scholarly journals Numerical Investigation on a Axial Slot Casing Treatment of a Large Circumferential Interval and Small Opening Area

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6181
Author(s):  
Zepeng Liu ◽  
Guoping Huang ◽  
Omer Musa
Keyword(s):  
Stability Margin ◽  
Field Analysis ◽  
Stall Margin ◽  
Small Opening ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Flow Field Analysis ◽  
The Stability ◽  
Slot Structure ◽  
Excessive Number

Axial slot casing treatment is a common method to extend the stall margin of a compressor. Based on the mechanism of unsteady flow control, this paper redesigns axial slots with large circumferential interval and small opening area. To test the effect of this axial slot structure, unsteady numerical simulations were carried out with different slot areas and circumferential intervals. The results show that this novel axial slot casing treatment can significantly improve compressor stall margin. Meanwhile, compared with the traditional axial slot, the efficiency loss is greatly reduced. The flow field analysis shows that the new axial slot structure proposed in this paper can suppress the development of tip leakage vortex and unsteadiness in the tip region at the near stall condition through decreasing the tip loading periodically. Moreover, we find that the slot area is proportional to the improvement of stability margin. Under the same slot area, an excessive number of slots is not conducive to the improvement of the stability margin.

Effect of Rotor Tip Casing Treatment on the Performance and Stability of a Transonic Axial Compressor

2021 ◽  
Author(s):  
Subbaramu Shivaramaiah ◽  
Mahesh K. Varpe ◽  
Mohammed Afzal
Keyword(s):  
Research Work ◽  
Stability Margin ◽  
Leakage Flow ◽  
Compressor Stage ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Stage Efficiency

Abstract In a transonic compressor rotor, tip leakage flow interacts with passage shock, casing boundary layer and secondary flow. This leads to increase in total pressure loss and reduction of compressor stability margin. Casing treatment is one of the passive endwall geometry modification technique to control tip leakage flow interaction. In the present investigation effect of rotor tip casing treatment is investigated on performance and stability of a NASA 37 transonic compressor stage. Existing literature reveals, that endwall casing treatment slots i.e., porous casing treatment, axial slots axially skewed slots, circumferential grooves, recirculating casing treatment etc. are able to improve compressor stability margin with penalty on stage efficiency. Turbomachinery engineers and scientists are still focusing their research work to identify an endwall casing treatment configuration with improves both compressor stall margin as well as stage efficiency. Hence in the current work, as an innovative idea, effect of casing treatment slot along rotor tip mean camber line is investigated on NASA 37 compressor stage. Casing treatment slot with rectangular cross-section was created along the rotor tip mean camber line. Four different casing treatment configurations were created by changing number of slots on rotor casing surface. In all four configurations casing treatment slot width and height remains same. Flow simulation of NASA 37 compressor stage was performed with all these four casing treatment configurations. A maximum stall margin improvement of 3% was achieved with a particular slot configuration, but without any increase in compressor stage efficiency.

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.

Impact of Exit Duct Dynamic Response on Compressor Stability

2019 ◽  
Author(s):  
Wenqiang Zhang ◽  
Mehdi Vahdati ◽  
Fanzhou Zhao
Keyword(s):  
Dynamic Response ◽  
Model Simulation ◽  
Stability Margin ◽  
Quantitative Relationship ◽  
Aerodynamic Stability ◽  
Stall Margin ◽  
Acoustic Reflection ◽  
Exit Nozzle ◽  
Fan Blade ◽  
The Stability

Abstract Abrupt distortions can appear as a result of transient crosswind or during rapid aircraft maneuvers. Such distortions are known to reduce the aerodynamic stability of engines and therefore present a major concern to all aero-engine manufacturers. To assess the aerodynamic stability of fan blades due to distortions, rig tests are usually carried out to establish the loss in stall margin. In such test campaigns, an exit duct (which is followed by a nozzle) is placed downstream of the fan blade and the operating condition of the fan is controlled by this nozzle. It is shown in this paper that in such rig tests the length of duct downstream of a fan has a significant impact on fan stall margin. The key contributor for such interaction is the dynamic response of the exit duct and the aerodynamic stability of the fan is affected by the acoustic reflection from the exit nozzle. To study the underlying physics, transient response in the exit duct downstream of a transonic fan stage was studied numerically using a simplified model. Simulation results, along with calculations based on analytical theories, confirmed the generation, propagation and reflection of waves induced by the inlet distortion. A quantitative relationship concerning the lengths of the compression system is introduced which determines whether a duct setup would have beneficial or detrimental influences on compressor aerodynamic stability. The findings of this research have great implications for the stability assessment of fans as the stability margin can be affected by the waves generated in bypass ducts.

