Breakdown of Tip Leakage Vortices in Compressors at Flow Conditions Close to Stall

1997 ◽  
Author(s):  
Stefan Schlechtriem ◽  
Michael Lötzerich
Keyword(s):  
Vortex Breakdown ◽  
Stability Limit ◽  
Flow Conditions ◽  
Mixed Flow ◽  
Stall Inception ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Flow Compressor ◽  
The Stability ◽  
Operating Points

The breakdown of tip leakage vortices at operating points close to the stability limit of transonic compressor rotors has been detected. The aerodynamic phenomenon is considered to have a major impact on stall inception. Computations have been carried out and a detailed visualization of the phenomenon is given. In addition the connection of vortex breakdown to rotating instabilities and stall is discussed. Furthermore the tip flow field of the axial rotor is compared to the results for a centrifugal and a mixed flow compressor operating at similar tip speeds.

Experimental Study on the Influence of Casing Treatment on Near-Stall Unsteady Behavior of a Mixed-Flow Compressor

2019 ◽  
Author(s):  
Juan Du ◽  
Felix Kauth ◽  
Jichao Li ◽  
Qianfeng Zhang ◽  
Joerg R. Seume
Keyword(s):  
Stability Limit ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Surprising Result ◽  
Mixed Flow ◽  
Stall Inception ◽  
Casing Treatment ◽  
Axial Compressors ◽  
Flow Compressor ◽  
Unsteady Behavior

Abstract This paper aims at experimentally demonstrating the effects of axial slot casing treatment and tip gap variation on compressor performance, unsteady tip clearance flow, and stall inception features in a highly-loaded mixed-flow compressor at partspeed. Two tip gaps (0.32% and 0.64% of rotor blade chord at mid-span) were tested at three rotational speeds. A semicircular axial slot casing treatment improves compressor stability. The experimental results show that this casing treatment significantly moves the stability limit at partial speeds towards lower mass flow for both tip gaps, compared to the reference case without casing treatment. In the case of the compressor with casing treatment, efficiency increases for the large tip gap and decreases for the small tip gap. Dynamic pressure transducers installed in the casing upstream and along the rotor tip chord direction are used to detect the unsteady behavior of tip region flow and stall inception signals of the compressor. The characteristic frequency in the tip region decreases, and the oscillating amplitude first decreases and then increases during the throttling process, regardless of tip gap size or casing treatment. For axial compressors, by contrast, the observation in previous work has been an increase of the oscillating amplitude with decreasing flow coefficient. This is a surprising result of our work. Neither experiment nor CFD so far was able to explain why the trend in this mixed-flow compressor is different from the trend expected from axial compressors. The compressor stalls through the spike stall inception both with and without casing treatment. This observation also differs from recent studies on axial compressors, which demonstrated that casing treatments could change the type of stall inception. The unstable disturbance indicating initial stall inception initially appears in the blade tip region from blade mid-chord to trailing edge, and then propagates upstream towards the leading edge. This disturbance might be generated by the reversed flow separation near mid-chord.

Study of the Tip Leakage Flow in a Compressor Cascade With Incidence Exceeding the Stability Limit

2019 ◽  
Author(s):  
Markus W. Leitner ◽  
Stephan Staudacher ◽  
Martin G. Rose
Keyword(s):  
Water Table ◽  
Vortex Breakdown ◽  
Stability Limit ◽  
Leakage Flow ◽  
Angle Of Incidence ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Unstable Flow ◽  
Tip Leakage ◽  
The Stability

Abstract In axial compressors, tip leakage flow is disadvantageous to efficiency and mass flow stability. We analyzed the tip leakage flow in a compressor cascade on a water table at various angles of incidence. When the angle of incidence is systematically increased, the flow rate is decreased and, finally, the stability limit is exceeded. To study the flow structures and vortex behavior, we installed Particle Tracking Velocimetry (PTV) on the water table. 3D-trajectories of the stable and unstable flow reveal significant effects. Increasing incidence generates a significant change in the nature of the flow. The tip leakage flow fluctuates and features unstable flow phenomena. A large blockage of the flow passage occurs, probably due vortex breakdown. Such a serious disturbance of the incoming flow may induce stall.

Investigation of Passage Flow Features in a Transonic Compressor Rotor With Casing Treatments

2011 ◽  
Author(s):  
M. W. Mu¨ller ◽  
H.-P. Schiffer ◽  
Melanie Voges ◽  
Chunill Hah
Keyword(s):  
Measurement Techniques ◽  
Stability Limit ◽  
Rotating Stall ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Tip Leakage ◽  
Operating Range ◽  
Transonic Compressor ◽  
The Stability ◽  
Casing Treatments

