity field can be (approximately) decomposed into independent throughflow and crossflow, since chordwise pressure gradients are much smaller than normal pressure gradients in the clearance region. As in the slender body approximation in external aerodynamics, this description implies that the three-dimensional, steady, clearance flow can be viewed as a two-dimensional, unsteady flow. Using this approach, a similarity scaling for the crossflow in the clearance region is developed and a generalized description of the clearance vortex is derived. Calculations based on the similarity scaling agree well with a wide range of experimental data in regard to flow features such as crossflow velocity field, static pressure field, and tip clearance vortex trajectory. The scaling rules also provide a useful way of exploring the parametric dependence of the vortex trajectory and strength for a given blade row. The emphasis of the approach is on the vortical structure associated with the tip clearance because this appears to be a dominant feature of the endwall flow; it is also shown that this emphasis gives considerable physical insight into overall features seen in the data.
27
Hoying, D. A., C. S. Tan, Huu Duc Vo e E. M. Greitzer. "Role of Blade Passage Flow Structurs in Axial Compressor Rotating Stall Inception". Journal of Turbomachinery 121, n. 4 (1 ottobre 1999): 735–42. http://dx.doi.org/10.1115/1.2836727.
Testo completoAbstract (sommario):
The influence of three-dimensional flow structures within a compressor blade passage has been examined computationally to determine their role in rotating stall inception. The computations displayed a short length-scale (or spike) type of stall inception similar to that seen in experiments; to the authors’ knowledge this is the first time such a feature has been simulated. A central feature observed during the rotating stall inception was the tip clearance vortex moving forward of the blade row leading edge. Vortex kinematic arguments are used to provide a physical explanation of this motion as well as to motivate the conditions for its occurrence. The resulting criterion for this type of stall inception (the movement of the tip clearance vortex forward of the leading edge) depends upon local flow phenomena related to the tip clearance with the implication that for this and possibly other stall mechanisms the flow structure within the blade passages must be addressed to explain the stability of an axial compression system that exhibits such short length-scale disturbances.
28
Brandstetter, Christoph, e Heinz-Peter Schiffer. "PIV measurements of the transient flow structure in the tip region of a transonic compressor near stability limit". Journal of the Global Power and Propulsion Society 2 (18 gennaio 2018): JYVUQD. http://dx.doi.org/10.22261/jgpps.jyvuqd.
Testo completoAbstract (sommario):
Abstract The flow structures in an axial compressor that lead to short-length scale stall inception are investigated using optical measurements in a high-speed one and a half stage compressor. During transient throttling procedures, velocity was measured in a tangential plane at 92% channel height, intersecting the tip leakage vortex. The results show large scale disturbances of the secondary flow structure, which results from unsteady breakdown of the tip leakage vortex. It was possible to resolve spill forward several revolutions before the occurrence of rotating stall. This effect leads to local flow separations on the blade suction side and the development of radial vortex structures. The vortices are transported to the adjacent blade and cause further separations. Both effects are described in literature but were measured directly for the first time in a transonic compressor in this investigation. They are visualized for several time steps during transient throttling maneuvers and compared to blade vibration amplitudes. During the final phase before rotating stall occurs, asynchronous blade vibrations correlate with axial velocity in the region around the blade leading edge.
29
Li, Jun, Jun Hu e Chenkai Zhang. "Experimental investigation of the tip leakage flow in a low-speed multistage axial compressor". Science Progress 103, n. 3 (luglio 2020): 003685042095107. http://dx.doi.org/10.1177/0036850420951070.
