Tip Leakage Behavior and Large Coherent Perturbation Analysis of an Axial-radial Combined Compressor with Outlet Distortion

2021 ◽  
Author(s):  
Li Fu ◽  
Ce Yang ◽  
Chenxing Hu ◽  
Xin Shi
Keyword(s):  
Transient Flow ◽  
Flow Instability ◽  
Complex Structure ◽  
Potential Effect ◽  
Structure Design ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Compact Structure ◽  
Tip Leakage ◽  
Flow Unsteadiness

Abstract Increasing performance requirements and compact structure design promote the generation of axial-radial combined compressors. However, its complex structure and asymmetrical outlet boundary cause difficulty to get an in-depth comprehension of the flow unsteadiness associated with spike-stall. In this work, unsteady full-annular simulations of an axial-radial combined compressor coupled with performance experiment validations were carried out. Based on the overall understanding of outlet distortion on each component, the general feature of tip leakage flow with asymmetrical outlet boundary was extracted. The temporal and spatial development of large coherent perturbations was revealed by the decomposition and reconstruction of the transient flow data with the DMD approach. The results demonstrate that the outlet distortion can propagate reversely to the compressor inlet and the degree of distortion decreases gradually, which leads to the highest possibility for radial rotor to suffer from flow unsteadiness. In the circumferential location with distortion affected, the leakage momentum of the adjacent blade LE is enhanced by the secondary leakage, inducing the expansion of TLV and causing flow instability. Besides organized perturbation structures related to mean flow and BPF, two large low-frequency stall perturbations approximately one-third and three-fourth RF was captured by the DMD method, which is caused by volute potential effect and stator/rotor interference, respectively. The former occurs in the radial rotor and decays during its propagation, while the latter always exists owing to the multiple rotor/stator or stator/rotor interference in the axial-radial combined compressor.

Study of the Standard k-ε Model for Tip Leakage Flow in an Axial Compressor Rotor

2016 ◽  
Vol 33 (4) ◽  
Author(s):  
Yanfei Gao ◽  
Yangwei Liu ◽  
Luyang Zhong ◽  
Jiexuan Hou ◽  
Lipeng Lu
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Turbulent Viscosity ◽  
Axial Compressor ◽  
Leakage Flow ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Compressor Rotor

AbstractThe standard k-ε model (SKE) and the Reynolds stress model (RSM) are employed to predict the tip leakage flow (TLF) in a low-speed large-scale axial compressor rotor. Then, a new research method is adopted to “freeze” the turbulent kinetic energy and dissipation rate of the flow field derived from the RSM, and obtain the turbulent viscosity using the Boussinesq hypothesis. The Reynolds stresses and mean flow field computed on the basis of the frozen viscosity are compared with the results of the SKE and the RSM. The flow field in the tip region based on the frozen viscosity is more similar to the results of the RSM than those of the SKE, although certain differences can be observed. This finding indicates that the non-equilibrium turbulence transport nature plays an important role in predicting the TLF, as well as the turbulence anisotropy.

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.

Modification of DDES Based on SST kω Model for Tip Leakage Flow in Turbomachinery

2020 ◽  
Author(s):  
Yanfei Gao ◽  
Yangwei Liu
Keyword(s):  
Reynolds Number ◽  
Flow Model ◽  
Turbulence Modeling ◽  
Streamwise Vortex ◽  
Original Model ◽  
Leakage Flow ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Modified Model ◽  
Tip Leakage

Abstract Both LES and DDES are conducted in a low-Reynolds number tip leakage flow model. The DDES uses the SST kω model and employs the same grid with the LES, but the turbulence field diverges from the LES result. Referring to the comparison between LES and DDES, a modification of the zonal function in the DDES model is proposed, which enhances the dissipation of the modeled turbulence thus promote the transition to fully LES in the tip region when the mesh is fine enough. It can generate much finer vortex structure than the original model, including the primary streamwise vortex, induced vortices and the vortex fragments after breakdown. The modification fixes the underestimation of the vorticity and pressure drop at the formation stage of the tip leakage vortex, and generates more reasonable turbulence field and energy spectra. The modified model is introduced to a real rotor simulation at engineering Reynolds number. Compared with the original model on both mean flow field and turbulence field, the modified model shows favorable agreements with the measurements. The study also gives a practical example of using the tip leakage flow model in turbulence modeling.

Three-Dimensional Navier-Stokes Analysis of Turbine Rotor and Tip-Leakage Flowfield

1997 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Three Dimensional ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The 3-D viscous flowfield in the rotor passage of a single-stage turbine, including the tip-leakage flow, is computed using a Navier-Stokes procedure. A grid-generation code has been developed to obtain embedded H grids inside the rotor tip gap. The blade tip geometry is accurately modeled without any “pinching”. Chien’s low-Reynolds-number k-ε model is employed for turbulence closure. Both the mean-flow and turbulence transport equations are integrated in time using a four-stage Runge-Kutta scheme. The computational results for the entire turbine rotor flow, particularly the tip-leakage flow and the secondary flows, are interpreted and compared with available data. The predictions for major features of the flowfield are found to be in good agreement with the data. Complicated interactions between the tip-clearance flows and the secondary flows are examined in detail. The effects of endwall rotation on the development and interaction of secondary and tip-leakage vortices are also analyzed.

