Experimental Characterization of the Evolution of Global Flow Structure in the Passage of an Axial Compressor

2021 ◽  
Author(s):  
Ayush Saraswat ◽  
Subhra Shankha Koley ◽  
Joseph Katz
Keyword(s):  
Flow Structure ◽  
Rotor Blade ◽  
Incidence Angle ◽  
Substantial Reduction ◽  
Axial Compressor ◽  
Suction Side ◽  
Rotor Wake ◽  
Tip Leakage ◽  
Blade Tip

Abstract Ongoing experiments conducted in a one-and-half stages axial compressor installed in the JHU refractive index-matched facility investigate the evolution of flow structure across blade rows. After previously focusing only on the rotor tip region, the present stereo-PIV (SPIV) measurements are performed in a series of axial planes covering an entire passage across the machine, including upstream of the IGV, IGV-rotor gap, rotor-stator gap, and downstream of the stator. The measurements are performed at flow rates corresponding to pre-stall condition and best efficiency point (BEP). Data are acquired for various rotor-blade orientations relative to the IGV and stator blades. The results show that at BEP, the wakes of IGV and rotor are much more distinct and the wake signatures of one row persists downstream of the next, e.g., the flow downstream of the stator is strongly affected by the rotor orientation. In contrast, under pre-stall conditions, the rotor orientation has minimal effect on the flow structure downstream of the stator. However, the wakes of the stator blades, where the axial momentum is low, are now wider. For both conditions, the flow downstream of the rotor is characterized by two regions of axial momentum deficit in addition to the rotor wake. A deficit on the pressure side of the rotor wake tip is associated with the tip leakage vortex (TLV) of the previous rotor blade, and is much broader at pre-stall condition. A deficit on the suction side of the rotor wake near the hub appears to be associated with the hub vortex generated by the neighboring blade, and is broader at BEP. At pre-stall, while the axial momentum upstream of the rotor decreases over the entire tip region, it is particularly evident near the rotor blade tip, where the instantaneous axial velocity becomes intermittently negative. Downstream of the rotor, there is a substantial reduction in mean axial momentum in the upper half of the passage, concurrently with an increase in the circumferential velocity. Consequently, the incidence angle upstream of the stator increases in certain regions by up to 30 degrees. These observations suggest that while the onset of the stall originates from the rotor tip flow, one must examine its impact on the flow structure in the stator passage as well.

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

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.

Flow Nonuniformities and Turbulent “Hot Spots” Due to Wake-Blade and Wake-Wake Interactions in a Multi-Stage Turbomachine

2002 ◽  
Vol 124 (4) ◽  
pp. 553-563 ◽  
Author(s):  
Yi-Chih Chow ◽  
Oguz Uzol ◽  
Joseph Katz
Keyword(s):  
Flow Structure ◽  
Hot Spots ◽  
Rotor Blade ◽  
Suction Side ◽  
Direct Result ◽  
Shear Stresses ◽  
Pressure Side ◽  
Rotor Wake ◽  
Multi Stage ◽  
Wake Interactions

This experimental study provides striking examples of the complex flow and turbulence structure resulting from blade-wake and wake-wake interactions in a multi-stage turbomachine. Particle image velocimetry (PIV) measurements are performed within the entire 2nd stage of a two-stage turbomachine. The experiments are performed in a facility that allows unobstructed view of the entire flow field, facilitated using transparent rotor and stator and a fluid that has the same optical index of refraction as the blades. This paper contains data on the phase-averaged flow structure including velocity, vorticity and strain-rate, as well as the turbulent kinetic energy and shear stress, at mid span, for several orientation of the rotor relative to the stator. Two different test setups with different blade geometries are used in order to highlight and elucidate complex phenomena involved, as well as to demonstrate that some of the interactions are characteristic to turbomachines and can be found in a variety of geometries. The first part of the paper deals with the interaction of a 2nd-stage rotor with the wakes of both the rotor and the stator of the 1st stage. Even before interacting with the blade, localized regions with concentrated mean vorticity and elevated turbulence levels form at the intersection of the rotor and stator wakes of the 1st stage. These phenomena persist even after being ingested by the rotor blade of the 2nd stage. As the wake segment of the 1st-stage rotor blade arrives to the 2nd stage, the rotor blades become submerged in its elevated turbulence levels, and separate the region with negative vorticity that travels along the pressure side of the blade, from the region with positive vorticity that remains on the suction side. The 1st-stage stator wake is chopped-off by the blades. Due to difference in mean lateral velocity, the stator wake segment on the pressure side is advected faster than the segment on the suction side (in the absolute frame of reference), creating discontinuities in the stator wake trajectory. The nonuniformities in phase-averaged velocity distributions generated by the wakes of the 1st stage persist while passing through the 2nd-stage rotor. The combined effects of the 1st-stage blade rows cause 10–12 deg variations of flow angle along the pressure side of the blade. Thus, in spite of the large gap between the 1st and 2nd rotors (compared to typical rotor-stator spacings in axial compressors), 6.5 rotor axial chords, the wake-blade interactions are substantial. The second part focuses on the flow structure at the intersection of the wakes generated by a rotor and a stator located upstream of it. In both test setups the rotor wake is sheared by the nonuniformities in the axial velocity distributions, which are a direct result of the “discontinuities” in the trajectories of the stator wake. This shearing creates a kink in the trajectory of the rotor wake, a quadruple structure in the distribution of strain, regions with concentrated vorticity, high turbulence levels and high shear stresses, the latter with a complex structure that resembles the mean strain. Although the “hot spots” diffuse as they are advected downstream, they still have elevated turbulence levels compared to the local levels around them. In fact, every region of wake intersection has an elevated turbulence level.

