Experimental Analysis on Tip Leakage and Wake Flow in an Axial Flow Fan According to Flow Rates

2004 ◽  
Vol 127 (2) ◽  
pp. 322-329 ◽  
Author(s):  
C.-M. Jang ◽  
D. Sato ◽  
T. Fukano
Keyword(s):  
Flow Rate ◽  
Experimental Analysis ◽  
Axial Velocity ◽  
High Velocity ◽  
Velocity Fluctuation ◽  
Axial Flow ◽  
Wake Flow ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage

The flow characteristics in the blade passage and in the wake region of a low-speed axial flow fan have been investigated by experimental analysis using a rotating hot-wire sensor and a five-hole probe for design and off-design operating conditions. The results show that the tip leakage vortex is moved upstream when the flow rate is decreased, thus disturbing the formation of wake flow near the rotor tip. That is, the tip leakage vortex interfaces with the blade suction surface and results in high velocity fluctuation near the blade suction surface. From axial velocity distributions downstream of the fan rotor, large axial velocity decay near the rotor tip is observed at near-stall condition, which results in a large blockage compared to that at the design condition. Finally, the wake flow downstream of the rotor blade is clearly measured at the design and off-design conditions. However, the trough of the high velocity fluctuation due to Karmann vortex street in the wake flow is observed at a higher flow condition than the design flow rate.

Numerical and Experimental Investigation of Tip Leakage Vortex Trajectory in an Axial Flow Pump

2013 ◽  
Author(s):  
Desheng Zhang ◽  
Weidong Shi ◽  
Suqing Wu ◽  
Dazhi Pan ◽  
Peipei Shao ◽  
...  
Keyword(s):  
Flow Rate ◽  
Axial Flow ◽  
Tip Clearance ◽  
High Speed Photography ◽  
Rate Condition ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Starting Point ◽  
Axial Flow Pump ◽  
Flow Pump

In this paper, the tip leakage vortex (TLV) structures in an axial flow pump were investigated by numerical and experimental methods. Based on the comparisons of different blade tip clearance size (i.e., 0.5 mm, 1mm and 1.5mm) and different flow rate conditions, TLV trajectories were obtained by Swirling Strength method, and simulated by modified SST k-ω turbulence model with refined high-quality structured grids. A high-speed photography test was carried out to capture the tip leakage vortex cavitation in an axial flow pump with transparent casing. Numerical results were compared with the experimental leakage vortex trajectories, and a good agreement is presented. The detailed trajectories show that the start point of tip leakage vortex appears near the leading edge at small flow rate, and it moves from trailing edge to about 30% chord span at rated flow rate. At the larger flow rate condition, the starting point of TLV shifts to the middle of chord, and the direction of TLV moves parallel to the blade hydrofoil. As the increasing of the tip size, the start point of TLV trajectories moves to the central of chord and the minimum pressure in vortex core is gradually reduced.

scholarly journals The Role of Tip Leakage Vortex Breakdown in Compressor Rotor Aerodynamics

1998 ◽  
Author(s):  
Masato Furukawa ◽  
Masahiro Inoue ◽  
Kazuhisa Saiki ◽  
Kazutoyo Yamada
Keyword(s):  
Flow Rate ◽  
Peak Pressure ◽  
Vortex Breakdown ◽  
Pressure Rise ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Rotor Aerodynamics ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Breakdown Region

The breakdown of tip leakage vortex has been investigated on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics are elucidated by Navier-Stokes flow simulations and visualization techniques for identifying the breakdown. The simulations show that the leakage vortex breakdown occurs inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown is characterized by the existence of the stagnation point followed by a bubble-like recirculation region. The onset of breakdown causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex. The expansion has an extremely large blockage effect extending to the upstream of the leading edge. The disappearance of the concentrated vorticity results in no rolling-up of the vortex downstream of the rotor and the disappearance of the pressure trough on the casing. The leakage flow field downstream of the rotor is dominated by the outward radial flow resulting from the contraction of the bubble-like structure of the breakdown region. It is found that the leakage vortex breakdown plays a major role in characteristic of rotor performance at near-stall conditions. As the flow rate is decreased from the peak pressure rise operating condition, the breakdown region grows rapidly in the streamwise, spanwise and pitchwise directions. The growth of the breakdown causes the blockage and the loss to increase drastically. Then, the interaction of the breakdown region with the blade suction surface gives rise to the three-dimensional separation of the suction surface boundary layer, thus leading to a sudden drop in the total pressure rise across the rotor.

