Some effects of non-axisymmetric tip clearance layout on axial compressor aerodynamics

2021 ◽  
pp. 095765092110470
Author(s):  
Haohao Zhang ◽  
Haowan Zhuang ◽  
Jinfang Teng ◽  
Mingmin Zhu ◽  
Xiaoqing Qiang
Keyword(s):  
Transient Flow ◽  
Axial Compressor ◽  
Flow Fields ◽  
Tip Clearance ◽  
Inlet Guide Vane ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Tip Leakage ◽  
Overall Performance

A steady and unsteady numerical research is carried out to explore some effects of a specific non-axisymmetric tip clearance layout on the overall performance and stability of an axial compressor stage. For a 4-stage low-speed research compressor (LSRC) in Shanghai Jiao Tong University (SJTU), one-eighth annulus of the inlet guide vane and the first stage rotor was modeled for this study. After the validation for the uniform tip clearance case, a specific non-axisymmetric tip clearance layout is chosen from several random cases generated by the Gaussian Probabilistic Density Function method. Unsteady time-averaged results at the near stall condition show that the chosen non-axisymmetric layout can improve the isentropic efficiency by 1.3% and extend the stall margin by 4%. Detailed analyses on flow fields are carried out to interpret the performance improvement. Due to the circumferential layout of clearance sizes, the inlet mass flow and incidence are redistributed in both the radial and circumferential directions. It leads to blade loading and tip leakage flow varying with the tip clearance size. The quantification of blockage manifests that the blockage arising from the tip leakage flow is significantly alleviated in the non-axisymmetric layout, which leads to improvements in overall performance and stall margin. Transient flow fields at the rotor tip are also analyzed at the near stall condition. For the non-axisymmetric layout, low-momentum regions originating from larger clearance sizes oscillate and develop downstream in one blade passage period.

A Proposal for Passive Wall Treatment Applied in High Performance Axial Flow Compressors

2020 ◽  
Author(s):  
Rubén Bruno Díaz ◽  
Jesuino Takachi Tomita ◽  
Cleverson Bringhenti ◽  
Francisco Carlos Elizio de Paula ◽  
Luiz Henrique Lindquist Whitacker
Keyword(s):  
Stokes Equations ◽  
Axial Compressor ◽  
Axial Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Smooth Wall ◽  
Tip Leakage Flow ◽  
Viscous Effects ◽  
Stall Margin ◽  
Tip Leakage

Abstract Numerical simulations were carried out with the purpose of investigating the effect of applying circumferential grooves at axial compressor casing passive wall treatment to enhance the stall margin and change the tip leakage flow. The tip leakage flow is pointed out as one of the main contributors to stall inception in axial compressors. Hence, it is of major importance to treat appropriately the flow in this region. Circumferential grooves have shown a good performance in enhancing the stall margin in previous researches by changing the flow path in the tip clearance region. In this work, a passive wall treatment with four circumferential grooves was applied in the transonic axial compressor NASA Rotor 37. Its effect on the axial compressor performance and the flow in the tip clearance region was analyzed and set against the results attained for the smooth wall case. A 2.63% increase in the operational range of the axial compressor running at 100%N, was achieved, when compared with the original smooth wall casing configuration. The grooves installed at compressor casing, causes an increase in the flow entropy generation due to the high viscous effects in this gap region, between the rotor tip surface and casing with grooves. These viscous effects cause a drop in the turbomachine efficiency. For the grooves configurations used in this work, an efficiency drop of 0.7% was observed, compared with the original smooth wall. All the simulations were performed based on 3D turbulent flow calculations using Reynolds Averaged Navier-Stokes equations, and the flow eddy viscosity was determined using the two-equation SST turbulence model. The details of the grooves geometrical dimensions and its implementation are described in the paper.

Numerical Study on Unsteadiness of Tip Clearance Flow Induced by Downstream Stator Row in Axial Compressor

2010 ◽  
Author(s):  
Yoojun Hwang ◽  
Shin-Hyoung Kang ◽  
Sungryoung Lee
Keyword(s):  
Flow Rate ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Performance Data ◽  
Tip Clearance ◽  
Inlet Guide Vane ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Rotating Instability

Numerical calculations were done to investigate unsteady flows through the tip clearance in an axial compressor. The first stage of a low speed research axial compressor with an inlet guide vane was examined after it had been confirmed that the numerically calculated performance data was in good agreement with the experimentally measured performance data. Special attention was paid to the flow during the operation of the compressor when the flow rate was low to study the flow behavior near stall. The estimated performance and the flow pattern of the compressor were found to be related to the unsteadiness of the tip leakage flow altered by the potential effect from the downstream stator row blades. It was shown that the unsteady flow calculations are necessary to predict the performance of an axial compressor, in particular, for low flow rates. On the other hand, rotating instability vortices developed due to unsteady tip leakage flow as the flow rate decreased. It was found that the flow structures corresponding to the rotating instability were merging as the flow rate decreased and the speed of the rotating instability varied with the operating conditions. Consequently, this leads to a non-synchronous vibration frequency.

