Tip Leakage Vortex Research Articles

Prediction method of tip vortex circulation based on hydrofoil load

In this paper, a theoretical derivation from the perspective of the force on the slender bodies arranged along the hydrofoil span is performed to explain why the vortex circulation Γvortex should theoretically be equal to the maximum bound circulation Γ0 around the hydrofoil. Then, a more accurate and operable prediction formulation based on hydrofoil load, Γvortex=kΓ0‾, is proposed, where k = 0.9–1. Γ0‾ is the averaged hydrofoil circulation along spanwise direction and its value can be obtained easily from hydrofoil load. To validate our new formulation, two typical vortex flows, i.e., tip leakage vortex (TLV) flow and tip vortex (TV) flow, are simulated with large eddy method. Our numerical results confirm that the variations of hydrofoil load along span would lead to streamwise vorticity, and then the rolling-up of latter leads to the vortex formation (Green, 1995). However, since the influential region of vortex is limited that not all streamwise vorticity could be entrained into the vortex and there are viscous and dissipation effects, the actual Γvortex cannot reach Γ0 but it is quite close to Γ0‾. The prediction formulation agrees well with the numerical results and available measured data.

The effect of tip clearance size on pre-stall flow features of a transonic axial compressor by using throttle model

This paper aims at the numerical analysis of the influence of tip clearance size on the pre-stall flow features of a transonic high-speed compressor by applying the throttle model at the exit of the compressor computational domain. Steady and unsteady calculations have been performed for design, double, and triple tip clearance sizes. The transition of the stall inception type when increasing the tip clearance size and the underlying flow physics has been analyzed in detail. The results show that the stall inception type transforms from spike to modal as the size of the tip clearance changes from design to triple tip clearance. The influence of the tip clearance size on the forward spillage of the tip leakage vortex near the stall limit, which is one of the two criteria for spike stall inception, is crucial for which type of stall inception would appear. For the design clearance case, a remarkable forward spillage of the tip leakage vortex occurs near the stall limit, leading to a typical strong spike stall inception. In the condition of double clearance, the intensity of tip leakage vortex spillage was weakened because the increase in the clearance size allows more low momentum tip leakage flow to go through the clearance instead of spilling from the leading edge. Thus, a weaker spike-type inception containing the content of modal disturbances was induced. Under the triple clearance condition, the high entropy gradient interface is located inside the blade passages all the time; thus, a typical modal-type stall inception appears.

Comparative study on the wake dynamics of pump-jet and ducted propeller based on dynamic mode decomposition

A comparative study on the wake dynamics of a pump-jet propulsor (PJP) and a ducted propeller (DP) is conducted to investigate the effects of the pre-swirl stator and corresponding stator–rotor interaction on the wake evolution and destabilization mechanisms of a PJP system. The flow field analysis, vortex structure identification, and dynamic mode decomposition (DMD) analysis are carried out based on the numerical results obtained from delayed detached eddy simulations. The numerical hydrodynamic loading and flow field of the PJP are compared with experimental results, and they are in good agreement. Compared with the DP, the stator trailing vortices of the PJP interact with the rotor trailing vortices as well as the hub vortex, accelerating their diffusion and viscous dissipation. The pre-swirl stator triggers the generation of secondary vortices and moderates the spiral behavior of tip leakage vortices, which dominates the wake instability of PJP. The DMD analysis revealed that the wake field evolution is primarily characterized by the different mode structures at blade passing frequency and its multiples, especially in the PJP due to its strong stator–rotor interaction. The modal energy decays faster in the PJP wake field owing to its more turbulent and earlier instability. The hub vortex plays an important role in the wake dynamics of the DP.

Effect of water spray on tip leakage flow in a inlet stage of high-speed compressor

Water spray can reduce the inlet air temperature of the compressor inlet stage of the high-altitude high-speed turbine engine. In this paper, the Euler-Lagrange method is used to simulate the gas-liquid two-phase flow with droplet evaporation in NASA Stage 35. The effects of water spray on the heat and mass transfer characteristics of the stage, the tip leakage vortex structure, the unsteady characteristics of tip leakage flow and compressor performance are analyzed. The results show that the water spray increases the inlet mass flow and tip leakage flow rate of the stage, decreases the tip temperature. The inlet mass flow and tip leakage flow rate increase with the growth of inject mass flow rate and the decrease of droplet size. Water spray increases the scale of the main tip leakage vortex, and deflects the secondary leakage flow in the flow direction. Water spray increases the amplitude of pressure fluctuation at the blade tip. The frequency of pressure fluctuation at dry air condition is 0.2BPF, which decreases to 0.15BPF after water spraying. The leakage vortex weakens the strength of shock wave which causes a decline in the diffusing ability of blade; the leakage vortex is mixed with the main stream, resulting in a large aerodynamic loss. Although the injection of droplets increases the loss of tip leakage flow, it optimizes the performance of NASA stage 35 significantly. Spray increases the total pressure ratio of the R domain from 1.835 to 1.9; the total temperature ratio of the stage reduces from 1.225 to 1.203 and decreases the rotor loss coefficient from 0.12 to 0.08.

