Experimental and numerical investigations of the tip leakage flow of axial fans with circumferential skewed blades under off-design conditions

2010 ◽  
Vol 224 (6) ◽  
pp. 1203-1216 ◽  
Author(s):  
G Y Jin ◽  
H Ouyang ◽  
Y D Wu ◽  
Z H Du
Keyword(s):  
Leading Edge ◽  
Tip Clearance ◽  
Spanwise Direction ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Noise Sources ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Numerical Investigations ◽  
Axial Fans

Experimental and numerical investigations of tip leakage flow of circumferential skewed axial fans were conducted under off-design conditions. Two circumferential skewed fans, with the blade skew angles of 8.3° forward and backward, respectively, and a base fan were investigated in this study. Aerodynamic and aeroacoustic performances were measured. The Navier—Stokes flow simulations were validated experimentally and the key analysis of tip leakage flow was based on computational fluid dynamics results. The simulations show that with a decrease in flowrate, the start of the tip leakage vortex moves towards the leading edge in the chordwise direction and towards the hub in the spanwise direction. These movements are less significant for the forward-skewed blade than for the backward-skewed blade. The strength of the tip leakage vortex decreases along the vortex line. The vortex strength for the forward-skew blade is significantly less than that for the backward-skewed blade. The aeroacoustic source intensity in the tip clearance region is reduced by employing circumferential skewed blades and changes with a change in flowrate in the same manner as the measured sound pressure level. The forward-skewed blade is found to be effective in eliminating noise sources in the tip clearance region and in controlling tip leakage flow to expand the stall-free operation range under off-design conditions.

Numerical investigations on tip leakage flow characteristics and vortex trajectory prediction model in centrifugal compressor

2016 ◽  
Vol 230 (8) ◽  
pp. 757-772 ◽  
Author(s):  
Huijing Zhao ◽  
Zhiheng Wang ◽  
Shubo Ye ◽  
Guang Xi
Keyword(s):  
Prediction Model ◽  
Flow Instability ◽  
Leading Edge ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip

To better understand the characteristics of tip leakage flow and interpret the correlation between flow instability and tip leakage flow, the flow in the tip region of a centrifugal impeller is investigated by using the Reynolds averaged Navier–Stokes solver technique. With the decrease of mass flow rate, both the tip leakage vortex trajectory and the mainflow/tip leakage flow interface are shifted towards upstream. The mainflow/tip leakage flow interface finally reaches the leading edge of main blade at the near-stall condition. A prediction model is proposed to track the tip leakage vortex trajectory. The blade loading at blade tip and the averaged streamwise velocity of main flow within tip clearance height are adopted to determine the tip leakage vortex trajectory in the proposed model. The coefficient k in Chen’s model is found to be not a constant. Actually, it is correlated with h/b (the ratio of blade tip clearance height to blade tip thickness), because h/b will significantly influence the flow structure across the tip clearance. The effectiveness of the proposed prediction model is further demonstrated by tracking the tip leakage vortex trajectories in another three centrifugal impellers characterized with different h/b (s).

scholarly journals Effects of Tip Leakage Flow on the Aerodynamic Performance and Stability of an Axial-Flow Transonic Compressor Stage

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4168
Author(s):  
Botao Zhang ◽  
Xiaochen Mao ◽  
Xiaoxiong Wu ◽  
Bo Liu
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Transonic Compressor

To explain the effect of tip leakage flow on the performance of an axial-flow transonic compressor, the compressors with different rotor tip clearances were studied numerically. The results show that as the rotor tip clearance increases, the leakage flow intensity is increased, the shock wave position is moved backward, and the interaction between the tip leakage vortex and shock wave is intensified, while that between the boundary layer and shock wave is weakened. Most of all, the stall mechanisms of the compressors with varying rotor tip clearances are different. The clearance leakage flow is the main cause of the rotating stall under large rotor tip clearance. However, the stall form for the compressor with half of the designed tip clearance is caused by the joint action of the rotor tip stall caused by the leakage flow spillage at the blade leading edge and the whole blade span stall caused by the separation of the boundary layer of the rotor and the stator passage. Within the investigated varied range, when the rotor tip clearance size is half of the design, the compressor performance is improved best, and the peak efficiency and stall margin are increased by 0.2% and 3.5%, respectively.

