scholarly journals Numerical Study on Rotating Stall in Finite Pitch Cascades

1994 ◽  
Author(s):  
Toshio Nishizawa ◽  
Hiroyuki Takata
Keyword(s):  
Numerical Study ◽  
Flow Behavior ◽  
Vortex Method ◽  
Rotating Stall ◽  
Axial Distance ◽  
Flow Angle ◽  
Guide Vanes ◽  
Stall Inception ◽  
Stall Cells ◽  
Inception Point

Flow behavior of rotating stall in finite pitch cascades is discussed through numerical analyses by means of a vortex method, which is particularly developed to solve unsteady flows through stalled cascades. It is shown that stall vortex and unstall vortex are, shed from each stalled blade periodically, and the behavior of these vortices has considerable effects on various properties of rotating stall, such as magnitude of flow fluctuation, propagation velocity, the number of stall cells, and so on. When a rotating stall is initiated and developed in an isolated cascade at smaller inlet flow angles around the stall inception point, a plural number of stall cells tend to propagate on the growing process, although only one stall cell survives eventually in a fully developed rotating stall. At larger flow angles, a single stall cell splits into two separate cells as it propagates. These processes are found for the first time through the analyses of finite pitch cascades. With the inlet guide vanes upstream, a plural number of stall cells can grow in a fully developed rotating stall, and the number of stall cells depends on the exit flow angle of the guide vanes and the axial distance between the two cascades. The numerical results agree well with experiments.

scholarly journals Measurement of Flow Pattern Within a Rotating Stall Cell in an Axial Compressor

2006 ◽  
Author(s):  
J. Lepicovsky ◽  
E. P. Braunscheidel
Keyword(s):  
Flow Direction ◽  
Flow Behavior ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Pressure Probe ◽  
Ensemble Averaging ◽  
Flow Angle ◽  
High Frequency Response ◽  
Actual Flow ◽  
Design Speed

Effective active control of rotating stall in axial compressors requires detailed understanding of flow instabilities associated with this compressor regime. Newly designed miniature high frequency response total and static pressure probes as well as commercial thermoanemometric probes are suitable tools for this task. However, during the rotating stall cycle the probes are subjected to flow direction changes that are far larger than the range of probe incidence acceptance, and therefore probe data without a proper correction would misrepresent unsteady variations of flow parameters. A methodology, based on ensemble averaging, is proposed to circumvent this problem. In this approach the ensemble averaged signals acquired for various probe setting angles are segmented, and only the sections for probe setting angles close to the actual flow angle are used for signal recombination. The methodology was verified by excellent agreement between velocity distributions obtained from pressure probe data, and data measured with thermoanemometric probes. Vector plots of unsteady flow behavior during the rotating stall regime indicate reversed flow within the rotating stall cell that spreads over to adjacent rotor blade channels. Results of this study confirmed that the NASA Low Speed Axial Compressor (LSAC) while in a rotating stall regime at rotor design speed exhibits one stall cell that rotates at a speed equal to 50.6% of the rotor shaft speed.

Investigation of the Influence of Hub Gap Size to the Performance of a Subsonic Compressor Stator

2012 ◽  
Author(s):  
Ke Shi ◽  
Haixin Chen ◽  
Song Fu ◽  
Ruben van Rennings ◽  
Frank Thiele
Keyword(s):  
Flow Behavior ◽  
Leading Edge ◽  
Surface Flow ◽  
Channel Height ◽  
Leakage Flow ◽  
Gap Size ◽  
Flow Angle ◽  
Back Flow ◽  
Guide Vanes ◽  
Inlet Guide Vanes

This paper presents a RANS study of the hub clearance effects on the performance of a subsonic compressor stator. The inlet boundary conditions are from the calculation of inlet guide vanes. The k-ω SST turbulence model is adapted to resolve the Reynolds stresses. The present numerical results are compared with the experiment carried out at Technical University Berlin. The circumferentially averaged total pressure has a strong decrease in the lower span region from hub to nearly 50% channel height, while the tangential flow angle reduces from approximately 40% channel height to the hub, linearly. The above phenomenon indicates that the leakage flow in the gap between stator blade and the hub does not turn sufficiently. This leads to a smaller incidence angle of the flow to the stator, thus, the lower span of the stator works in smaller attack angle, 0 to 13 degrees lower than the higher span. Surface flow patterns on the hub and both side of the blade surfaces are compared with the oil flow visualization in the experiment. The compressor stator is shown to operate under large separation and strong back flow conditions. The hub leakage flow is studied together with the endwall flow phenomenon for full gap configuration. Two separation lines are observed on the hub. One is lying in front of the blade leading edge plane indicating the separation due to the leading edge leakage flow which spills out of the passage before the flow enters the passage. The other is caused by the interaction between the strong hub leakage flow and the incoming flow. This separation line undergoes an abrupt turning just after the flow leaving the stator passage. The effect of the hub gap size on the leakage flow and the whole flow passage in the stator, including the strength and location of the vortex structure, the location and size of the separation bubble, as well as the back flow behavior, is analyzed. With the help of a novel vortex identification method, the flow field of this subsonic compressor stator and the inlet guide vanes can be visualized illustrating the behavior at the operation point when rotating instability occurs. The parameter η4 can help identifying the stretching and relaxation of the vortex. This approach reveals significant flow details [1]. Combined with DPH (Dynamic Pressure Head) contour and streamlines, the detailed vortices structures and topology in a subsonic compressor can also be further elucidated. The study illustrates different vortices structures in the compressor, as well as their behavior in different gap size configurations.