Effects of Tip Gap Size on the Flow Structure in the Tip Region of an Axial Turbomachine

2015 ◽  
Author(s):  
Yuanchao Li ◽  
David Tan ◽  
Huang Chen ◽  
Joseph Katz
Keyword(s):  
Boundary Layer ◽  
Flow Structure ◽  
Cross Sections ◽  
Substantial Reduction ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Rotor Blades ◽  
Gap Size

This experimental study examines the effect of tip gap size on the flow structure and turbulence in the tip region of an axial turbomachine. The experiments have been performed in the Johns Hopkins University (JHU) optically index-matched facility using an axial compressor settings designed based on the geometry of the inlet guide vanes (IGV) and the first stage of the Low Speed Axial Compressor (LSAC) facility at NASA Glenn. Two sets of rotor blades with similar cross sections, but with tip gap sizes of 0.49% and 2.3% of the blade chord (or 1.1% and 5.4% of the blade span) have been installed and tested. The measurements include performance tests, visualization of the tip leakage vortex (TLV) using cavitation, and stereo PIV (SPIV) measurements in several meridional planes. Increasing the tip gap size causes a substantial reduction in pressure rise across the machine for the same flow rate. The cavitation images, whose trends agree with the velocity and vorticity distributions obtained by the SPIV measurements, show that TLV rollup in the less loaded blade occurs at later chordwise location, and that the vortex remains located closer to the suction side (SS) corner of the originating blade. The delayed detachment from the blade with increasing gap is attributed to the increase of distance of the ‘image vortex’ (wall interaction) from the TLV. The wider gap also reduces the entrainment by the TLV of the endwall boundary layer after it separates at the point where the backward leakage flow meets the main passage flow. The previously observed TLV breakup, which is evident for the narrow gap in the aft part of the rotor passage, is delayed significantly for the wider gap. Consistent changes also appear in the distributions of turbulent kinetic energy, which peaks in the vicinity of the TLV core, the endwall boundary layer separation, and in the shear layer connecting the TLV center to the SS corner of the blade tip.

Stator-Averaged, Rotor Blade-to-Blade Near-Wall Flow in a Multistage Axial Compressor With Tip Clearance Variation

1992 ◽  
Vol 114 (3) ◽  
pp. 668-674 ◽  
Author(s):  
I. N. Moyle ◽  
G. J. Walker ◽  
R. P. Shreeve
Keyword(s):  
Rotor Blade ◽  
Axial Compressor ◽  
Suction Side ◽  
Tip Clearance ◽  
Pressure Side ◽  
Second Stage ◽  
Rotor Wall ◽  
Blade Tip ◽  
Wall Flow ◽  
Multistage Axial Compressor

This paper describes the effect of tip clearance changes on the pressure at the case wall of a second-stage rotor. Wall shear distributions under the rotor tip are also presented. The results show low-pressure areas extending along the rotor suction side but lying away from the blade. Pressure contours indicate the tangential loading at the tip is lower than predicted by two-dimensional calculations; however, the predicted loading is observed between the lowest pressure’s path in the passage and the blade pressure side. The results suggest that a viscous or shearing layer, due to blade-to-wall relative motion, is generated on the blade side of the tip gap, which modifies the inviscid relative flow field and produces an unloading on the blade tip.

