scholarly journals On Scaling Method to Investigate High-Speed Over-Tip-Leakage Flow at Low-Speed Condition

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Hongmei Jiang ◽  
Li He ◽  
Qiang Zhang ◽  
Lipo Wang
Keyword(s):  
High Speed ◽  
Turbine Blades ◽  
Flow Distribution ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Scaling Method ◽  
Low Speed ◽  
Tip Leakage ◽  
Speed Condition

Modern high-pressure turbine blades operate at high-speed conditions. The over-tip-leakage (OTL) flow can be high-subsonic or even transonic. From the consideration of problem simplification and cost reduction, the OTL flow has been studied extensively in low-speed experiments. It has been assumed a redesigned low-speed blade profile with a matched blade loading should be sufficient to scale the high-speed OTL flow down to the low-speed condition. In this paper, the validity of this conventional scaling approach is computationally examined. The computational fluid dynamics (CFD) methodology was first validated by experimental data conducted in both high- and low-speed conditions. Detailed analyses on the OTL flows at high- and low-speed conditions indicate that, only matching the loading distribution with a redesigned blade cannot ensure the match of the aerodynamic performance at the low-speed condition with that at the high-speed condition. Specifically, the discrepancy in the peak tip leakage mass flux can be as high as 22%, and the total pressure loss at the low-speed condition is 6% higher than the high-speed case. An improved scaling method is proposed hereof. As an additional dimension variable, the tip clearance can also be “scaled” down from the high-speed to low-speed case to match the cross-tip pressure gradient between pressure and suction surfaces. The similarity in terms of the overall aerodynamic loss and local leakage flow distribution can be improved by adjusting the tip clearance, either uniformly or locally.

scholarly journals On Scaling Method to Investigate High-Speed Over-Tip-Leakage Flow at Low-Speed Condition

2017 ◽  
Author(s):  
Hongmei Jiang ◽  
Li He ◽  
Qiang Zhang ◽  
Lipo Wang
Keyword(s):  
High Speed ◽  
Flow Distribution ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Scaling Method ◽  
Low Speed ◽  
Aerodynamic Loss ◽  
Tip Leakage ◽  
Speed Condition

Modern High Pressure Turbine (HPT) blades operate at high speed conditions. The Over-Tip-Leakage (OTL) flow, which plays a major role in the overall loss generation for HPT, can be high-subsonic or even transonic. In practice from the consideration of problem simplification and cost reduction, the OTL flow has been studied extensively in low speed experiments. It has been assumed a redesigned low speed blade profile with a matched blade loading should be sufficient to scale the high speed OTL flow down to the low speed condition. In this paper, the validity of this conventional scaling approach is computationally examined. The CFD methodology was firstly validated by experimental data conducted in both high and low speed conditions. Detailed analyses on the OTL flows at high and low speed conditions indicate that, only matching the loading distribution with a redesigned blade cannot ensure the match of the aerodynamic performance at the low speed condition with that at the high-speed condition. Specifically, the discrepancy in the peak tip leakage mass flux can be as high as 22.2%, and the total pressure loss at the low speed condition is 10.7% higher than the high speed case. An improved scaling method is proposed hereof. As an additional dimension variable, the tip clearance can also be “scaled” down from the high speed to low speed case to match the cross-tip pressure gradient between pressure and suction surfaces. The similarity in terms of the overall aerodynamic loss and local leakage flow distribution can be improved by adjusting the tip clearance, either uniformly or locally. The limitations of this proposed method are also addressed in this paper.

The Dual Mechanisms and Implementations of Stability Enhancement With Discrete Tip Injection in Axial Flow Compressors

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Jichao Li ◽  
Feng Lin ◽  
Zhiting Tong ◽  
Chaoqun Nie ◽  
Jingyi Chen
Keyword(s):  
High Speed ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Clearance Ratio ◽  
Momentum Ratio ◽  
Low Speed ◽  
Tip Leakage ◽  
Tip Injection ◽  
Stability Enhancement

The mechanisms and implementation scheme of discrete tip air injection are studied in this paper. A map that summarized the routes to stall is then proposed. It is argued that there exists a critical tip clearance ratio that separates two different routes to stall, which infers that the stability enhancement can also be based on two different mechanisms. A summation of tip injection test data in the literatures demonstrates that this is actually the case. For each compressor, there are two trends in the curve of stall margin improvement (SMI) versus injected momentum ratio, which is separated by a demarcation ratio of injected momentum. A series of tests are done in a low-speed compressor to show that the micro injection, wherein the injected momentum ratio is less than the demarcation ratio, can only act on the tip leakage flow (TLF) and thus provide small SMI by weakening the self-induced unsteadiness of the tip leakage flow (UTLF), while in contrast the macro injection can provide much larger SMI by acting on the main flow, decreasing the inlet angle-of-attack and thus unloading the blade tip. Based on these findings, a novel detecting-actuating scheme is designed and implemented onto a low-speed axial compressor. A cross-correlation coefficient is used to detect the UTLF in the prestall process way before stall inception and then to guide the opening of proportional electromagnetic valves. The injected flow rate can be smoothly varied to cover both micro- and macro-injection, which saves energy when the compressor is stable, and provides protection when it is needed. The same principle is applied to a high-speed compressor with a recirculation injection and the preliminary test results are very encouraging.

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.

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.

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

2005 ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage

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 110 degrees and blade chord of 1.0 m. Data was 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 (PIV) 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 endwall 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 under-tip flow near the endwall due to the moving wall is observed and the effect on the tip leakage vortex examined.

