Control of Tip-Clearance Flow in a Low Speed Axial Compressor Rotor With Plasma Actuation

2010 ◽  
Author(s):  
Giridhar Jothiprasad ◽  
Robert C. Murray ◽  
Katherine Essenhigh ◽  
Grover A. Bennett ◽  
Seyed Saddoughi ◽  
...  
Keyword(s):  
Leading Edge ◽  
Suction Side ◽  
Tip Clearance ◽  
Edge Plasma ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Low Speed ◽  
Gap Flow ◽  
End Wall ◽  
Tip Gap Flow

This research investigates different dielectric barrier discharge (DBD) actuator configurations for affecting tip leakage flow and suppressing stall inception. Computational investigations were performed on a low-speed rotor with a highly loaded tip region that was responsible for stall-onset. The actuator was mounted on the casing upstream of the rotor leading edge. Plasma injection had a significant impact on the predicted tip-gap flow and improved stall margin. The effect of changing the actuator forcing direction on stall margin was also studied. The improvement in stall margin was closely correlated with a reduction in loading parameter that quantifies mechanisms responsible for end-wall blockage generation. The actuation reduced end-wall losses by increasing the static pressure of tip-gap flow emerging from blade suction-side. Lastly, an approximate speed scaling developed for the DBD force helped estimate force requirements for stall enhancement of transonic rotors.

Control of Tip-Clearance Flow in a Low Speed Axial Compressor Rotor With Plasma Actuation

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Giridhar Jothiprasad ◽  
Robert C. Murray ◽  
Katherine Essenhigh ◽  
Grover A. Bennett ◽  
Seyed Saddoughi ◽  
...  
Keyword(s):  
Leading Edge ◽  
Suction Side ◽  
Tip Clearance ◽  
Edge Plasma ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Low Speed ◽  
Gap Flow ◽  
End Wall ◽  
Tip Gap Flow

This research investigates different dielectric barrier discharge (DBD) actuator configurations for affecting tip leakage flow and suppressing stall inception. Computational investigations were performed on a low speed rotor with a highly loaded tip region that was responsible for stall-onset. The actuator was mounted on the casing upstream of the rotor leading edge. Plasma injection had a significant impact on the predicted tip-gap flow and improved stall margin. The effect of changing the actuator forcing direction on stall margin was also studied. The reduction in stalling flow was closely correlated with a reduction in loading parameter that quantifies mechanisms responsible for end-wall blockage generation. The actuation reduced end-wall losses by increasing the static pressure of tip-gap flow emerging from blade suction-side. Lastly, an approximate speed scaling developed for the DBD force helped estimate force requirements for stall margin enhancement of transonic rotors.

The Impact of Casing Groove Location on Stall Margin and Tip Clearance Flow in a Low-Speed Axial Compressor

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Du Juan ◽  
Li Jichao ◽  
Gao Lipeng ◽  
Lin Feng ◽  
Chen Jingyi
Keyword(s):  
Axial Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Stall Inception ◽  
Stall Margin ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
The Impact

In this study, the impact of single grooves at different locations on compressor stability and tip clearance flow are numerically and experimentally investigated. Initially, the numerical stall margin improvement (SMI) curve is examined using experimental data. Then, the evolution of the interface between the tip leakage flow (TLF) and the incoming main flow (MF) in the prestall and stall inception processes for two typical grooves, i.e., the worst and the optimal grooves in terms of their SMI, are compared with the smooth casing. The results show two different interface behaviors throughout the throttling process. The compressor with the worst single groove casing first experiences a long-length-scale disturbance after the interface near the blade suction side spills in front of the rotor leading-edge plane, and then goes through spikes after the whole interface spills. With the smooth casing and the optimal single groove near midchord, the interface reaches the rotor leading edge at the last stable operating point and spikes appear once the whole interface spills over the rotor leading edge. A model that illustrates the spillage patterns of the interface for the two stall precursors is thus proposed accordingly and used to explain their effectiveness in terms of the SMI. At last, the relevance of these results to the preliminary selection of groove locations for multigroove casing treatments (CTs) is verified by test data and discussed.

Aerodynamic Investigation of the Tip Leakage Flow for Blades With Different Tip Squealer Geometries at Transonic Conditions

2009 ◽  
Author(s):  
Toma´sˇ Hofer ◽  
Tony Arts
Keyword(s):  
Heat Transfer ◽  
Mass Flow ◽  
Suction Side ◽  
Loss Coefficient ◽  
Leakage Flow ◽  
Pressure Side ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Gap Flow ◽  
Tip Gap Flow

