scholarly journals Influence of Shock Wave on Loss and Breakdown of Tip-Leakage Vortex in Turbine Rotor with Varying Backpressure

2021 ◽  
Vol 11 (11) ◽  
pp. 4991
Author(s):  
Zuojun Wei ◽  
Guangming Ren ◽  
Xiaohua Gan ◽  
Ming Ni ◽  
Weijie Chen
Keyword(s):  
Shock Wave ◽  
Vortex Breakdown ◽  
Axial Direction ◽  
Turbine Rotor ◽  
Effective Control ◽  
Tip Leakage Flow ◽  
Low Velocity ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Centrifugal Instability

In modern turbine rotors, tip-leakage flow is a common phenomenon that accounts for about 1/3 of the stage loss. Studies show that as the imposed load increases, a shock wave appears in the tip region, which causes a significant interference on the leakage vortex. In the present study, numerical simulations are carried out to investigate the influence of the shock wave on the loss and breakdown of the tip-leakage vortex. The obtained results indicate that with no effective control on the flow, the loss of the leakage vortex has an approximate exponential growth up to about 10 times as the outlet Mach number increases from 0.67 to 1.15 and the corresponding proportion in the total loss increases sharply to 30.2%. It is found that the stagnation position of the breakdown changes with the backpressure and the amplitude of variation along the axial direction is up to 0.13 Cx. It is inferred that the breakdown of the leakage vortex core may be affected by the periodical passing of downstream blade and the induced pressure fluctuation may result in additional vibration in this rotor blade. The leakage vortex is unstable in supersonic flow with a shock wave and it may transfer to a flow with a low-velocity bubble in its core region. It is concluded that the leakage vortex breakdown mainly originates from interferences of the shock wave, while the internal cause of such breakdown is the centrifugal instability of the vortex.

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.

Study of Shock/Blade Tip Leakage Vortex/Boundary Layer Interaction in a Transonic Rotor With IDDES Method

2013 ◽  
Author(s):  
Ke Shi ◽  
Song Fu
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Vortex Breakdown ◽  
Leading Edge ◽  
Wave Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Layer Interaction ◽  
Boundary Layer Interaction ◽  
Blade Tip

In the present study, Improved Delayed Detached Eddy Simulation (IDDES) based on k-ω-SST turbulence model is applied to study the unsteady phenomenon in a transonic compressor rotor. Particular emphasis is on the understanding of the complex underlying mechanisms for the flow unsteadiness caused by the interaction of passage shock, blade tip leakage vortex (BTLV) and the blade boundary layer. The sources of the significant unsteadiness of the flow are shown. At the lower span height, where the BTLV is far away, the shock wave ahead of the blade leading edge impinges on the suction surface boundary layer of the adjacent blade, causing the shock wave/boundary layer interaction (SWBLI). Boundary layer thickness grows, while flow separates after the interaction. Predicted by IDDES calculation, this shock-induced separation exists as a separation bubble. The flow reattaches very soon after separation. At the near tip region, the shock wave surface deforms due to the strong interaction between the shock and the BTLV. Oscillation of the shock wave surface near the vortex core infers an unsteady contend between the shock and the vortex. Iso-surfaces of the Q parameter are applied to identify the vortex and its structure. Normally, the vortex breakdown in the rotor passage will lead to stall. However, in the present transonic case, the vortex breakdown was observed even at the near peak efficiency point. While the mass flow rate decreases, the shock waves formed ahead of the rotor blade leading edge were pushed upstream, causing earlier casing wall boundary layer separation. Upstream moving behavior of the shock is considered a new stall process.

Effects of Stream Surface Inclination on Tip Leakage Flow Fields in Compressor Rotors

1998 ◽  
Vol 120 (4) ◽  
pp. 683-692 ◽  
Author(s):  
M. Furukawa ◽  
K. Saiki ◽  
K. Nagayoshi ◽  
M. Kuroumaru ◽  
M. Inoue
Keyword(s):  
Boundary Layer ◽  
Vortex Breakdown ◽  
Axial Flow ◽  
Flow Fields ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Wall Boundary Layer ◽  
Wall Boundary

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.

