Excitation Mechanism for Standing Stall of Centrifugal Compressors

1998 ◽  
Author(s):  
Y. N. Chen ◽  
D. Hagelstein ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Pressure Wave ◽  
Reverse Flow ◽  
Incidence Angle ◽  
Leading Edge ◽  
Forward Direction ◽  
Rotating Stall ◽  
Low Flow ◽  
Experimental Investigations ◽  
Centrifugal Compressors ◽  
Suction Surface

The standing stall of the centrifugal compressors appears with pulsating or switching pattern at operating points slightly away from the stall line. It is a weak form of the rotating stall and stands still in the absolute frame. The reverse flow of the compressed warm fluid travelling from the impeller’s outlet along the shroud surface towards the inlet is not yet powerful enough to generate rotating stall. The experimental investigations revealed that in the low-flow-rate off-design region, the inlet flow to the impeller has a large positive incidence angle. Nose bubbles are formed on the suction surface of the blade after the leading edge. Once the reverse flow as a pressure wave reaches the inlet of the blades, the nose bubble is stagnated to an enlarged size. The corresponding disturbance sends a rarefaction wave in the forward direction into the impeller. This wave of cool fluid meets the reverse pressure wave of the warm fluid at a circular front around the circumference of the impeller. Since this circular front has a weak baroclinicity, it cannot develop into Rossby waves which initiate the rotating stall. Instead it will either pulsate concentrically or switch linearly. We then experience a standing stall with the corresponding pattern.

Jet, Wake and Intrinsic Motion in Impellers of Centrifugal Compressors

1996 ◽  
Author(s):  
Y. N. Chen ◽  
U. Seidel ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Reverse Flow ◽  
Vortex Pair ◽  
Leading Edge ◽  
Rotating Stall ◽  
Secondary Flows ◽  
Low Flow ◽  
Experimental Result ◽  
Vaned Diffuser ◽  
Measured Velocity ◽  
Intrinsic Motion

It was shown in a previous paper of the authors (1991) that jet and wake in the flow of the impeller of the centrifugal compressor are developed from the Dean’s type vortex pair formed in the curvature of the blade channel. The jet rotating against the sense of the impeller is weakened, and the wake rotating in the sense of the impeller is enhanced during travelling with the flow toward the outlet. This property is attributed to the conservation of the potential vorticity of the vortex. The experimental result obtained by Krain (1984) has confirmed this theory. The secondary flows found by Farge and Johnson (1990) enable the determination of the vorticity of the wake at the outlet of the impeller. It amounts to 6.9 Ω and 5.8 Ω for the radial-blading and the 60°-backswept blading impeller, respectively. The intensity of the vortex jet is weakened to undetectable value for both the impellers. The patterns of these secondary flow fields are also quite different between these two kinds of impellers. Whilst that of the former is controlled by the intrinsic motion, that of the latter is governed by the relative velocity along the blades. Furthermore, the experimental result obtained by the injection of colored dye at the impeller outlet and the measured velocity field around the impeller reveal an intense reverse flow in the radial blading impeller, travelling from the outlet toward the inlet, along the shroud. It can be shown that this reverse flow is caused by the intrinsic motion occuring in this impeller and impinging on the leading edge of the diffuser vane. As the rotating stall is introduced by the reverse flow, the low-solidity vaned diffuser, and still better the vaneless diffuser can therefore shift the stall line to a very low flow rate.

A Meanline Model for Impeller Flow Recirculation

2008 ◽  
Author(s):  
Xuwen Qiu ◽  
David Japikse ◽  
Mark Anderson
Keyword(s):  
Flow Rate ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Low Flow ◽  
Suction Surface ◽  
Blade Loading ◽  
Flow Recirculation ◽  
Impeller Outlet ◽  
Active Flow ◽  
Low Flow Rate

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.

