scholarly journals Numerical Research on the Impact of Axial Position of Endwall Suction Slot on Tip Leakage Flow

2020 ◽  
Vol 13 (04) ◽  
Keyword(s):  
Axial Position ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Numerical Research ◽  
The Impact ◽  
Suction Slot

Prediction of Tip Leakage Vortex Dynamics in an Axial Compressor Cascade Using RANS Analyses

2020 ◽  
Author(s):  
Martina Ricci ◽  
Roberto Pacciani ◽  
Michele Marconcini ◽  
Andrea Arnone
Keyword(s):  
Vortex Dynamics ◽  
Eddy Viscosity ◽  
Axial Compressor ◽  
Viscosity Model ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Eddy Viscosity Model ◽  
The Impact

Abstract The tip leakage flow in turbine and compressor blade rows is responsible for a relevant fraction of the total loss. It contributes to unsteadiness, and have an important impact on the operability range of compressor stages. Experimental investigations and, more recently, scale-resolving CFD approaches have helped in clarifying the flow mechanism determining the dynamics of the tip leakage vortex. Due to their continuing fundamental role in design verifications, it is important to establish whether RANS/URANS approaches are able to reproduce the effects of such a flow feature, in order to correctly drive the design of the next generation of turbomachinery. Base studies are needed in order to accomplish this goal. In the present work the tip leakage flow in axial compressor rotor blade cascade have been studied. The cascade was tested experimentally in Virginia Tech Low Speed Cascade Wind Tunnel in both stationary and moving endwall configurations. Numerical analyses were performed using the TRAF code, a state-of-the-art in-house-developed 3D RANS/URANS flow solver. The impact of the numerical framework was investigated selecting different advection schemes including a central scheme with artificial dissipation and a high-resolution upwind strategy. In addition, two turbulence models have been used, the Wilcox linear k–ω model and a non-linear eddy viscosity model (Realizable Quadratic Eddy Viscosity Model), which accounts for turbulence anisotropy. The numerical results are scrutinized using the available measurements. A detailed discussion of the vortex evolution inside the blade passage and downstream of the blade trailing edge is presented in terms of streamwise velocity, streamwise vorticity, and turbulent kinetic energy contours. The purpose is to identify guidelines for obtaining the best representation of the vortex dynamics, with the methodologies usually employed in routine design iterations and, at the same time, evidence their weak aspects that need further modelling efforts.

Numerical analysis of the effects of circumferential groove casing suction in a counter-rotating axial flow compressor

2020 ◽  
pp. 095765092095169
Author(s):  
Tian Liang ◽  
Bo Liu ◽  
Stephen Spence ◽  
Liying Jiao
Keyword(s):  
Axial Flow ◽  
Main Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Tip Leakage ◽  
Axial Flow Compressor ◽  
Circumferential Groove ◽  
Flow Compressor ◽  
The Impact

To extend the current understanding of the circumferential groove casing suction applied to a counter-rotating axial flow compressor, the impact of different axial locations of the circumferential suction groove on the characteristics of the tip leakage flow (TLF) and the corresponding physical mechanisms producing the stability enhancement have been studied based on validated numerical simulations. The results show that the optimal location for the suction groove is at around 20% axial chord, which demonstrated a high potential for reducing additional stall mass flow coefficient with about 8.4% increment in the stall margin. After the casing suction groove was applied, the interface between the incoming main flow and TLF was pushed significantly downstream in the second rotor. The blade loading in the region below the groove, the tip leakage flow angle and the reversed axial momentum flux injected into main flow passage through the tip gap were all reduced, which contributed to the stall margin improvement. Detailed analysis of the tip leakage flow structures showed that the TLF originating from different chord locations played different roles in the stall inception process. It was found to be more effective to improve stall margin and adiabatic efficiency by controlling the front part of the TLF, which was most sensitive.

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.

