Experimental Investigation of the Flow in a Forward Swept Transonic Compressor Rotor at Stall Inception

2007 ◽  
Author(s):  
Jo¨rg Bergner ◽  
Heinz-Peter Schiffer
Keyword(s):  
Flow Field ◽  
Stability Limit ◽  
Leading Edge ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Numerical Work ◽  
Stall Inception ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Tip Clearance Vortex

Three-dimensional laser-2-focus measurements complemented by measurements of the instantaneous static wall pressure in the casing above the rotor are used to investigate short length-scale rotating stall inception in an axial transonic compressor rotor. The data was collected at the Darmstadt Transonic Compressor using the forward swept “Rotor-3”. Detailed analysis of the experimental data reveals that in this configuration with pronounced forward sweep stall is not directly caused by the blockage created by the shock vortex interaction. Due to the reduced aerodynamic loading, the tip clearance vortex passes the shock without significant deceleration but shows some great fluctuation in terms of vortex strength. As the compressor is throttled to near stall, the tip clearance vortex eventually reaches the leading edge of the adjacent blade. It can be suggested that as an result, spill forward and so-called “self-induced vortex-oscillation” occurs. A phase-lock of both of these phenomena might be the trigger for a spike-type disturbance of the flow-field. The investigation underpins the great importance of the unsteady flow phenomena at near stall. For a thorough understanding of the flow features at the stability limit of a compressor, which is the basis of any effort to increase the operation range, special attention has to be paid to the unsteadiness of the flow in both experimental and numerical work. To study the mechanism of stall inception it might even be necessary to analyze the flow field around the whole annulus, as there appears to be significant interaction of the flow between neighboring passages.

Characteristics of Tip Clearance Flow Instability in a Transonic Compressor

2010 ◽  
Author(s):  
Chunill Hah ◽  
Melanie Voges ◽  
Martin Mueller ◽  
Heinz-Peter Schiffer
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Flow Instability ◽  
Tip Clearance ◽  
Piv Measurements ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Tip Clearance Vortex

In the present study, unsteady flow phenomena due to tip clearance flow instability in a modern transonic axial compressor rotor are studied in detail. First, unsteady flow characteristics due the oscillating tip clearance vortex measured with the particle image velocimetry (PIV) and casing-mounted unsteady pressure transducers are analyzed and compared to numerical results with a large eddy simulation (LES). Then, measured characteristic frequencies of the unsteady flow near stall operation are investigated. The overall purpose of the study is to advance the current understanding of the unsteady flow field near the blade tip in an axial transonic compressor rotor near the stall operating condition. Flow interaction between the tip leakage vortex and the passage shock is inherently unsteady in a transonic compressor. The currently applied PIV measurements indicate that the flow near the tip region is unsteady even at the design condition. This self-induced unsteadiness increases significantly as the compressor operates toward the stall condition. PIV data show that the tip clearance vortex oscillates substantially near stall. The calculated unsteady characteristics from LES agree well with the PIV measurements. Calculated unsteady flow fields show that the formation of the tip clearance vortex is intermittent and the concept of vortex breakdown from steady flow analysis does not seem to apply in the current flow field. Fluid with low momentum near the pressure side of the blade close to the leading edge periodically spills over into the adjacent blade passage. The spectral analysis of measured end wall and blade surface pressure shows that there are two dominant frequencies near stall. One frequency is about 40–60% of the rotor rotation and the other dominant frequency is about 40–60% of the blade passing frequency (BPF). The first frequency represents the movement of a large blockage over several consecutive blade passages against the rotor rotation. The second frequency represents traditional tip flow instability, which has been widely observed in subsonic compressors. The LES simulations show that the second frequency is due to movement of the instability vortex.

Investigation of Unsteady Compressor Flow Structure With Tip Injection Using Particle Image Velocimetry

2011 ◽  
Author(s):  
Roland Matzgeller ◽  
Melanie Voges ◽  
Michael Schroll
Keyword(s):  
Flow Field ◽  
Leading Edge ◽  
Fast Response ◽  
Rotating Stall ◽  
Fluid Injection ◽  
Pressure Transducers ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Response Pressure ◽  
Tip Injection

