Effects of Fan Speed on Rotating Stall Inception and Recovery

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Minsuk Choi ◽  
Mehdi Vahdati ◽  
Mehmet Imregun
Keyword(s):  
Aspect Ratio ◽  
Flow Rate ◽  
Reverse Flow ◽  
Recovery Process ◽  
Rotating Stall ◽  
Navier Stokes ◽  
Implicit Time ◽  
Stall Inception ◽  
Stall Cells ◽  
Fan Speed

An implicit, time-accurate 3D compressible Reynolds-averaged Navier-Stokes (RANS) solver is used to simulate rotating stall inception and recovery, the so-called rotating stall hysteresis, in the case of a modern fan geometry. In the first instance, rotating stall was simulated for 70%, 80%, and 90% fan speeds using a whole-annulus fan model with a variable-area nozzle downstream. As the fan speed is increased, the stall cells also increase in size but their number decreases. One large stall cell is predicted to rotate along the annulus at 80% and 90% speeds, while there are three smaller cells at 70% speed. In all cases, the reverse flow is confined to the near-tip region and the rotating stall does not develop into a full-span stall because of the fan blade’s high-aspect ratio. To simulate stall recovery, the nozzle area was increased gradually at 70% and 90% speeds and the flow was seen to recover from rotating stall to reach an unstalled operating condition. The recovery process was found to be affected by the fan speed. At 70% speed, the large disturbances decay first to form almost symmetric stall cells. Thereafter, the stall cells shrink into smaller ones as the mass flow rate increases further. At 90% fan speed, a single stall cell rotates along the annulus, the disappearance of which results in recovery. An attempt has been made to explain the dependence of the stall inception and recovery patterns on the fan speed.

Effects of Fan Speed on Rotating Stall Inception and Recovery

2010 ◽  
Author(s):  
Minsuk Choi ◽  
Mehdi Vahdati ◽  
Mehmet Imregun
Keyword(s):  
Aspect Ratio ◽  
Flow Rate ◽  
High Aspect Ratio ◽  
Reverse Flow ◽  
Recovery Process ◽  
Rotating Stall ◽  
Implicit Time ◽  
Stall Inception ◽  
Stall Cells ◽  
Fan Speed

An implicit, time-accurate 3D compressible RANS solver is used to simulate rotating stall inception and recovery, the so-called rotating stall hysteresis, in a modern fan geometry. In the first instance, rotating stall was simulated for 70%, 80% and 90% fan speeds using a whole-annulus fan model with a variable-area nozzle downstream. As the fan speed is increased, the stall cell also increases in size but the number of stall cells decreases. One large stall cell is predicted to rotate along the annulus at 80% and 90% speeds, while there are three smaller cells at 70% speed. In all cases, the reverse flow is confined to the near-tip region and the rotating stall does not develop into a full-span stall because of the fan blade’s high-aspect ratio. To simulate stall recovery, the nozzle area was increased gradually at 70% and 90% speeds and the flow was seen to recover from rotating stall to reach an unstalled operating condition. The recovery process was found to be affected by the fan speed. At 70% speed, the large disturbances decay first to form almost symmetric stall cells. Thereafter, the stall cells shrink into smaller ones as the mass flow rate decreases further. At 90% fan speed, a single stall cell rotates along the annulus, the disappearance of which results in recovery. An attempt has been made to explain the dependence of the stall inception and recovery patterns on the fan speed.

Transient Process of Rotating Stall in Radial Vaneless Diffusers

1994 ◽  
Author(s):  
H. Watanabe ◽  
S. Konomi ◽  
I. Ariga
Keyword(s):  
Flow Rate ◽  
Reverse Flow ◽  
Flow Region ◽  
Rotating Stall ◽  
Lower Side ◽  
Hot Wire ◽  
Vaneless Diffuser ◽  
Reversed Flow ◽  
Stall Inception ◽  
Wire Probe

This paper describes the process of rotating stall inception in a radial vaneless diffuser. Unsteady flow and rotating stall were investigated by measuring the wall static pressures and velocity distributions using X hot-wire probe. From the measurements of the velocity fluctuation, it is confirmed that the periodical disturbance in the reverse flow region as the prestall symptom occurs prior to the onset of stall and then the growth of that periodical disturbance leads to the rotating stall with fully developed non axisymmetric reversed flow. On the process of the rotating stall inception, reverse flow regions in the diffuser grow from the diffuser exit toward the inlet along the shroud and hub wall, and the rotating stall occurs when the reverse flow region on the shroud wall reaches to the impeller exit. In this paper, the effects of the diffuser exit blockage on the process of stall inception were also described. The flow rate of stall onset is moved to the lower side by the restriction of the diffuser exit width, however, this restriction does not affect the distribution of the reverse flow regions. That restriction suppresses the prestall disturbance in the reverse flow regions and then stabilize the flow in the diffuser.