Testo completoAbstract (sommario):
Casing pressure measurements and Stereoscopic Particle-Image Velocimetry (SPIV) measurements are used together to characterize the behavior of the rotor tip leakage flow at both the design and near-stall conditions in a low-speed multistage axial compressor. A three-dimensional Navier-Stokes solver is also performed for the multistage compressor and the prediction of tip leakage flow is compared with SPIV data and casing dynamic static pressure data. During the experiment 10 high-frequency Kulite transducers are mounted in the outer casing of the rotor 3 to investigate the complex flow near the compressor casing and Fourier analyses of the dynamic static pressure on the casing of the rotor 3 are carried out to investigate the tip leakage flow characteristics. At the same time, the two CCD cameras are arranged at the same side of the laser light sheet, which is suitable for investigating unsteady tip leakage flow in the multistage axial compressor. The SPIV measurements identify that the tip leakage flow exists in the rotor passage. The influence of tip leakage flow leads to the existence of low axial velocity region in the rotor passage and the alternating regions of positive and negative radial velocity indicates the emergence of tip leakage vortex (TLV). The trajectory of the tip leakage vortex moves from the suction surface toward the pressure surface of adjacent blade, which is aligned close to the rotor at the design point (DP). However, the tip leakage vortex becomes unstable and breaks down at the near-stall point (NS), making the vortex trajectory move upstream in the rotor passage and causing a large blockage in the middle of the passage.
30
Chen, Y. N., U. Haupt e M. Rautenberg. "The Vortex-Filament Nature of Reverse Flow on the Verge of Rotating Stall". Journal of Turbomachinery 111, n. 4 (1 ottobre 1989): 450–61. http://dx.doi.org/10.1115/1.3262293.
Testo completoAbstract (sommario):
On the verge of rotating stall, very orderly reverse flow forms from the outlet of the rotor/impeller along the casing/shroud toward the inlet in axial/centrifugal compressors (Koch, 1970; Haupt, et al., 1987). The experiment on a centrifugal compressor reveals furthermore that the reverse flow is composed of stable spiral vortex filaments. Their vorticity can be transferred to the inlet tip vortex, known as prerotation. The behavior of these vortex filaments is examined based on the fundamental research work on rotating bodies available in the literature. This result shows that the vortex filaments are composed of Taylor’s vortex pairs, but with unequal vortex strengths within the pair. They form the transition range from a laminar to a turbulent three-dimensional boundary layer with a very steep tangential velocity profile. This profile is associated with the appearance of a toroidal ring vortex in the rotor/impeller, acting as a recirculatig secondary flow. It can be further shown from the analysis of the extensive literature that the orderly path of the reverse flow is enabled by the cessation of the leakage flow of the rotor tip clearance. The reason for this is that the growing tangential flow field extends beyond the rotor tip up to the close proximity of the endwall, so that the tip clearance is blocked.
31
Ortmanns, J., C. Pixberg e V. Gümmer. "Numerical investigation of vortex generators to reduce cross-passage flow phenomena in compressor stator end-walls". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 225, n. 7 (9 settembre 2011): 877–85. http://dx.doi.org/10.1177/0957650911414323.
Testo completoAbstract (sommario):
The numerical results presented in this article demonstrate the ability of single-vortex generators to reduce the cross-passage secondary flow in a high-turning stator vane passage. The sensitivities of the induced vortex flow are determined in an initial study by varying the geometrical parameters. The visualization of the flow patterns and the determination of the stator vane performance show that the efficiency and the working range can be increased by applying single-vortex generators. The vortex generator design has to achieve a balance between the magnitude of vorticity induced to reduce the secondary flow phenomena and the additional losses associated with the produced vortex flow.
32
Zhao, Peng-Fei, Yan Liu e Xiao-Fang Wang. "Analysis of vortices and performance of different diffusers in a large mass flow coefficient centrifugal compressor". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 231, n. 4 (27 marzo 2017): 253–73. http://dx.doi.org/10.1177/0957650917701339.