Blade tip leakage flow and heat transfer characteristics over a gas turbine blade at subsonic and transonic exit conditions

The present study numerically investigates the blade tip leakage flow (TLF) over a gas turbine blade cascade at low speed ( M ex = 0.1) and transonic ( M ex = 0.92) blade exit Mach numbers, with and without shroud motion. Various blade tip flow phenomena like flow separation and reattachment, flow choking, shock-boundary layer interaction (SBLI), and tip leakage vortex (TLV) are studied, and their influence on the heat transfer coefficient (HTC) distributions over the blade tip and near tip blade suction surface is investigated. The study has found some new zones of heat transfer due to the interaction of horseshoe vortices (HSV) with the blade tip. In addition to the primary TLV, a secondary TLV is formed, which increases near tip blade suction surface heat transfer. The flow transitions to supersonic speed in the aft portion of the blade tip for the transonic case resulting in complex heat transfer distribution due to SBLI, compared to near-uniform distribution for the low speed case. This supersonic flow results in a smaller flow separation zone near the aft portion of the pressure side tip edge for the transonic case compared to the low speed case. The qualitative nature of HTC near the leading edge of the blade tip resembles for low speed and transonic cases. However, near the trailing edge of the blade tip, the qualitative nature of HTC for the transonic case shows a substantial difference due to supersonic flow compared to the low speed case.

A New Unsteady Flow Control Technology of Centrifugal Compressor Based on Negative Circulation Concept

The tip leakage vortex (TLV) induced by the tip clearance flow has a significant impact on the performance of centrifugal compressors, causing impeller flow losses and reducing the stall margin. To solve this problem, an unsteady flow control technology called the NCFC method is proposed based on the concept of negative circulation control, realized by a vortex generator placed in a tube connected with the shroud through a hole. The approach is derived from a theoretical study of the compressor TLV by introducing a two-dimensional vortex model. A numerical simulation is then performed to verify the effectiveness of the NCFC method. The result shows that the NCFC method can greatly stabilize the flow field at the blade tip and improve the stall margin and efficiency of the compressor without reducing the total pressure ratio of the compressor, which has the characteristics of both unsteadiness and negative circulation effect. In addition, a HC method with only unsteady excitation effect is also studied for comparison, which only slightly stabilizes the blade tip flow and increases the stall margin of the compressor, suggesting that the NCFC is more effective than the HC. Finally, it is highly recommended to improve the efficiency of any unsteady jet/suction and separation flow interaction.

The unsteadiness of tip leakage vortex breakdown and its role in rotating instability

The unsteadiness due to tip leakage vortex (TLV) breakdown was studied using a special experimental test campaign in parallel with numerical simulations. The back flow vortex (BFV), an isolated vortex caused by TLV spiral-type breakdown, was found to play a key role in rotating instability (RI). High-speed pressure transducers were used to measure the unsteady pressure field at the casing end wall of the blade in an isolated subsonic compressor rotor, which identified a low-frequency fluctuation at the near stall condition. A single-passage unsteady Reynolds-averaged Navier–Stokes simulation was used to study the evolution of unsteady flow structures, validated by the experimental measurements. Two distinct kinds of periodically unsteady flow were revealed by the simulations. A high-frequency fluctuation corresponding to 1.0 blade pass frequency (BPF) was caused by the spiral-type breakdown of the TLV. The other low-frequency fluctuation corresponding to 0.5BPF was caused by the feedback interaction between the BFV and the blade loading. The BFV was generated by the TLV breakdown, which was separated from the twisted vortex core of the TLV, and it moved downstream along the pressure side of the adjacent blade. A larger sized BFV reduced the local loading of the adjacent blade. The TLV was weakened as a consequence of the reduced loading, resulting in a smaller sized BFV. The blade tip loading was relatively less affected by the small sized BFV rather than the larger sized BFV. Therefore, the blade loading recovered and the size of the BFV increased, repeating the cycle. This feedback mechanism produced a pressure fluctuation with a frequency equal to 0.5BPF, which was closely related to RI.