Numerical Investigation on the Effect of Bleed Port With Self-Recirculating Casing Treatment on the Stability of a 1.5-Stage Transonic Compressor

2019 ◽  
Author(s):  
Yiming Zhong ◽  
WuLi Chu ◽  
HaoGuang Zhang
Keyword(s):  
Pressure Ratio ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Stability Margin ◽  
Axial Position ◽  
Stable Operation ◽  
Stall Margin ◽  
Casing Treatment ◽  
Transonic Compressor ◽  
Compressor Efficiency

Abstract Compared to the traditional casing treatment, the self-recirculating casing treatment (SCT) can improve or not decrease the compressor efficiency while achieving the stall margin improvement. For the bleed port, the main design indicator is to reduce the flow loss caused by suction, while providing sufficient jet flow and jet pressure to the injector. In order to gain a better study of the bleed port stabilization mechanisms, the bleed configuration was parameterized with the bleed port inlet width and the bleed port axial position. Five kinds of recirculating casing treatments were applied to a 1.5-stage transonic axial compressor with the method of three-dimensional unsteady numerical simulation. Fifteen identical self-recirculating devices are uniformly mounted around the annulus. The numerical results show that the SCT can improve compressor total pressure ratio and stability, shift the stall margin towards lower mass flows. Furthermore, it has no impact on compressor efficiency. The optimal case presents that stability margin is improved by 6.7% employing 3.1% of the annulus mass flow. Expanding bleed port inlet width to an intermediate level can further enhance compressor stability, but excessive bleed port inlet width will reduce the stabilization effect. The optimal bleed port position is located in the blocked area of the low energy group at the top of the rotor. In the case of solid casing, stall inception was the tip blockage, which was mainly triggered by the interaction of the tip leakage vortex and passage shock. From radial distribution, the casing treatment predominantly affects the above 70% span. The reduction of tip reflux region by suction effect is the main reason for the extension of stable operation range. The SCT also has an obvious stability improvement in tip blockage stall, while delaying the occurrence of compressor stall.

Effect of Various Trench Designs on Axial Compressor Blade Tip Aerodynamics

2019 ◽  
Author(s):  
Ashwin Ashok ◽  
Patur Ananth Vijay Sidhartha ◽  
Shine Sivadasan
Keyword(s):  
Axial Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Tip Leakage Vortex ◽  
Stall Margin ◽  
Casing Treatment ◽  
Tip Leakage

Abstract Tip clearance of axial compressor blades allows leakage of the flow, generates significant losses and reduces the compressor efficiency. The present paper aims to discuss the axial compressor tip aerodynamics for various configurations of tip gap with trench. The various configurations are obtained by varying the clearance, trench depth, step geometry and casing contouring. In this paper the axial compressor aerodynamics for various configurations of tip gap with trench have been studied. The leakage flow structure, vorticity features and entropy generations are analyzed using RANS based CFD. The linear compressor cascade comprises of NACA 651810 blade with clearance height varied from 0.5% to 2% blade span. Trail of the tip leakage vortex and the horseshoe vortex on the blade suction side are clearly seen for the geometries with and without casing treatments near the stalling point. Since the trench side walls are similar to forward/backing steps, a step vortex is observed near the leading edge as well as trailing edge of the blade and is not seen for the geometry without the casing treatment. Even though the size of the tip leakage vortex seams to be reduces by providing a trench to the casing wall over the blade, the presence of additional vortices like the step vortex leads to comparatively higher flow losses. An increase in overall total pressure loss due to the application of casing treatment is observed. However an increase in stall margin for the geometries with casing is noted.

