Periodic Unsteadiness of Tip Clearance Vortex in an Axial Compressor Rotor

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.

Download Full-text

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

Journal of Turbomachinery ◽

10.1115/1.2836564 ◽

1995 ◽

Vol 117 (4) ◽

pp. 522-532 ◽

Cited By ~ 23

Author(s):

W. C. Zierke ◽

K. J. Farrell ◽

W. A. Straka

Keyword(s):

Reynolds Number ◽

Flow Visualization ◽

Vortex Core ◽

Rotor Blade ◽

High Reynolds Number ◽

Tip Clearance ◽

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. 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.

Download Full-text

Numerical Investigation of Relation Between Unsteady Behavior of Tip Leakage Vortex and Rotating Disturbance in a Transonic Axial Compressor Rotor

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

10.1115/gt2008-50779 ◽

2008 ◽

Cited By ~ 5

Author(s):

K. Yamada ◽

K. Funazaki ◽

H. Sasaki

Keyword(s):

Vortex Breakdown ◽

Axial Compressor ◽

Tip Clearance ◽

Tip Leakage Vortex ◽

Tip Clearance Flow ◽

Tip Leakage ◽

Compressor Rotor ◽

Clearance Flow ◽

Transonic Axial Compressor ◽

Rotating Instability

The purpose of this study is to have a better understanding of the unsteady behavior of tip clearance flow at near-stall condition from a multi-passage simulation and to clarify the relation between such unsteadiness and rotating disturbance. This study is motivated by the following concern. A single passage simulation has revealed the occurrence of the tip leakage vortex breakdown at near-stall condition in a transonic axial compressor rotor, leading to the unsteadiness of the tip clearance flow field in the rotor passage. These unsteady flow phenomena were similar to those in the rotating instability, which is classified in one of the rotating disturbances. In other words it is possible that the tip leakage vortex breakdown produces a rotating disturbance such as the rotating instability. Three-dimensional unsteady RANS calculation was conducted to simulate the rotating disturbance in a transonic axial compressor rotor (NASA Rotor 37). The four-passage simulation was performed so as to capture a short length scale disturbance like the rotating instability and the spike-type stall inception. The simulation demonstrated that the unsteadiness of tip leakage vortex, which was derived from the vortex breakdown at near-stall condition, invoked the rotating disturbance in the rotor, which is similar to the rotating instability.

Download Full-text

Effects of Tip Clearance Size on Flowfield in a Low-Speed Axial Compressor Rotor

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.543-547.158 ◽

2014 ◽

Vol 543-547 ◽

pp. 158-163 ◽

Cited By ~ 1

Author(s):

Zhen Zhen Duan ◽

Yang Wei Liu ◽

Li Peng Lu

Keyword(s):

Flow Condition ◽

Axial Compressor ◽

Tip Clearance ◽

Primary Role ◽

Tip Leakage Vortex ◽

Low Speed ◽

Tip Leakage ◽

Compressor Rotor ◽

Overall Performance ◽

Corner Vortex

The simulations of a low-speed axial compressor rotor with two tip clearance sizes, 0.5% chord and 1.5% chord, were performed in the study. Overall performance and detailed flow fields at near stall condition are analyzed. The results show that the rotor stall occurs at higher mass flow condition with large tip clearance. For the small tip clearance the tip leakage vortex and the corner vortex both contribute significantly to the rotor stall, and the interaction between the vortices promotes the stall generation. While for the large tip clearance the tip leakage vortex plays a primary role, and the vortices interaction is ignorable.

Download Full-text

Impact of Sinusoidal Tip Gaps on Axial Compressor Rotor Performance: A Flow Field Investigation

Volume 1: Compressors, Fans, and Pumps; Turbines; Heat Transfer; Structures and Dynamics ◽

10.1115/gtindia2019-2574 ◽

2019 ◽

Author(s):

Shraman Goswami ◽

Ashima Malhotra

Keyword(s):

Flow Field ◽

Axial Compressor ◽

Field Investigation ◽

Tip Clearance ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage Vortex ◽

Stall Margin ◽

Tip Leakage ◽

Compressor Rotor

Abstract Performance of an axial compressor rotor depends largely on the tip leakage flow. Tip leakage flow results in tip leakage vortex which is a source of loss. This has an impact on the compressor efficiency as well as stall margin. A lot of work has been done to understand the tip leakage flow and controlling the same. Active and passive stall margin improvement methods mainly target the tip leakage vortex. In the current study, numerical investigations are carried out to understand flow fields near tip region of rotors. The blade tip designed to have a tip gap as sine and cosine waves (single and double waves). Numerical methodology is validated with NASA Rotor37 test results. The performance parameters of the rotors with modified tip gap shapes are compared with constant tip clearance rotor. A detailed flow field investigation is presented to compare the tip flow structure and its impact on overall performance of the compressor.