About the Numerical Simulation of Rotating Stall Mechanisms in Axial Compressors

2006 ◽  
Author(s):  
N. Gourdain ◽  
S. Burguburu ◽  
G. J. Michon ◽  
N. Ouayahya ◽  
F. Leboeuf ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Stall Inception ◽  
Axial Compressors ◽  
Time Frequency ◽  
Flow Phenomena ◽  
Temporal Modes ◽  
Inception Point

This paper deals with the first instability which occurs in compressors, close to the maximum of pressure rise, called rotating stall. A numerical simulation of these flow phenomena is performed and a comparison with experimental data is made. The configuration used for the simulation is an axial single-stage and low speed compressor (compressor CME2, LEMFI). The whole stage is modeled with a full 3D approach and tip clearance is taken into account. The numerical simulation shows that at least two different mechanisms are involved in the stall inception. The first one leads to a rotating stall with 10 cells and the second one leads to a configuration with only 3 cells. Unsteady signals from the computation are analyzed thanks to a time-frequency spectral analysis. An original model is proposed, in order to predict the spatial and the temporal modes which are the results of the interaction between stall cells and the compressor stage. A comparison with measurements shows that the computed stall inception point corresponds to the experimental limit of stability. The performance of the compressor during rotating stall is also well predicted by the simulation.

Passive Control of Rotating Stall in Vaneless Diffuser With Radial Grooves: Detailed Numerical Study

2009 ◽  
Author(s):  
Chuang Gao ◽  
Chuangang Gu ◽  
Tong Wang ◽  
Bo Yang
Keyword(s):  
Passive Control ◽  
Numerical Study ◽  
Design Procedure ◽  
Flow Distribution ◽  
Rotating Stall ◽  
Field Variation ◽  
Vaneless Diffuser ◽  
Flow Angle ◽  
Diffuser Flow ◽  
Computational Fluid Dynamics Cfd

According to experiments described in the literature, radial grooves in vaneless diffuser walls are simple and powerful devices for suppressing rotating stall. To understand the mechanism behind the grooves and find some guidelines for diffuser designers, a detailed numerical study based on Computational Fluid Dynamics (CFD) was carried out. Not only the flow field variation caused by the grooves but also a simple model graphing the underlying nature was established. Also, the classic boundary layer integral method widely used in practical design procedure was adopted to calculate the diffuser flow distribution to verify the model. The CFD analysis indicated that the effectiveness of the grooves increases the flow angle thus delaying the diffuser wall flow reversals. The recommended placement of the grooves was in the region with reversed flow. Such locally fixed groove could effectively delay the stall without too much pressure loss. Also, a combined variable, representing the overall geometry of grooves was established and verified. The detailed study given in this paper gives guidelines for using grooves as a stall delay method.

Performance Evaluation of Contra-Rotating Fans Operating Under Different Speed Combinations

2019 ◽  
Author(s):  
Navjot Joshi ◽  
Manas Madasseri Payyappalli ◽  
A. M. Pradeep
Keyword(s):  
Numerical Study ◽  
Pressure Ratio ◽  
Axial Direction ◽  
Flow Coefficient ◽  
Suction Surface ◽  
Flow Angle ◽  
Tip Leakage Vortex ◽  
Stall Inception ◽  
Tip Leakage ◽  
Flow Mechanisms

Abstract One of the advantages of a contra-rotating fan is its possibility to operate both the rotors at different speeds. Owing to this possibility, the performance of a contra-rotating fan can be controlled by operating it at different speed combinations. A numerical study of a low aspect ratio contra-rotating fan in low subsonic regime is carried out under various speed combinations of the rotors. Both steady state and Nonlinear Harmonic (NLH) simulations are performed to identify the important flow mechanisms in the contra-rotating fan. The results show that the diffusion factor of rotor-2 is significantly high towards the hub region which implies that large separations are likely to occur at the hub. The wake of rotor-1 is observed to impinge on the suction surface of rotor-2. Rotor-2 generates a strong suction effect at high rotational speeds and thereby delays the stall inception in the whole stage and shows an improvement in the stage pressure ratio. The upstream effect strongly influences the performance of rotor-1. When rotor-2 rotates at higher rotational speed, due to the suction effect, the flow angle at the exit of rotor-1 decreases which allows the fan to operate at lower flow coefficient. When the suction effect is very strong, it pulls the tip leakage vortex of rotor-1 towards the axial direction. Due to the suction effect, the location of the appearance of tip-leakage vortex moves further downstream. The tip-leakage vortex makes a higher angle with the blade chord at near stall conditions for speed combination Nd – 1.5Nd in contrast to a lower angle for speed combination Nd – 0.5Nd. In summary, the paper describes the performance changes, flow physics and the rotor-rotor interaction mechanisms for different speed combinations of a contra-rotating fan.