Numerical Study on the Response of Tip Leakage Flow Unsteadiness to Micro Tip Injection in a Low-Speed Isolated Compressor Rotor

2007 ◽  
Author(s):  
Shaojuan Geng ◽  
Hongwu Zhang ◽  
Jingyi Chen ◽  
Weiguang Huang
Keyword(s):  
Numerical Study ◽  
The Self ◽  
Axial Position ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Low Speed ◽  
Tip Leakage ◽  
Flow Unsteadiness ◽  
Compressor Rotor ◽  
Tip Injection

A numerical study on the unsteady tip leakage flow with discrete micro tip injection from casing shroud in a low-speed isolated axial compressor rotor is presented. The main target is to clarify the flow mechanism of how the stall control measures act on the tip leakage flow typified by its self-induced unsteady flow characteristics. At operating condition near stall point, a series of calculations have been carried out for different axial position of injector and different injected mass flow rate. The computation results of flow field near rotor tip region show that under the influence of injected flow, the transient pressure distribution fluctuates along blade chord on both pressure and suction sides with respect to the relative position of injector and rotor. The pressure difference across the pressure and suction sides of compressor blade changes correspondingly, thus introduces a forced flow unsteadiness interacting with the unsteady tip leakage flow. When the injection is relatively strong and able to meet the tip leakage flow at its origination, the self-induced unsteadiness of tip leakage flow can be suppressed completely. In most cases, both frequency components of the self-induced unsteadiness and forced-induced unsteadiness are co-existing. The corresponding transient flow contours show that a local high pressure spot appears near blade pressure side, which moves downstream and shifts the tip leakage flow trajectory with less or without touching the neighboring pressure surface of the blade. Based on this understanding of discrete tip injection as force-induced flow unsteadiness, the numerical results are also analyzed to optimize the effect of injection in changing the route of tip leakage flow trajectories and therefore the chance of stability improvement of the compressor rotor.

Numerical Research on Effects of Shroud Contraction on Tip Leakage Flow and Overall Performance of Axial Compressors

2017 ◽  
Author(s):  
Yufan Zhang ◽  
Jiabin Li ◽  
Lucheng Ji
Keyword(s):  
Great Influence ◽  
Axial Compressor ◽  
Detailed Comparison ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Axial Compressors ◽  
Tip Leakage ◽  
Numerical Research ◽  
Overall Performance ◽  
Inclined Angle

In the design of an axial compressor, many designers take advantage of this technology and employ contracted shroud. What is its impact on tip leakage flow and overall performance of the axial compressor? What is its mechanism? In this paper, the NASA Rotor67 is taken as a research case, and parameterized study is conducted to investigate the effects of shrouds with different inclined angles. The inclined angles range from 0° to 13°. Based on the above described plan, numerical simulations are conducted to the original rotor67 and its modified versions with inclined shroud. To remove factors that might interfere the results, original Rotor 67 and all the blades with modified shroud should be compared to their optimal design status. Adjoint optimization is used to give the optimum blade corresponding to each shroud with different blade inclined angles. Then adjoint optimization was used again to give the optimum meridional flowpath for all the cases with different shroud inclined angles. This provides a powerful tool to evaluate the accuracy of the aforementioned prediction. A detailed comparison is made between the original flowpath and the optimized ones. Numerical results are analyzed in detail between original Rotor67 and its modified versions. The results show that the shroud inclined angle has an effect on the overall performance of the blade. It will also redistribute the velocity triangles and the chordwise distribution of aero load in the tip region. Hence it exerts great influence on the tip leakage flow field in the meantime. Shroud with suitable inclined angles can suppress the developing of leakage vortex , and the best-inclined angle for rotor 67 is found to be roughly 11°.