Parametric study of injection from the casing in an axial turbine

2019 ◽  
Vol 234 (5) ◽  
pp. 582-593
Author(s):  
Sarallah Abbasi ◽  
Afshin Gholamalipour
Keyword(s):  
Flow Structure ◽  
Control Method ◽  
Turbine Blades ◽  
Leading Edge ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Axial Turbine ◽  
Tip Leakage ◽  
Turbine Performance

Tip leakage flow reduces both efficiency and performance of axial turbines and damages turbine blades as well. Therefore, it is of great importance to identify and control tip leakage flow. This study investigated the effect of flow injection (from the casing), alongside flow structure, on turbine performance. Additionally, the effect of different injection parameters, including injection mass flow rate, angle, location, and diameter on the turbine performance are evaluated. A numerical analysis of the flow in a two-stage axial turbine was employed by using CFX software. To ensure the accuracy of the results, turbine performance curves were compared with the experimental results, which are in good agreement. Analyses revealed that active control method reduces tip leakage flow, improves turbine performance, and increases the efficiency by 1% to 5% as well. A parametric investigation of the tip injection has sought to identify how various parameters affect the turbine performance. The cross-section diameter and the angle of injection had no significant increase on efficiency. Additionally, results showed that at a point 9 mm further from the leading edge, the injection degree of effectiveness is optimum. Finally, analysis of the flow structure in the tip clearance region supported the tip leakage flow reduction.

Numerical Study on Tip Leakage Flow Structure of an Axial Flow Compressor Rotor

2014 ◽  
Author(s):  
Chenkai Zhang ◽  
Jun Hu ◽  
Zhiqiang Wang ◽  
Wei Yan ◽  
Chao Yin ◽  
...  
Keyword(s):  
Flow Structure ◽  
Large Scale ◽  
Numerical Study ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage

To deepen the knowledge of tip leakage flow/vortex flow structure in the tip clearance of axial compressor rotors, this paper presents steady numerical studies on a subsonic rotor. The rotor and its related low-speed large-scale repeating-stage axial compressor are used for low-speed model testing of a modern high-pressure compressor. Results were first compared with available experimental data to validate adopted numerical method. Then complex endwall flow structure and flow loss mechanism at design operating point were studied. At last, comparisons were made for tip leakage vortex structure, interface of the leakage flow/main flow, endwall blockage and loss between design and near-stall operating points. Results show that only the spilled flows below 62.5% clearance height at the leading edge will roll into tip leakage vortex for this rotor. In addition, tip leakage vortex plays a secondary important role for higher positions, where secondary leakage flow occurs and occupies broader chordwise range. Although tip leakage vortex would expand and strongly mix with the mainflow when it propagates downstream, which leads to a rapid reduction of the normalized streamwise vorticity, the value of the normalized helicity shows that concentrated vortex feature is still maintained.

scholarly journals Commencement and Development Processes of Flow Unsteadiness at Tip Clearance Region of a Low Speed Axial Compressor Rotor Blade Row

2017 ◽  
Vol 61 (4) ◽  
pp. 288
Author(s):  
Marhamat Zeinali ◽  
Sarallah Abbasi ◽  
Abolfazl Hajizadeh Aghdam
Keyword(s):  
Three Dimensional ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Low Speed ◽  
Tip Leakage ◽  
Blade Row ◽  
Development Processes ◽  
Flow Frequency

Commencement and development processes of unsteadiness, caused by blade row tip leakage flow in a low speed axial compressor, are investigated and results are presented in this paper. Analyses are based on results obtained through numerical simulation of unsteady three dimensional viscous flows. Discretization of the Navier-Stokes’s equations has been carried out based on upwind second-order scheme and k-ω-SST turbulence modeling was used for estimation of eddy viscosity.Three different circumstances, including design point and two near stall conditions are considered for investigation and discussion. Tip leakage flow frequency spectrums were examined through surveying instantaneous static pressure signals imposed on the blades surfaces. Focusing on time dependent flow structure results signified existence of some pressure peaks at near stall conditions. These regions, which are created as a result of interaction between main inflow and tip leakage flow, lead to occurrence of self-induced unsteadiness. However, at design condition, flow is more affected by the main inflow instead of the tip leakage flow. By occurrence of self-induced unsteadiness, which occurs at near stall condition, tip leakage vortex flow starts to fluctuate at a frequency about the blade passing frequency. Further decrease in the flow rate up to a specified value showed no significant variations in the leakage flow frequency, but, on the other hand, magnified amplitudes of this unsteadiness.

scholarly journals A Prediction of 3-D Viscous Flow and Performance of the NASA Low-Speed Centrifugal Compressor

1990 ◽  
Author(s):  
John Moore ◽  
Joan G. Moore
Keyword(s):  
Centrifugal Compressor ◽  
Three Dimensional ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Present Calculation ◽  
Tip Leakage Flow ◽  
Flow Measurements ◽  
Low Speed ◽  
Tip Leakage ◽  
Flow Mixing

A prediction of the three-dimensional turbulent flow in the NASA Low-Speed Centrifugal Compressor Impeller has been made. The calculation was made for the compressor design conditions with the specified uniform tip clearance gap. The predicted performance is significantly worse than that predicted in the NASA design study. This is explained by the high tip leakage flow in the present calculation and by the different model adopted for tip leakage flow mixing. The calculation gives an accumulation of high losses in the shroud/pressure-side quadrant near the exit of the impeller. It also predicts a region of meridional backflow near the shroud wall. Both of these flow features should be extensive enough in the NASA impeller to allow detailed flow measurements, leading to improved flow modelling. Recommendations are made for future flow studies in the NASA impeller.

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.

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