Testo completoAbstract (sommario):
An appropriate diffuser following an impeller is critical to realize a high efficiency and a wide operating range for a centrifugal compressor stage. The purpose of this study is to investigate the effect of different types of vaned diffusers on a large mass flow coefficient centrifugal compressor stage performance under different operating conditions and to reveal the loss mechanisms in the vaned diffusers. Five vaned diffusers are studied. Flow fields and vortices in a conventional diffuser and a rib diffuser are first examined. Then, vortices and flow fields in three different tandem diffusers are analyzed in detail. For the three tandem diffusers, only circumferential position of first row vanes relative to the second row vanes is different. Results show that the stage with the conventional diffuser possesses the shortest operating range. The rib diffuser has less loss due to the weaker tip leakage vortex, while its static pressure recovery coefficient is lower, and the loss in the following return part is higher. Comparison results between the three tandem diffusers imply that when the trailing edge of the first row vane is close to the pressure surface of the second row vane, the stage with the tandem diffuser has a better performance. This is ascribed to the interaction of the tip leakage vortex and suction surface vortex, which decreases the total loss, especially reduces the loss induced by the suction surface vortex. When the trailing edge of the first row vanes is close to the suction surface of the second row vane, the loss is increased since the leading edge vortex has a large strength and surrounds the suction surface vortex. Therefore, the reasonable interaction of vortices in a tandem diffuser can bring a high performance of the centrifugal compressor.
33
SAWAGUCHI, Yutaka, Hiromoto KURODA e Shigeo OBATA. "Compressor Performance due to Leakage Vortex in Circular Cascade". Proceedings of Yamanashi District Conference 2002 (2002): 189–90. http://dx.doi.org/10.1299/jsmeyamanashi.2002.189.
Testo completo
34
Zhao, Wenfeng, Qun Zheng, Bin Jiang e Aqiang Lin. "A Passive Control Method of Hub Corner Stall in a 1.5-Stage Axial Compressor under Low-Speed Conditions". Energies 13, n. 11 (27 maggio 2020): 2691. http://dx.doi.org/10.3390/en13112691.
Testo completoAbstract (sommario):
Since the use of the compressor of a ship gas turbine is unavoidable at a low-speed operation, the flow field characteristics and stall mechanism at off-design speeds are important aspects for compressor designers. In this study, the first 1.5 stages of an eight-stage compressor are numerically simulated. The mechanism of compressor rotor instability at lower speeds is identified. The characteristic lines of compressors with various partial clearance are calculated at low speed (0.6 N). The flow field of the same outlet pressure (near stall point of the original compressor without clearance) is compared and analyzed. The results show that, at the near stall point, the suction surface separation and backflow occur in the main flow of the rotor top. It develops along the blade span and finally blocks the flow passage of the rotor, which results in the compressor stall. At the same time, the stall also occurs at the corner of the stator hub. In this paper, the characteristics of partial clearance in four different positions of the stator hub are analyzed. The near stall point and the working point are selected for the flow field analysis. It is concluded that the radial development of the stall vortex on the suction surface of the stator can be restrained by the partial clearance at the stator. In this paper, a passive control method by partial clearance is used in the real compressors, which is different from previous studies on cascades. The margin increases at low speeds.
35
Zhao, Fengtong, Bo Cui, Fei Wu, Shan Jiang, Mingsui Yang e Yuying Chen. "Investigation on Characterization of Typical Characteristic in Compressor Based on Flat Plate Model". Applied Sciences 12, n. 10 (13 maggio 2022): 4956. http://dx.doi.org/10.3390/app12104956.