Download Full-text

Study of Radial Tip Clearance Effects in a Low-Speed Axial Compressor Rotor

Volume 1: Turbomachinery ◽

10.1115/96-gt-037 ◽

1996 ◽

Cited By ~ 1

Author(s):

I. G. Nikolaou ◽

K. C. Giannakoglou ◽

K. D. Papailiou

Keyword(s):

Dimensional Space ◽

Three Dimensional ◽

Axial Compressor ◽

Axial Flow ◽

Tip Clearance ◽

Tip Leakage ◽

Compressor Rotor ◽

Curved Blade ◽

Blade Tip ◽

Flow Compressor

A three-dimensional space marching code is used for the numerical modelling of the flow in an isolated axial flow compressor rotor. The rotor is analyzed at four operating points, up to near stall conditions. Numerical results are first validated versus available experimental data and then further exploited in order to illuminate flow patterns in the inter-blade region. The tip leakage impact on the main passage flow and losses level as well as the effect of blade loading on the hub corner stall extent and the radial displacement of the flow are fully detailed. In order to account for the rotor geometry, the modifications performed in an existing software are mainly concerned with the accurate modelling of the clearance which is formed above the curved blade tip; for this purpose, a local H-type mesh is embedded to the main passage grid.

Download Full-text

Effects of Tip Clearance on the Stall Inception Process in an Axial Compressor Rotor

Volume 6C: Turbomachinery ◽

10.1115/gt2013-95479 ◽

2013 ◽

Cited By ~ 12

Author(s):

Kazutoyo Yamada ◽

Hiroaki Kikuta ◽

Masato Furukawa ◽

Satoshi Gunjishima ◽

Yasunori Hara

Keyword(s):

Vortex Breakdown ◽

Axial Compressor ◽

Leading Edge ◽

Tip Clearance ◽

Tip Leakage Vortex ◽

Stall Inception ◽

Tip Leakage ◽

Compressor Rotor ◽

Flow Phenomena ◽

Casing Pressure

The paper presents experimental and numerical studies on the effects of tip clearance on the stall inception process in a low-speed axial compressor rotor with a large tip clearance. It has been revealed that in the small tip clearance case, shortly after the spike disturbance which results from the leading-edge separation near the rotor tip appears, the tornado-like vortex is generated by the separation, and soon the compressor falls into stall. In the large tip clearance case, the experiment showed that the performance characteristic differs from that in the small tip clearance case at near-stall conditions. This implies that the stall inception process differs with the tip clearance size. The flow phenomenon in the stall inception leading to such difference has been investigated in this study. Pressure and velocity fields which were ensemble-averaged and phase-locked by the periodic multi-sampling technique were measured on the casing wall and downstream of the rotor, respectively. In addition, to capture the unsteady flow phenomena inside the rotor, “Instantaneous Casing Pressure Field Measurement” was carried out: instantaneous casing pressure fields in one rotor passage region were measured by 30 high response pressure transducers mounted on the casing wall. In order to investigate further details of near-stall flow field for the large tip clearance, DES (Detached Eddy Simulation) has been conducted using a computational mesh with 120 million points. The results are compared with those from previous studies for the small tip clearance. As expected, the measurement results show notable differences in the near-stall flow field between the two tip clearance cases. The results from the casing pressure measurement show that high pressure fluctuation appears on the pressure side near the rotor leading-edge in the large tip clearance case. In the result of the velocity field measurement downstream of the rotor, high turbulence intensity is found near the casing in the large tip clearance case. The numerical results reveal that the vortex breakdown occurs in the tip leakage vortex and induces the oscillation of the tip leakage vortex with its unsteady nature. The flow phenomena confirmed in the experimental results are clearly explained by considering the breakdown of the tip leakage vortex. The vortex breakdown gives rise to not only large blockage but also the rotating disturbance through the interaction of the fluctuating tip leakage vortex with the pressure surface of the adjacent blade, and governs the stall inception process.