Contributions of Tip Leakage and Inlet Diffusion on Inducer Backflow

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
D. Tate Fanning ◽  
Steven E. Gorrell ◽  
Daniel Maynes ◽  
Kerry Oliphant
Keyword(s):  
Leading Edge ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Low Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Flow Recirculation ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

Inducers are used as a first stage in pumps to minimize cavitation and allow the pump to operate at lower inlet head conditions. Inlet flow recirculation or backflow in the inducer occurs at low flow conditions and can lead to instabilities and cavitation-induced head breakdown. Backflow of an inducer with a tip clearance (TC) of τ = 0.32% and with no tip clearance (NTC) is examined with a series of computational fluid dynamics simulations. Removing the TC eliminates tip leakage flow; however, backflow is still observed. In fact, the NTC case showed a 37% increase in the length of the upstream backflow penetration. Tip leakage flow does instigate a smaller secondary leading edge tip vortex that is separate from the much larger backflow structure. A comprehensive analysis of these simulations suggests that blade inlet diffusion, not tip leakage flow, is the fundamental mechanism leading to the formation of backflow.

Modeling of 2-D Leakage Jet Cavitation as a Basic Study of Tip Leakage Vortex Cavitation

2000 ◽  
Vol 123 (1) ◽  
pp. 50-56 ◽  
Author(s):  
Satoshi Watanabe ◽  
Hiraku Seki ◽  
Seiji Higashi ◽  
Kazuhiko Yokota ◽  
Yoshinobu Tsujimoto
Keyword(s):  
Initial Pressure ◽  
Vortex Method ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Basic Study ◽  
Ambient Flow ◽  
Tip Leakage ◽  
Numerical Investigations ◽  
D Model

As the first step of the study of cavitation in the tip leakage flow in turbomachinery, experimental and numerical investigations on characteristics of 2-D leakage jet cavitation are conducted. The experiments using 2-D model apparatus are carried out for three values of initial pressure and for three values of tip clearance. The numerical methods are constructed by combining the vortex method with three types of cavity models. Through the comparisons with the experiments, it is found that one of the models, which takes account of the effects of cavity behavior on the ambient flow, simulate the location and the size of the cavity fairly well in spite of its simplicity.

PIV Maps of Tip Leakage and Secondary Flow Fields on a Low-Speed Turbine Blade Cascade With Moving End Wall

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage ◽  
End Wall

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110deg and blade chord of 1.0m. Data were obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0×105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle image velocimetry was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip end-wall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the undertip flow near the end wall due to the moving wall is observed and the effect on the tip leakage vortex examined.

The Influence of Tip Clearance Momentum Flux on Stall Inception in a High-Speed Axial Compressor

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Joshua D. Cameron ◽  
Matthew A. Bennington ◽  
Mark H. Ross ◽  
Scott C. Morris ◽  
Juan Du ◽  
...  
Keyword(s):  
Momentum Flux ◽  
High Speed ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Axial Position ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage

Experimental and numerical studies were conducted to investigate tip-leakage flow and its relationship to stall in a transonic axial compressor. The computational fluid dynamics (CFD) results were used to identify the existence of an interface between the approach flow and the tip-leakage flow. The experiments used a surface-streaking visualization method to identify the time-averaged location of this interface as a line of zero axial shear stress at the casing. The axial position of this line, denoted xzs, moved upstream with decreasing flow coefficient in both the experiments and computations. The line was consistently located at the rotor leading edge plane at the stalling flow coefficient, regardless of inflow boundary condition. These results were successfully modeled using a control volume approach that balanced the reverse axial momentum flux of the tip-leakage flow with the momentum flux of the approach fluid. Nonuniform tip clearance measurements demonstrated that movement of the interface upstream of the rotor leading edge plane leads to the generation of short length scale rotating disturbances. Therefore, stall was interpreted as a critical point in the momentum flux balance of the approach flow and the reverse axial momentum flux of the tip-leakage flow.

