The Effect of an Upstream Turbine on a Low-Aspect Ratio Vane

2004 ◽  
Author(s):  
R. J. Miller ◽  
R. W. Moss ◽  
R. W. Ainsworth ◽  
N. W. Harvey
Keyword(s):  
High Pressure ◽  
Aspect Ratio ◽  
Leading Edge ◽  
Streamwise Vortex ◽  
Relative Magnitude ◽  
Large Radius ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Interaction Mechanisms ◽  
Low Aspect Ratio

The interaction between a high-pressure rotor and a downstream vane is dominated by vortex-blade interaction. Each rotor blade passing period two co-rotating vortex pairs, the tip-leakage and upper passage vortex and the lower passage and trailing shed vortex, impinge on, and are cut by, the vane leading edge. In addition to the streamwise vortex the tipleakage flow also contains a large velocity deficit. This causes the interaction of the tip-leakage flow with a downstream vane to differ from typical vortex blade interaction. This paper investigates the effect these interaction mechanisms have on a downstream vane. The test geometry considered was a low aspect ratio second stage vane located within a S-shaped diffuser with large radius change mounted downstream of a shroudless high-pressure turbine stage. Experimental measurements were conducted at engine-representative Mach and Reynolds numbers, and data was acquired using a fastresponse aerodynamic probe upstream and downstream of the vane. Time-resolved numerical simulations were undertaken with and without a rotor tip gap in order to investigate the relative magnitude of the interaction mechanisms. The presence of the upstream stage is shown to significantly change the structure of the secondary flow in the vane and to cause a small drop in its performance.

Unsteady winglet-cavity tip on leakage flow in a high-pressure turbine stage of low-aspect ratio

2017 ◽  
Vol 232 (20) ◽  
pp. 3708-3721 ◽  
Author(s):  
Zhihua Zhou ◽  
Shaowen Chen ◽  
Songtao Wang
Keyword(s):  
High Pressure ◽  
Aspect Ratio ◽  
Flow Characteristics ◽  
Leakage Flow ◽  
Turbine Stage ◽  
High Pressure Turbine ◽  
Tip Leakage ◽  
Low Aspect Ratio ◽  
Passage Vortex ◽  
Blade Tip

In an unshrouded high-pressure turbine, the upstream vane wake, vane–blade interaction and blade tip leakage flow indicate complex and unsteady flow characteristics. Considering a high-pressure turbine stage of low-aspect ratio, the effects of the flat tip, cavity tip and winglet-cavity tip on the unsteady flow characteristics are investigated by numerical simulation. The exit Mach number and Reynolds number based on the chord of vane are 0.9 and 5.5×105, respectively. The pressure ratio of stage is 2.4. The time-resolved results indicate that the winglet-cavity tip scheme has smaller time variation of the total performance parameters and obtains a smaller tip leakage mass flow and a higher turbine stage efficient than the other cases. The vane–rotor interaction affects the pressure distribution at the region of blade leading edge remarkably and leads to a large time variation of tip leakage mass flow at the front of blade tip. The unsteady aerodynamic performance is analyzed with entropy-increase distribution at stage outlet and the vane–rotor interaction is discussed by the entropy-increase phase–time and phase–phase diagrams at blade outlet. Compared with the flat tip and cavity tip, the upper passage vortex loss is reduced obviously by the winglet-cavity tip. Thus, it is evaluated that the improvement of turbine stage coefficient with winglet-cavity tip results from the reduction of the upper passage vortex loss.

scholarly journals Effects of Tip Leakage Flow on the Aerodynamic Performance and Stability of an Axial-Flow Transonic Compressor Stage

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4168
Author(s):  
Botao Zhang ◽  
Xiaochen Mao ◽  
Xiaoxiong Wu ◽  
Bo Liu
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Transonic Compressor

To explain the effect of tip leakage flow on the performance of an axial-flow transonic compressor, the compressors with different rotor tip clearances were studied numerically. The results show that as the rotor tip clearance increases, the leakage flow intensity is increased, the shock wave position is moved backward, and the interaction between the tip leakage vortex and shock wave is intensified, while that between the boundary layer and shock wave is weakened. Most of all, the stall mechanisms of the compressors with varying rotor tip clearances are different. The clearance leakage flow is the main cause of the rotating stall under large rotor tip clearance. However, the stall form for the compressor with half of the designed tip clearance is caused by the joint action of the rotor tip stall caused by the leakage flow spillage at the blade leading edge and the whole blade span stall caused by the separation of the boundary layer of the rotor and the stator passage. Within the investigated varied range, when the rotor tip clearance size is half of the design, the compressor performance is improved best, and the peak efficiency and stall margin are increased by 0.2% and 3.5%, respectively.

scholarly journals Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters

2016 ◽  
Author(s):  
Christopher Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent: current practice for a low aspect ratio vane; a design exempt from thickness constraints; and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitters geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flowfield was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

Tip Leakage Flow Instability in a Centrifugal Compressor

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Teng Cao ◽  
Tadashi Kanzaka ◽  
Liping Xu ◽  
Tobias Brandvik
Keyword(s):  
Shear Layer ◽  
Centrifugal Compressor ◽  
Large Scale ◽  
Flow Instability ◽  
Leading Edge ◽  
Main Stream ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Unstable Flow ◽  
Tip Leakage

