Measurements of the Tip Clearance Flow for a High-Reynolds-Number Axial-Flow Rotor

A high-Reynolds-number pump (HIREP) facility has been used to acquire flow measurements in the rotor blade tip clearance region, with blade chord Reynolds numbers of 3,900,000 and 5,500,000. The initial experiment involved rotor blades with varying tip clearances, while a second experiment involved a more detailed investigation of a rotor blade row with a single tip clearance. The flow visualization on the blade surface and within the flow field indicate the existence of a trailing-edge separation vortex, a vortex that migrates radially upward along the trailing edge and then turns in the circumferential direction near the casing, moving in the opposite direction of blade rotation. Flow visualization also helps in establishing the trajectory of the tip leakage vortex core and shows the unsteadiness of the vortex. Detailed measurements show the effects of tip clearance size and downstream distance on the structure of the rotor tip leakage vortex. The character of the velocity profile along the vortex core changes from a jetlike profile to a wakelike profile as the tip clearance becomes smaller. Also, for small clearances, the presence and proximity of the casing endwall affects the roll-up, shape, dissipation, and unsteadiness of the tip leakage vortex. Measurements also show how much circulation is retained by the blade tip and how much is shed into the vortex, a vortex associated with high losses.

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Measurements of the Tip Clearance Flow for a High Reynolds Number Axial-Flow Rotor: Part 2 — Detailed Flow Measurements

Volume 1: Turbomachinery ◽

10.1115/94-gt-454 ◽

1994 ◽

Cited By ~ 1

Author(s):

W. C. Zierke ◽

K. J. Farrell ◽

W. A. Straka

Keyword(s):

Reynolds Number ◽

Rotor Blade ◽

High Reynolds Number ◽

Axial Flow ◽

Tip Clearance ◽

Flow Measurements ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Blade Tip ◽

High Reynolds

A high Reynolds number pump (HIREP) facility has been used to acquire flow measurements in the rotor blade tip clearance region-with blade chord Reynolds numbers of 3,900,000 and 5,500,000. The initial experiment involved rotor blades with varying tip clearances, while a second experiment involved a more detailed investigation of a rotor blade row with a single tip clearance. This paper focuses on detailed flow measurements of the tip leakage vortex. These detailed measurements show the effects of tip clearance size and downstream distance on the structure of the rotor tip leakage vortex. The character of the velocity profile along the vortex core changes from a jet-like profile to a wake-like profile as the tip clearance becomes smaller. These vortex velocity profiles-as well as the levels of unsteadiness-dominate the rotor wake structure in the endwall region. Also, for small clearances, the presence and proximity of the casing endwall affects the roll-up, shape, dissipation, and unsteadiness of the tip leakage vortex. Measurements also show how much circulation is retained by the blade tip and how much is shed into the vortex-a vortex associated with high losses.

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Measurements of the Tip Clearance Flow for a High Reynolds Number Axial-Flow Rotor: Part 1 — Flow Visualization

Volume 1: Turbomachinery ◽

10.1115/94-gt-453 ◽

1994 ◽

Cited By ~ 1

Author(s):

W. C. Zierke ◽

K. J. Farrell ◽

W. A. Straka

Keyword(s):

Reynolds Number ◽

Flow Visualization ◽

Rotor Blade ◽

High Reynolds Number ◽

Rotor Blades ◽

Tip Clearance ◽

Trailing Edge ◽

Tip Leakage ◽

High Reynolds ◽

Edge Separation

A high Reynolds number pump (HIREP) facility has been used to acquire flow measurements in the rotor blade tip clearance region-with blade chord Reynolds numbers of 3,900,000 and 5,500,000. The initial experiment involved rotor blades with varying tip clearances, while a second experiment involved a more detailed investigation of a rotor blade row with a single tip clearance. This paper focuses on flow visualization, employing techniques unique for use in water. The flow visualization on the blade surface and within the flow field indicate that the combination of centripetal acceleration and separation near the trailing edge of the rotor blade suction surface results in the formation of a trailing-edge separation vortex-a vortex which migrates radially upwards along the trailing edge and then turns in the circumferential direction near the casing, moving in the opposite direction of blade rotation. Flow visualization also helps in establishing the trajectory of the tip leakage vortex core. The trailing-edge separation vortex, which lies closer to the endwall than the tip leakage vortex, seems to have an influence on this trajectory. Finally, the periodic interaction of the rotor blades with wakes from the upstream inlet guide vanes-as well as freestream turbulence and vortex structure instabilities-affects the unsteadiness of the vortex.