Rotor-Tip Flow Fields Near Inception Point of Rotating Instability in an Axial-Flow Fan

2011 ◽  
Author(s):  
Takahiro Nishioka ◽  
Toshio Kanno ◽  
Kiyotaka Hiradate
Keyword(s):  
Vortex Breakdown ◽  
Rotor Blades ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Stall Inception ◽  
Tip Leakage ◽  
Rotating Instability ◽  
End Wall ◽  
Stagger Angle

Stall inception patterns at three stagger-angle settings for the highly loaded rotor blades were experimentally investigated in a low-speed axial-flow fan. Rotor-tip flow fields were also numerically investigated to clarify the mechanism behind the stall inception from a rotating instability. The rotating instability is confirmed near stall condition at the high stagger-angle settings for the highly loaded rotor blades as same as that for the moderate loaded rotor blades. The rotating instability is induced by an interaction between the incoming flow, the reversed tip-leakage flow, and the end-wall backflow from the trailing edge. At the high stagger-angle settings for the rotor blades, the interface between the incoming flow and the reversed tip leakage flow becomes parallel to the leading edge plane near and at the stall condition. Moreover, the tip leakage flow spills from the leading edge of the adjacent blade at the stall condition. The changes in the end-wall flow at the rotor tip are consistent with the criteria for the spike initiation suggested by Vo et al. and Hah et al. However, the short length-scale stall cell is not observed at the high stagger-angle settings. The tip-leakage vortex breakdown is confirmed at the three stagger-angle settings. The end-wall blockage induced by the tip-leakage vortex breakdown influences the development of the stall cell. Moreover, the development of the three-dimensional separation vortex induced by the tip-leakage vortex breakdown seems to be one of the criteria for spike-type stall inception.

Controlling Tip Leakage Flow Over a Shrouded Turbine Rotor Using an Air-Curtain

2009 ◽  
Author(s):  
Eric M. Curtis ◽  
John D. Denton ◽  
John P. Longley ◽  
Budimir Rosic
Keyword(s):  
Axial Direction ◽  
Turbine Rotor ◽  
Test Facility ◽  
Jet Flows ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Air Curtain ◽  
Tip Leakage ◽  
Turbine Efficiency ◽  
Air Turbine

This paper describes an experimental and computational investigation into the performance of an air-curtain seal used to control the leakage flow over the tip shroud of a turbine rotor. The results show that a seal of this type has the potential to reduce or eliminate shroud leakage whilst having a practical level of clearance between the stationary and moving components. The experimental measurements were undertaken using a single-stage low-speed air turbine equipped with a continuous circumferential nozzle in the casing to deliver an axisymmetric jet into the cavity over the rotor shroud. The jet was angled at 45° to the axial direction so that its momentum opposed the shroud leakage flow. In this arrangement the air-curtain was able to sustain the pressure difference between the inlet and outlet of the rotor blade row without any leakage. The test facility had comprehensive instrumentation for obtaining accurate measurements of turbine efficiency that were corrected for the externally supplied additional flow required for the air-curtain. Measurements were obtained for a range of jet flows and show the change in the turbine efficiency as the jet flow is increased. The measurements have been compared with calculations.

Computational analysis of vortices near casing in a transonic axial compressor rotor

2017 ◽  
Vol 233 (2) ◽  
pp. 710-724
Author(s):  
Yanhui Wu ◽  
Guangyao An ◽  
Zhiyang Chen ◽  
Bo Wang
Keyword(s):  
Shock Wave ◽  
Graphical Representation ◽  
Boundary Layer Separation ◽  
Tip Vortex ◽  
Vortex Identification ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Identification Methods ◽  
Tip Leakage ◽  
Compressor Rotor

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.

PIV Maps of Tip Leakage and Secondary Flow Fields on a Low Speed Turbine Blade Cascade With Moving Endwall

2005 ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110 degrees and blade chord of 1.0 m. Data was obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0 × 105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle Image Velocimetry (PIV) was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip endwall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the under-tip flow near the endwall due to the moving wall is observed and the effect on the tip leakage vortex examined.