Stall Behavior in an Ultra-High-Pressure-Ratio Centrifugal Compressor: Backward-Traveling Rotating Stall

2021 ◽  
pp. 1-51
Author(s):  
Yingjie Zhang ◽  
Xingen Lu ◽  
Yanfeng Zhang ◽  
Ziqing Zhang ◽  
Xu Dong ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Shock Intensity ◽  
Incidence Angle ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Rotating Stall ◽  
High Pressure Ratio ◽  
Ultra High Pressure

Abstract This paper describes the stall mechanism in an ultra-high-pressure-ratio centrifugal compressor. A model comprising all impeller and diffuser blade passages is used to conduct unsteady simulations that trace the onset of instability in the compressor. Backward-traveling rotating stall waves appear at the inlet of the radial diffuser when the compressor is throttled. Six stall cells propagate circumferentially at approximately 0.7% of the impeller rotation speed. The detached shock of the radial diffuser leading edge and the number of stall cells determine the direction of stall propagation, which is opposite to the impeller rotation direction. Dynamic mode decomposition is applied to instantaneous flow fields to extract the flow structure related to the stall mode. This shows that intensive pressure fluctuations concentrate in the diffuser throat as a result of changes in the detached shock intensity. The diffuser passage stall and stall recovery are accompanied by changes in incidence angle and shock wave intensity. When the diffuser passage stalls, the shock-induced boundary-layer separation region near the diffuser vane suction surface gradually expands, increasing the incidence angle and decreasing the shock intensity. The shock is pushed from the diffuser throat toward the diffuser leading edge. When the diffuser passage recovers from stall, the shock wave gradually returns to the diffuser throat, with the incidence angle decreasing and the shock intensity increasing. Once the shock intensity reaches its maximum, the diffuser passage suffers severe shock-induced boundary-layer separation and stalls again.

Numerical Investigation of the Effect of Inlet Flow Angle on Film Cooling Performance for the Blade Tip With Suction Surface Squealer Rim

2019 ◽  
Author(s):  
Zhiqiang Yu ◽  
Jianjun Liu ◽  
Chen Li ◽  
Baitao An
Keyword(s):  
Mass Flow ◽  
Film Cooling ◽  
Incidence Angle ◽  
Leading Edge ◽  
Flow Ratio ◽  
Suction Surface ◽  
Cooling Performance ◽  
Tip Leakage ◽  
Pressure Surface ◽  
Mass Flow Ratio

Abstract Numerical investigations have been performed to study the effect of incidence angle on the aerodynamic and film cooling performance for the suction surface squealer tip with different film-hole arrangements at τ = 1.5% and BR = 1.0. Meanwhile, the full squealer tip as baseline is also investigated. Three incidence angles at design condition (0 deg) and off-design conditions (± 7 deg) are investigated. The suction surface, pressure surface, and the camber line have seven holes each, with an extra hole right at the leading edge. The Mach number at the cascade inlet and outlet are 0.24 and 0.52, respectively. The results show that the incidence angle has a significant effect on the tip leakage flow characteristics and coolant flow direction. The film cooling effectiveness distribution is altered, especially for the film holes near the leading edge. When the incidence angle changes from +7 deg to 0 and −7 deg, the ‘re-attachment line’ moves downstream and the total tip leakage mass flow ratio decreases, but the suction surface tip leakage mass flow ratio near leading edge increases. In general, the total tip leakage mass flow ratio for suction surface squealer tip is 1% greater than that for full squealer tip at the same incidence angle. The total pressure loss coefficient of suction surface squealer tip is larger than that for full squealer tip. The full squealer tip with film holes near suction surface and the suction surface squealer tip with film hole along camber line show high film cooling performance, and the area averaged film cooling effectiveness at positive incidence angle +7 deg is higher than that at 0 and −7 deg. The coolant discharged from film holes near pressure surface only cools narrow region near pressure surface.

Numerical investigation on vibration and pressure fluctuation characteristics in a centrifugal pump under low flow rate

2020 ◽  
pp. 095440622096972
Author(s):  
Like Wang ◽  
Jinling Lu ◽  
Weili Liao ◽  
Pengcheng Guo ◽  
Guojun Zhu ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Pressure Fluctuation ◽  
Reverse Flow ◽  
Leading Edge ◽  
Low Flow ◽  
Main Shaft ◽  
Unstable Flow ◽  
Tip Leakage ◽  
Flow Vortex ◽  
Tip Separation Vortex