The Unsteady Pre-Stall Behavior of the Spike-Type Rotating Stall Within an Airfoil Vaned-Diffuser

2018 ◽  
Author(s):  
Jiayi Zhao ◽  
Guang Xi ◽  
Zhiheng Wang ◽  
Yang Zhao
Keyword(s):  
Pressure Rise ◽  
Leading Edge ◽  
Suction Side ◽  
Rotating Stall ◽  
Vaned Diffuser ◽  
Stall Inception ◽  
Impeller Outlet ◽  
Inception Point ◽  
Transient Measurement ◽  
Couple Effect

The spike-type rotating stall (RS) inception inside the vaned-diffuser, which seriously restricts the performance range and brings the problems of blade fatigue, still seems to be a ‘mystery’ since its randomness. The paper intends to explain the mechanisms of this stall inception. To quantitatively assess the critical unsteady behavior to the initiation of RS inception, the transient measurement characterizes the process falling into the RS through the parameter of ‘blade passing irregularity’. The underlying vortex disturbance, related to the growing of the flow complexity and the final spike-type precursor, is further revealed by the full-annulus simulation. The results show the propagation principle of the vortexes from the design to the stall inception point, reflected by the distribution of ‘blade passing irregularity’. The performance change of different sub-components due to the vortex behavior is presented. At the RS limit, the sudden ramp-up of the ‘blade passing irregularity’ near the leading edge (LE), accompanied with the drop of the static pressure rise in the sub-component between the semi-vaneless and throat, corresponds to the spike-type inception in the form of a clockwise vortex connecting the suction side of the diffuser vane and the pressure side of the adjacent vane. Besides, when approaching the spike-type inception point, the couple effect of the growing potential of the diffuser vane and the enhanced vortex disturbance at the impeller outlet degrades the diffuser inlet flow.

Delayed Detached Eddy Simulation of Rotating Stall for a Full Annulus Transonic Axial Compressor Stage

2016 ◽  
Author(s):  
Jiaye Gan ◽  
Hong-Sik Im ◽  
Ge-Cheng Zha
Keyword(s):  
Stokes Equations ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Stall Inception ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Stall Cells

This paper solves the filtered Navier-Stokes equations to simulate stall inception of NASA compressor transonic Stage 35 with delayed detached eddy simulation (DDES). A low diffusion E-CUSP Riemann solver with a 3rd order MUSCL scheme for the inviscid fluxes and a 2nd order central differencing for the viscous terms are employed. A full annulus of the rotor-stator stage is simulated with an interpolation sliding boundary condition (BC) to resolve the rotor-stator interaction. The tip clearance is fully gridded to accurately resolve tip vortices and their effect on stall inception. The DDES results show that the stall inception of Stage 35 is initialized by a weak harmonic disturbance with the length scales of the full annulus and grows rapidly with two emerging spike like disturbance. The two spike disturbances propagate in counter rotational direction with about 42% of rotor speed. The spike stall cells cover about 6 blades. They lead to two stall cells grown circumferentially and inwardly.

Influence of Rotor Stagger Angle on Rotating Stall Inception in an Axial-Flow Fan

2003 ◽  
Author(s):  
Takahiro Nishioka ◽  
Shuuji Kuroda ◽  
Tadashi Kozu
Keyword(s):  
Flow Rate ◽  
Axial Flow ◽  
Rotating Stall ◽  
Short Length ◽  
Rotor Blades ◽  
Length Scale ◽  
Axial Flow Fan ◽  
Stall Inception ◽  
Stall Cells ◽  
Stagger Angle

Inception patterns of rotating stall in a low-speed axial flow fan have been investigated experimentally. Experiments have been carried out at two different stagger angle settings for rotor blades. Pressure and velocity fluctuations were measured to elucidate the features of the stall cells and the stall inception patterns. At the design stagger angle setting for the rotor blades, a short length-scale stall cell known as a “spike” and multiple short length-scale stall cells appear when the slope of pressure-rise characteristic is almost zero. These stall cells grow into a long length-scale stall cell as flow rate decreases. The spike and the multiple short length-scale stall cells do not make the slope of the characteristic positive. However, the long length-scale stall cell induces a full-span stall, and makes the slope of the characteristic positive. At the small stagger angle, a long length-scale disturbance known as a “modal oscillation” is observed first, when the slope of the characteristic is positive. Then the spikes appear together with the modal oscillation as flow rate decreases. The long length-scale stall cell is generated by the spikes without change in the size of the modal oscillation. Suction-tip corner stall occurs in the stator passage near the peak of the characteristic at both the design and the small stagger angle settings. At the design stagger angle, however, the corner stall does not induce the modal oscillation and does not make the characteristic positive. In contrast, the corner stall at the small stagger angle induces the modal oscillation and makes the characteristic positive because it is larger than that at the design stagger angle. It is concluded from these results that the rotating stall inception patterns depend on the rotor stagger angle, which influences blade loading and rotor-stator matching.

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