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Periodic Unsteadiness of Tip Clearance Vortex in an Axial Compressor Rotor

Volume 2E: Turbomachinery ◽

10.1115/gt2020-15167 ◽

2020 ◽

Author(s):

Fan Yang ◽

Yanhui Wu ◽

Ziyun Zhang ◽

Zhenyang Wang

Keyword(s):

Vortex Core ◽

Axial Compressor ◽

Tip Clearance ◽

Small Range ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Compressor Rotor ◽

Blade Tip ◽

Periodic Fluctuations ◽

Tip Clearance Vortex

Abstract A series of unsteady simulations, supported by experimental data, are used to characterize the periodic unsteadiness of the tip clearance vortex in an axial compressor rotor. The numerical probes detect significant periodic fluctuations in the blade tip region at near stall conditions. A reduced frequency at different condition is limited to a small range although there exist a large difference on the natural frequency. Physical explanations of the periodic fluctuations are made in terms of vortex-core identification, contour, etc. The nature of the periodic unsteadiness in the tip region is the periodic bubble-type breakdown of the tip leakage vortex induced by the broken vortex core generated by the previous breakdown. The life cycle of the broken vortex core can be summarized as three processes, generation, propagation and inducing breakdown of tip leakage vortex. The broken vortex core arrives at mid-chord of the adjacent blade, resulting in change of momentum in the tip clearance and pressure in the leading edge of the adjacent blade. The flow in this blade tip region is similarly affected by another adjacent blade. The tip leakage vortex core is bent, then the breakdown of tip clearance happens and a new broken vortex core appears accompanied by a back flow region.

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Effects of Tip Clearance on Unsteady Flow Characteristics in an Axial Turbine Stage

Volume 7: Turbomachinery, Parts A and B ◽

10.1115/gt2009-59828 ◽

2009 ◽

Author(s):

Hao Sun ◽

Jun Li ◽

Zhenping Feng

Keyword(s):

Flow Field ◽

Unsteady Flow ◽

Rotor Blade ◽

Suction Side ◽

Tip Clearance ◽

Leakage Flow ◽

Turbine Stage ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Blade Tip

The clearance between the rotor blade tip and casing wall in turbomachinery passages induces leakage flow loss and thus degrades aerodynamic performance of the machine. The flow field in turbomachinery is significantly influenced by the rotor blade tip clearance size. To investigate the effects of tip clearance size on the rotor-stator interaction, the turbine stage profile from Matsunuma’s experimental tests was adopted, and the unsteady flow fields with two tip clearance sizes of 0.67% and 2.00% of blade span was numerical simulated based on Harmonic method using NUMECA software. By comparing with the domain scaling method, the accuracy of the harmonic method was verified. The interaction mechanism between the stator wake and the leakage flow was investigated. It is found that the recirculation induced by the stator wake is separated by a significant “interaction line” from the flow field close to the suction side in the clearance region. The trend of the pressure fluctuation is contrary on both sides of the line. When the stator wakes pass by the suction side, the pressure field fluctuates and the intensity of the tip leakage flow varies. With the clearance size increasing, the “interaction line” is more far away from the suction side and the intensity of tip leakage flow also fluctuates more strongly.

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

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650916673230 ◽

2016 ◽

Vol 230 (8) ◽

pp. 757-772 ◽

Cited By ~ 6

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).

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Tip Clearance Flow Visualization of a Turbine Blade Cascade With Active and Passive Flow Control

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-50703 ◽

2008 ◽

Cited By ~ 4

Author(s):

Daniel K. Van Ness ◽

Thomas C. Corke ◽

Scott C. Morris

Keyword(s):

Flow Control ◽

Flow Visualization ◽

Total Pressure ◽

Plasma Actuator ◽

Tip Clearance ◽

Tip Clearance Flow ◽

Tip Leakage ◽

Blade Cascade ◽

Clearance Flow ◽

Blade Tip

The secondary flow in the tip clearance region of a stationary linear low pressure turbine blade cascade was studied using two types of surface flow visualization and documented using wake pressure measurements in order to identify the potential means and impact of flow control to reduce losses associated with the tip clearance flow. An evaporating fluid mixture was used for flow visualization on the casing surface of the tip clearance. An oil ink-dot tracing method was used on the blade tip. These measurements illustrate the important features of the near-casing flow physics, including the size and chordwise extent of the blade tip separation bubble, separation lines on the casing, the flow direction on the blade tip and casing, the size and exit trajectory of the tip leakage and passage vortices, as well as the total pressure loss and secondary velocity vectors downstream of the blade. The flow was visualized in this way for a plain, flat tip, a tip mounted plasma actuator, and a partial suction side squealer tip. Both flow control devices were observed to affect the flow in the clearance. The plasma actuator was shown to improve the total pressure loss in the tip leakage vortex by as much as 9% from the loss over the plain tip blade. The tests were performed over a Reynolds numbers range between 5.3 × 104 and 1.04 × 105 at a fixed tip clearance of 2% of axial chord.