Abstract In this paper, an unsteady tip leakage flow phenomenon is identified and investigated in a centrifugal compressor with a vaneless diffuser at near-stall conditions. This phenomenon is associated with the inception of a rotating instability in the compressor. The study is based on numerical simulations that are supported by experimental measurements. The study confirms that the unstable flow is governed by a Kelvin–Helmholtz type instability of the shear layer formed between the main-stream flow and the tip leakage flow. The shear layer instability induces large-scale vortex roll-up and forms vortex tubes, which propagate circumferentially, resulting in measured pressure fluctuations with short wavelength and high amplitude which rotate at about half of the blade speed. The 3D vortex tube is also found to interact with the main blade leading edge, causing the reduction of the blade loading identified in the experiment. The paper also reveals that the downstream volute imposes a once-per-rev circumferential nonuniform back pressure at the impeller exit, inducing circumferential loading variation at the impeller inducer, and causing circumferential variation in the unsteady tip leakage flow.

Influence of different blade numbers on the performance of “saddle zone” in a mixed flow pump

2021 ◽  
pp. 095765092110460
Author(s):  
Leilei Ji ◽  
Wei Li ◽  
Weidong Shi ◽  
Fei Tian ◽  
Shuo Li ◽  
...  
Keyword(s):  
Flow Field ◽  
Leading Edge ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Mixed Flow ◽  
Impeller Blade ◽  
Flow Angle ◽  
Tip Leakage ◽  
Vorticity Transport ◽  
Flow Pump

In order to study the effect of different numbers of impeller blades on the performance of mixed-flow pump “saddle zone”, the external characteristic test and numerical simulation of mixed-flow pumps with three different impeller blade numbers were carried out. Based on high-precision numerical prediction, the internal flow field and tip leakage flow field of mixed flow pump under design conditions and stall conditions are investigated. By studying the vorticity transport in the stall flow field, the specific location of the high loss area inside the mixed flow pump impeller with different numbers of blades is located. The research results show that the increase in the number of impeller blades improve the pump head and efficiency under design conditions. Compared to the 4-blade impeller, the head and efficiency of the 5-blade impeller are increased by 5.4% and 21.9% respectively. However, the increase in the number of blades also leads to the widening of the “saddle area” of the mixed-flow pump, which leads to the early occurrence of stall and increases the instability of the mixed-flow pump. As the mixed-flow pump enters the stall condition, the inlet of the mixed-flow pump has a spiral swirl structure near the end wall for different blade numbers, but the depth and range of the swirling flow are different due to the change in the number of blades. At the same time, the change in the number of blades also makes the flow angle at 75% span change significantly, but the flow angle at 95% span is not much different because the tip leakage flow recirculates at the leading edge. Through the analysis of the vorticity transport results in the impeller with different numbers of blades, it is found that the reasons for the increase in the values of the vorticity transport in the stall condition are mainly impacted by the swirl flow at the impeller inlet, the tip leakage flow at the leading edge and the increased unsteady flow structures.

scholarly journals Effect of Tip Clearance on Helico-Axial Flow Pump Performance at Off-Design Case

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1653
Author(s):  
Nengqi Kan ◽  
Zongku Liu ◽  
Guangtai Shi ◽  
Xiaobing Liu
Keyword(s):  
Optimization Design ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Leading Edge ◽  
Tip Clearance ◽  
Hydraulic Loss ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Axial Flow Pump ◽  
Flow Pump

To reveal the effect of tip clearance on the flow behaviors and pressurization performance of a helico-axial flow pump, the standard k-ε turbulence model is employed to simulate the flow characteristics in the self-developed helico-axial flow pump. The pressure, streamlines and turbulent kinetic energy in a helico-axial flow pump are analyzed. Results show that the tip leakage flow (TLF) forms a tip-separation vortex (TSV) when it enters the tip clearance and forms a tip-leakage vortex (TLV) when it leaves the tip clearance. As the blade tip clearance increases, the TLV moves along the blade from the leading edge (LE) to trailing edge (TE). At the same time, the entrainment between the TLV and the main flow deteriorates the flow pattern in the pump and causes great hydraulic loss. In addition, the existence of tip clearance also increases the possibility of TLV cavitation and has a great effect on the pressurization performance of the helico-axial flow pump. The research results provide the theoretical basis for the structural optimization design of the helico-axial flow pump.

Leading Edge and Wing Tip Flow Control on Low Aspect Ratio Wings

2010 ◽  
Author(s):  
Stefan Vey ◽  
David Greenblatt ◽  
Christian Nayeri ◽  
Christian Paschereit
Keyword(s):  
Aspect Ratio ◽  
Flow Control ◽  
Leading Edge ◽  
Low Aspect Ratio ◽  
Wing Tip ◽  
Low Aspect Ratio Wings

scholarly journals On the lift-optimal aspect ratio of a revolving wing at low Reynolds number

2018 ◽  
Vol 15 (143) ◽  
pp. 20170933 ◽  
Author(s):  
T. Jardin ◽  
T. Colonius
Keyword(s):  
Aspect Ratio ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Rossby Number ◽  
Subsequent Work ◽  
High Lift ◽  
Low Aspect Ratio ◽  
Axis Of Rotation ◽  
Edge Vortex ◽  
Convergent Solution

Lentink & Dickinson (2009 J. Exp. Biol. 212 , 2705–2719. ( doi:10.1242/jeb.022269 )) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.

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