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

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.

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.

Extensive Experimental Study of Circumferential Single Groove in an Axial Flow Compressor

2014 ◽  
Author(s):  
Jichao Li ◽  
Feng Lin ◽  
Sichen Wang ◽  
Juan Du ◽  
Chaoqun Nie ◽  
...  
Keyword(s):  
Experimental Study ◽  
Unsteady Flow ◽  
Axial Compressor ◽  
Axial Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Good Tool ◽  
Stall Margin ◽  
Casing Treatment ◽  
Tip Leakage

Circumferential single-groove casing treatment becomes an interesting topic in recent few years, because it is a good tool to explore the interaction between the groove and the flow in blade tip region. The stall margin improvement (SMI) as a function of the axial groove location has been found for some compressors, such a trend cannot be predicted by steady high-fidelity CFD simulations. Recent efforts show that to catch such a trend, multi-passage, unsteady flow simulations are needed as the stalling mechanism itself involves cross-passage flows and unsteady dynamics. This indicates a need to validate unsteady numerical simulation results. In this paper, an extensive experimental study of a total of fifteen single casing grooves in a low-speed axial compressor rotor is presented, the groove location varies from 0.4% to 98.3% of axial tip chord are tested. The unsteady pressure data both at casing and at the blade wake with different groove locations are measured and processed, including the movement of trajectory of tip leakage flow, the evolution of unsteadiness of tip leakage flow (UTLF), the unsteady spectrum signature during the stall process, and the outlet unsteady flow characteristic along the span. These data provide a case study for validation of the unsteady CFD results, and may be helpful for further interpretation on the stalling mechanism affected by circumferential casing grooves.

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.

Numerical Analysis of Transonic Compressor With Various Tip Clearance Gap

2016 ◽  
Author(s):  
Yasunori Sakuma ◽  
Toshinori Watanabe ◽  
Takehiro Himeno
Keyword(s):  
Tip Clearance ◽  
Leakage Flow ◽  
Numerical Instability ◽  
Tip Leakage Flow ◽  
Trailing Edge ◽  
Stall Margin ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Blade Tip ◽  
Edge Separation

Computational analysis has been conducted on the NASA Rotor 37 transonic compressor with various tip clearance gap heights. Using steady rotor-only analysis, the change in overall performance, basic flow characteristics, and near-casing phenomena have been carefully observed. The results have clarified that the peak efficiency of the compressor decreases almost linearly with the increase in gap height. Meanwhile, the stall margin was prone to deterioration in cases of significantly small or significantly large clearance gaps. The peak stall margin was attained when the gap was set to 75% of the original height. Focusing on the flow structures, the tip leakage flow and tip leakage vortex seemed to be dominant loss sources in the case of a large tip clearance gap. On the other hand, trailing edge separation at the blade tip was the major loss source in case of a small tip clearance gap. The difference in the near-casing flow structure also determined the onset process of numerical instability. In case of a large tip clearance gap, the advance of the interface between the main flow and tip leakage flow seemed to cause an accumulation of blockage in the region near the casing, possibly triggering the tip-initiated stall. In the case of a small tip clearance gap, interaction among the wall separation, blade tip trailing edge separation, and shockwave /boundary layer interaction was significant. These phenomena appeared to play a major role in the onset of numerical instability in the blade tip region.

Numerical Research on Effects of Shroud Contraction on Tip Leakage Flow and Overall Performance of Axial Compressors

2017 ◽  
Author(s):  
Yufan Zhang ◽  
Jiabin Li ◽  
Lucheng Ji
Keyword(s):  
Great Influence ◽  
Axial Compressor ◽  
Detailed Comparison ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Axial Compressors ◽  
Tip Leakage ◽  
Numerical Research ◽  
Overall Performance ◽  
Inclined Angle

In the design of an axial compressor, many designers take advantage of this technology and employ contracted shroud. What is its impact on tip leakage flow and overall performance of the axial compressor? What is its mechanism? In this paper, the NASA Rotor67 is taken as a research case, and parameterized study is conducted to investigate the effects of shrouds with different inclined angles. The inclined angles range from 0° to 13°. Based on the above described plan, numerical simulations are conducted to the original rotor67 and its modified versions with inclined shroud. To remove factors that might interfere the results, original Rotor 67 and all the blades with modified shroud should be compared to their optimal design status. Adjoint optimization is used to give the optimum blade corresponding to each shroud with different blade inclined angles. Then adjoint optimization was used again to give the optimum meridional flowpath for all the cases with different shroud inclined angles. This provides a powerful tool to evaluate the accuracy of the aforementioned prediction. A detailed comparison is made between the original flowpath and the optimized ones. Numerical results are analyzed in detail between original Rotor67 and its modified versions. The results show that the shroud inclined angle has an effect on the overall performance of the blade. It will also redistribute the velocity triangles and the chordwise distribution of aero load in the tip region. Hence it exerts great influence on the tip leakage flow field in the meantime. Shroud with suitable inclined angles can suppress the developing of leakage vortex , and the best-inclined angle for rotor 67 is found to be roughly 11°.