Investigation on the entropy production distribution in a multiphase pump considering gas–liquid two-phase velocity slip

To study the energy loss characteristics of a semi-open mixed-flow multiphase pump, an improved entropy generation theory considering the slip velocity was established to locate local areas with high energy loss. The relationships among local entropy generation, phase interface entropy generation, wall entropy generation, and unstable flow were analyzed for each component. The results showed that magnitude of interface entropy generation was similar to turbulent entropy generation and wall entropy generation, which could not be ignored. The interface entropy generation was mainly distributed at the leading edge, trailing edge, hub, and blade tip clearance. With an increased inlet gas volume fraction, the proportion of interfacial entropy production loss to total entropy production loss increased. As the inlet gas volume fraction increased to 30%, the interface entropy generation loss accounted for 70% of the local entropy generation loss at leading edge and 63% at trailing edge. The high interface entropy generation zone at the tip clearance region began to extend from the pressure side of the blade to the suction side of the blade. During the evolution of tip leakage vortex, the generation, unstable stretching, and breakup–regeneration stages were accompanied by a large loss of interface entropy generation.

Investigation of the orifice flow of over-the-rotor liner and its interaction with the rotor flow field

The emergence of ultra-high bypass ratio engines calls for advanced noise control technology. A promising technology is installing the acoustic liner at the casing over the rotor (OTR), forming the so-called OTR liner. Experiments have shown that this treatment could compensate for the reduced noise absorption due to the shortened intake length. Compared with the conventional liner receiving a pure acoustic pressure excitation, the OTR liner is exposed to the combined aerodynamic pressure perturbance and high acoustic pressure excitation, leading to complex flow mechanisms in the liner orifices. In this work, the large-eddy simulation method is used to investigate the flow phenomenon of OTR liner where each liner orifice is explicitly modeled to capture the flow behaviors at the blade tip proximity. Interesting findings are as follows: first, OTR liner orifices have an asynchronous dynamic response with a phase lag corresponding to the blade traversing speed; second, oscillating flow, resembling that in a classical Helmholtz resonator, is formed in the upstream liner orifices, while a bias flow appears in the downstream liner orifices. The dramatically different flow behaviors lead to non-uniform energy dissipation among orifices, implying the uniform impedance assumption in conventional acoustic liner definition fails when installing the liner near the rotor blade. Results also show that the orifice flow interacts with the blade tip leakage flow, affecting the development of the tip leakage vortex that may impact the rotor–stator interaction noise.

Internal Flow Phenomena of Two-Way Contra-Rotating Axial-Flow Pump-Turbine with Various Numbers of Blades in Pump Mode

The focus of this paper is to investigate how various numbers of blades impact the performance of a two-way contra-rotating axial-flow pump-turbine when operating in pump mode. In order to meet the two-way operation of the pump-turbine, the front and rear impellers are mirror-symmetric with the same hydraulic model, which ensures the consistent performance of the forward and reverse working conditions. However, when the two-stage impellers have the same number of blades, the dynamic–dynamic interference can be severe, which can threaten the stability of the unit. The present study explores the use of two-stage impellers with varying numbers of blades as a means of enhancing the performance of tidal energy units. By conducting numerical simulations on the front and rear impellers under different flow rates in pump mode, the impact of increasing the number of blades in each stage on the external characteristics of the pump-turbine is revealed. The internal flow characteristics of different models are analyzed, and the impact of the number of blades on the vortex is studied. Different blade numbers will have a certain impact on the internal flow of the two-way contra-rotating axial-flow pump–turbine. Increasing the number of blades will affect the development of tip-leakage vortices and promote their intersection with the wake. In addition, changes in the number of blades will have an impact on the location of the leading edge (LE) water impact on the rear impeller, which in turn affects the contours of vorticity of the rear impeller near the LE and the location of the suction surface (SS) flow separation. The findings of this study offer valuable insights for future research on the operation of contra-rotating axial-flow pump-turbines.

