The Application of PIV in the Study of Impeller-Diffuser Interaction in Centrifugal Fan: Part I — Impeller-Vaneless Diffuser Interaction

2001 ◽  
Author(s):  
Tarek Mekhail ◽  
Zhang Li ◽  
Du Zhaohui ◽  
Willem Jansen ◽  
Chen Hanping
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
High Speed ◽  
Maximum Flow ◽  
Image Processing Technique ◽  
High Speed Photography ◽  
Centrifugal Fan ◽  
Performance Measurements ◽  
Vaneless Diffuser ◽  
Unstable Flow

Abstract The PIV (Particle Image Velocimetry) technology is a brand-new technique of measuring velocity. It started in the 1980’s with the development of high-speed photography and the image processing technique of computers. This article deals with PIV applied to the study of unsteady impeller-vaneless diffuser interaction in centrifugal fen. Experiments were carried out at The Turbomachinery Laboratory of Shanghai Jiaotong University. The test rig consists of a centrifugal, shrouded impeller, diffuser and volute casing all made of plexiglass. A series of performance measurements were carried out at different speeds and different vaneless diffuser widths. PIV measurements were applied to measure the unsteady flow at the exit part of the impeller and the inlet part of the diffuser for the case of the same width vaneless diffuser. The absolute flow field is measured at medium flow rate and at maximum flow rate. It is informative to capture the whole flow field at the same instant of time, and it might be more revealing to observe the unstable flow in real time.

Investigation of the instability mechanisms in a turbocharger centrifugal compressor with a vaneless diffuser by means of unsteady simulations

2016 ◽  
Vol 231 (11) ◽  
pp. 1558-1567 ◽  
Author(s):  
Xinqian Zheng ◽  
Anxiong Liu ◽  
Zhenzhong Sun
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
High Speed ◽  
Simulation Method ◽  
Great Accuracy ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Low Velocity

The stable-flow range of a compressor is predominantly limited by surge and stall. In this paper, an unsteady simulation method was employed to investigate the instability mechanisms of a high-speed turbocharger centrifugal compressor with a vaneless diffuser. In comparison with the variation in the pressure obtained by dynamic experiments on the same compressor, unsteady simulations show a great accuracy in representing the stall behaviour. The predicted frequency of the rotating stall is 22.5% of the rotor frequency, which agrees with to the value for the high-frequency short-term rotating stall obtained experimentally. By investigating the instability of the flow field, it is found that the unstable flow of the turbocharger compressor at high rotational speeds is caused by the tip clearance leakage flow and the ‘backflow vortices’ originating from the interaction of the incoming flow and the backflow in the tip region of the passages. The asymmetric volute helps to induce the occurrence of stall in certain impeller passages because it generates an asymmetric flow field. The high-pressure low-velocity area from the 180° circumferential position to the 270° circumferential position is dominant and strengthens the backflow at the trailing edge of the impeller, finally triggering the stall.

Experimental Characterization of a Modified Airlift Pump

2014 ◽  
Author(s):  
Afshin Goharzadeh ◽  
Keegan Fernandes
Keyword(s):  
Water Flow ◽  
Flow Rate ◽  
High Speed ◽  
Water Flow Rate ◽  
High Speed Photography ◽  
Two Phase ◽  
Inner Diameter ◽  
Airlift Pump ◽  
Flow Map ◽  
Churn Flow

This paper presents an experimental investigation on a modified airlift pump. Experiments were undertaken as a function of air-water flow rate for two submergence ratios (ε=0.58 and 0.74), and two different riser geometries (i) straight pipe with a constant inner diameter of 19 mm and (ii) enlarged pipe with a sudden expanded diameter of 19 to 32 mm. These transparent vertical pipes, of 1 m length, were submerged in a transparent rectangular tank (0.45×0.45×1.1 m3). The compressed air was injected into the vertical pipe to lift the water from the reservoir. The flow map regime is established for both configurations and compared with previous studies. The two phase air-water flow structure at the expansion region is experimentally characterized. Pipeline geometry is found to have a significant influence on the output water flow rate. Using high speed photography and electrical conductivity probes, new flow regimes, such as “slug to churn” and “annular to churn” flow, are observed and their influence on the output water flow rate and efficiency are discussed. These experimental results provide fundamental insights into the physics of modified airlift pump.