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Flow and Heat Transfer in Turbine Tip Gaps

Journal of Turbomachinery ◽

10.1115/1.3262269 ◽

1989 ◽

Vol 111 (3) ◽

pp. 301-309 ◽

Cited By ~ 47

Author(s):

J. Moore ◽

J. G. Moore ◽

G. S. Henry ◽

U. Chaudhry

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

High Reynolds Number ◽

Reynolds Numbers ◽

Large Separation ◽

Flow And Heat Transfer ◽

Blade Tip ◽

Flow Through ◽

High Mach ◽

High Reynolds

The effects of Reynolds number on flow through a tip gap are investigated by performing laminar flow calculations for an idealized two-dimensional tip gap geometry. The results of the calculations aid in understanding and reconciliation of low Much number turbine tip gap measurements, which range in tip gap Reynolds number from 100 to 10,000. For the higher Reynolds numbers, both the calculations and the measurements show a large separation off the sharp edge of the blade tip corner. For a high Reynolds number, fully turbulent flow calculations were also made. These also show a large separation and the results are compared with heat transfer measurements. At high Mach numbers, there are complex shock structures in the tip gap. These are modeled experimentally using a water table.

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Experimental Study on the Three-Dimensional Flow Within a Compressor Cascade With Tip Clearance: Part II—The Tip Leakage Vortex

Journal of Turbomachinery ◽

10.1115/1.2929271 ◽

1993 ◽

Vol 115 (3) ◽

pp. 444-450 ◽

Cited By ~ 32

Author(s):

S. Kang ◽

C. Hirsch

Keyword(s):

Vortex Core ◽

Three Dimensional ◽

Leading Edge ◽

Tip Clearance ◽

Tip Vortex ◽

Vortex Center ◽

Compressor Cascade ◽

Suction Surface ◽

Tip Leakage Vortex ◽

Tip Leakage

An analysis of the experimental data of a linear compressor cascade with tip clearance is presented with special attention to the development of the tip leakage vortex. A method for determining the tip vortex core size, center position, and vorticity or circulation from the measured data is proposed, based on the assumption of a circular tip vortex core. It is observed that the axial velocity profile passing through the tip vortex center is wavelike. The vorticity of the tip vortex increases rapidly near the leading edge and reaches its highest values at a short distance downstream, from which it gradually decreases. In the whole evolution, its size is growing and its center is moving away from both the suction surface and the endwall, approximately in a linear way.

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On the Stability of Transonic Compressor With Wet Compression and Blade Tip Water Injection

Volume 3: Cycle Innovations; Education; Electric Power; Fans and Blowers; Industrial and Cogeneration ◽

10.1115/gt2012-69133 ◽

2012 ◽

Cited By ~ 1

Author(s):

Mingcong Luo ◽

Qun Zheng ◽

Lanxin Sun ◽

Qingfeng Deng ◽

Jiyou Chen ◽

...

Keyword(s):

Total Pressure ◽

Rotor Blade ◽

Water Injection ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Transonic Compressor ◽

Compressor Rotor ◽

Blade Tip ◽

Compressor Performance ◽

Wet Compression

The rotor blade tip leakage flow and associated formation of the tip leakage vortex and interaction of the tip leakage vortex with the shockwave, particularly in the case of a transonic compressor rotor have significant impact on the compressor performance and its stability. Air injection upstream of the compressor rotor tip has been shown to improve compressor performance and enhance its stability. The air required for rotor blade tip injection is generally taken from the later stages of the compressor thus causing penalty on the gas turbine performance. In this study, effects of water injection at the rotor tip with and without the wet compression on the compressor performance and its stability have been examined. To achieve the stated objectives, the well tested transonic compressor rotor stage, NASA rotor stage 37, has been numerically simulated. The evaluation of results on various performance parameters such as total pressure ratio, inlet flow capacity and adiabatic efficiency combined with contours of total pressure losses, entropy, Mach No., and temperature including limiting streamlines, shows that the blade tip water injection could help in reducing low energy region downstream of the shockwave and strength of the tip leakage vortex with the compressor operating at its rotating stall boundary condition. The extent of reduction depends on the droplet size, injection flow rate and its velocity. Furthermore, results show that combined case of the blade tip water injection and the wet compression could provide better stall margin enhancement than the blade tip water injection case.

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