Mechanism investigation of enhancing the stability of an axial flow rotor by blade angle slots

2019 ◽  
Vol 233 (13) ◽  
pp. 4750-4764 ◽  
Author(s):  
Haoguang Zhang ◽  
Wenhao Liu ◽  
Enhao Wang ◽  
Yanhui Wu ◽  
Weidong Yao
Keyword(s):  
Axial Flow ◽  
Maximum Efficiency ◽  
Smooth Wall ◽  
Blade Angle ◽  
Stall Margin ◽  
Casing Treatment ◽  
Flow Losses ◽  
Stable Operating ◽  
Stall Margin Improvement ◽  
The Stability

This paper seeks to reveal the mechanisms of enhancing the stability of a subsonic axial flow rotor by applying blade angle slots casing treatment (BSCT). When blade angle slots are applied, there is about 9% stall margin improvement for the experiment and about 8% stall margin improvement for the calculation, but the decrease in the rotor maximum efficiency is about 11% for the experiment and the calculation. The compared results between smooth wall and blade angle slots indicate that the backflow in the rotor top passage is weakened by the injected and sucked flows formed inside the slots of BSCT. Moreover, the injected flows inside the slots interfere with the flows in the rotor passage upstream, and this interference leads to large flow losses. Therefore, the rotor efficiency for blade angle slots is much lower than that for smooth wall. To confirm that the structural optimization of blade angle slots can effectively improve the compressor stability with small efficiency losses, optimized blade angle slots casing treatment (BSCT1) was designed according to the past experience of slot casing treatment. The calculated result shows that the optimized blade angle slots generate about 59% stall margin improvement, and the compressor maximum efficiency with the optimized blade angle slots is about 0.05% more than that for smooth wall. The flow field analyses show that the strong sucked flows formed inside the slots for BSCT1 can prevent the backflow, which exists in the rotor top passage for BSCT, from appearing. In addition, the level of interference of the flows in the rotor passage upstream for BSCT1 is much lower than that for BSCT, and the corresponding losses with BSCT1 become lower. Therefore, the rotor with BSCT1 has a larger stable operating range and better efficiencies than that with BSCT.

Design of Casing Treatment on a Mixed-Flow Compressor

2017 ◽  
Author(s):  
Juan Du ◽  
Joerg R. Seume
Keyword(s):  
Pressure Ratio ◽  
Leading Edge ◽  
Area Ratio ◽  
Open Area ◽  
Tip Leakage Flow ◽  
Mixed Flow ◽  
Stall Margin ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Flow Compressor

Casing treatments (CTs) have been proved to beneficially affect the behavior of tip clearance flow and compressor stability. This paper presents the design of casing treatment for a mixed-flow compressor with a very small tip gap of 0.1mm. In the first part, the potential of applying two traditional types of casing treatments, i.e. circumferential grooves and axial slots, to enhance the stability of a mixed-flow compressor is investigated. The flow details in the reference compressor with smooth casing are examined first. It is found that a separating vortex is formed due to the reversed flow on the blade suction side near the rotor trailing edge at the near-stall point. It is supposed to be responsible for the decrease in total pressure ratio when the compressor approaches to stall. The numerical stall, i.e. the breakdown of the simulation, is initiated from the spillage of tip leakage flow over the rotor blade leading edge. The effect of circumferential grooves on the compressor performances is not remarkable. The implement of axial slots ameliorates the total pressure ratio and extend the flow range substantially, but with higher efficiency penalty than the circumferential grooves. The recirculation formed in the axial skewed slots eliminates the separation vortex near the trailing edge and suppresses the spillage of the tip leakage flow forward the rotor leading edge simultaneously. The axial skewed slots are further designed and optimized numerically by DoE (Design of Experiments). As DoE factors the axial length, the height, the open area ratio, and the number per blade passage of the slots are varied. Their effects on the two target values stall margin and polytropic efficiency are investigated. The plot of stall margin improvement (SMI) with a function of the peak efficiency improvement (PEI) indicates that the SMI changes reversely with the PE. There are two trends in the correlation curves of SMI with PE. For the configurations with the open area ratio of 20%, the SMI is changed from 9% to 23% with 1% decrease in PE by varying other three factors. For the CTs with the open area ratio of 60% the augment in SMI from 17.8% to 26.3% produces extra efficiency loss of 4.2%.