Fluid injection at the tip of highly loaded compressor rotors is known to be very effective in suppressing the onset of rotating stall and eventually compressor instability. To understand the effects of tip injection, the flow field at the tip region of a transonic compressor rotor with and without fluid injection was investigated in this paper. Using results acquired by phase-locked PIV measurements as well as the static pressure field obtained by fast response pressure transducers, the unsteady interaction between the injection jet and the rotor could be described thoroughly. Both, an influence of the rotor’s flow field on the jet as well of the jet on the rotor was clearly visible. Since unsteady inflow conditions to the front rotor in the relative frame of reference were imposed by the injection jets, the rotor’s unsteady response was investigated by inspection of the position of the tip leakage vortex trajectory. It could be shown that due to a short time for the flow to adapt at the rotor’s leading edge, its position didn’t change distinctly. Because a significantly longer time was needed for the overall passage flow to adapt, it was concluded that this causes the beneficial effect of tip injection.

Short Length-Scale Rotating Stall Inception in a Transonic Axial Compressor: Criteria and Mechanisms

2006 ◽  
Author(s):  
Chunill Hah ◽  
Jo¨rg Bergner ◽  
Heinz-Peter Schiffer
Keyword(s):  
Axial Compressor ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Stall Inception ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Eddy Simulation ◽  
Clearance Flow ◽  
Flow Mechanisms ◽  
Tip Clearance Vortex

The current paper reports on investigations aimed at advancing the understanding of the flow mechanism that leads to the onset of short-length scale rotating stall in a transonic axial compressor. Experimental data show large oscillation of the tip clearance vortex as the rotor operates near the stall condition. Inception of spike-type rotating stall is also measured in the current transonic compressor with high response pressure transducers. Computational studies of a single passage and the full annulus were carried out to identify flow mechanisms behind the spike-type stall inception in the current transonic compressor rotor. Steady and unsteady single passage flow simulations were performed, first to get insight into the interaction between the tip clearance vortex and the passage shock. The conventional Reynolds-averaged Navier-Stokes method with a standard turbulence closure scheme does not accurately reproduce tip clearance vortex oscillation and the measured unsteady pressure field. Consequently, a Large Eddy Simulation (LES) was carried out to capture more relevant physics in the computational simulation of the rotating stall inception. The unsteady random behavior of the tip clearance vortex and it’s interaction with the passage shock seem to be critical ingredients in the development of spike-type rotating stall in a transonic compressor. The Large Eddy Simulation was further extended to the full annulus to identify flow mechanisms behind the measured spike-type rotating stall inception. The current study shows that the spike-type rotating stall develops after the passage shock is fully detached from the blade passages. Interaction between the tip clearance vortex and the passage shock creates a low momentum area near the pressure side of the blade. As the mass flow rate decreases, this low momentum area moves further upstream and reversed tip clearance flow is initiated at the trailing edge plane. Eventually, the low momentum area near the pressure side reaches the leading edge and forward spillage of the tip clearance flow occurs. The flows in the affected blade passage or passages then stall. As the stalled blade passages are formed behind the passage shock, the stalled area rotates counter to the blade rotation just like the classical Emmon’s type rotating stall. Both the measurements and the computations show that the rotating stall cell covers one to two blade passage lengths and rotates at roughly 50% of the rotor speed.

Role of Blade Passage Flow Structurs in Axial Compressor Rotating Stall Inception

1999 ◽  
Vol 121 (4) ◽  
pp. 735-742 ◽  
Author(s):  
D. A. Hoying ◽  
C. S. Tan ◽  
Huu Duc Vo ◽  
E. M. Greitzer
Keyword(s):  
Leading Edge ◽  
Rotating Stall ◽  
Short Length ◽  
Tip Clearance ◽  
Length Scale ◽  
Central Feature ◽  
Local Flow ◽  
Stall Inception ◽  
Blade Passage ◽  
Tip Clearance Vortex

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.

Role of Tip-Leakage Vortices and Passage Shock in Stall Inception in a Swept Transonic Compressor Rotor

2004 ◽  
Author(s):  
Chunill Hah ◽  
Douglas C. Rabe ◽  
Aspi R. Wadia
Keyword(s):  
Boundary Layer ◽  
Flow Fields ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Stall Inception ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Tip Clearance Vortex