Testo completoAbstract (sommario):
The acoustic resonance of aero-engine compressors is very harmful, which can lead to the failure of components such as blades. The mechanism of acoustic resonance is very complicated. To solve this problem, characteristics of the noise signal under the abnormal vibration state of the rotor blade are analyzed through the noise measurement in the compressor in the paper. The frequency spectrum characteristics, sound pressure level, and phase relationship of the noise signal corresponding to the abnormal vibration of the rotor blade are captured, and the feature of “frequency locked” which is consistent with the acoustic resonance in the compressor is obtained. Numerical simulation is a better way to study the mechanism of acoustic resonance. Therefore, based on the Parker model, a research method of acoustic resonance characteristics and mechanism based on acoustic analogy is proposed from the solution of the sound-induced in the pipe cavity. The vortex system and sound field characteristics when the acoustic resonance occurs are calculated. The results show that the distribution characteristics of the shedding vortex can be recognized, which are consistent with the experimental results of Welsh when the acoustic resonance occurs. The error of the acoustic resonance frequency from numerical simulation results to experimental is 3.6%. The characteristic of “frequency locked” and Parker β mode of the acoustic resonance is captured. The acoustic analogy method is suitable for the characterization of the acoustic resonance performance and mechanism in the pipeline and in the aeroengine compressor.
36
Fu, Li, Ce Yang, Wenrui Bao, Hanzhi Zhang, Changmao Yang e Yanzhao Li. "Effect of circumferential static pressure nonuniformity caused by volute on tip leakage flow in a centrifugal compressor". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, n. 14 (26 marzo 2019): 5134–49. http://dx.doi.org/10.1177/0954410019836905.
Testo completoAbstract (sommario):
For a centrifugal compressor with volute, the flow field is circumferentially nonuniform because of the volute asymmetrical structure and leads to a circumferential difference in the tip leakage flow. In this work, the compressor performance and the casing wall static pressure distribution are measured, and the results are compared with the time-averaged results of the unsteady calculation to verify the reliability of the simulation. The results show a relationship between the tip leakage vortex trajectory and the high static pressure region in the diffuser, based on which a prediction model is established for the reverse propagation of pressure waves caused by a volute tongue. Influenced by the volute asymmetric structure, the trajectory, shape, and strength of the tip leakage vortex at different circumferential positions differs significantly. The tip leakage vortex trajectory affected by the high static pressure is more inclined to a circumferential direction because the tip leakage flow velocity flowing out of the suction surface is reduced, and the tip leakage flow with low velocity is subjected to the high-pressure gradient in a passage. Moreover, the tip leakage vortex breakdown in different passages differs significantly. A tip leakage vortex core more inclined towards the streamwise direction is more likely to break down than a tip leakage vortex core inclined towards the circumferential direction because of the larger reverse pressure gradient.
37
Puterbaugh, S. L., e W. W. Copenhaver. "Flow Field Unsteadiness in the Tip Region of a Transonic Compressor Rotor". Journal of Fluids Engineering 119, n. 1 (1 marzo 1997): 122–28. http://dx.doi.org/10.1115/1.2819097.
Testo completoAbstract (sommario):
An experimental investigation concerning tip flow field unsteadiness was performed for a high-performance, state-of-the-art transonic compressor rotor. Casing-mounted high frequency response pressure transducers were used to indicate both the ensemble averaged and time varying flow structure present in the tip region of the rotor at four different operating points at design speed. The ensemble averaged information revealed the shock structure as it evolved from a dual shock system at open throttle to an attached shock at peak efficiency to a detached orientation at near stall. Steady three-dimensional Navier Stokes analysis reveals the dominant flow structures in the tip region in support of the ensemble averaged measurements. A tip leakage vortex is evident at all operating points as regions of low static pressure and appears in the same location as the vortex found in the numerical solution. An unsteadiness parameter was calculated to quantify the unsteadiness in the tip cascade plane. In general, regions of peak unsteadiness appear near shocks and in the area interpreted as the shock-tip leakage vortex interaction. Local peaks of unsteadiness appear in mid-passage downstream of the shock-vortex interaction. Flow field features not evident in the ensemble averaged data are examined via a Navier-Stokes solution obtained at the near stall operating point.
38
Duan, Zhen Zhen, Yang Wei Liu e Li Peng Lu. "Effects of Tip Clearance Size on Flowfield in a Low-Speed Axial Compressor Rotor". Applied Mechanics and Materials 543-547 (marzo 2014): 158–63. http://dx.doi.org/10.4028/www.scientific.net/amm.543-547.158.