An Experimental Investigation of the Effects of Grooved Tip Geometry on the Flow Field in a Turbine Cascade Passage Using Stereoscopic PIV

2017 ◽  
Author(s):  
Yangtao Tian ◽  
Hongwei Ma ◽  
Lixiang Wang
Keyword(s):  
Flow Field ◽  
Vortex Breakdown ◽  
Tracer Particle ◽  
Tip Clearance ◽  
Small Scale ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Turbine Efficiency

In the unshrouded axial turbine, the tip clearance gap can cause the losses of turbine efficiency and the penalty of turbine performance. Based on previous investigations, changing the blade tip geometry plays an important role in improving the turbine efficiency and performance. In this paper, the Stereoscopic Particle Imaging Velocimetry (SPIV) measurements were conducted to study the effects of grooved tip geometry on the flow field inside a turbine cascade passage. During the measurements, the double-frame CCD cameras were configured at different sides of the laser light sheet. Additionally, the Diisooctyl Sebacate (DEHS) was treated as the tracer particle. The tip clearance gap of both grooved tip and flat tip was set to 1.18% of the blade chord. The groove height was specified as 2.94% of the blade chord. In this study, the flow field results of eight measured planes were presented. Some typical features of the complicated flow structures, such as tip leakage vortex formation, development, breakdown and the dissipation, the variations of turbulence intensity and Reynolds stress, the blockage characteristic, were discussed as well. The experimental results show that the tip leakage flow/vortex is weakened by the grooved tip. The blockage effect and the flow capacity of the turbine passage are also improved. The tip leakage vortex breaks down at about 70% camber line, but the pattern of leakage vortex has changed into an ellipse at 60% camber line, which is an indication of the vortex breakdown. As for the decomposed and reconstructed flow, the first modal flow is the most similar to the original flow field. And it can capture the dominant flow features in flow field. And the flow of mode 2 and mode 3 generates many eddies with small scale.

Analysis on the unsteady flow structures in the tip region of axial compressor

2021 ◽  
pp. 095765092199511
Author(s):  
Mo-Ru Song ◽  
Bo Yang
Keyword(s):  
Shock Wave ◽  
Axial Compressor ◽  
Leading Edge ◽  
Main Flow ◽  
The Self ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Low Velocity ◽  
Tip Leakage ◽  
Unsteady Characteristics

The unsteady characteristic in the tip region of an axial compressor has been numerically studied with the help of the dynamic mode decomposition analysis. The characteristics of frequency and dynamic modes are compared and discussed under different operating points and different parameters, such as tip clearance and rotating speeds. For the flowfield structures in the tip region, such as tip leakage flow, separation flow and shock wave, their relationships with the unsteadiness are studied in detail. Except for the unsteadiness caused by the interaction between rotating rotor and the stationary boundaries, it is found that the unsteadiness is attributed to the moving of the low-velocity cell. Based on the generation and the development of the low-velocity cell, the unsteady characteristics in tip region are divided into 4 types: BPF-dominated, shedding-dominated, self-induced and separation-dominated. When the tip leakage flow is weak, the unsteadiness in the tip region is only triggered by the blade sweeping. As the tip leakage flow gets stronger to a certain extent, the low-velocity cell is shed into the flow passage and mixed with the main-flow. When the main-flow is weaker under the low flowrate condition, the interaction between the low-velocity cell and the pressure side occurs and generates a new low-velocity cell near the leading-edge of the neighboring blade. The frequency of the new cell generation is actually the self-induced frequency. In the zero and small clearance model, the low-velocity is shed by the separation in the leading-edge and the casing-suction corner. By understanding these unsteady characteristics, the change tendency of the leading frequency in the rotor tip is easily explained and forecasted. Furthermore, under the transonic operation condition, the low-velocity cell is decelerated and eliminated by the shock wave in the unsteadiness of the self-induced type and the separation-dominated type, respectively. Thus, the leading frequency in the tip flow field is moderated.

Effects of Stream Surface Inclination on Tip Leakage Flow Fields in Compressor Rotors

1997 ◽  
Author(s):  
Masato Furukawa ◽  
Kazuhisa Saiki ◽  
Kenya Nagayoshi ◽  
Motoo Kuroumaru ◽  
Masahiro Inoue
Keyword(s):  
Boundary Layer ◽  
Vortex Breakdown ◽  
Axial Flow ◽  
Flow Fields ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Wall Boundary Layer ◽  
Wall Boundary

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 degrees and 45 degrees, 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 the behavior of the tip leakage flow 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.

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