Modern high pressure turbines operate at high velocity and high temperature conditions. The gap existing above a turbine rotor blade is responsible for an undesirable tip leakage flow. It is a source of high aerodynamic losses and high heat transfer rates. A better understanding of the tip flow behaviour is needed to provide a more efficient cooling design in this region. The objective of this paper is to investigate the tip leakage flow for a blade with two different squealer tips and film-cooling applied on the pressure side and through tip dust holes in a non-rotating, linear cascade arrangement. The experiments were performed in the VKI Light Piston Compression Tube facility, CT-2. The tip gap flow was investigated by oil flow visualisations and by wall static and total pressure measurements. Two geometries were tested — a full squealer and a partial suction side squealer. The measurements were performed in the blade tip region, including the squealer rim and on the corresponding end-wall for engine representative values of outlet Reynolds and Mach numbers. The main flow structures in the cavity were put in evidence. Positive influence of the coolant on the tip gap flow and on the aerodynamic losses was found for the full squealer tip case: increasing the coolant mass-flow increased the tip gap flow resistance. The flow through the clearance therefore slows down, the tip gap mass-flow and the heat transfer respectively decreases. No such effect of cooling was found in the case of the partial suction side squealer geometry. The absence of a pressure side squealer rim resulted in a totally different tip gap flow topology, indifferent to cooling. The influence of cooling on the overall mass-weighted thermodynamic loss coefficient, which takes into account the different energies of the mainstream and coolant flows was found marginal for both geometries. Finally the overall loss coefficient was found to be higher for the partial suction side squealer tip than for the full squealer tip.

PIV Maps of Tip Leakage and Secondary Flow Fields on a Low-Speed Turbine Blade Cascade With Moving End Wall

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage ◽  
End Wall

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110deg and blade chord of 1.0m. Data were obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0×105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle image velocimetry was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip end-wall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the undertip flow near the end wall due to the moving wall is observed and the effect on the tip leakage vortex examined.

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 Study of Tip Clearance Effects Under Transonic Flow Conditions

1996 ◽  
Author(s):  
M. Wehner ◽  
A. Bölcs ◽  
J. Bütikofer
Keyword(s):  
Test Section ◽  
Static Pressure ◽  
Suction Side ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Blade Loading ◽  
Gap Flow ◽  
Inlet Conditions ◽  
Axial Turbines ◽  
Tip Gap Flow

An idealized 3 blade test section has been used to study tip clearance effects which occur in transonic axial turbines. At subsonic inlet conditions (Mis1 = 0.56) the flow leaves the test section supersonic (Mis2 = 1.26). The tip clearance was varied from 0 to 15% of the chord length. Extensive laser-2-focus anemometry was used to determine the tip gap mass flow based on the velocity vectors for gaps with 6, 10 and 15% chord. At small clearances the tip gap flow is mainly influenced by the pressure drop between pressure and suction side, while for larger gaps the main flow field dominates the tip gap flow. The variation of the blade loading with the tip clearance was measured by static pressure tappings at 50% and 90% Span. Furthermore the static pressure along the tip surface was measured for varying tip clearances. Pitot probe traverses in the tip vortex region at different downstream positions revealed the vortex structures and vortex core evolution. For tip gaps of 3 and 6%, multiple vortices were detected which were not fully mixed downstream. The origin of these vortices moves towards the trailing edge for larger gaps.

scholarly journals Stall margin improvement in a low-speed axial compressor rotor using a blockage-optimised single circumferential casing groove

2021 ◽  
Vol 5 ◽  
pp. 79-89
Author(s):  
Ahmad Fikri Mustaffa ◽  
Vasudevan Kanjirakkad
Keyword(s):  
Axial Compressor ◽  
Pressure Rise ◽  
Leading Edge ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Low Speed ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Stall Margin Improvement ◽  
Edge Based

The stall margin of tip-critical axial compressors can be improved by using circumferential casing grooves. From previous studies, in the literature, the stall margin improvement due to the casing grooves can be attributed to the reduction of the near casing blockage. The pressure rise across the compressor as the compressor is throttled intensifies the tip leakage flow. This results in a stronger tip leakage vortex that is thought to be the main source of the blockage. In this paper, the near casing blockage due to the tip region aerodynamics in a low-speed axial compressor rotor is numerically studied and quantified using a mass flow-based blockage parameter. The peak blockage location at the last stable operating point for a rotor with smooth casing is found to be at about 10% of the tip chord aft of the tip leading edge. Based on this information, an optimised single casing groove design that minimises the peak blockage is found using a surrogate-based optimisation approach. The implementation of the optimised groove is shown to produce a stall margin improvement of about 5%.