Validation of Numerical Simulation for Rotating Stall in a Transonic Fan

2011 ◽  
Author(s):  
Minsuk Choi ◽  
Nigel H. S. Smith ◽  
Mehdi Vahdati
Keyword(s):  
Mass Flow ◽  
Transient Flow ◽  
Rotating Stall ◽  
Implicit Time ◽  
Stall Inception ◽  
Rotating Speed ◽  
Design Speed ◽  
Fan Speed ◽  
Loading Parameter ◽  
Transonic Fan

This paper addresses a comparison of numerical stall simulations with experimental data at 60% (subsonic) and 95% (supersonic) of the design speed in a modern transonic fan rig. The unsteady static pressures were obtained with high frequency Kulite transducers mounted on the casing upstream and downstream of the fan. The casing pressure variation was clearly visible in the measurements when a stall cell passed below the transducers. Numerical stall simulations were conducted using an implicit, time-accurate 3D compressible RANS solver. The comparisons between the experiment and simulation mainly cover performance curves and time-domain pressure traces of Kulites during rotating stall. At two different fan speeds, the stall characteristics such as the number and rotating speed of the stall cells were well-matched to the experimental values. The mass flow rate and the loading parameter under the fully-developed rotating stall also showed good agreement with the experiment. In both numerical and experimental results, a large stall cell was eventually formed after stall inception regardless of the fan speed. Based on the validation, the detailed flow has been evaluated to understand rotating stall in a transonic fan. In addition, it was found that the mass flow measurement using casing static pressure might be wrong during transient flow if the Kulites were mounted too close to the fan blade.

Validation of Numerical Simulation for Rotating Stall in a Transonic Fan

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Minsuk Choi ◽  
Nigel H. S. Smith ◽  
Mehdi Vahdati
Keyword(s):  
Mass Flow ◽  
Transient Flow ◽  
Rotating Stall ◽  
Navier Stokes ◽  
Implicit Time ◽  
Stall Inception ◽  
Rotating Speed ◽  
Design Speed ◽  
Loading Parameter ◽  
Transonic Fan

This paper addresses a comparison of numerical stall simulations with experimental data at 60% (subsonic) and 95% (supersonic) of the design speed in a modern transonic fan rig. The unsteady static pressures were obtained with high frequency Kulite transducers mounted on the casing upstream and downstream of the fan. The casing pressure variation was clearly visible in the measurements when a stall cell passed below the transducers. Numerical stall simulations were conducted using an implicit, time-accurate, 3D compressible Reynolds-averaged Navier-Stokes (RANS) solver. The comparisons between the experiment and simulation mainly cover performance curves and time-domain pressure traces of Kulites during rotating stall. At two different fan speeds, the stall characteristics such as the number and rotating speed of the stall cells were well-matched to the experimental values. The mass flow rate and the loading parameter under the fully-developed rotating stall also showed good agreement with the experiment. In both the numerical and experimental results, a large stall cell was eventually formed after stall inception regardless of the fan speed. Based on the validation, the detailed flow has been evaluated to understand rotating stall in a transonic fan. In addition, it was found that the mass flow measurement using casing static pressure might be wrong during transient flow if the Kulites were mounted too close to the fan blade.

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.

Stall Warning Using the Rotor Tip Pressure in a Transonic Axial Compressor With Circumferential Grooves

2018 ◽  
Author(s):  
Byeung Jun Lim ◽  
Tae Choon Park ◽  
Young Seok Kang
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Single Stage ◽  
Stall Inception ◽  
Casing Treatment ◽  
Stall Warning ◽  
Transonic Axial Compressor

In this study, characteristics of stall inception in a single-stage transonic axial compressor with circumferential grooves casing treatment were investigated experimentally. Additionally, the characteristic of increasing irregularity in the pressure inside circumferential grooves as the compressor approaches the stall limit was applied to the stall warning method. Spike-type rotating stall was observed in the single-stage transonic axial compressor with smooth casing. When circumferential grooves were applied, the stall inception was suppressed and the operating point of the compressor moved to lower flow rate than the stall limit. A spike-like disturbance was developed into a rotating stall cell and then the Helmholtz perturbation was overlapped on it at N = 80%. At N = 70 %, the Helmholtz perturbation was observed first and the amplitude of the wave gradually increased as mass flow rate decreased. At N = 60%, spike type stall inceptions were observed intermittently and then developed into continuous rotating stall at lower mass flow rate. Pressure measured at the bottom of circumferential grooves showed that the level of irregularity of pressure increased as flow rate decreased. Based on the characteristic of increasing irregularity of the pressure signals inside the circumferential grooves as stall approaches, an autocorrelation technique was applied to the stall warning. This technique could be used to provide warning against stall and estimate real-time stall margins in compressors with casing treatments.