scholarly journals Analysis of the Formation Mechanism of Secondary Tip Leakage Vortex (S-TLV) in an Axial Flow Pump

Machines ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 41
Author(s):  
Hu Zhang ◽  
Jianbo Zang ◽  
Desheng Zhang ◽  
Weidong Shi ◽  
Jiean Shen
Keyword(s):  
Formation Mechanism ◽  
Axial Flow ◽  
Cavitation Number ◽  
Low Flow ◽  
Suction Surface ◽  
Low Velocity ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Rotation Direction ◽  
Sst Turbulence Model

Studies on the tip leakage vortex (TLV) are extensive, while studies on the secondary tip leakage vortex (S-TLV) are rare. To advance the understanding of the formation mechanism of the S-TLV, turbulent cavitating flows were numerically investigated using the shear stress transport (SST) turbulence model and the Zwart–Gerber–Belamri cavitation model. The morphology and physical quantity distribution of the S-TLV under two cavitation conditions were compared, and its formation mechanism was analyzed. The results reveal that in the lower cavitation number case, there is a low-velocity zone of circumferential flow near the tip in the back half of the blade. The shear vortices formed by the leakage jet gradually accumulate and concentrate in the low-velocity area, which is one of the main sources of the S-TLV. Meanwhile, the radial jet pushes the vortices on the suction surface to the tip, which mixes with the S-TLV. The flow path formed by the radial jet and the leakage jet is in accordance with the rotation direction of the S-TLV, which promotes the S-TLV’s further development. Under the conditions of a small cavitation number and low flow rate, the circumferential velocity and radial velocity of the fluid near the gap have altered significantly, which is conducive to the formation of the S-TLV.

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.

Numerical Study of Tip Leakage Vortex Around a NACA0009 Hydrofoil

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
Zhen Bi ◽  
Xueming Shao ◽  
Lingxin Zhang
Keyword(s):  
Axial Velocity ◽  
Numerical Study ◽  
Axial Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Vortex Center ◽  
Long Distance ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
The Impact

Abstract In the tip clearance flow, the dominant vortex is the tip leakage vortex (TLV), which has a significant impact on the hydraulic and cavitation performance of axial flow machineries. In order to reveal the impact mechanism of the gap size on the TLV, gap flows with two gap sizes, i.e., τ=0.2 (2 mm) and τ=1.0 (10 mm), are numerically investigated. A NACA0009 hydrofoil is selected to create the gap flow, with an incoming velocity of 10 m/s and an attack angle of 10 deg. The results show that the two flow cases are significantly different in terms of vortex feature and the leakage flow distribution. In the small gap, a type of jet-pattern flow appears, whereas a type of rolling-pattern flow passes over the large gap. The vertical velocity gradient of the leakage flow has a decisive influence on the TLV trajectory. In addition, for the large gap, the axial velocity in the vortex center exceeds the incoming flow. This jet-like state of axial velocity can be maintained for a long distance, making the vortex more stable. However, the axial velocity in the case of τ=0.2 cannot stay at the jet-like state and rapidly switches to a wake-like state.

scholarly journals Numerical Analysis of the Effect of Cavitation on the Tip Leakage Vortex in an Axial-Flow Pump

2021 ◽  
Vol 9 (7) ◽  
pp. 775
Author(s):  
Hu Zhang ◽  
Jun Wang ◽  
Desheng Zhang ◽  
Weidong Shi ◽  
Jianbo Zang
Keyword(s):  
Axial Flow ◽  
Strength Distribution ◽  
Cavitating Flows ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Clearance Flow ◽  
Axial Flow Pump ◽  
Vorticity Transport ◽  
Flow Pump

To understand the effect of cavitation on the tip leakage vortex (TLV), turbulent cavitating flows were numerically investigated using the shear-stress transport (SST) k–ω turbulence model and the Zwart–Gerber–Belamri cavitation model. In this work, two computations were performed—one without cavitation and the other with cavitation—by changing the inlet pressure of the pump. The results showed that cavitation had little effect on the pressure difference between the blade surfaces for a certain cavitation number. Instead, it changed the clearance flow and TLV vortex structure. Cavitation caused the TLV core trajectory to be farther from the suction surface and closer to the endwall upstream of the blade. Cavitation also changed the vortex strength distribution, making the vortex more dispersed. The vortex flow velocity and turbulent kinetic energy were lower, and the pressure pulsation was more intense in the cavitating case. The vorticity transport equation was used to further analyze the influence of cavitation on the evolution of vortices. Cavitation could change the vortex stretching term and delay the vortex bending term. In addition, the vortex dilation term was drastically changed at the vapor–liquid interface.