Effects of Non-Axisymmetric Volute on Rotating Stall in the Vaneless Diffuser of a Centrifugal Compressor

2020 ◽  
Author(s):  
Zitian Niu ◽  
Zhenzhong Sun ◽  
Baotong Wang ◽  
Xinqian Zheng
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Stability Boundary ◽  
Rotating Stall ◽  
Evolution Process ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Centrifugal Compressors ◽  
Specific Location

Abstract Rotating stall is an important unstable flow phenomenon that leads to performance degradation and limits the stability boundary in centrifugal compressors. The volute is one of the sources to induce the non-axisymmetric flow in a centrifugal compressor, which has an important effect on the performance of compressors. However, the influence of volute on rotating stall is not clear. Therefore, the effects of volute on rotating stall by experimental and numerical simulation have been explored in this paper. It’s shown that one rotating stall cell generates in a specific location and disappears in another specific location of the vaneless diffuser as a result of the distorted flow field caused by the volute. Also, the cells cannot stably rotate in a whole circle. The frequency related to rotating stall captured in the experiment is 43.9% of the impeller passing frequency (IPF), while it is 44.7% of IPF captured by three-dimensional unsteady numerical simulation, which proves the accuracy of the numerical method in this study. The numerical simulation further reveals that the stall cell initialized in a specific location can be split into several cells during the evolution process. The reason for this is that the blockage in the vaneless diffuser induced by rotating stall is weakened by the mainstream from the impeller exit to make one initialized cell disperse into several ones. The volute has an important influence on the generation and evolution process of the rotating stall cells of compressors. By optimizing volute geometry to reduce the distortion of the flow field, it is expected that rotating stall can be weakened or suppressed, which is helpful to widen the operating range of centrifugal compressors.

Velocity characteristics in a multiphase pump under different tip clearances

2020 ◽  
pp. 095765092094653
Author(s):  
Guangtai Shi ◽  
Zongku Liu ◽  
Yexiang Xiao ◽  
Helin Li ◽  
Xiaobing Liu
Keyword(s):  
Velocity Distribution ◽  
Flow Rate ◽  
High Speed ◽  
Stokes Equations ◽  
Design Flow ◽  
Tip Clearance ◽  
High Speed Photography ◽  
Hydraulic Loss ◽  
Impeller Blade ◽  
Multiphase Pump

To investigate the effect of tip clearance on the velocity distribution in a multiphase pump, the internal flow and velocity distribution characteristics in pump under different tip clearances are studied using experimental and numerical methods. Simulations based on the Reynolds-Averaged Navier-Stokes equations (RANS) and the standard k-ε turbulence model are carried out using ANSYS CFX. Under conditions of inlet gas void fraction (IGVF) is 5% at the flow rate of 0.6Q, 0.7Q and 0.8Q (Q is the design flow rate), the accuracy of the numerical method is verified by comparing with the experimental data using high-speed photography. Results show that the leakage flow interacts with the main flow and evolves into the tip leakage vortex (TLV). Due to the TLV, the pressure, velocity, turbulent kinetic energy (TKE), vorticity and streamlines on the S2 stream surface in the impeller and diffuser are changed greatly under different tip clearances. The velocities at the impeller outlet and diffuser inlet along the radial direction are also changed. The axial velocity distribution is similar to the meridional velocity distribution at the impeller blade outlet. While the relative velocity and absolute velocity distribution show the opposite trends. In addition, the vorticity is larger near the tip separated vortex and the hydraulic loss in pump is also increased due to the TLV.

scholarly journals Research on the Deposition Characteristics of Integrated Prefabricated Pumping Station

Symmetry ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 760
Author(s):  
Kai Wang ◽  
Jianbin Hu ◽  
Houlin Liu ◽  
Zixu Zhang ◽  
Li Zou ◽  
...  
Keyword(s):  
Deposition Rate ◽  
Flow Rate ◽  
High Speed ◽  
Particle Diameter ◽  
High Speed Photography ◽  
Pump Operation ◽  
Pumping Station ◽  
Movement Trajectories ◽  
Pump Station ◽  
The Right