Testo completoAbstract (sommario):
The simulations of a low-speed axial compressor rotor with two tip clearance sizes, 0.5% chord and 1.5% chord, were performed in the study. Overall performance and detailed flow fields at near stall condition are analyzed. The results show that the rotor stall occurs at higher mass flow condition with large tip clearance. For the small tip clearance the tip leakage vortex and the corner vortex both contribute significantly to the rotor stall, and the interaction between the vortices promotes the stall generation. While for the large tip clearance the tip leakage vortex plays a primary role, and the vortices interaction is ignorable.
39
Jawad, Layth H., Shahrir Abdullah, Zulkifli R. e Wan Mohd Faizal Wan Mahmood. "Effect of Vaned Diffuser on a Modified Turbocharger Centrifugal Compressor Performance". Applied Mechanics and Materials 663 (ottobre 2014): 347–53. http://dx.doi.org/10.4028/www.scientific.net/amm.663.347.
Testo completoAbstract (sommario):
A numerical study that was made in a three-dimensional flow, carried out in a modified centrifugal compressor, having vaned diffuser stage, used as an automotive turbo charger. In order to study the influence of vaned diffuser meridional outlet section with a different width ratio of the modified centrifugal compressor. Moreover, the performance of the centrifugal compressor was dependent on the proper matching between the compressor impeller along the vaned diffuser. The aerodynamic characteristics were compared under different meridional width ratio. In addition, the velocity vectors in diffuser flow passages, and the secondary flow in cross-section near the outlet of diffuser were analysed in detail under different meridional width ratio. Another aim of this research was to study and simulate the effect of vaned diffuser on the performance of a centrifugal compressor. The simulation was undertaken using commercial software so-called ANSYS CFX, to predict numerically the performance charachteristics. The results were generated from CFD and were analysed for better understanding of the fluid flow through centrifugal compressor stage and as a result of the minimum width ratio the flow in diffuser passage tends to be uniformity. Moreover, the backflow and vortex near the pressure surface disappear, and the vortex and detachment near the suction surface decrease. Conclusively, it was observed that the efficiency was increased and both the total pressure ratio and static pressure for minimum width ratio are increased.
40
Mustaffa, Ahmad Fikri, e Vasudevan Kanjirakkad. "Stall margin improvement in a low-speed axial compressor rotor using a blockage-optimised single circumferential casing groove". Journal of the Global Power and Propulsion Society 5 (3 maggio 2021): 79–89. http://dx.doi.org/10.33737/jgpps/133912.
Testo completoAbstract (sommario):
The stall margin of tip-critical axial compressors can be improved by using circumferential casing grooves. From previous studies, in the literature, the stall margin improvement due to the casing grooves can be attributed to the reduction of the near casing blockage. The pressure rise across the compressor as the compressor is throttled intensifies the tip leakage flow. This results in a stronger tip leakage vortex that is thought to be the main source of the blockage. In this paper, the near casing blockage due to the tip region aerodynamics in a low-speed axial compressor rotor is numerically studied and quantified using a mass flow-based blockage parameter. The peak blockage location at the last stable operating point for a rotor with smooth casing is found to be at about 10% of the tip chord aft of the tip leading edge. Based on this information, an optimised single casing groove design that minimises the peak blockage is found using a surrogate-based optimisation approach. The implementation of the optimised groove is shown to produce a stall margin improvement of about 5%.
41
Yoon, Yong Sang, Seung Jin Song e Hyoun-Woo Shin. "Influence of Flow Coefficient, Stagger Angle, and Tip Clearance on Tip Vortex in Axial Compressors". Journal of Fluids Engineering 128, n. 6 (27 marzo 2006): 1274–80. http://dx.doi.org/10.1115/1.2354522.