Download Full-text

Factors Affecting Measured Axial Compressor Tip Clearance Vortex Circulation

Journal of Turbomachinery ◽

10.1115/1.2835685 ◽

1995 ◽

Vol 117 (3) ◽

pp. 487-490 ◽

Cited By ~ 1

Author(s):

S. A. Khalid

Keyword(s):

Viscous Flow ◽

Three Dimensional ◽

Axial Compressor ◽

Tip Clearance ◽

Radial Transport ◽

Factors Affecting ◽

Blade Tip ◽

Tip Clearance Vortex ◽

The Relationship ◽

Principal Contributor

The relationship between turbomachinery blade circulation and tip clearance vortex circulation measured experimentally is examined using three-dimensional viscous flow computations. It is shown that the clearance vortex circulation one would measure is dependent on the placement of the fluid contour around which the circulation measurement is taken. Radial transport of vorticity results in the magnitude of the measured clearance vortex circulation generally being less than the blade circulation. For compressors, radial transport of vorticity shed from the blade tip in proximity to the endwall is the principal contributor to the discrepancy between the measured vortex circulation and blade circulation. Further, diffusion of vorticity shed at the blade tip toward the endwall makes it impossible in most practical cases to construct a fluid contour around the vortex that encloses all, and only, the vorticity shed from the blade tip. One should thus not expect agreement between measured tip clearance vortex circulation and circulation around the blade.

Download Full-text

Physical Explanations of Tip Leakage Flow Field in an Axial Compressor Rotor

Volume 1: Turbomachinery ◽

10.1115/98-gt-091 ◽

1998 ◽

Cited By ~ 7

Author(s):

Masahiro Inoue ◽

Masato Furukawa ◽

Kazuhisa Saiki ◽

Kazutoyo Yamada

Keyword(s):

Boundary Layer ◽

Vortex Core ◽

Leakage Flow ◽

Surface Boundary ◽

Suction Surface ◽

Surface Boundary Layer ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Compressor Rotor ◽

Vortex Lines

Structure of a tip leakage flow field in an axial compressor rotor has been investigated by detailed numerical simulations and appropriate post-processing. Physical explanations of the structure are made in terms of vortex-core identification, normalized helicity, vortex-lines, limiting streamlines, etc. The onset of the discrete tip leakage vortex is located on the suction surface at some distance from the leading edge. The vortex core with high vorticity is generated from a shear layer between the leakage jet flow and the main flow. The streamlines in the leakage flow are coiling around the vortex core. All the vortex-lines in the tip leakage vortex core link to ones in the suction surface boundary layer. The other vortex-lines in the suction surface boundary layer link to the vortex-lines in the pressure surface boundary layer and in the casing wall boundary layer. There are two mechanisms to reduce intensity of the tip leakage vortex: one is reduction of discharged vorticity caused by the linkage of vortex-lines between the suction surface and casing wall boundary layers, and another is diffusion of vorticity from the tip leakage vortex. Relative motion of the endwall has a substantial influence on the structure of the leakage flow field. In the case of a compressor rotor, it intensifies streamwise vorticity of the leakage vortex but reduces leakage flow loss.

Download Full-text

Characteristics of the Tip Leakage Vortex in a Low-Speed Axial Compressor With Different Rotor Tip Gaps

Volume 8: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2012-69148 ◽

2012 ◽

Cited By ~ 3

Author(s):

Zhibo Zhang ◽

Xianjun Yu ◽

Baojie Liu

Keyword(s):

Axial Compressor ◽

Pressure Rise ◽

Operating Conditions ◽

Stereoscopic Particle Image Velocimetry ◽

Tip Clearance ◽

Test Facility ◽

Tip Leakage Flow ◽

Tip Leakage Vortex ◽

Low Speed ◽

Tip Leakage

The detailed evolutionary processes of the tip leakage flow/vortex inside the rotor passage are still not very clear for the difficulties of investigating of them by both experimental and numerical methods. In this paper, the flow fields near the rotor tip region inside the blade passage with two tip gaps, 0.5% and 1.5% blade height respectively, were measured by using stereoscopic particle image velocimetry (SPIV) in a large-scale low speed axial compressor test facility. The measurements are conducted at four different operating conditions, including the design, middle, maximum static pressure rise and near stall conditions. In order to analyze the variations of the characteristics of the tip leakage vortex (TLV), the trajectory, concentration, size, streamwise velocity, and the blockage parameters are extracted from the ensemble-averaged results and compared at different compressor operating conditions and tip gaps. The results show that the formation of the TLV is delayed with large tip clearance, however, its trajectory moves much faster in an approximately linear way from the blade suction side to pressure side. In the tested compressor, the size of the tip gap has little effects on the scale of the TLV in the spanwise direction, on the contrary, its effects on the pitch-wise direction is very prominent. Breakdown of the TLV were both found at the near-stall condition with different tip gaps. The location of the initiation of the TLV breakdown moves downstream from the 60% chord to 70% chord as the tip gap increases. After the TLV breakdown occurs, the flow blockage near the rotor tip region increases abruptly. The peak value of the blockage effects caused by the TLV breakdown is doubled with the tip gap size increasing from 0.5% to 1.5% blade span.

Download Full-text