Based on the discrete phase model (DPM) solid–liquid two-phase flow model and MATLAB image processing technology, an integrated prefabricated pumping station was taken as the research object to study deposition characteristics under different flow rates, different particle diameters, and different liquid levels. Considering the incomplete symmetry of the internal flow of the prefabricated pumping station, deposition characteristics of the prefabricated pumping station under single/double pumps were also analyzed. Double pumps were symmetrically distributed in the integrated prefabricated pump station, and the movement trajectories of particles at the bottom of the pump pit under the closing inlet valve were measured through the use of a high-speed photography experiment. Results showed that with the increase of the flow rate, the deposition rate of the separated prefabricated pumping station decreased. With an increase of the particle diameter, the movement of particles was farther away from the vertical barrier weir. In the range of particle diameter of 6 to 10 mm, the deposition rate decreased with the increase of the particle diameter. With the increase of the liquid level, the deposition rate decreased, first, and then increased again. In the case of the single pump operation, the deposition rate of the right pump operation was smaller than that of the left pump operation. The variation of the deposition rate when the right pump operated was basically the same as that when the dual pumps operated. The movement path of particle N1 was longer. With the decrease of the flow rate and the increase of the particle diameter, the following feature of the particle decreased, and it was easier to impact the walls and edges, which caused long-term deposition. The research results could provide some suggestions for the design of anti-deposition performance of prefabricated pumping station.

Experimental and Numerical Investigation on Pressure Fluctuation of the Impeller in an Axial Flow Pump

2019 ◽  
Author(s):  
Xi Shen ◽  
Desheng Zhang ◽  
Bin Xu ◽  
Yongxin Jin ◽  
Xiongfa Gao
Keyword(s):  
Pressure Fluctuation ◽  
High Speed ◽  
Axial Flow ◽  
Suction Side ◽  
High Speed Photography ◽  
Detached Eddy Simulation ◽  
Transient Pressure ◽  
Unstable Flow ◽  
Axial Flow Pump ◽  
Flow Pump

Abstract The Detached Eddy Simulation (DES) has been used to simulate the pressure fluctuation of the impeller in an axial flow pump. The results were combined with experiments including high-speed photography and transient pressure measurements to investigate the unstable flow induced by tip leakage vortex (TLV). Numerical results show that maximum predictive error values of head is 2.9%, compared with experimental results. The pressure fluctuation at different monitoring points present a certain regularity, with 3 peaks and 3 troughs in a period, corresponding to the number of blades. The amplitude of pressure fluctuation at P1 (impeller inlet) is the highest among those monitoring points, where the amplitude decreases with the flow rates. The dominant frequency of pressure fluctuation at impeller under cavitation condition is the blade passing frequency (BPF). Besides, there are also N* = 6, 9, 12 and other more harmonic frequencies. The cavitation flow was analyzed with the pressure fluctuation of the blade tip. For the existence of the pressure difference between pressure side and suction side, the pressure at monitoring points change alternately. The amplitude of the fluctuation near tip is affected seriously by the cavitation bubbles, as the cavitation could is a low pressure region with unstable fluctuation.

Non-Axisymmetric Flow Structure in Vaneless Diffuser of Centrifugal Compressor for Turbochargers

2012 ◽  
Author(s):  
Chuanjie Lan ◽  
Xinqian Zheng ◽  
Hideaki Tamaki
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Internal Combustion Engines ◽  
Combustion Engines ◽  
Vaneless Diffuser ◽  
Asymmetric Flow ◽  
Oil Flow ◽  
Flow Visualizations

Turbocharger technology is widely used in internal combustion engines. With the downsizing of internal combustion engines and the introduction of strict emission regulations, there is urgent demand for turbochargers featuring centrifugal compressors with a wide flow range. The flow in a centrifugal compressor of a turbocharger is non-axisymmetric due to the inherent asymmetry of the discharge volute. The asymmetric flow field inside the diffuser has great influence on the performance of centrifugal compressor. In order to develop a flow control method that facilitates a wider flow range of turbocharger compressors, further understanding of the asymmetric flow structure is very important. The main subject of this study is to reveal the asymmetrical characteristics of the flow field in the vaneless diffuser of a centrifugal compressor followed by a volute. Oil flow visualizations and numerical simulations were used. The results of the numerical simulations are consistent with that of the oil flow visualizations near choke and at designed flow rate. The results show that a “dual-zone mode” asymmetric flow structure exists near the shroud of the vaneless diffuser at near choke condition. A bifurcation point at the volute tongue that divides the flow and creates two distinct flow patterns was found. The asymmetry of the flow structure near the hub was much less significant than that near the shroud. At the design flow rate, asymmetric flow patterns are found neither near shroud nor near hub. At near surge condition, the pattern of the oil flow traces near the shroud is very different from those near choke.