An experimental investigation on casing treatments in a one-stage transonic compressor is presented. The reference case consists of a radially staggered blisk and six circumferential grooves. Speedlines show that this axisymmetric treatment already provided a substantial increase in operating range with relatively small losses in efficiency. Since the onset of rotating stall in tip-critical high-speed compressors is always linked to the tip-leakage flow and the build-up of blockage within the blade passage. High-resolution measurement techniques have been employed to investigate the corresponding effects. Results with Particle Image Velocimetry show that the interaction between the tip leakage vortex and the shock front cause a blockage area. When throttled further, the blockage increases. The shock structure changes similar to the phenomena of vortex breakdown described by different researchers in the past, but a stagnation point is not present. Before reaching the stability limit, the interface line between the incoming flow and the blocked area moves towards the inlet plane of the rotor indicating spike-type stall inception. Wall pressure measurements confirmed this theory for the smooth wall, but with circumferential grooves applied, a part span stall cell develops prior to the stability limit. In order to assess the performance of circumferential grooves, two additional configurations are presented. The corresponding measurements addressed the questions whether circumferential grooves also provide an operating range extension when applied to an optimized rotor design with higher initial stall margin. Therefore, an identical casing treatment is applied to a forward swept rotor. The second question is, how circumferential grooves perform in direct comparison to a non-axisymmetric endwall structure. Axial slots have been applied to the radially staggered rotor. While the stall margin exceeds all other configurations, detrimential effects in efficiency are observed. A detailed anaylsis of probe data shows the changes of the radial profile at the rotor outlet which allows recommendations for more efficient CT designs. Parameters allowing to evaluate the CT influence are presented.

Unsteady Pressure Measurement in a Single Stage Axial Transonic Compressor Near the Stability Limit

2008 ◽  
Author(s):  
Christoph Biela ◽  
Martin W. Mu¨ller ◽  
Heinz-Peter Schiffer ◽  
Carsten Zscherp
Keyword(s):  
Total Pressure ◽  
Sampling Rate ◽  
Stability Limit ◽  
Wall Pressure ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Vortex Pattern ◽  
Relative Standard ◽  
The Stability

With the help of piezoelectric high frequency pressure probes measurements are undertaken to investigate the flow during stable compressor operation close to the stability limit. Fourteen static pressure probes record the static wall pressure and ten total pressure probes record the total pressure at the rotor exit, both in the absolute frame of reference. The data is then visualised as ensemble averaged contour and spectrum plots. With the help of wall and exit pressure, the tip leakage vortex is localised. Oscillations of the tip leakage vortex are seen as well in terms of high relative standard deviation as well as in an excitation of a frequency band around 1/2 BPF. Further investigation of the frequency spectrum with the help of the pseudo-unsteady wall pressure reveal the occurrence of rotating tip leakage vortex disturbances forming a two-passage periodic vortex pattern. The presented measurements were obtained using Rotor-1 from the TU Darmstadt rotor family. With a sampling rate of 125kHz the pressure field is resolved with 23 measurements per passage (at 20.000 rpm, design speed).

Numerical Analysis of Flow in a Transonic Compressor With a Single Circumferential Casing Groove: Application to Two Different Compressor Rotors

2014 ◽  
Author(s):  
Yasunori Sakuma ◽  
Toshinori Watanabe ◽  
Takehiro Himeno ◽  
Dai Kato ◽  
Takeshi Murooka ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow Behavior ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Stall Inception ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
The Stability

The effect of a single circumferential casing groove on the stability enhancement of two different transonic compressors has been examined with CFD analysis. The differences in flow field and stall inception mechanism between two rotors are presented with principal focus on passage blockage and tip leakage flow behavior. Detailed observation showed that the blockage flow which leads the compressor to stall was different between each other. A parametric study conducted with respect to the axial location of the groove has clarified that the effect which groove has on the tip leakage flow behavior changes according to the blade tip loading and the design tip clearance gap at the location where the groove is applied. When the casing treatment was applied to the compressors with different instability mechanism, whether the casing treatment could enhance the stability of compressor or not was not only dependant on the extent of the influence which it had on the flow field but also on whether it could affect the original stall-initiating phenomena at the adequate location.

Flow Field Unsteadiness in the Tip Region of a Transonic Compressor Rotor

1997 ◽  
Vol 119 (1) ◽  
pp. 122-128 ◽  
Author(s):  
S. L. Puterbaugh ◽  
W. W. Copenhaver
Keyword(s):  
Flow Field ◽  
High Performance ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Vortex Interaction ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Operating Points

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.

Numerical Investigation Into the Mechanism of Tip Flow Unsteadiness in a Transonic Compressor

2017 ◽  
Author(s):  
Guangyao An ◽  
Yanhui Wu ◽  
Jinhua Lang ◽  
Zhiyang Chen ◽  
Bo Wang ◽  
...  
Keyword(s):  
Vortex Breakdown ◽  
Pressure Oscillation ◽  
Operating Point ◽  
Recirculation Region ◽  
Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Flow Unsteadiness ◽  
Transonic Compressor ◽  
Evolution And Development