Circumferential Propagation Characteristic of Unsteady Flow in a Subsonic Axial Flow Compressor Rotor at Different Reynolds Numbers

2019 ◽  
Author(s):  
Zhiyang Chen ◽  
Yanhui Wu ◽  
Yanwen Zhang ◽  
Junwen Gan ◽  
Jinhuaiyuan An
Keyword(s):  
Unsteady Flow ◽  
Frequency Band ◽  
Radial Flow ◽  
Propagation Characteristic ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Characteristic Frequencies ◽  
Tip Leakage ◽  
Flow Unsteadiness ◽  
Compressor Rotor

Abstract This paper studies the circumferential propagation characteristic of unsteady flow that occurs close to stall in a subsonic axial compressor rotor at different Reynolds number (Re). Experimental measurements are first conducted at high Re on the ground, and numerical investigations are carried out at two altitudes to explore the mechanism of circumferential propagation characteristic at different Re. The stability operating range of the compressor rotor gets small with the decrease of Re. Rotating instability (RI) is observed in the blade passage near the stall limit of the test rotor at high Re on the ground, which is characterized by a hump frequency band in the spectrum. Characteristic frequencies of numerical pressure signals at fixed frame are limited in the frequency band of RI at high Re. The cross power spectrums of numerical pressure signals detected in the neighboring passages suggest that circumferential disturbances rotates in the flow fields at different Re. Characteristic frequencies of the flow unsteadiness change with the decrease of Re. At high Re, the circumferential propagation of tip leakage flow unsteadiness is controlled by the interaction of the tip leakage flow and incoming flow, which is linked to RI. When the Re is reduced, the tip leakage flow gets weak and the radial flow from the hub to tip induced by the suction surface flow separation is dominant in the tip region. Thereafter, both the tip leakage flow and radial flow are associated with the blade tip loading, which changes the flow mechanism of RI.

Evolution of Pressure Signature Dominated by Unsteady Tip Leakage Flow

2013 ◽  
Author(s):  
Shaojuan Geng ◽  
Xiaoyu Zhang ◽  
Jichao Li ◽  
Long Zhao ◽  
Hongwu Zhang ◽  
...  
Keyword(s):  
Reference Frames ◽  
Fluid Dynamic ◽  
Critical Mass ◽  
Leakage Flow ◽  
Band Pass Filter ◽  
Tip Leakage Flow ◽  
Initiation Mechanism ◽  
Pass Filter ◽  
Tip Leakage ◽  
Flow Unsteadiness

This paper deals with the detailed numerical analyses of diverse manifestations of unsteady features induced by periodical oscillation of tip leakage flow under different operating points for the cases with uniform and hub distorted inlet conditions. The characteristics evolutions of pressure signature near rotor tip region during compressor throttling process are studied and compared with the experimental results. Monitors circumferentially arranged and aligned with blade chord are imposed to collect static pressure signals. Analysis methods of coordinate transformation between the rotor relative and absolute stationary reference frames, fast Fourier transform and frequency band pass filter are used. The modulated frequency features along blade chord in two reference frames are analyzed. Typically for the dominated frequency components, the circumferential propagation characteristics are studied, such as propagation speed and mode orders. And the unified evolution trends of modulated frequency relation for dominant components between two reference frames and circumferential propagation features during throttling process are summarized. A critical mass flow point is found to distinguish the different change trend of the characteristics of tip leakage flow unsteadiness. Based on the different speeds between circumferential propagation of tip leakage flow unsteadiness and revolution of compressor rotor, the fluid dynamic reason for the decrease of autocorrelation coefficient of pressure signals from transducer mounted on compressor casing is elucidated. All the results are helpful to further unveil the initiation mechanism of stall inception.

Numerical Analysis of Flow in a Transonic Compressor With a Single Circumferential Casing Groove: Influence of Groove Location and Depth on Flow Instability

2013 ◽  
Author(s):  
Yasunori Sakuma ◽  
Toshinori Watanabe ◽  
Takehiro Himeno ◽  
Dai Kato ◽  
Takeshi Murooka ◽  
...  
Keyword(s):  
Flow Instability ◽  
Flow Behavior ◽  
Vortical Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Optimal Position ◽  
Stall Inception ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Stability Enhancement

The effect of circumferential single grooved casing treatment on the stability enhancement of NASA Rotor 37 has been examined with CFD analysis. Stall inception mechanism of Rotor 37 is presented first with principal focus on the tip leakage flow behavior, passage blockage, and the vortical flow structures. Detailed observation showed that the combined interaction of the stagnated flow of tip leakage vortex breakdown and the jet-like leakage flow from the mid-chord region leads to the blade tip-initiated stall inception. The result of numerical parametric study is then demonstrated to show the effect of varying the axial location and the depth of a circumferential single groove. The evaluation based on stall margin improvement showed a higher potential of deeper grooves in stability enhancement, and the optimal position for the groove to be located was indicated to exist near the leading edge of the blade.

