Self-Regulating Casing Treatment for Axial Compressor Stability Enhancement

2011 ◽  
Author(s):  
Stephanie Weichert ◽  
Ivor Day ◽  
Chris Freeman
Keyword(s):  
High Pressure ◽  
Treatment Effectiveness ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Tip Clearance ◽  
The Self ◽  
Optimized Design ◽  
Stall Margin ◽  
Casing Treatment ◽  
Operating Range

The operating range of an axial compressor is often restricted by a safety imposed stall margin. One possible way of regaining operating range is with the application of casing treatment. Of particular interest here is the type of casing treatment which extracts air from a high pressure location in the compressor and re-injects it through discrete loops into the rotor tip region. Existing re-circulation systems have the disadvantage of reducing compressor efficiency at design conditions because worked flow is unnecessarily re-circulated at these operating conditions. Re-circulation is really only needed near stall. This paper proposes a self-regulating casing treatment in which the re-circulated flow is minimized at compressor design conditions and maximized near stall. The self-regulating capability is achieved by taking advantage of changes which occur in the tip clearance velocity and pressure fields as the compressor is throttled toward stall. In the proof-of-concept work reported here, flow is extracted from the high pressure region over the rotor tips and re-injected just upstream of the same blade row. Parametric studies are reported in which the flow extraction and re-injection ports are optimized for location, shape and orientation. The optimized design is shown to compare favorably with a circumferential groove tested in the same compressor. The relationship between stall inception type and casing treatment effectiveness is also investigated. The self-regulating aspect of the new design works well: stall margin improvements from 2.2 to 6.0% are achieved for just 0.25% total air re-circulated near stall and half that near design conditions. The self-regulating capability is achieved by the selective location and orientation of the extraction hole; a simple model is discussed which predicts the optimum axial location.

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.

Experimental and Numerical Investigation of Effect of Center Offset Degree on Compressor Stability With Circumferential Grooved Casing Treatment

2016 ◽  
Author(s):  
HaoGuang Zhang ◽  
Feng Tan ◽  
YanHui Wu ◽  
WuLi Chu ◽  
Wei Wang ◽  
...  
Keyword(s):  
Axial Compressor ◽  
Leading Edge ◽  
Groove Depth ◽  
Tip Clearance ◽  
Central Difference ◽  
Stall Margin ◽  
Casing Treatment ◽  
Compressor Rotor ◽  
Stall Margin Improvement ◽  
Blade Tip

For compressor blade tip stall, one effective way of extending stable operating range is with the application of circumferential grooved casing treatment and its validity was proved by a lot of experimental and numerical investigations. The emphases of most circumferential grooved investigations are focused on the influence of groove depth and groove number on compressor stability, and there is few investigations dealt with the center offset degree of circumferential grooves casing treatment. Hence, an axial compressor rotor with casing treatment (CT) was investigated with experimental and numerical methods to explore the effect of center offset degree on compressor stability and performance. In the work reported here, The center offset degree is defined as the ratio of the central difference between rotor tip axial chord and CT to the axial chord length of rotor tip. When the center of CT is located within the upstream direction of the center of rotor tip axial chord, the value of center offset degree is positive. The experimental and numerical results show that stall margin improvement gained with CT is reduced as the value of center offset degree varies from 0 to 0.33 or −0.33, and the CT with −0.33 center offset degree achieves the lowest value of stall margin improvement at 53% and 73% design rotational speed. The detailed analysis of the flow-field in compressor tip indicates that there is not positive effect made by grooves on leading edge of rotor blade tip when the value of center offset degree is −0.33. As the mass flow of compressor reduces further, tip clearance leakage flow results in the outlet blockage due to the absence of the positive action of grooves near blade tip tail when the value of center offset degree is 0.33. Blockage does not appear in rotor tip passage owing to utilizing the function of all grooves with CT of 0 center offset degree.

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.