Numerical Investigation on Loss Mechanism and Performance Improvement for a Zero Inlet Swirl Turbine Rotor

2017 ◽  
Author(s):  
Wei Zhao ◽  
Qingjun Zhao ◽  
Xiuming Sui ◽  
Weiwei Luo ◽  
Jianzhong Xu
Keyword(s):  
Suction Side ◽  
Turbine Rotor ◽  
Axial Position ◽  
Leakage Flow ◽  
Blade Profile ◽  
Tip Leakage Flow ◽  
Loss Mechanism ◽  
Tip Leakage ◽  
Stagnation Points ◽  
Inlet Swirl

A zero inlet swirl turbine rotor (ZISTR) is originally presented as the first stage in a multistage vaneless counter-rotating turbine (MVCT), which only consists of 4 rotors without any vanes. The vanes upstream of a ZISTR are removed to reduce the turbine weight and length, as well as the viscous losses and coolants associated with vanes. However, due to the lack of inlet swirl the stagger angles for ZISTR blade profiles are high and the blade deflections are very small, resulting in almost straight cambers and very thin airfoils. The motivation of this paper is to reveal the overall performance and key loss sources of a ZISTR associated with its special blade profile, and provide corresponding optimization approaches for its practical usages. The 3D viscous numerical results show that the wake, the suction side trailing edge shock and the tip leakage flow have substantial influence on the rotor performance. To optimize the performance of a ZISTR, reducing blade solidity is proposed to decrease the viscous and shock losses by increasing the portion of the inviscid mainstream. Leaned blade is also presented to restrict the tip leakage flow by adjusting the axial position of stagnation points on the blade profile, obtaining an increase in efficiency of 0.9%. The off-design performance of the optimized rotor is also presented to show the effect of the blade lean on efficiency at various rotating speeds and back pressures.

Impact of Passive Tip-Injection on Tip-Leakage Flow in Axial Low Pressure Turbine Stage

2015 ◽  
Author(s):  
Pouya Ghaffari ◽  
Reinhard Willinger ◽  
Sabine Bauinger ◽  
Andreas Marn
Keyword(s):  
Aerodynamic Resistance ◽  
Low Pressure ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Low Pressure Turbine ◽  
Blade Tip ◽  
Tip Injection ◽  
The Impact

In addition to geometrical modifications of the blade tip for reducing tip-leakage mass flow rate the method of passive tip-injection serves as an aerodynamic resistance towards the tip-leakage flow. The impact of this method has been investigated thoroughly at unshrouded blades in linear cascades. Furthermore combinations of shrouded blades with passive tip-injection have been investigated analytically as well as via numerical simulations for incompressible flow in linear cascades. The objective of this paper is to consider a real uncooled low pressure turbine stage with shrouded blades and to investigate the effect of passive tip-injection on various operational characteristics. CFD calculations have been carried out in a rotational frame taking into consideration compressible flow and serve for evaluating the method of passive tip-injection in the given turbine stage. Experimental data obtained from the machine without tip-injection serve as boundary conditions for the CFD calculations.

A Numerical Investigation of the Flow Mechanisms in a HPC Front Stage With Axial Slots

2003 ◽  
Author(s):  
I. Wilke ◽  
H.-P. Kau
Keyword(s):  
Rotor Blade ◽  
Flow Stability ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Blade Passage ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Front Stage ◽  
The Impact ◽  
Compressor Efficiency

This paper describes the impact of axial slots on the flow field in a transonic rotor blade row. The presented results are completely based on time-accurate 3-dimensional numerical simulations of a high pressure compressor front stage with and without casing treatment. Two different axial positions of a casing treatment consisting of axial slots were tested for their impact on flow stability and efficiency. The first tested position (configuration 1) was chosen in a conventional way. The slots extend approximately from the leading up to the trailing edge of the rotor blades. As expected, the simulations of the compressor stage with this configuration showed a significant increase in flow stability near surge compared to the solid wall case. However, a non negligible decrease in efficiency is also observed. Analyses of flow interactions between casing treatment and rotor blade rows under transonic conditions lead to the general conclusion that the stabilizing effect of circumferential grooves or axial slots mainly results from their impact on the tip leakage flow and its resulting vortex. A characteristic vortex inside the slots is observed in the simulations with the conventionally positioned casing treatment. This vortex removes fluid out of downstream parts of the blade passage and feeds it back into the main flow further upstream. The resulting impact on the tip leakage flow is responsible for the increased flow stability. However, the interaction between the configuration 1 casing treatment flow and the blade passage flow results in a significant relocation of the blade passage shock in the downstream direction. This explains the observed decrease in compressor efficiency. A second slot position (configuration 2) was tested with the objective to improve compressor efficiency. The casing treatment was shifted upstream, so that only 25% of the blade chord remained under the slots. The simulations carried out demonstrate that this shift positively effects the resulting efficiency, but maintains the increased level of flow stability. A time-accurate analysis of the flow shows clearly that the modified casing treatment stabilizes the tip leakage vortex and reduces the influence on the flow inside the blade passage.