Testo completoAbstract (sommario):
Experiments have been performed on the low speed research compressor (LSRC) at General Electric Aircraft Engines to investigate the effects of flow coefficient, stagger angle, and tip clearance on tip vortex. Time resolved casing pressure distributions over the third stage rotor have been acquired with high-frequency-response pressure transducers. Also, tip vortex strength and trajectory have been estimated from the casing pressure fluctuations which have been obtained simultaneously from various axial locations. As flow coefficient decreases, tip vortex gets strengthened and migrates upstream. The stagger angle increase weakens the tip vortex and moves it downstream slightly because the blade loading is decreased. However, tip leakage vortex is influenced mainly by tip clearance, and there exists a “critical” tip clearance which determines the type of tip vortex trajectory (“straight” or “kinked”). As predicted by others, tip vortex gets strengthened with increasing tip clearance. However, unlike the predictions, the tip vortex trajectory moves upstream with increasing tip clearance. Furthermore, with tip clearance above a “critical” value, the tip vortex trajectory is no longer straight but shows a kink in the passage.
42
Zhang, Botao, Xiaochen Mao, Xiaoxiong Wu e Bo Liu. "Effects of Tip Leakage Flow on the Aerodynamic Performance and Stability of an Axial-Flow Transonic Compressor Stage". Energies 14, n. 14 (10 luglio 2021): 4168. http://dx.doi.org/10.3390/en14144168.
Testo completoAbstract (sommario):
To explain the effect of tip leakage flow on the performance of an axial-flow transonic compressor, the compressors with different rotor tip clearances were studied numerically. The results show that as the rotor tip clearance increases, the leakage flow intensity is increased, the shock wave position is moved backward, and the interaction between the tip leakage vortex and shock wave is intensified, while that between the boundary layer and shock wave is weakened. Most of all, the stall mechanisms of the compressors with varying rotor tip clearances are different. The clearance leakage flow is the main cause of the rotating stall under large rotor tip clearance. However, the stall form for the compressor with half of the designed tip clearance is caused by the joint action of the rotor tip stall caused by the leakage flow spillage at the blade leading edge and the whole blade span stall caused by the separation of the boundary layer of the rotor and the stator passage. Within the investigated varied range, when the rotor tip clearance size is half of the design, the compressor performance is improved best, and the peak efficiency and stall margin are increased by 0.2% and 3.5%, respectively.
43
Shi, Lei, Hongwei Ma e Lixiang Wang. "Analysis of Different POD Processing Methods for SPIV-Measurements in Compressor Cascade Tip Leakage Flow". Energies 12, n. 6 (15 marzo 2019): 1021. http://dx.doi.org/10.3390/en12061021.
Testo completoAbstract (sommario):
Though the proper orthogonal decomposition (POD) method has been widely adopted in flow analysis, few publications have systematically studied the influence of different POD processing methods on the POD results. This paper investigates the effects of different decomposition regions and decomposition dimensionalities on POD decomposition and reconstruction concerning the tip flow in the compressor cascade. Stereoscopic particle image velocimetry (SPIV) measurements in the blade channel are addressed to obtain the original flow field. Through vortex core identification, development of the tip leakage vortex along the chord is described. Afterwards, each plane is energetically decomposed by POD. Using the identified vortex core center as the geometric center, the effects of different decomposition regions with respect to the vortex core are analyzed. Furthermore, the effects of different single velocity-components as well as their combination are compared. The effect of different decomposition regions on the mode 1 energy fraction mainly impacts the streamwise velocity component. Though the addition of W velocity component in the decomposition does change the spatial structures of high-order modes, it does not change the dynamic results of reconstruction using a finite number of POD modes. UV global analysis is better for capturing the kinetic physics of the tip leakage vortex (TLV) wandering.