Tip Gap Variation on a Transonic Rotor in the Presence of Tip Blowing

2014 ◽  
Author(s):  
Cyril Guinet ◽  
J. Anton Streit ◽  
Hans-Peter Kau ◽  
Volker Gümmer
Keyword(s):  
Negative Impact ◽  
Axial Flow ◽  
Stability Margin ◽  
Stability Control ◽  
Tip Clearance ◽  
Injection Velocity ◽  
Stall Margin ◽  
Casing Treatment ◽  
Stability Control System ◽  
The Impact

High stability and efficiency are the main two objectives in the design of an axial-flow compressor. Stability usually reduces at higher stage loading, and the stability margin critically drops in transient operation and through the life cycle of an engine. A major reason for this to happen is the growing tip gap. A recirculating tip blowing casing treatment has shown the ability to enhance stability. To be able to use it as a stability control system at varying tip clearances in aircraft engines, the behavior of this casing treatment at different tip clearances was considered important and investigated in this paper. The present study investigates in depth the ability of a tip blowing casing treatment to postpone stall at three different tip clearances. The results prove a substantial beneficial effect for design and increased tip gaps and show some negative impact of the casing treatment for a small tip gap. The study is carried out on a 1.5 stage research compressor. The investigated rotor was already investigated with an axial-slot casing treatment for different tip gap heights at the Institute for Flight Propulsion. The design of a recirculating tip blowing casing treatment is simulated with an equivalent numerical setup. A tip blowing casing treatment consists of a bleed port connected to a tip blowing upstream of the rotor. The streamwise pressure gradient drives the tip blowing with a high injection velocity. A design speed line is simulated for three tip clearance values with and without the tip blowing casing treatment. The impact of the interaction between the tip blowing and the tip gap vortex is analyzed. A detailed analysis of the passage flow is conducted. A comparison of the stall margin is made. The study is carried out using URANS simulations.

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.

Investigation of Passage Flow Features in a Transonic Compressor Rotor With Casing Treatments

2011 ◽  
Author(s):  
M. W. Mu¨ller ◽  
H.-P. Schiffer ◽  
Melanie Voges ◽  
Chunill Hah
Keyword(s):  
Measurement Techniques ◽  
Stability Limit ◽  
Rotating Stall ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Tip Leakage ◽  
Operating Range ◽  
Transonic Compressor ◽  
The Stability ◽  
Casing Treatments

An experimental investigation on casing treatments in a one-stage transonic compressor is presented. The reference case consists of a radially staggered blisk and six circumferential grooves. Speedlines show that this axisymmetric treatment already provided a substantial increase in operating range with relatively small losses in efficiency. Since the onset of rotating stall in tip-critical high-speed compressors is always linked to the tip-leakage flow and the build-up of blockage within the blade passage. High-resolution measurement techniques have been employed to investigate the corresponding effects. Results with Particle Image Velocimetry show that the interaction between the tip leakage vortex and the shock front cause a blockage area. When throttled further, the blockage increases. The shock structure changes similar to the phenomena of vortex breakdown described by different researchers in the past, but a stagnation point is not present. Before reaching the stability limit, the interface line between the incoming flow and the blocked area moves towards the inlet plane of the rotor indicating spike-type stall inception. Wall pressure measurements confirmed this theory for the smooth wall, but with circumferential grooves applied, a part span stall cell develops prior to the stability limit. In order to assess the performance of circumferential grooves, two additional configurations are presented. The corresponding measurements addressed the questions whether circumferential grooves also provide an operating range extension when applied to an optimized rotor design with higher initial stall margin. Therefore, an identical casing treatment is applied to a forward swept rotor. The second question is, how circumferential grooves perform in direct comparison to a non-axisymmetric endwall structure. Axial slots have been applied to the radially staggered rotor. While the stall margin exceeds all other configurations, detrimential effects in efficiency are observed. A detailed anaylsis of probe data shows the changes of the radial profile at the rotor outlet which allows recommendations for more efficient CT designs. Parameters allowing to evaluate the CT influence are presented.

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