Influence of Blade Tip Fillet Structure on Aerodynamic Performance of a Compressor Rotor

2020 ◽  
Author(s):  
Haohao Wang ◽  
Lei Zhao ◽  
Limin Gao ◽  
Yongzeng Li ◽  
Chi Ma
Keyword(s):  
Rotor Blade ◽  
Axial Compressor ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Operating Range ◽  
Compressor Rotor ◽  
Blade Tip ◽  
Tip Separation Vortex

Abstract This paper deals with the numerical simulation of a passive control technology to increase the performance of the first rotor in a counter-rotating axial compressor. The objective is to extend the stable operating range of an axial compressor rotor using blade tip fillet structure that located on the blade tip pressure side. Firstly, the behavior of the tip leakage flow is investigated for the compressor rotor without passive treatment. The simulations show the loading of blade tip increases as the mass flow rate decreases, which pushed the location of tip leakage vortex and tip separation vortex forward to leading edge. A blockage in the rotor blade passage is also observed at near stall conditions. Then, a rotor blade tip fillet structure (TFS) is tested in order to control leakage flow in the tip region. Steady calculations were conducted to investigate the impact of TFS on the performance of the compressor rotor. The results show that TFS could extend the operating range with no penalty for efficiency when the fillet structure located on the blade tip pressure side. The flow control mechanisms of tip leakage flow are that TFS has a good ability to weaken the tip separation vortex and make the tip leakage vortex closer to the blade suction surface compared to origin rotor blade. It is founded that TFS may lead to a increase of leakage flow mass rate near tip clearance region that resulted in the addition of mixing loss. It is significant to obtain a balance between the benefits of weakening the tip separation vortex and the damage of mixing loss.

Flow Non-Uniformities and Turbulent “Hot Spots” Due to Wake-Blade and Wake-Wake Interactions in a Multistage Turbomachine

2002 ◽  
Author(s):  
Yi-Chih Chow ◽  
Oguz Uzol ◽  
Joseph Katz
Keyword(s):  
Flow Structure ◽  
Hot Spots ◽  
Rotor Blade ◽  
Suction Side ◽  
Direct Result ◽  
Shear Stresses ◽  
Pressure Side ◽  
Rotor Wake ◽  
Flow Angle ◽  
Wake Interactions

This experimental study provides striking examples of the complex flow and turbulence structure resulting from blade-wake and wake-wake interactions in a multi-stage turbomachine. Particle Image Velocimetry (PIV) measurements are performed within the entire 2nd stage of a two-stage turbomachine. The experiments are performed in a facility that allows unobstructed view of the entire flow field, facilitated using transparent rotor and stator and a fluid that has the same optical index of refraction as the blades. This paper contains data on the phase-averaged flow structure including velocity, vorticity and strain-rate, as well as the turbulent kinetic energy and shear stress, at mid span, for several orientation of the rotor relative to the stator. Two different test setups with different blade geometries are used in order to highlight and elucidate complex phenomena involved, as well as to demonstrate that some of the interactions are characteristic to turbomachines and can be found in a variety of geometries. The first part of the paper deals with the interaction of a 2nd stage rotor with the wakes of both the rotor and the stator of the 1st stage. Even before interacting with the blade, localized regions with concentrated mean vorticity and elevated turbulence levels form at the intersection of the rotor and stator wakes of the 1st stage. These phenomena persist even after being ingested by the rotor blade of the 2nd stage. As the wake segment of the 1st stage rotor blade arrives to the 2nd stage, the rotor blades become submerged in its elevated turbulence levels, and separate the region with positive vorticity that travels along the pressure side of the blade, from the region with negative vorticity that remains on the suction side. The 1st stage stator wake is chopped-off by the blades. Due to difference in mean tangential velocity, the stator wake segment on the pressure side is advected faster than the segment on the suction side (in the absolute frame of reference), creating discontinuities in the stator wake trajectory. The non-uniformities in phase-averaged velocity distributions generated by the wakes of the 1st stage persist while passing through the 2nd stage rotor. The combined effects of the 1st stage blade rows cause 10°–12° variations of flow angle along the pressure side of the blade. Thus, in spite of the large gap between the 1st and 2nd rotors (compared to typical rotor-stator spacings in axial compressors), 6.5 rotor axial chords, the wake-blade interactions are substantial. The second part focuses on the flow structure at the intersection of the wakes generated by a rotor and a stator located upstream of it. In both test setups the rotor wake is sheared by the non-uniformities in the horizontal velocity distributions, which are a direct result of the “discontinuities” in the trajectories of the stator wake. This shearing creates a kink in the trajectory of the rotor wake, a quadruple structure in the distribution of strain, regions with concentrated vorticity, high turbulence levels and high shear stresses, the latter with a complex structure that resembles the mean strain. Although the “hot spots” diffuse as they are advected downstream, they still have elevated turbulence levels compared to the local levels around them. In fact, every region of wake intersection has an elevated turbulence level.