Experimental and numerical investigation of tip leakage vortex cavitation in an axial flow pump under design and off-design conditions

2020 ◽  
pp. 095765092090629
Author(s):  
Xi Shen ◽  
Desheng Zhang ◽  
Bin Xu ◽  
Changliang Ye ◽  
Weidong Shi
Keyword(s):  
Shear Stress ◽  
Turbulence Model ◽  
Axial Velocity ◽  
Axial Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Sheet Cavitation ◽  
Shear Stress Transport ◽  
Axial Flow Pump ◽  
Flow Pump

The interaction of tip leakage flow and main flow in an axial flow pump can induce the tip leakage vortex, which causes the unstable flow and complex cavitation structures. In the present research, the modified shear stress transport k–ω turbulence model was utilized to predict the cavitating flow of the model pump under design and off-design conditions. Validations were carried out using high-speed photography techniques. Results show that the simulation results about cavitation performance based on the modified shear stress transport k–ω turbulence model agree well with the experimental results. Cavitation inception occurs more possible at part-load conditions, and with the increase of the flow rate, the starting point of tip leakage vortex gradually moves to the back edge of the blade chord. Both the sheet cavitation and the triangular cavitation cloud that formed in the blade tip grow in size and intensity gradually with the decrease of cavitation number. Distributions of the cavity area fraction and axial velocity show that the tip leakage vortex cavitation locates at the radial coefficient r* = 0.95–1.0 with peaks at about r* = 0.97, while the sheet cavitation is found at r* = 0.5–0.9 on the suction side (SS). The cavitation structures lead to a significant decrease in the axial velocity, especially in the tip region of the blade.

Numerical investigation of tip flow dynamics and main flow characteristics with varying tip clearance widths for an axial-flow pump

2018 ◽  
Vol 233 (4) ◽  
pp. 476-488 ◽  
Author(s):  
Simin Shen ◽  
Zhongdong Qian ◽  
Bin Ji ◽  
Ramesh K Agarwal
Keyword(s):  
Flow Rate ◽  
Axial Flow ◽  
Tip Clearance ◽  
Main Stream ◽  
Specific Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Tip Separation Vortex ◽  
Flow Pump

The effects of varying tip clearance widths on tip flows dynamics and main flows characteristics for an axial-flow pump are studied employing computational fluid dynamics method. An analysis is presented for the distributions of turbulent kinetic energy, mean axial velocity, and mean vorticity magnitude at the specific flow rate of 0.7 Q BEP , focusing on flow patterns in the tip region with different tip clearance widths and associated flows. From the simulation results we find that the flow structure of tip vortex and its transportation strongly depend on the tip clearance width, especially for the extension of tip leakage vortex, appearance of induced vortex and the area of tip separation vortex. For a small clearance of 0.15 mm at 0.7 Q BEP, there is no tip separation vortex at the tip. When tip clearance width becomes larger, a tip separation vortex attaches more on the surface of blade tip as well as vortex intensity of tip flows increases. For tip clearances of 0.9 and 1.2 mm, there is a small part of induced vortex near the blade leading edge. Meanwhile, no induced vortex can be captured for tip clearances of 0.15 and 0.45 mm. The relative angle between the blade chord and tip leakage vortex trajectory reduces gradually when tip clearance width increases from 0.45 to 1.2 mm. Additionally, the radial position of tip leakage vortex core moves inwards as tip clearance width increases. Furthermore, a larger tip clearance width has greater effects on the main-stream characteristics especially near the shroud, which is due to more energy being exchanged between tip flows and main flows. At the flow rate 0.7 Q BEP, both the efficiency and head of the pump reduce with an increasing tip clearance because of greater energy loss.

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