Understanding of tip clearance flow structure in high speed mixed flow compressor

This paper addresses the necessity to make a physical interpretation of a highly complex three-dimensional tip clearance flow field study for high-speed mixed-flow compressor having stage exit static pressure to inlet total pressure ratio of 3.8 with 39,836 rpm rotor speed. The four different tip configurations namely the constant (λ = 0.016 and 0.019) and variable (λ = 0.011 (inlet)-0.019 (exit) and 0.019 (inlet)-0.022 (exit)) tip clearances were numerically analysed using available experimental data-set. The numerical investigation reveals that in contrast to the classic jet-wake pattern, two anomalous velocity profiles formed at the impeller exit which results in pressure losses in the vaneless diffuser. Near the impeller inlet, the tip leakage flow rolls up to discrete tip leakage vortex structure for each tip clearance configuration. This results in the formation of a region of momentum deficit, recirculation zone, which gets weakened as it moves downstream. The tip clearance configuration is observed to profoundly influence the extent and vorticity of the tip leakage vortex. In the splitter blade passage, the tip leakage flow and Coriolis flow interact with passage flow, resulting in the formation of two secondary passage vortices that move downstream along the pressure and suction surface of the splitter blade. The tip clearance configuration directly influences the impeller exit jet-wake pattern by modulating the secondary passage vortices trajectory and vorticity. Moreover, off-design analysis for tip clearances λ = 0.016 and λ = 0.019, depict distinctive tip leakage vortex characteristics. When operating near the stall conditions (80% of design mass flow rate), λ = 0.019 exhibits bubble shape tip leakage vortex breakdown occurring near the impeller inlet. This result in a substantial change in the tip leakage vortex nature; expansion of the recirculation zone and early weakening of the vorticity in the tip leakage vortex. It is observed that vortex breakdown plays a vital role in characteristics of the passage flow field structure and compressor performance near the stall conditions.

Interaction mechanism between incoming vortex and tip leakage vortex breakdown of a compressor cascade

Tip leakage vortex breakdown (TVB) is an important flow character that affects the performance of axial compressors. In this study, the interaction mechanism between incoming vortex (IV) and TVB is investigated to improve the performance of compressor cascade. First, the pitchwise location effect, swirling direction effect, and intensity effect are investigated under steady condition; then, an unsteady investigation is conducted based on the steady results. Under steady condition, TVB can be completely removed by the incoming vortex near the suction surface with different swirling directions, and the normalized circulation at the edge of incoming vortex is 0.7. The loss coefficient caused by TVB is also reduced; however, a new loss is induced by IV. The flow mechanism is that the interaction between the incoming vortex and tip leakage vortex (TLV) can increase the chordwise momentum at the vortex core and the stability of the TLV. For TLV and IV, the two vortices have a tendency to combine downstream of the compressor cascade if they have the same swirling directions. However, when the swirling directions are different, TLV and IV propagate separately, and the intensity and stability of TLV are much higher. The loss of TLV is higher for the anticlockwise IV scheme because the intensity of the TLV is greater due to the interaction between TLV and IV. By utilizing the incoming vortex under unsteady condition, the TVB can also be reduced. The unsteadiness of the compressor cascade with the incoming vortex is significantly reduced by reducing the TVB.

Flow structure and vortex dynamics of blade surface transitional flow in the near-tip region of a compressor cascade

The mean flow topology and vortex dynamics of the blade surface transitional flow in the near-tip region of a C4 compressor blade were investigated using particle image velocimetry measurements with two configurations. The experiment was conducted in a compressor cascade at a chord Reynolds number of 24 000 and an incidence angle of 0°, and a laminar separation bubble was detected on the aft portion of the blade. In the half-span region of the blade, the separation is essentially two-dimensional without reattachment. The vortex dynamics are dominated by the periodic shedding of separated shear layer vortices and their interaction with the trailing edge vortices. The progressive spanwise evolution in the flow structures and vortex dynamics occur near the blade tip (70%–80% blade height), leading to an advanced, thinner separation. In contrast, the tip leakage vortex dominated region is restricted to approximately 20% of blade height from the blade tip. In this region, secondary flow effects are intensive enough to prevent laminar separation. Between the above two regions, there is a transition region (90% blade height), where the influence of the tip flow on the blade surface flow is relatively slight that merely suppresses the vortex shedding of the separated boundary layer, nor the whole shear layer. In the transition region, the velocity fluctuations are significantly reduced.