Numerical investigation of tip clearance size effect on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor

2017 ◽  
Vol 231 (3) ◽  
pp. 474-484 ◽  
Author(s):  
Xiaochen Mao ◽  
Bo Liu
Keyword(s):  
Size Effect ◽  
Axial Compressor ◽  
Size Variation ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Remarkable Effect ◽  
Tip Leakage ◽  
Dual Stage ◽  
The Impact

Based on a validation of the numerical methods with an experiment, numerical simulations are carried out to study the effect of tip clearance size on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor. The predicted results showed that the variation of the tip clearance size in rotor2 has a more significant impact on the overall performance and stall margin of the compressor. In addition, the impact of the tip clearance size effect is mainly on the rotor with the tip clearance size variation. The variation of the tip clearance size in rotor2 almost has no influence on the performance of rotor1, while the performance of rotor2 is increased about 1.37% at near-stall point when the tip clearance size of rotor1 is increased to 1.0 mm from 0.5 mm. At peak efficiency condition, the tip clearance size variation in rotor1 has remarkable influence on the tip leakage vortex intensity, onset point and trajectory in rotor1, but has little influence on those in rotor2. However, the tip clearance size variation in rotor2 has remarkable effect on those in both rotors. Different tip clearance size combination schemes can impact the stall-free characteristic in the counter-rotating axial compressor.

On the Interactions of a Rotor Blade Tip Flow With Axial Casing Grooves in an Axial Compressor Near the Best Efficiency Point

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Huang Chen ◽  
Yuanchao Li ◽  
Joseph Katz
Keyword(s):  
Rotor Blade ◽  
Leading Edge ◽  
Secondary Flows ◽  
Maximum Efficiency ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Flow Angle ◽  
Tip Leakage ◽  
Blade Tip ◽  
The Impact

Experiments in a refractive index-matched axial turbomachine facility show that semicircular skewed axial casing grooves (ACGs) reduce the stall flowrate by 40% but cause a 2.4% decrease in the maximum efficiency. Aiming to elucidate mechanism that might cause the reduced efficiency, stereo-PIV measurements examine the impact of the ACGs on the flow structure and turbulence in the tip region near the best efficiency point (BEP), and compare them to those occurring without grooves and at low flowrates. Results show that the periodic inflow into the groove peaks when the rotor blade pressure side (PS) overlaps with the downstream end of the groove, but diminishes when this end faces the suction side (SS). Entrainment of the PS boundary layer and its vorticity generates a vortical loop at the entrance to the groove, and a “discontinuity” in the tip leakage vortex (TLV) trajectory. During exposure to the SS, the backward tip leakage flow separates at the entrance to the groove, generating a counter-rotating circumferential “corner vortex,” which the TLV entrains into the passage at high flowrates. Interactions among these structures enlarge the TLV and create a broad area with secondary flows and elevated turbulence near the groove's downstream corner. A growing shear layer with weaker turbulence also originates from the upstream corner. The groove also increases the flow angle upstream of the blade tip and varies it periodically. Accordingly, the circulation shed from the blade tip and strength of leakage flow increase near the blade leading edge (LE).

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