It is well known that tip flow unsteadiness has profound effects on both performance and stability of axial compressors. A number of numerical simulations have been performed in transonic compressors to uncover the nature of tip flow unsteadiness. From this research, tip flow unsteadiness can be attributed to many factors, such as the movement of the primary and secondary leakage flow, the interaction between shock and vortex, and the tip leakage vortex breakdown. However, no final conclusion has yet been reached on this matter. The current investigation is carried out to explore the origin of tip flow unsteadiness from the perspective of the evolution and development of tip leakage vortex breakdown. In this paper, unsteady RANS simulations have been performed to investigate the fluid dynamic processes in a tip-critical transonic compressor, NASA Rotor 35. A vortex core visualization method based on an eigenvector method is introduced as an important tool to identify the vortex arising from tip leakage flow. As the flow rate varies, three critical operating points with distinctive features of flow unsteadiness are observed. At the first critical operating point, bubble-type breakdown occurs, and gives rise to a weak unsteadiness with high frequency in the rotor passage due to the oscillation of the recirculation region induced by the tip leakage vortex breakdown. At the second critical operating point, the vortex breakdown has transformed from bubble-type to spiral-type, which leads to the frequency of the pressure oscillation reduced almost by half and the amplitude increased significantly. At the third critical operating point, a new vortex that is perpendicular to the pressure surface comes into being in the tip region, which leads to a prominent pressure oscillation of the tip flow and another jump in amplitude. As a result, the evolution and development of tip leakage vortex breakdown are closely related to the tip flow unsteadiness of the investigated rotor.

Stall inception mechanisms in a contra-rotating fan operating at different speed combinations

2019 ◽  
Vol 234 (8) ◽  
pp. 1041-1052 ◽  
Author(s):  
MP Manas ◽  
AM Pradeep
Keyword(s):  
Pressure Ratio ◽  
Pressure Sensors ◽  
Stability Limit ◽  
Leading Edge ◽  
Axial Direction ◽  
Tip Leakage Flow ◽  
Stall Inception ◽  
Unsteady Pressure ◽  
Stall Cells ◽  
The Stability

Contra-rotating fan is a concept that can possibly replace the present-day conventional fans due to its several aerodynamic advantages. It has the potential to improve the stability limit and can achieve a higher pressure ratio per stage. One of the advantages of a contra-rotating fan is its capability to operate both the rotors at different speeds. In the present study, experiments are carried out at different speed combinations of the rotors and the stall inception phenomenon is captured using high-response unsteady pressure sensors placed on the casing upstream of the leading edge of rotor-1. The unsteady pressure data are investigated using wavelet and Fourier analysis techniques. It is observed that the mechanism of stall inception is different for different speed combinations. The pre-stall disturbances fall in different frequency ranges for different speed combinations. For the range of speed combinations investigated, the frequency of appearance of stall cells of rotor-1 does not depend on the speed of rotor-2. A higher speed of rotation of rotor-1 leads to a higher frequency of appearance of stall cells and a lower speed of rotation of rotor-1 leads to a lower frequency of appearance of stall cells. For all the speed combinations, there is a range of frequency where no disturbance is observed and this range is termed as the ‘no-disturbance zone’. Disturbances are observed at lower frequencies and at frequencies close to the blade passing frequency. In order to understand the flow physics in detail, computational analysis is carried out for different speed combinations of the rotors. For a higher speed of rotor-2, it is observed that the suction effect of rotor-2 is significant enough to pull the tip-leakage flow towards the axial direction. Thus, the suction effect of rotor-2 plays a significant role in determining the stall of the stage.

Behavior of Tip Leakage Flow in an Axial Flow Compressor Rotor

2006 ◽  
Author(s):  
Yanhui Wu ◽  
Wuli Chu ◽  
Xingen Lu ◽  
Junqiang Zhu
Keyword(s):  
Boundary Layer ◽  
Vortex Breakdown ◽  
Axial Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Flow Compressor

The current paper reports on investigations with an aim to advance the understanding of the flow field near the casing of a small-scale high-speed axial flow compressor rotor. Steady three dimensional viscous flow calculations are applied to obtain flow fields at various operating conditions. To demonstrate the validity of the computation, the numerical results are first compared with available measured data. Then, the numerically obtained flow fields are analyzed to identify the behavior of tip leakage flow, and the mechanism of blockage generation arising from flow interactions between the tip clearance flow, the blade/casing wall boundary layers, and non-uniform main flow. The current investigation indicates that the “breakdown” of the tip leakage vortex occurs inside the rotor passage at the near stall condition. The vortex “breakdown” results in the low-energy fluid accumulating on the casing wall spreads out remarkably, which causes a sudden growth of the casing wall boundary layer having a large blockage effect. A low-velocity region develops along the tip clearance vortex at the near stall condition due to the vortex “breakdown”. As the mass flow rate is further decreased, this area builds up rapidly and moves upstream. This area prevents incoming flow from passing through the pressure side of the passage and forces the tip leakage flow to spill into the adjacent blade passage from the pressure side at the leading edge. It is found that the tip leakage flow exerts little influence on the development of the blade suction surface boundary layer even at the near stall condition.

Numerical investigation of the unsteady tip leakage flow and rotating stall inception in a transonic compressor

2010 ◽  
Vol 19 (4) ◽  
pp. 310-317 ◽  
Author(s):  
Yanfeng Zhang ◽  
Xingen Lu ◽  
Wuli Chu ◽  
Junqiang Zhu
Keyword(s):  
Numerical Investigation ◽  
Rotating Stall ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Stall Inception ◽  
Tip Leakage ◽  
Transonic Compressor
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