Investigation of Vaned-Recessed Casing Treatment in a Low-Speed Axial Flow Compressor, Part I: Time-Averaged Results

This paper investigates the effects of two modifications to a vaned recessed casing treatment. First, the shape of a circular curve was used in the top of the treated casing. Second, a fully curved guide vane was also applied. The goals of the modifications are to enhance the flow recirculation as well as to relieve the low-speed flow, which is normally accumulated within the corners of the vaned recessed casing treatment. The solid casing in addition to the two vaned recessed configurations with 23.2% and 53.5% rotor blade tip axial chord exposure have been studied numerically. The results indicated that two mechanisms are involved in the stall margin enhancement. First, the circumferential pressure gradient is reduced for both configurations. The reduction in pressure gradient largely reduces the development of tip leakage vortex and, thus, the generation of low-speed fluid is diminished. Second, the main flow/tip leakage interface moves toward downstream and the movement of interface toward the leading edge is delayed. The second configuration with a greater rotor blade tip exposure enables extra flow recirculation due to decreasing surface area and, therefore, could be superior to the application of the first casing treatment configuration. The major streamlines within the casing treatment are also discussed. The time-averaged results are presented in this paper, while the unsteady results including instantaneous flow fields, origins of the unsteadiness and frequency analysis are discussed in part II.

Flow physics and loss mechanisms of tip leakage flow in variable-blade-pitch-angle ducted fans

This paper investigates a ducted fan, which is able to adjust the output characteristics to meet different requirements of VTOL (Vertical Take-Off and Landing) aircrafts at various states, e.g., take-off, landing and high-speed cruise. The variable-blade-pitch-angle method is employed for the ducted fan, so that the fan can present more various performance. The loss mechanisms of the ducted fan are analyzed at seven different blade pitch angles ranging from −15 degrees to 15 degrees, and the importance of the tip leakage flow on the aerodynamic performance of the fan is highlighted. Results show that there exists a critical value for the blade pitch angle, and below the critical value, the tip leakage vortex sweeps to the adjacent blade tip and simultaneously causes the double tip leakage, which results in the high relative-total-pressure loss and a severe deterioration of rotor efficiency. The flow physics and loss mechanisms are discussed in detail. In addition, an analytical model of the tip leakage flow is established, and the effects of blade solidity on the critical blade pitch angle are discussed. The results provide useful guidelines on the design and the control of the variable-blade-pitch-angle fans.

Large eddy simulation of tip-leakage cavitating flow around twisted hydrofoil with effects of tip clearance and skew angle

Tip-leakage cavitating flow around hydrofoils has attracted much research interest, but the complex structures of tip separation vortex (TSV) and tip-leakage vortex (TLV) have not been clearly resolved and discussed with the effects of tip clearance and skew angle yet. In the present work, large eddy simulation (LES) with multi-level octree grid refinement is used to investigate the tip-leakage flows around a series of twisted hydrofoils with various skew angle and tip clearance. High resolution is guaranteed by the normalized grid sizes of y+<1, Δx+∼50 and Δz+∼10, through which the predicted flow meets the criterion that at least 80% of the turbulent kinetic energy is resolved. The TSVs are identified to grow from the entire lower edge of the tip and twine with the TLV into a primary vortex tube, which leads to counter-rotating induced vortices (IV) strongly twisted around the primary vortex in the case of medium tip clearance but weakened for small one. Cavitation effect significantly accelerates the roll-up process of the vortices so that the primary vortex is formed earlier. The tip-leakage flow turns from wake-like to jet-like when the clearance is reduced, but the jet velocity diminishes markedly for extremely small clearance. The hydrofoil skewness barely makes a lift on the vortex tube, distinctive from the effect of tip clearance variation. The adverse pressure gradient induced by the skew angle has significant effect on the laminar–turbulent​ transition of the flow. The tip vortex flow induces strongly characterized laminar ant turbulent flow regions on the suction side, which continuously changes with the variation of the skewness.

Data-driven estimation of entropy production by large scale motions in an intermediate turbine duct

In modern gas turbines, the physics of three-dimensional inflow for aggressive intermediate turbine ducts are strongly associated with large-scale coherent motions, which contribute to the production of irreversible aerodynamic and thermodynamic energy losses. To address this problem, an extended data-driven approach for estimating the irreversible losses through viscosity dissipation and heat transfer in turbulent flows is proposed. An aggressive intermediate turbine duct connected to a high-pressure turbine is numerically investigated using the detached-eddy simulation framework. The influence of tip leakage vortices and rotor wakes on the aerodynamics in the duct is assessed through quadruple proper orthogonal decomposition analysis. The entropy production rate corresponding to the coherent structures is then identified, and the irreversible losses in the duct subject to unsteady flow motions are quantitatively evaluated. The results indicate that the coherent structures in the intermediate turbine duct are strongly associated with the upstream conditions, including the tip leakage flow and rotor wakes. Direct viscous dissipation accounts for the majority of the irreversible losses, with coherent perturbed dissipation contributing to 7.25% and 5.54% of the total for tip gap sizes of 1.5% and 3.5% span, respectively. The streamwise development of coherent perturbations is restricted compared with that in the mean structure, and the stochastic part contributes little to the viscous dissipation. The proposed method provides a systematic procedure for estimating the irreversible energy losses in unsteady turbulent flow, and highlights the significance of unsteady aero-thermodynamics in the design of turbomachinery.