The current paper reports on investigations aimed at advancing the understanding of the flow field near the casing of a forward-swept transonic compressor rotor. The role of tip clearance flow and its interaction with the passage shock on stall inception are analyzed in detail. Steady and unsteady three-dimensional viscous flow calculations are applied to obtain flow fields at various operating conditions. The numerical results are first compared with available measured data. Then, the numerically obtained flow fields are interrogated to identify the roles of flow interactions between the tip clearance flow, the passage shock, and the blade/endwall boundary layers. In addition to the flow field with nominal tip clearance, two more flow fields are analyzed in order to identify the mechanisms of blockage generation: one with zero tip clearance, and one with nominal tip clearance on the forward portion of the blade and zero clearance on the aft portion. The current study shows that the tip clearance vortex does not break down, even when the rotor operates in a stalled condition. Interaction between the shock and the suction surface boundary layer causes the shock, and therefore the tip clearance vortex, to oscillate. However, for the currently investigated transonic compressor rotor, so-called breakdown of the tip clearance vortex does not occur during stall inception. The tip clearance vortex originates near the leading edge tip, but moves downward in the spanwise direction inside the blade passage. A low momentum region develops above the tip clearance vortex from flow originating from the casing boundary layer. The low momentum area builds up immediately downstream of the passage shock and above the core vortex. This area migrates toward the pressure side of the blade passage as the flow rate is decreased. The low momentum area prevents incoming flow from passing through the pressure side of the passage and initiates stall inception. It is well known that inviscid effects dominate tip clearance flow. However, complex viscous flow structures develop inside the casing boundary layer at operating conditions near stall.

The improvement of transonic compressor performance by the self-circulating casing treatment

2020 ◽  
pp. 095440622094226
Author(s):  
Song Yan ◽  
Wuli Chu
Keyword(s):  
Flow Field ◽  
Axial Flow ◽  
Leading Edge ◽  
Tip Clearance ◽  
The Self ◽  
Casing Treatment ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Blade Tip ◽  
Stability Effect

The performance curve of the compressor is limited by the surge boundary, so it is of great significance to increase the stable working range of the compressor. The self-circulating casing treatment is an effective way to improve the stable working range of the compressor. In this paper, the study of the influence of the injector position of the self-circulating casing treatment on the transonic axial flow compressor rotor performance is carried out by using the numerical simulation. The influence mechanism of the injector position on the enhancing stability effect of the self-circulating casing treatment is revealed. It is found that the self-circulating casing treatment can reduce the blade tip blockage by restraining the blade tip clearance leakage flow and changing the trajectory of the tip clearance leakage vortex, thus delaying the deterioration of the rotor tip flow field and improving the rotor stability. When the injector position of the self-circulating casing treatment moves from the upstream of the leading edge of the blade tip to the trailing edge of the blade tip, the enhancing stability effect of the self-circulating casing treatment increases first and then decreases. But the high-velocity jet from the injector of the self-circulating casing treatment aggravates the mixing loss of the rotor tip flow field, so that the rotor efficiency slightly decreases after using the self-circulating casing treatment.

The Effect of a Bend-Slot Casing Treatment on the Blade Tip Flow Field of a Transonic Compressor Rotor

2013 ◽  
Author(s):  
M. Voges ◽  
C. Willert ◽  
R. Mönig ◽  
H.-P. Schiffer
Keyword(s):  
Flow Field ◽  
Numerical Simulations ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Fluid Exchange ◽  
Effective Measure ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Blade Tip ◽  
Tip Clearance Vortex

The application of casing treatments (CT) is an effective measure to increase the stable operating range of modern aero engine or gas turbine compressors. As the development and design process of optimized CT geometries is primarily based on numerical simulations, the need for accurate experimental flow field data for related code validation is increasing with the number of applications. While the stall margin enhancement and other stage characteristics can be verified using conventional measurement techniques such as pressure and temperature probes, a deeper insight to the aerodynamic effect of the CT on the rotor flow field can only be provided using non-intrusive, laser-based flow field diagnostics, given that optical access to the compressor stage can be established. The investigation presented herein involved particle image velocimetry (PIV) measurements at high spatial resolution in the blade tip region of the Darmstadt Transonic Compressor Rotor-1 under the influence of a bend-slot CT. Tangential PIV measurement planes were placed at 95% span as well as in the tip gap of the rotor. The investigation included operating conditions at the aerodynamic design point (peak efficiency) and near stall conditions at 100% rpm. Additional reference measurements were performed with the untreated, smooth casing. The experimental study was complimented by numerical simulations of the same compressor and CT geometry using the DLR TRACE code. Based on the combination of both, experimental and numerical flow field results, a detailed analysis of the shock structures and the tip clearance vortex under the influence of the CT was performed. Under the influence of the CT, the fluid exchange between rotor passage and CT slots — driven by the pressure gradient over the blade tip and the leading edge bow shock, respectively — induces secondary flow structures in the tip vortex regime. At near stall conditions the periodical injection of energized fluid out of the CT cavities was identified to be one of the major effects stabilizing the tip clearance vortex and hence delaying the onset of rotating stall.