On the 3D Structure of Elasticity-Induced Unstable Flow in the Curved Microchannel by Using Confocal Micro-PIV and Polarized Camera

2015 ◽  
Author(s):  
Xiao-Bin Li ◽  
Masamichi Oishi ◽  
Marie Oshima ◽  
Feng-Chen Li ◽  
Song-Jing Li
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
3D Structure ◽  
Three Dimensional ◽  
Working Fluid ◽  
Wall Region ◽  
Unstable Flow ◽  
Solution Flow ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv

In this paper, the three-dimensional (3D) structures of a micellar solution flow in the curvilinear microchannel have been investigated by means of confocal micro particle image velocimetry (PIV). The working fluid is aqueous solution of CTAC/NaSal (cetyltrimethylammonium / Sodium Salysilate). As the flow rate increases, the flow gradually gets into the irregular motion. It is found that the inside flow seems not completely chaotic, but in a manner of oscillation. To be specific, the flow nonlinearity grows as the flow rate increases, the inside flow shows different structures near the wall region and in the bulk due to the elongation of viscoelastic surfactant. Typically, two sub-streams were twisted together, and their flow directions change at the locations where the signs of geometric curvature change. The oscillation stripes represented the area of high extensional stress in the viscoelastic fluid, and were further identified by using polarized high-speed camera. Moreover, statistics shows that the viscoelastic flow field inside the curved microchannel shares the main features of elastic turbulence.

scholarly journals Experimental and Numerical Investigation of Bubble–Bubble Interactions during the Process of Free Ascension

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1977 ◽  
Author(s):  
Huang Ying ◽  
Gao Puzhen ◽  
Wang Chaoqun
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Momentum Equation ◽  
Velocity Variation ◽  
High Speed Photography ◽  
Movement Trajectory ◽  
Bubble Interactions ◽  
Cyclical Process ◽  
Velocity Changes ◽  
Two Bubbles

The shape and rising behavior of the horizontally arranged twin bubbles in a steady liquid are experimentally studied employing high-speed photography and digital image processing, and numerically studied by the Volume-Of-Fluid (VOF) method, in combination with a momentum equation coupled with a surface tension model. The movement trajectory and the velocity variation in horizontal and vertical directions of the horizontally arranged twin bubbles rising side by side, as observed in experiments, are described. According to the results, when two bubbles rise side by side, their horizontal velocity changes by the simple harmonic law; there is a cyclical process of two bubbles repeatedly attracted to and bounced against each other, rather than at constant distance between each other, and the bubbles swing up and down periodically in the water. The mathematical model and its numerical implementation are presented in detail. The validation of the model is confirmed by comparing the numerical and experimental results, which are in good agreement with each other; the numerical simulation can accurately reproduce the deformation, attraction, and repulsion of the bubble pairs. The phenomenon of attraction and repulsion is comprehensively analyzed from the viewpoint of a flow field. It is considered that the interaction between the bubbles is mainly influenced by the changes of the flow field due to vortex counteraction and wake merging effects.

A Study on Matching Between Centrifugal Compressor Impeller and Low Solidity Diffuser and its Extension to Vaneless Diffuser

2018 ◽  
Author(s):  
Hideaki Tamaki
Keyword(s):  
High Pressure ◽  
Flow Rate ◽  
Centrifugal Compressor ◽  
Maximum Flow ◽  
Maximum Flow Rate ◽  
Pressure Recovery ◽  
Low Flow ◽  
Vaneless Diffuser ◽  
Operating Range ◽  
Wide Operating

A centrifugal compressor requires a wide operating range as well as a high efficiency. At high pressure ratios, the impeller discharge velocity becomes transonic and effective pressure recovery in a vaned or vaneless diffuser is necessary. At high pressure ratios, a vaned diffuser is used as it has high pressure recovery, but may have a narrow operating range. At low flow, diffuser stall may trigger surge. At high flow, choking in the throat of the vanes may limit the maximum flow rate. A low solidity diffuser allows a good pressure recovery because it has vanes to guide the flow and a wide operating range as there is no geometrical throat to limit the maximum flow. In experimental studies at a pressure ratio around 4:1, the author has replaced vaned diffusers with a range of low solidity diffusers to try to broaden the operating range. The test results showed that the low solidity diffuser also chokes. In this paper, a virtual throat is defined and its existence is confirmed by flow visualization and pressure measurements. A method to select low solidity diffusers is proposed based on test data and the fundamental nature of the flow. The extension of the proposed method to the selection of a vaneless diffuser is examined and a design approach for a vaneless diffuser system to minimize surge flow rate without limiting the attainable maximum flow rate is proposed.

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