A Passive Flow Control to Mitigate the Corner Separation in an Axial Compressor by a Slotted Rotor Blade

2019 ◽  
Author(s):  
Sungho Yoon ◽  
Rao Ajay ◽  
Venkata Chaluvadi ◽  
Vittorio Michelassi ◽  
Ramakrishna Mallina
Keyword(s):  
Flow Control ◽  
Rotor Blade ◽  
Substantial Reduction ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Suction Side ◽  
Pressure Side ◽  
Stall Margin ◽  
Radial Migration ◽  
Corner Separation

Abstract The operability of the axial compressor is generally limited by endwall flows; either at the casing mainly due to the tip leakage flows or at the hub mainly due to three-dimensional corner separations. Therefore, it is crucial to improve flows near the endwalls to enhance the operability of the compressor. Based on a last-stage with cantilevered stator vanes, a small endwall slot was introduced to a rotor blade to mitigate the hub corner separation and maximize the aerodynamic operating range of axial compressors by natural aspiration. The developed flow control technology is numerically analyzed based on the in-house High-Speed Research Compressor (HSRC) which, in turn, represents the rear stage of a modern compressor. This compressor was predicted to stall due to hub corner separation on a rotor blade based on multistage CFD analysis. A small spanwise endwall slot, connecting the pressure side and the suction side of a compressor rotor blade, was introduced near the hub to provide the by-pass flows from the pressure side to the suction side (see Figure 1). This naturally-aspirated jet significantly reduced the three-dimensional corner separation which generally occurs where the suction side meets the hub. The substantial reduction of the three-dimensional corner separation, in turn, improved the aerodynamic stall margin of the compressor. The benefit is accomplished because the low momentum region near the hub was energized due to the naturally-aspirated jet through the endwall slot and the radial migration of the low momentum flow on the suction side was significantly reduced. A systematic parametric study was conducted to better understand the flow details and optimize the flow control without sacrificing aerodynamic efficiency. It was discovered that a very small slot, smaller than 10% of span, located near the endwall, was sufficient to have a more than 6% improvement of the stall margin with a negligible efficiency penalty (less than 0.1%). The naturally-aspirated flow through the small slot eliminates the source of the corner separation at the hub platform by strengthening the flow near the hub. This, in turn, reduces the overall aerodynamic blockage by decreasing the radial migration of the low momentum flow over a third of the span. Finally, evaluations of the mechanical strength and structural dynamics of slotted rotor blades, as well as the aerodynamic impact in a multi-stage environment were conducted and its results were discussed.

scholarly journals Stator Averaged, Rotor Blade-to-Blade Near Wall Flow in a Multistage Axial Compressor With Tip Clearance Variation

1991 ◽  
Author(s):  
I. N. Moyle ◽  
G. J. Walker ◽  
R. P. Shreeve
Keyword(s):  
Rotor Blade ◽  
Axial Compressor ◽  
Suction Side ◽  
Tip Clearance ◽  
Pressure Side ◽  
Second Stage ◽  
Rotor Wall ◽  
Blade Tip ◽  
Wall Flow ◽  
Multistage Axial Compressor

This paper describes the effect of tip clearance changes on the pressure at the case wall of a second stage rotor. Wall shear distributions under the rotor tip are also presented. The results show low pressure areas extending along the rotor suction side but lying away from the blade. Pressure contours indicate the tangential loading at the tip is lower than predicted by two dimensional calculations, however, the predicted loading is observed between the lowest pressure’s path in the passage and the blade pressure side. The results suggest a viscous or shearing layer, due to blade-to-wall relative motion, is generated on the blade side of the tip gap which modifies the inviscid relative flow field and produces an unloading on the blade tip.

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

1995 ◽  
Vol 117 (4) ◽  
pp. 522-532 ◽  
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.

On the Recessed Blade Tip With and Without a Porous Material in an Axial Compressor

2014 ◽  
Author(s):  
Young-Jin Jung ◽  
Tae-Gon Kim ◽  
Minsuk Choi
Keyword(s):  
Porous Material ◽  
Axial Compressor ◽  
Internal Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Flow Solver ◽  
Stall Margin ◽  
Tip Leakage ◽  
Blade Tip ◽  
Strong Vortex

This paper addresses the effect of the recessed blade tip with and without a porous material on the performance of a transonic axial compressor. A commercial flow solver was employed to analyze the performance and the internal flow of the axial compressor with three different tip configurations: reference tip, recessed tip and recessed tip filled with a porous material. It was confirmed that the recessed blade tip is an effective method to increase the stall margin in an axial compressor. It was also found in the present study that the strong vortex formed in the recess cavity on the tip pushed the tip leakage flow backward and weakened the tip leakage flow itself, consequently increasing the stall margin without any penalty of the efficiency in comparison to the reference tip. The recessed blade tip filled with a porous material was suggested with hope to obtain the larger stall margin and the higher efficiency. However, it was found that a porous material in the recess cavity is unfavorable to the performance in both the stall margin and the efficiency. An attempt has been made to explain the effect of the recess cavity with and without a porous material on the flow in an axial compressor.

Sign in / Sign up

Export Citation Format

Share Document