44
Ibaraki, Seiichi, Tetsuya Matsuo, Hiroshi Kuma, Kunio Sumida e Toru Suita. "Aerodynamics of a Transonic Centrifugal Compressor Impeller". Journal of Turbomachinery 125, n. 2 (1 aprile 2003): 346–51. http://dx.doi.org/10.1115/1.1540117.
Testo completoAbstract (sommario):
High-pressure ratio centrifugal compressors are applied to turbochargers and turboshaft engines because of their small dimensions, high efficiency, and wide operating range. Such a high-pressure ratio centrifugal compressor has a transonic inlet condition accompanied with a shock wave in the inducer portion. It is generally said that extra losses are generated by interaction of the shock wave and the boundary layers on the blade surface. To improve the performance of high-pressure ratio centrifugal compressor, it is necessary to understand the flow phenomena. Although some research works on transonic impeller flow have been published, some unknown flow physics are still remaining. The authors designed a transonic impeller, with an inlet Mach number about 1.3, and conducted detailed flow measurements by using laser doppler velocimetry (LDV). In the result, the interaction between the shock wave and tip leakage vortex at the inducer and flow distortion at the downstream of inducer were observed. The interaction of the boundary layer and the shock wave was not observed. Also, computational flow analysis was conducted and compared with experimental results.
45
Dayyabu, Gambo Kofar Bai, Hai Zhang, Qun Zheng e Salman Abdu. "Flow Assessment on the Effects of Water Droplets on Rotor Region of Wet Compression". Defect and Diffusion Forum 374 (aprile 2017): 131–47. http://dx.doi.org/10.4028/www.scientific.net/ddf.374.131.
Testo completoAbstract (sommario):
Wet compression process has been widely accepted as a measure of increasing the performance of industrial gas turbine, in the present work, in-depth analysis on the principle aspects of wet compression, more specifically, the influence of injected water droplets diameter, surface temperature, and their effects on the behavior of axial flow transonic compressor and gas turbine performance were analyzed using computational fluid dynamic. Injected water droplets and gas flow phase change was most intense in the area adjacent to shockwaves and were the slip velocity of the droplet is highest. Water injection in to the compressor rotor is a little perturbation to the flow field due to the formation of flow separation, evaporation rate, increasing weber number, reduction in the inlet temperature, and velocity vortex pattern relatively different from that of the dry case. The effects of water droplets on the rotor region at injection rate of 1%, shows decrease in the inlet temperature of 11%, outlet temperature 5% and uplift the efficiency to 1.5%.
46
Kang, S., e C. Hirsch. "Tip Leakage Flow in Linear Compressor Cascade". Journal of Turbomachinery 116, n. 4 (1 ottobre 1994): 657–64. http://dx.doi.org/10.1115/1.2929458.
Testo completoAbstract (sommario):
Tip leakage flow in a linear compressor cascade of NACA 65-1810 profiles is investigated, for tip clearance levels of 1.0, 2.0, and 3.25 percent of chord at design and off-design flow conditions. Velocity and pressure data are collected from three transverse sections inside tip clearance and sixteen sections within flow passage. Tip separation vortex influence is identified from the data. Leakage flow mixing is clearly present inside the clearance and has a significant influence on the internal loss.
47
Ma, Shan, Wuli Chu, Haoguang Zhang, Xiangjun Li e Haiyang Kuang. "Effects of modified micro-vortex generators on aerodynamic performance in a high-load compressor cascade". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 233, n. 3 (29 luglio 2018): 309–23. http://dx.doi.org/10.1177/0957650918790018.