A Study of Performance and Flow Mechanism of a Slot-Groove Hybrid Casing Treatment in a Low-Speed Compressor

2015 ◽  
Author(s):  
Juan Du ◽  
Fan Li ◽  
Jichao Li ◽  
Ning Ma ◽  
Feng Lin ◽  
...  
Keyword(s):  
Axial Compressor ◽  
Suction Side ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Low Speed ◽  
High Entropy ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Flow Loss ◽  
The Difference

A “slot-groove” hybrid casing treatment (CT) is proposed elicited from the recent research on the role of axial location for stall margin improvement (SMI). This combination is expected to display the advantages of both slots and grooves while minimizing their disadvantages. A comparative study is conducted among the “slot-groove”, traditional circumferential groove CT (called the “full-groove” CT) and axial skewed slot CT (known as the “full-slot” CT) to evaluate performance and to explore the stability enhancement and efficiency loss mechanisms of the “slot-groove” CT in a low-speed axial compressor. Results of the combination of laboratory tests and computational fluid dynamics (CFD) data demonstrate that the performance level of the hybrid CT lies in between those two traditional CTs. Simulation results indicate that the difference in the SMIs generated by CTs is closely related to their influences on the vortex trajectory of tip leakage. The stronger and tighter the vortex is, the more the vortex trajectory is inclined toward the blade suction side. Consequently, the interface between tip leakage flow and incoming main flow is pushed downstream and stability is enhanced. The flow loss induced by CTs is explored based on the entropy contours, and the high entropy in the “slot-groove” treated casing produces more efficiency decrease than the “full-groove” CT. Incorporating the “full-slot” CT not only increases entropy generation in the axial skewed slots but also induces considerable flow loss in the blade passage near the casing, thus reducing efficiency most significantly.

Rake impact on turboshaft compressors, a numerical study

2020 ◽  
Vol 92 (8) ◽  
pp. 1169-1176
Author(s):  
Valeriu Dragan ◽  
Oana Dumitrescu ◽  
Ion Malael ◽  
Adrian Daniel Azoitei
Keyword(s):  
Transport Model ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Rake Angle ◽  
Content Type ◽  
Gap Flow ◽  
Tip Gap Flow

Purpose Turboshaft engines usually include one centrifugal compressor due to its high-pressure ratio, stability and compactness. Many designers rely on positive raking to decrease tip gap flow and therefore losses. However recent optimization studies revealed geometries contradicting this canonic view. Hence, this paper aims to investigate how the rake angle alone can influence performance and to which extent. Design/methodology/approach A turboshaft representative impeller was chosen and altered for null and +/−30° rake angles. Menter's shear stress transport model is used for steady computational fluid dynamics simulations, sweeping the nominal speedline at various tip clearances. Backsweep distribution is identical in all cases, isolating rake influence. Findings Pressure ratio was lowered for the both positively and negatively raked blades, but through distinct aerodynamic mechanisms. Although the flow through the tip gap was lower for the positive rake, this is due to lower blade loading. Splitter comparison reveal that these effects are more pronounced in the radial regions. Practical implications Some of the findings may extend beyond turboshaft engines, into turbochargers, home appliances or industrial blowers. However, all extrapolations must consider specific differences between these applications. Turboshaft compressors designers can benefit from this study when setting up their free parameters and penalty functions in the early concept stages. Originality/value Only few similar studies can be found in the literature to date, none similar to turboshaft applications. Also, this impeller is designed to eliminate leading edge shocks and suction side boundary layer separation, which makes it easier to isolate the tip gap flow effects. The authors also provide a framework on which semi-empirical design equations can be further developed to incorporate rake into 1D design tools.

scholarly journals Axial Flow Compressor Stability Enhancement: Circumferential T-Shape Grooves Performance Investigation

Aerospace ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 12
Author(s):  
Marco Porro ◽  
Richard Jefferson-Loveday ◽  
Ernesto Benini
Keyword(s):  
Vortex Breakdown ◽  
Pressure Ratio ◽  
Axial Flow ◽  
Suction Side ◽  
Treatment Technique ◽  
Tip Leakage Flow ◽  
Stall Inception ◽  
Stall Margin ◽  
Casing Treatment ◽  
Stall Margin Improvement

This work focuses its attention on possibilities to enhance the stability of an axial compressor using a casing treatment technique. Circumferential grooves machined into the case are considered and their performances evaluated using three-dimensional steady state computational simulations. The effects of rectangular and new T-shape grooves on NASA Rotor 37 performances are investigated, resolving in detail the flow field near the blade tip in order to understand the stall inception delay mechanism produced by the casing treatment. First, a validation of the computational model was carried out analysing a smooth wall case without grooves. The comparisons of the total pressure ratio, total temperature ratio and adiabatic efficiency profiles with experimental data highlighted the accuracy and validity of the model. Then, the results for a rectangular groove chosen as the baseline case demonstrated that the groove interacts with the tip leakage flow, weakening the vortex breakdown and reducing the separation at the blade suction side. These effects delay stall inception, improving compressor stability. New T-shape grooves were designed keeping the volume as a constant parameter and their performances were evaluated in terms of stall margin improvement and efficiency variation. All the configurations showed a common efficiency loss near the peak condition and some of them revealed a stall margin improvement with respect to the baseline. Due to their reduced depth, these new configurations are interesting because they enable the use of a thinner light-weight compressor case as is desirable in aerospace applications.

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