Three-Dimensional Computational Fluid Dynamics Prediction of Turbocharger Centrifugal Compression System Instabilities

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Rick Dehner ◽  
Ahmet Selamet
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Rate ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Rotating Stall ◽  
Flow Reversal ◽  
Constant Speed ◽  
Local Flow ◽  
Stall Cells

The present work combines experimental measurements and unsteady, three-dimensional computational fluid dynamics predictions to gain further insight into the complex flow-field within an automotive turbocharger centrifugal compressor. Flow separation from the suction surface of the main impeller blades first occurs in the mid-flow range, resulting in local flow reversal near the periphery, with the severity increasing with decreasing flow rate. This flow reversal improves leading-edge incidence over the remainder of the annulus, due to (a) reduction of cross-sectional area of forward flow, which increases the axial velocity, and (b) prewhirl in the direction of impeller rotation, as a portion of the tangential velocity of the reversed flow is maintained when it mixes with the core flow and transitions to the forward direction. As the compressor operating point enters the region where the slope of the constant speed compressor characteristic (pressure ratio versus mass flow rate) becomes positive, rotating stall cells appear near the shroud side diffuser wall. The angular propagation speed of the diffuser rotating stall cells is approximately 20% of the shaft speed, generating pressure fluctuations near 20% and 50% of the shaft frequency, which were also experimentally observed. For the present compressor and rotational speed, flow losses associated with diffuser rotating stall are likely the key contributor to increasing the slope of the constant speed compressor performance curve to a positive value, promoting the conditions required for surge instabilities. The present mild surge predictions agree well with the measurements, reproducing the amplitude and period of compressor outlet pressure fluctuations.

An Unsteady Numerical Investigation on the Hysteresis Stall Loop of a Counter-Rotating Compressor

2011 ◽  
Author(s):  
Zhuoqi Wang ◽  
Wei Yuan ◽  
Qiushi Li ◽  
Yajun Lu
Keyword(s):  
Numerical Simulation ◽  
Recovery Process ◽  
Characteristic Line ◽  
Rotor Speed ◽  
Stall Inception ◽  
Rotating Speed ◽  
Flow Phenomena ◽  
Stall Cells ◽  
Unsteady Numerical Simulation ◽  
Good Agreement

For investigating the flow phenomena in the stall process, a full annular unsteady numerical simulation has been carried out on a low speed counter-rotating compressor. The numerical results are in good agreement with experimental results. According to the CFD results, the stall inception was found in the tip region of the front rotor. The rotating speed of stall cells in the front rotor are about 41% of the rotor speed and the direction is the same with the rotor rotating direction. The stall cells occupies about 20% of the blade span away from the casing wall when the compressor is in deep stall. The flow phenomena is well captured which explained why the compressor characteristic line appears as a hysteresis loop in the stall inception-recovery process.

Computations of bladerow stall inception in transonic flows

1999 ◽  
Vol 103 (1025) ◽  
pp. 317-324 ◽  
Author(s):  
L. He ◽  
J. O. Ismael
Keyword(s):  
Three Dimensional ◽  
Rotating Stall ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Stall Inception ◽  
Tip Leakage ◽  
Blade Row ◽  
Inflow Condition ◽  
Shock Oscillation ◽  
Transonic Fan

Abstract A three-dimensional unsteady Navier-Stokes solver has been used to simulate stall inception in a single row ten passage segment of a transonic fan, the NASA rotor-67. At subsonic flow conditions, the 3D results illustrate a rotating stall inception with short scale part-span cells rotating at around 80% rotor speed, similar to that observed in some low speed experiments. However, at a supersonic relative inflow condition, the results show that an isolated blade row tends to stall in a one-dimensional breakdown pattern without first experiencing rotating stall. At near-stall conditions, significant self-excited unsteadiness is generated by the interaction between the tip-leakage vortex and the passage shock wave. Further computations for two-dimensional configurations indicate that it is possible to have a rotating pattern of instability in transonic blade rows associated with circumferential synchronised shock oscillation.

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