Testo completoAbstract (sommario):
In the current study, the effects of micro-vortex generators on the flow characteristics of a high-load compressor cascade are investigated, and four types of micro-vortex generators including “rectangular,” “curved rectangular,” “trapezoidal,” and “curved trapezoidal” are considered and named VGR, VGCR, VGT, and VGCT separately. The calculated results show that a rising reverse flow region, which is considered a main reason for occurring stall at +8° incidence, collapses rapidly from the leading edge in the cascade. Therefore, the micro-vortex generators are all mounted on the end-wall in front of the passage to suppress the development of the secondary flow, and the stall occurrence is delayed from +8° to +11° incidence by applying VGCT. At the design condition, the VGT can make the total pressure loss decrease by 0.54%. The modified micro-vortex generators show an obvious superiority when the range of incidence is between +3° and +8°. At the stall condition, the VGCT can make the total pressure loss decrease by 9.36%. Moreover, the reduction of the secondary flow loss is considered a main goal of the adoption of micro-vortex generators which is an achievement for decreasing the total pressure loss, and the highest reduction of the secondary flow loss reaches 34.6% at the stall condition in the cascade with VGCT.
48
Parafeinik, V. P., Yu A. Bondarenko e V. I. Reznikov. "Nonstationary phenomena in the flow section of a vortex compressor". Chemical and Petroleum Engineering 27, n. 3 (marzo 1991): 157–61. http://dx.doi.org/10.1007/bf01150088.
Testo completo
49
Sonoda, T., T. Arima e M. Oana. "The Influence of Downstream Passage on the Flow Within an Annular S-Shaped Duct". Journal of Turbomachinery 120, n. 4 (1 ottobre 1998): 714–22. http://dx.doi.org/10.1115/1.2841782.
Testo completoAbstract (sommario):
Experimental and numerical investigations were carried out to gain a better understanding of the flow characteristics within an annular S-shaped duct, including the influence of the shape of the downstream passage located at the exit of the duct on the flow. A duct with six struts and the same geometry as that used to connect the compressor spools on our new experimental small two-spool turbofan engine was investigated. Two types of downstream passage were used. One type had a straight annular passage and the other a curved annular passage with a meridional flow path geometry similar to that of the centrifugal compressor. Results showed that the total pressure loss near the hub is large due to instability of the flow, as compared with that near the casing. Also, a vortex related to the horseshoe vortex was observed near the casing. In the case of the curved annular passage, the total pressure loss near the hub was greatly increased compared with the case of the straight annular passage, and the spatial position of this vortex depends on the passage core pressure gradient. Furthermore, results of calculation using an in-house-developed three-dimensional Navier–Stokes code with a low-Reynolds-number k–ε turbulence model were in good qualitative agreement with experimental results. According to the simulation results, a region of very high pressure loss is observed near the hub at the duct exit with the increase of inlet boundary layer thickness. Such regions of high pressure loss may act on the downstream compressor as a large inlet distortion, and strongly affect downstream compressor performance.
50
Ye, Shubo, Qingjun Zhao, Xiaoyong Zhou, Guang Xi e Jianzhong Xu. "The impact of circumferential casing grooves on rotating instability in a transonic axial compressor". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, n. 8 (11 luglio 2018): 2868–93. http://dx.doi.org/10.1177/0954410018786094.
Testo completoAbstract (sommario):
The impact of circumferential casing grooves on rotating instability is first assessed for both design and part speed operations in a transonic axial compressor, with the purpose of developing the next generation casing treatments for vibration control. Multi-passage time-resolved computations are performed to capture the origination and propagation behavior of the instability for cases with and without casing grooves. Probed pressure signals in different passages show a nonsynchronous fluctuation of tip flow. It proves tip leakage vortex and its self-excited oscillation is responsible for this type of inconsistence, regardless of the compressor operation speed. Although flow separation on blade suction surface and the consequent shedding vortex contributes to another origin of instability, the resulted flow appears to be consistent. Casing grooves are able to enhance the synchronization by greatly suppressing both tip leakage vortex oscillations and the intermittently shedding separation vortex, especially in the front part of blade passage. Both types of instability are constrained in several separated axial scope by casing grooves, which essentially increase the damping of flow oscillations. Thus, further improvement of casing treatment design can be expected if the axial transport of the instability in the tip region is restrained more efficiently, for both extending stall margin and enhancing aerodynamic stability.