Numerical investigations on tip leakage flow characteristics and vortex trajectory prediction model in centrifugal compressor

2016 ◽  
Vol 230 (8) ◽  
pp. 757-772 ◽  
Author(s):  
Huijing Zhao ◽  
Zhiheng Wang ◽  
Shubo Ye ◽  
Guang Xi
Keyword(s):  
Prediction Model ◽  
Flow Instability ◽  
Leading Edge ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip

To better understand the characteristics of tip leakage flow and interpret the correlation between flow instability and tip leakage flow, the flow in the tip region of a centrifugal impeller is investigated by using the Reynolds averaged Navier–Stokes solver technique. With the decrease of mass flow rate, both the tip leakage vortex trajectory and the mainflow/tip leakage flow interface are shifted towards upstream. The mainflow/tip leakage flow interface finally reaches the leading edge of main blade at the near-stall condition. A prediction model is proposed to track the tip leakage vortex trajectory. The blade loading at blade tip and the averaged streamwise velocity of main flow within tip clearance height are adopted to determine the tip leakage vortex trajectory in the proposed model. The coefficient k in Chen’s model is found to be not a constant. Actually, it is correlated with h/b (the ratio of blade tip clearance height to blade tip thickness), because h/b will significantly influence the flow structure across the tip clearance. The effectiveness of the proposed prediction model is further demonstrated by tracking the tip leakage vortex trajectories in another three centrifugal impellers characterized with different h/b (s).

scholarly journals Effect of Tip Clearance Size on Tubular Turbine Leakage Characteristics

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1481
Author(s):  
Xinrui Li ◽  
Zhenggui Li ◽  
Baoshan Zhu ◽  
Weijun Wang
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Flow Instability ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage

To study the effect of tip clearance on unsteady flow in a tubular turbine, a full-channel numerical calculation was carried out based on the SST k–ω turbulence model using a power-plant prototype as the research object. Tip leakage flow characteristics of three clearance δ schemes were compared. The results show that the clearance value is directly proportional to the axial velocity, momentum, and flow sum of the leakage flow but inversely proportional to turbulent kinetic energy. At approximately 35–50% of the flow direction, velocity and turbulent kinetic energy of the leakage flow show the trough and peak variation law, respectively. The leakage vortex includes a primary tip leakage vortex (PTLV) and a secondary tip leakage vortex (STLV). Increasing clearance increases the vortex strength of both parts, as the STLV vortex core overlaps Core A of PTLV, and Core B of PTLV becomes the main part of the tip leakage vortex. A “right angle effect” causes flow separation on the pressure side of the tip, and a local low-pressure area subsequently generates a separation vortex. Increasing the gap strengthens the separation vortex, intensifying the flow instability. Tip clearance should therefore be maximally reduced in tubular turbines, barring other considerations.

Investigation of Turbulence Characteristics in a Tip Leakage Flow Model Using Large-Eddy Simulation

2019 ◽  
Author(s):  
Yanfei Gao ◽  
Yangwei Liu ◽  
Lipeng Lu
Keyword(s):  
Large Eddy Simulation ◽  
Flow Model ◽  
Side Wall ◽  
Leakage Flow ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Turbulence Characteristics ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Large Eddy

Abstract A simple tip leakage flow (TLF) model which consists of a square duct with a longitudinal slit on the top of a side wall is proposed to reproduce the jet flow/main flow shear mechanism of the tip leakage vortex (TLV) rolling-up in turbomachinery. Large-eddy simulation (LES) is employed to investigate the turbulence characteristics of the flow model under low Reynolds number condition. The geometry and boundary conditions of the flow model are simplified from a compressor rotor and modified to apply to low-Re condition for LES. The vortex structures and turbulence characteristics of the LES results are compared with the measurements of the rotor. It is found that the flow model could reproduce similar flow field and turbulence structures compared with the TLF in the real rotor, thus it can be used to investigate the turbulence in practical flows. Reynolds-Averaged Navier-Stokes (RANS) calculations are also carried out. The mean flow and turbulence behaviors of different cases are analyzed. The budgets of turbulent kinetic energy (k) are analyzed to investigate the turbulence transport nature in the TLF model, indicating that the non-equilibrium transport process of k is significant, especially the pressure and turbulent transport, which is not predicted by RANS.

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