Vibration characteristic is an important factor in evaluating operation stability of centrifugal pump. The vibration of main shaft was measured using a laser vibrometer, internal flow field was simulated via the shear stress transport turbulence model, and distribution law of vibration and pressure fluctuation in the impeller were analysed to explore the induction factor of vibration and the inherent relationship with pressure fluctuation in a semi-open centrifugal pump under low flow rate condition. Results of the numerical simulation are consistent with the experimental data. In addition to rotation frequency caused by impeller rotation, vibration frequency also includes characteristic frequency with high amplitude induced by unstable flow. The complex vortex in the impeller is composed of tip leakage vortex (TLV), reverse flow vortex, passage vortex and tip separation vortex. The primary tip leakage vortex (PTLV) formed by the streamline spills from 0 to 0.2λ where λ is the dimensionless distance from leading edge to trailing edge collides with tip leakage flow, the leading edge overflow and reverse flow vortex at the frequency of 1.6 fn ( fn is the rotating frequency) and 2.2 fn appear, respectively. The tip separation vortex formed in the tip clearance induced a frequency of 1.2 fn. The frequency of unstable flow phenomenon was consistent with the vibration frequency of main shaft, which induced the vibration of centrifugal pump.

An Investigation of Axial Pump Backflow and a Method for its Control

1988 ◽  
Author(s):  
M. Abramian ◽  
J. H. G. Howard ◽  
P. Hermann
Keyword(s):  
Flow Field ◽  
Laser Doppler Velocimetry ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Axial Flow ◽  
Leading Edge ◽  
Low Flow ◽  
Flow Conditions ◽  
Axial Pump ◽  
Swirl Velocity

The flow field within an axial flow inducer pump near the blade leading edge was explored by laser-Doppler velocimetry to extend the previous studies of the recirculation zone which is observed at low flow rates. Although a considerable region of upstream reverse flow and swirl was observed, the recirculation zone within the impeller was of limited axial extent and was confined to the pressure side of the passage. In an attempt to reduce the flow reversal, a series of perforated disks were placed in front of the inducer. The optimum disk geometry produced minor changes in the pump performance. LDV measurements of the flow field ahead and behind the disk showed considerable reduction of the swirl velocity under reverse flow conditions, with the observed upstream swirl opposite to the inducer rotation.

scholarly journals ЗБІЛЬШЕННЯ ДІАПАЗОНУ СТІЙКОЇ РОБОТИ СТУПЕНЯ ВІДЦЕНТРОВОГО КОМПРЕСОРА З БЕЗЛОПАТКОВИМ ДИФУЗОРОМ

2019 ◽  
pp. 4-9
Author(s):  
Микола Васильович Калінкевич ◽  
Микола Іванович Радченко
Keyword(s):  
Mathematical Model ◽  
Gas Injection ◽  
Rotating Stall ◽  
Low Flow ◽  
Stable Operation ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Flow Separation Control ◽  
Flow Part ◽  
Vaneless Diffusers

Centrifugal compressors often operate at different capacities, so it is important to ensure their stable operation over a wide flow range. Stages with vaneless diffusers have several advantages compared to stages with other types of diffusers: they are more technologically advanced to manufacture, and more uniform pressure distribution behind the impeller improves the dynamics of the rotor. At low flows, due to the occurrence of a rotating stall and surge, the efficiency of stages with vaneless diffusers rapidly decreases. The occurrence of unstable operating modes of centrifugal compressor stages at low flow rates is associated with the appearance of developed backflows in the flow part. To expand the range of stable operation of the stages, it is necessary to use methods of flow separation control. Separation of the flow can be controlled either by special profiling the flow part channels or by actively influencing the flow, for example, by injecting gas. To solve this problem, a mathematical model of the gas flow in a vaneless diffuser with gas injection is developed. The characteristics and parameters of the flow in the vaneless diffusers with various meridional profiles with and without injecting gas were calculated. A comparison of the calculated and experimental characteristics of the vaneless diffusers and flow parameters in diffusers with different geometries and with different injection modes confirms the adequacy of the mathematical model. Investigations have confirmed the possibility of improving the characteristics of the stages of centrifugal compressors through the use of vaneless diffusers and diffusers with gas injection. Gas injection diffusers extend the stable operation range of the stages. The use of gas injection in a vaneless diffuser allows reducing the power consumption during antisurge control in comparison with the widespread bypass suction system at the entrance to the impeller