Numerical Investigation on Slot Casing Treatment in a Transonic Axial Compressor Stage: Part 1 — Casing Treatment Design

2016 ◽  
Author(s):  
Mingmin Zhu ◽  
Xiaoqing Qiang ◽  
Jinfang Teng
Keyword(s):  
Axial Compressor ◽  
Leakage Flow ◽  
Compressor Stage ◽  
Tip Leakage Flow ◽  
Suction Surface ◽  
Stall Margin ◽  
Rotating Speed ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Stall Margin Improvement

Slot-type casing treatment generally has a great potential of enhancing the operating range for tip-critical compressor rotors, however, with remarkable efficiency drop. Part I of this two-part paper was committed to develop a slot configuration with desired stall margin improvement and minimized efficiency loss. Steady simulation was carried out in a 1.5 transonic axial compressor stage at part design rotating speed. At this rotating speed this compressor stage operated at a subsonic condition and showed a rather narrow operating range, which needed to be improved badly. Flow fields analysis at peak efficiency and near stall point showed that the development of tip leakage vortex and resulting blockage near casing resulted in numerical stall. Three kinds of skewed slots with same rotor exposure and casing porosity were designed according to the tip flow field and some empirical strategies. Among three configurations, arc-curved skewed slot showed minimum peak efficiency drop with considerable stall margin improvement. Then rotor exposure and casing porosity were varied based on the original arc-curved skewed slot, with a special interest in detecting their impact on the compressor stability and overall efficiency. Result showed that smaller rotor exposure and casing porosity leaded to less efficiency drop. But meanwhile, effectiveness of improving compressor stability was weakened. The relation between efficiency drop and stall margin improvement fell on a smooth continuous curve throughout all slots configurations, indicating that the detrimental effect of casing treatment on compressor was inevitable. Flow analysis was carried out for cases of smooth casing and three arc-curved configurations at smooth casing near stall condition. The strength of suction/injection, tip leakage flow behavior and removal of blockage near casing were detailed examined. Larger rotor tip exposure and slots number contributed to stronger injection flow. The loss generated within the mixing process of injection flow with main flow and leakage flow is the largest source of entropy increase. Further loss mechanisms were interpreted at eight axial cuts, which were taken through the blade row and slots to show the increase in entropy near tip region. Entropy distributions manifested that loss generations with smooth casing were primarily ascribed to low-momentum tip leakage flow/vortex and suction surface separation at leading edge. CU0 slot, the arc-curved slots with 50% rotor tip exposure, was capable of suppressing the suction surface separation loss. Meanwhile, accelerated tip leakage flow brought about additional loss near casing and pressure surface. Upstream high entropy flow would be absorbed into the rear portion of slots repeatedly, resulting in further loss.

Numerical Study on the Effects of Casing Treatment on Unsteadiness of Tip Leakage Flow in an Axial Compressor

2012 ◽  
Author(s):  
Yoojun Hwang ◽  
Shin-Hyoung Kang
Keyword(s):  
Numerical Study ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Operating Range ◽  
Compressor Rotor ◽  
Flow Through

A low speed axial compressor with casing treatment of axial slots was numerically investigated. Time-accurate numerical calculations were performed to simulate unsteady flow in the rotor tip region and the effects of casing treatment on the flow. Since the compressor rotor had a large tip clearance, it was found that the tip leakage flow had an inherent unsteady feature that was not associated with rotor rotation. The unsteadiness of the tip leakage flow was induced by changes in the blade loading due to the pressure distribution formed by the tip leakage flow. This characteristic is called rotating instability or self-induced unsteadiness. The frequency of the flow oscillation was found to decrease as the flow rate was reduced. On the other hand, as expected, the operating range was improved by casing treatment, as shown by calculations in good agreement with the experimentally measured data. The unsteadiness of the tip leakage flow was alleviated by the casing treatment. The interaction between the flow in the tip region and the re-circulated flow through the axial slots was observed in detail. The removal and injection of flow through the axial slots were responsible not only for the extension of the operating range but also for the alleviation of the unsteadiness. Analyses of instantaneous flow fields explained the mechanism of the interaction between the casing treatment and the unsteady oscillation of the tip leakage flow. Furthermore, the effects of changes in the amount of re-circulation and the location of the removal and injection flow on the unsteadiness of the tip leakage flow were examined.

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