Effects of tip clearance size on the unsteady flow behaviors and performance in a counter-rotating axial flow compressor

2017 ◽  
Vol 233 (3) ◽  
pp. 1059-1070 ◽  
Author(s):  
Xiaochen Mao ◽  
Bo Liu ◽  
Hang Zhao
Keyword(s):  
Unsteady Flow ◽  
Incidence Angle ◽  
Axial Flow ◽  
Leading Edge ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Axial Flow Compressor ◽  
Flow Compressor

This paper presents the studies performed to better understand the effects of increased tip clearance size on the unsteady flow behaviors and overall performance under the rotor–rotor interaction environment in a counter-rotating axial flow compressor. The investigation method is based on the three-dimensional unsteady Reynolds-averaged Navier–Stokes simulations. The results show that the intensified tip leakage flow in front rotor (R1) caused by the increased tip clearance size will lead to the growth of incoming incidence angle near the tip of the rear rotor (R2). The increasing of double leakage flow range plays a significant role in the sensitivity of the efficiency to tip clearance size and its extent is enlarged gradually with the increase of tip clearance size. As the tip clearance size is increased to 1.5τ (τ represents the designed tip clearance size) from 0.5τ, the results of the fast Fourier transform for the static pressure near blade tip show that two other new fluctuating frequency components appear due to the happening of tip leakage flow self-unsteadiness in R1 and R2, respectively. Additionally, the fluctuating strength near the tip in R2 is significantly increased. However, both the overall fluctuation in R1 caused by the potential effect from downstream and the oscillation in the hub corner on the pressure side of R2 are decreased obviously. The relative inflow angle tends to increase when the incoming wakes and tip leakage flow from R1 encounter the blade leading edge of R2, which leads to the result that the trajectory of tip leakage flow is shifted more upstream.

scholarly journals Effect of Tip Clearance Size on Tubular Turbine Leakage Characteristics

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1481
Author(s):  
Xinrui Li ◽  
Zhenggui Li ◽  
Baoshan Zhu ◽  
Weijun Wang
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Flow Instability ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage

To study the effect of tip clearance on unsteady flow in a tubular turbine, a full-channel numerical calculation was carried out based on the SST k–ω turbulence model using a power-plant prototype as the research object. Tip leakage flow characteristics of three clearance δ schemes were compared. The results show that the clearance value is directly proportional to the axial velocity, momentum, and flow sum of the leakage flow but inversely proportional to turbulent kinetic energy. At approximately 35–50% of the flow direction, velocity and turbulent kinetic energy of the leakage flow show the trough and peak variation law, respectively. The leakage vortex includes a primary tip leakage vortex (PTLV) and a secondary tip leakage vortex (STLV). Increasing clearance increases the vortex strength of both parts, as the STLV vortex core overlaps Core A of PTLV, and Core B of PTLV becomes the main part of the tip leakage vortex. A “right angle effect” causes flow separation on the pressure side of the tip, and a local low-pressure area subsequently generates a separation vortex. Increasing the gap strengthens the separation vortex, intensifying the flow instability. Tip clearance should therefore be maximally reduced in tubular turbines, barring other considerations.

Nonaxisymmetric Study of Tip Leakage Flow in a Centrifugal Compressor With a Volute During Stall Process

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Ce Yang ◽  
Botai Su ◽  
Li Fu ◽  
Hang Zhang
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Leading Edge ◽  
Work Capacity ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
High Static Pressure ◽  
Circumferential Nonuniformity

Abstract Tip leakage flow (TLF) patterns, which affect compressor performance, are closely related to compressor stability. To date, minimal attention has been given to circumferential nonuniformity of the TLF in a centrifugal compressor with a nonaxisymmetric volute structure. In this study, the circumferential difference of the TLF in a centrifugal compressor with a volute during the stall process is analyzed. The circumferential nonuniformity of tip leakage vortex (TLV) trajectories, loading distribution near the tip, and distance between the TLV core and the leading edge (LE) of splitter blades were also investigated. It is shown that in the circumferential direction, there are two peaks associated with the angle (α) between the TLV trajectory of the seven main blades and the axial direction. As the stall process progresses, the blade whose LE is affected by the high static pressure band (PP) induced by the volute tongue (VT) loses its work capacity first and the α difference between this blade and the other blades increases. In addition, the tip loading and TLF velocity of the blade whose LE is affected by the high static pressure band induced by the VT are at a minimum, and the flow loss in the tip clearance is higher. There is a phenomenon of the TLV breakdown. When the blade trailing edge (TE) is located in the low static pressure region, TLV streamlines appear as a significant turn at the breakdown point. However, the TLV streamlines at other circumferential positions do not exhibit this phenomenon.

PIV Maps of Tip Leakage and Secondary Flow Fields on a Low Speed Turbine Blade Cascade With Moving Endwall

2005 ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110 degrees and blade chord of 1.0 m. Data was obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0 × 105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle Image Velocimetry (PIV) was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip endwall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the under-tip flow near the endwall due to the moving wall is observed and the effect on the tip leakage vortex examined.

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