Performance Desensitization for a High-Speed Axial Compressor

2018 ◽  
Author(s):  
Yassine Souleimani ◽  
Huu Duc Vo ◽  
Hong Yu
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Lower Sensitivity ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Casing Treatment ◽  
Compressor Rotor

The increase in compressor tip clearance over the lifespan of an aero-engine leads to a long-term degradation in its fuel consumption and operating envelope. A highly promising recent numerical study on a theoretical high-speed axial compressor rotor proposed a novel casing treatment to decrease performance and stall margin sensitivity to tip clearance increase. This paper aims to apply and analyze, through CFD simulations, this casing treatment concept to a representative production axial compressor rotor with inherently lower sensitivity to tip clearance increase and complement the explanation on the mechanism behind the reduction in sensitivity. Simulations of the baseline rotor showed that the lower span region contribute as much to the pressure ratio sensitivity as the tip region which is dominated by tip leakage flow. In contrast, the efficiency sensitivity is mainly driven by losses occurring in the tip region. The novel casing treatment was successfully applied to the baseline rotor through a design refinement. Although the casing treatment causes some penalty in nominal performance, it completely reversed the pressure ratio sensitivity (i.e. pressure ratio increases with tip clearance) and reduced the efficiency sensitivity. The reversed pressure ratio sensitivity is explained by a rotation in the core flow in the lower span region indirectly induced by the flow injection from the casing treatment. The lower efficiency sensitivity comes from a reduction in the amount of fluid that crosses the tip clearance of two adjacent blades, known as double leakage. The casing treatment’s beneficial effect on stall margin sensitivity is less obvious because of the stall inception type of the baseline rotor and its change in the presence of the casing treatment.

scholarly journals Stability Enhancement of a Single-Stage Transonic Axial Compressor Using Inclined Oblique Slots

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2346
Author(s):  
Tien-Dung Vuong ◽  
Kwang-Yong Kim
Keyword(s):  
Pressure Ratio ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Single Stage ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Optimized Design ◽  
Stall Margin ◽  
Casing Treatment ◽  
Transonic Axial Compressor

A casing treatment using inclined oblique slots (INOS) is proposed to improve the stability of the single-stage transonic axial compressor, NASA Stage 37, during operation. The slots are installed on the casing of the rotor blades. The aerodynamic performance was estimated using three-dimensional steady Reynolds-Averaged Navier-Stokes analysis. The results showed that the slots effectively increased the stall margin of the compressor with slight reductions in the pressure ratio and adiabatic efficiency. Three geometric parameters were tested in a parametric study. A single-objective optimization to maximize the stall margin was carried out using a Genetic Algorithm coupled with a surrogate model created by a radial basis neural network. The optimized design increased the stall margin by 37.1% compared to that of the smooth casing with little impacts on the efficiency and pressure ratio.

scholarly journals A Study of Casing Treatment Stall Margin Improvement Phenomena

1975 ◽  
Author(s):  
D. C. Prince ◽  
D. C. Wisler ◽  
D. E. Hilvers
Keyword(s):  
Rotor Blade ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Blade Angle ◽  
Normal Surface ◽  
Peak Efficiency ◽  
Stall Margin ◽  
Casing Treatment ◽  
Circumferential Groove ◽  
Wall Boundary Layer

The results of a program of experimental and analytical research in casing treatments over axial compressor rotor blade tips are presented. Circumferential groove, axial-skewed slot, and blade angle slot treatments were tested at low speeds. With the circumferential groove treatment the stalling flow was reduced 5.8 percent at negligible efficiency sacrifice. The axial-skewed slot treatment improved the stalling flow by 15.3 percent; 1.8 points in peak efficiency were sacrificed. The blade angle slot treatment improved the stalling flow by 15.0 percent; 1.4 points in peak efficiency were sacrificed. These values are consistent with previous experience at transonic speeds. The favorable stalling flow situations correlated well with observations of higher-than-normal surface pressures on the rotor blade pressure surfaces in the tip region, and with increased maximum diffusions on the suction surfaces. Annulus wall pressure gradients, especially in the 50 to 75 percent chord region, are also increased and blade surface pressure loadings are shifted toward the trailing edge for treated configurations. Rotor blade wakes may be somewhat thinner in the presence of good treatments, particularly under operating conditions close to the baseline stall. Annulus wall boundary layer profiles are only slightly influenced by casing treatment.

Axial-Slot Casing Treatments Improve the Efficiency of Axial Flow Compressors: Aerodynamic Effects of a Rotor Redesign

2013 ◽  
Author(s):  
J. Anton Streit ◽  
Frank Heinichen ◽  
Hans-Peter Kau
Keyword(s):  
Axial Flow ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Negative Effects ◽  
Stall Margin ◽  
Casing Treatment ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Flow Phenomena ◽  
Casing Treatments