Three-Dimensional Turbulent Flow in the Tip Region of an Axial Compressor Rotor Passage at a Near Stall Condition

2001 ◽  
Author(s):  
Hongwei Ma ◽  
Haokang Jiang
Keyword(s):  
Turbulent Flow ◽  
Large Scale ◽  
Three Dimensional ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Compressor Rotor

This paper presents an experimental study of the three-dimensional turbulent flow field in the tip region of an axial flow compressor rotor passage at a near stall condition. The investigation was conducted in a low-speed large-scale compressor using a 3-component Laser Doppler Velocimetry and a high frequency pressure transducer. The measurement results indicate that a tip leakage vortex is produced very close to the leading edge, and becomes the strongest at about 10% axial chord from the leading edge. Breakdown of the vortex periodically occurs at about 1/3 chord, causing very strong turbulence in the radial direction. Flow separation happens on the tip suction surface at about half chord, prompting the corner vortex migrating toward the pressure side. Tangential migration of the low-energy fluids results in substantial flow blockage and turbulence in the rear of a rotor passage. Unsteady interactions among the tip leakage vortex, the separated vortex and the corner flow should contribute to the inception of the rotating stall in a compressor.

LDV Measurements of a Mixed-Flow Impeller at Design and Near Stall

1991 ◽  
Author(s):  
John Robert Fagan ◽  
Sanford Fleeter
Keyword(s):  
Reverse Flow ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Surface Characteristic ◽  
Rotating Stall ◽  
Mean Flow ◽  
Suction Surface ◽  
Mixed Flow ◽  
Velocity Deficit ◽  
Compressor Impeller

A series of experiments are performed to investigate and quantify the design and off-design three-dimensional mean flow in a centrifugal compressor impeller. The experiments entail the acquisition and analysis of LDV data in the impeller passages of a low speed research mixed-flow compressor operating at its design point and at a point near the inception of rotating stall. The LDV data at both operating points show regions near the impeller exit with a significant velocity deficit on the shroud surface characteristic of the traditional jet-wake structure observed in many centrifugal compressors. At design, the maximum velocity deficit occurs at a location 70% of the passage width from the pressure to the suction surface. At the incipient stall point, the maximum velocity deficit occurs in the shroud suction surface corner, with the data indicating reverse flow.

Unsteady Behavior of Diffuser Stall in a Centrifugal Compressor With Vaned Diffuser

2017 ◽  
Author(s):  
Nobumichi Fujisawa ◽  
Daiki Ema ◽  
Yutaka Ohta
Keyword(s):  
Centrifugal Compressor ◽  
Vortical Structure ◽  
Leading Edge ◽  
Rotating Stall ◽  
Longitudinal Vortex ◽  
Suction Surface ◽  
Vaned Diffuser ◽  
Edge Vortex ◽  
Flow Blockage ◽  
Unsteady Behavior

In this study, the unsteady behavior of a diffuser rotating stall in a centrifugal compressor with a vaned diffuser was investigated through experiments and numerical analyses. From the casing static pressure measurements, it was determined that the diffuser stall propagated at 25% of impeller rotational speed in the vaneless space. The numerical results revealed the presence of a typical vortical structure on the diffuser’s leading edge. Under partial flow condition, a tornado-type vortex was generated on the diffuser’s leading edge. Furthermore, a longitudinal vortex at the shroud/suction surface corner (i.e., leading edge vortex (LEV)) was induced by the rolling-up flow on the diffuser suction surface. As the velocity was decreased, the development of the tornado-type vortex and LEV forms a substantial flow blockage within the diffuser passages. Furthermore, the diffuser stall cell was caused by the systematic vortical structure which consisted of the tornado-type vortex, LEV, and vortex in the throat area of diffuser passages. In addition to this, the developed LEV interacted with the next diffuser leading edge and formed the throat area blockage with the passage of time. Then, the tornado-type vortex and LEV developed by the throat area blockage and diffuser stall cell, which was caused by the systematic vortical structure, propagated to the succeeding diffuser vane. Therefore, the diffuser stall in the centrifugal compressor was caused by the evolution of the tornado-type vortex and LEV.

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