Role of unsteady tip leakage flow in acoustic resonance inception of a multistage compressor

In previous studies, a theoretical model was developed after Acoustic Resonance (AR) was experimentally detected in a four-stage compressor, and AR inception was proposed to be triggered by an unknown sound source, which is a pressure perturbation of a specific frequency with a suitable circumferential propagation speed. The present paper, which is not dedicated to the simulation of acoustic field, aims to identify the specific sound source generated by the unsteady tip leakage flow using the unsteady Computational Fluid Mechanics (CFD) approach. After a comprehensive analysis of an Unsteady Reynolds Averaged Navier-Stokes (URANS) simulation, a pressure perturbation of non-integer multiple of rotor frequency is found at the blade tip. Since the essence of the tip leakage flow is a jet flow driven by the pressure difference between two sides of blade, a simplified tip leakage flow model is adopted using Large Eddy Simulation (LES) in order to simulate the jet flow through a tip clearance. It is found that the convection velocity of shedding vortices fits the expected propagation speed of the sound source, the frequency is also close to one of the dominating frequencies in the URANS simulation, and the resultant combination frequency coincides with the experimentally measured AR frequency. Since such a simplified model successfully captures the key physical mechanisms, it is concluded that this paper provides a piece of unambiguous evidence on the role of unsteady tip leakage vortex in triggering the AR inception of the multistage compressor.

The effects of stator-rotor interaction on unsteady characteristics of turbine tip leakage flow

The unsteady flow characteristics of tip leakage flow significantly affect the operation stability of the turbine blade. However, there is currently a lack of research on the unsteady flow characteristics of the tip leakage flow under the stator-rotor interaction. Through experiments with a rotating turbine and simulations of the entire stage and full-annulus turbine stage flow using a self-adaptive method, this study investigates both experimentally and theoretically the impacts of rotor-stator interaction on the dynamic behavior of the tip leakage flow in the turbine. The impacts of stator-rotor interaction on pressure oscillations, mixing, and vortex evolution within the tip leakage flow are investigated. Furthermore, the mechanisms underlying the influence of stator-rotor interaction on the dynamic behavior of the tip leakage flow at different rotor speeds and different tip gaps are also analyzed. The results indicate that the passage vortex (PV) of the guide vane aggravates the instability phases experienced by the tip leakage vortex (TLV), namely vortex wandering and breakdown. Besides, the pulsation intensity of the tip leakage flow decreases, while the pulsation frequency increases as the rotational speed increases. Additionally, it is also observed that there is a significant increase in high-frequency and large-amplitude oscillations in the tip leakage flow with increasing tip gap heights.

Decoupling and reconstruction analysis in a transonic axial compressor using the dynamic mode decomposition method

Unsteady flow is highly related to flow loss and aerodynamic performance degradation in the axial compressor. In this paper, the dynamic mode decomposition method was used to investigate in-depth flow structures and related evolutionary mechanisms of the internal flow field. Four main flow structures were observed through flow field decoupling: the oscillation of the tip leakage vortex (TLV) region, the circumferential migration of the leakage-induced vortex (LIV), the axial migration of the rear part of the leakage vortex (RLV), and the oscillation of the leading edge vortex (LEV). All of those four structures indicated the presence of internal high disturbance regions. The reconstruction of the dominant mode flow field revealed that the unsteady evolutionary mechanism of the flow field mainly consisted of two components: the axial evolution of the RLV and the circumferential evolution of the LIV. It was further revealed that the axial evolution of the RLV was the primary reason for the formation of low-energy fluid mass within the passage; under the influence of the “leading edge overflow,” the LIV eventually fused with the LEV. The blocking effect of the LEV led to the formation of a high oscillation region at the leading edge of the adjacent blade pressure surface, resulting in a synchronous moment between the emergence of the LIV and the LEV. The analysis of the two unsteady evolution mechanism components further supported TLV breakdown as the main cause of flow unsteadiness. This study laid the foundation for further accurate flow unsteadiness control.