A state-of-the-art transonic compressor rotor has a distinct potential for increased efficiency if modified for improved interaction with an axial-slot type casing treatment. Reducing the number of blades and thus the surface lowers friction losses but increases tip clearance effects and deteriorates the stall margin due to the higher aerodynamic blade loading. The latter two negative effects can be compensated for by the casing treatment, thus restoring the required stall margin and gaining an overall reduction of losses. For the specific compressor rotor under investigation, the potential in polytropic efficiency is as high as 0.7%. The present study was performed using time-accurate CFD (URANS) simulations. Both the reference rotor as well as the modified design are analyzed regarding their interaction with the casing treatment. The traceability of the conclusions is assured by interpreting the detailed flow phenomena. The newly designed rotor is found to be favorably influenced by the casing treatment at design operating conditions whilst the reference only benefits at throttled operating points. Casing treatments are commonly used to broaden the operating range of existing compressors without changing the design of the compressor rotor itself. This study aims to show the possible transformation of this potential in the stall margin into efficiency at design operating conditions by implementing an appropriate rotor design.

Part-Circumference Casing Treatment and the Effect on Compressor Stall

1989 ◽  
Author(s):  
N. A. Cumpsty
Keyword(s):  
Axial Compressor ◽  
Tip Clearance ◽  
Start Time ◽  
Stall Inception ◽  
Stall Margin ◽  
Tip Clearance Flow ◽  
Casing Treatment ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Stall Margin Improvement

Results are presented and discussed from an axial compressor rotor operated with an axial skewed slot casing treatment over part of the circumference. The compressor was one for which stall was initiated in the tip region and for this type there is some potential for stall margin improvement with lower loss using this. The main significance of the experiments is, however, the possibility of looking at aspects of stall inception. Normally stall inception is a brief transient with an unknown start time and is difficult to study but with the partial casing treatment it was possible to make the untreated section operate continuously in such a way that it underwent the processes normally leading to stall. For a tip stalling rotor the experiments identify the annulus boundary layer as the crucial region of the flow and spillage of the tip-clearance flow forward of the blades as a process leading to the rapid build up of blockage prior to instability and stall.

scholarly journals Investigation of Performance and Rotor Tip Flow Field in a Low Speed Research Compressor with Circumferential Groove Casing Treatment at Varying Tip Clearance

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Matthias Rolfes ◽  
Martin Lange ◽  
Ronald Mailach
Keyword(s):  
Flow Field ◽  
Operating Conditions ◽  
Single Stage ◽  
Tip Clearance ◽  
Experimental Investigations ◽  
Low Speed ◽  
Pressure Transducers ◽  
Casing Treatment ◽  
Operating Range ◽  
Circumferential Groove

Experimental investigations in a single-stage low speed axial research compressor are presented. The influence of four different rotor tip clearances on the overall compressor performance and on the rotor tip flow field is investigated in configurations with and without circumferential groove casing treatments. Piezo-resistive pressure transducers are used to capture the unsteady flow field in the rotor tip region. The investigated casing groove is effectively working at the three largest investigated tip clearance sizes. The largest achieved operating range increase by the groove is 6.9%. The groove can delay the upstream movement of the flow interface between leakage flow and main flow and thus increase the stable operating range. Rotating instabilities are shown to exist at large tip clearance sizes in throttled operating conditions. Their amplitudes can be damped by the casing groove. No modal activities could be detected in the current single-stage compressor build.

Influence of axial skewed slots on the rotating instability of a low-speed axial compressor

2020 ◽  
pp. 095441002094433
Author(s):  
Tao Li ◽  
Yadong Wu ◽  
Hua Ouyang
Keyword(s):  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Frequency Spectra ◽  
Stall Margin ◽  
Tip Clearance Flow ◽  
Low Speed ◽  
Casing Treatment ◽  
Rotating Instability

Experimental and numerical analyses were performed on a low-speed axial compressor rotor to investigate the aerodynamic and acoustic effects of axial skewed slots casing treatment on the rotating instability. The experimental results showed that the stall margin could be improved by 8.0% and the frequency broadband hump owing to the rotating instability was suppressed effectively. In the noise spectra, the two dominant broadband humps on both sides of the blade-passing frequency also reduced in amplitude. Full-annulus unsteady computational fluid dynamics simulations were performed near the design condition. Time- and frequency-domain analyses as well as a proper orthogonal decomposition method were applied to obtain the oscillation, frequency, energy and flow characteristics of the rotating instability. Axial skewed slots casing treatment causes a distinct reduction in the amplitude of the pressure fluctuations and frequency spectra with a decrease in the energy of the rotating instability modes. The slots alleviated the tip flow blockage by the periodic injection and removal of the fluid from the passage, which enabled a high tip clearance flow downstream with little impingement on the neighbouring blade tip.

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