scholarly journals Observations of the Growth and Decay of Stall Cells during Stall and Surge in an Axial Compressor

2017 ◽  
Vol 2017 ◽  
pp. 1-11
Author(s):  
Adam R. Hickman ◽  
Scott C. Morris
Keyword(s):  
Flow Field ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Leading Edge ◽  
Cell Development ◽  
Rotating Stall ◽  
Trailing Edge ◽  
Stall Inception ◽  
Compressor Rotor

This research investigated unsteady events such as stall inception, stall-cell development, and surge. Stall is characterized by a decrease in overall pressure rise and nonaxisymmetric throughflow. Compressor stall can lead to surge which is characterized by quasi-axisymmetric fluctuations in mass flow and pressure. Unsteady measurements of the flow field around the compressor rotor are examined. During the stall inception process, initial disturbances were found within the rotor passage near the tip region. As the stall cell develops, blade lift and pressure ratio decrease within the stall cell and increase ahead of the stall cell. The stall inception event, stall-cell development, and stall recovery event were found to be nearly identical for stable rotating stall and surge cases. As the stall cell grows, the leading edge of the cell will rotate at a higher rate than the trailing edge in the rotor frame. The opposite occurs during stall recovery. The trailing edge of the stall cell will rotate at the approximate speed as the fully developed stall cell, while the leading edge decreases in rotational speed in the rotor frame.

scholarly journals Effects of Tip Leakage Flow on the Aerodynamic Performance and Stability of an Axial-Flow Transonic Compressor Stage

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4168
Author(s):  
Botao Zhang ◽  
Xiaochen Mao ◽  
Xiaoxiong Wu ◽  
Bo Liu
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Transonic Compressor

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.

Numerical Investigation of Effect of Inlet Distortion on Compressor Flow Field and Stability

2017 ◽  
Author(s):  
HaoGuang Zhang ◽  
Kang An ◽  
Feng Tan ◽  
YanHui Wu ◽  
WuLi Chu
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Total Pressure ◽  
Tip Clearance ◽  
Numerical Work ◽  
Stall Margin ◽  
Numerical Investigations ◽  
Inlet Distortion ◽  
Compressor Rotor ◽  
The Stability

The compressor aerodynamic design is conducted under the condition of clean inlet in general, but a compressor often operates under the condition of inlet distortion in the practical application. It has been proven by a lot of experimental and numerical investigations that inlet distortion can decrease the performance and stability of compressors. The circumferential or radial distorted inlet in mostly numerical investigations is made by changing the total pressure and total temperature in the inlet ring surface of the compressors. In most of inlet distortion experiments, distorted inlets are usually created by using wire net, flashboards, barriers or the generator of rotating distortion. The fashion of generating distorted inlet for experiment is different from that for numerical simulation. Consequently, the flow mechanism of affecting the flow field and stability of a compressor with distorted inlet for experiment is partly different than that for numerical simulation. In the numerical work reported here, the inlet distortion is generated by setting some barriers in the inlet ring surface of an axial subsonic compressor rotor. Two kinds of distorted inlet are investigated to exploring the effect of distorted range on the flow field and stability of the compressor with ten-passage unsteady numerical method. The numerical results show that the inlet distortions not only degrade the total pressure and efficiency of the compressor rotor, but also decrease the stability of the rotor. The larger the range of distorted inlet is, the stronger the adverse effect is. The comprehensive stall margin for the inlet distortion of 24 degrees and 48 degrees of ten-passages is reduced about 3.35% and 5.88% respectively. The detailed analysis of the flow field in the compressor indicates that the blockage resulted from tip clearance leakage vortex (TLV) and the flow separation near the suction surfaces of some blades tip for distorted inlet is more serious than that resulted from TLV for clean inlet. Moreover, the larger the range of distorted inlet is, the larger the range of the blockage is. The analysis of unsteady flow shows that during this process, which is that one rotor blade passes through the region affected by the distorted inlet, the range of the blockage in the rotor passage increases first, then reduces, and increases last.

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