Zonal Detached-Eddy Simulation of tip-leakage flow sensitivity for a compressor rotor

An attempt is made in the present paper to apply DES (Detached Eddy Simulation), which is based on S-A model of RANS, for investigating the flow field around a subsonic compressor rotor with a tip clearance of 2% blade height. Comparison of the results by DES and S-A model shows that DES model can capture more intensive vortex flow, such as tip leakage flow, double leakage flow, as well as interaction between the leakage flow and wake flow downstream of the rotor passage. DES model predicts more complicated flow at the separation region near the hub. DES simulation for different operation conditions also reveals interesting details. The shedding angle and strength of the tip leakage flow changes with the blade loading. The starting point of the leakage vortex moves towards the leading edge when the blade loading increases. Double leakage is observed only at the design and higher loading conditions, and is not at a lower loading condition. The tip leakage vortex splits into two branches downstream of the rotor blade due to interaction with the wake flow. Instantaneous results show unsteadiness of the tip leakage vortex. Alternating regions of higher and lower loss is found along the time-averaged leakage vortex trajectory. Obvious is also the unsteadiness in the separation region near the hub.

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Unsteadiness of Tip Leakage Flow in the Detached-Eddy Simulation on a Transonic Compressor Rotor

10.33737/gpps19-tc-030 ◽

2019 ◽

Author(s):

Xiangyu Su ◽

◽

Xuesong Li ◽

Xiaodong Ren ◽

Chunwei Gu ◽

...

Keyword(s):

Leakage Flow ◽

Detached Eddy Simulation ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Transonic Compressor ◽

Eddy Simulation ◽

Compressor Rotor

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Unsteadiness of Tip Leakage Flow in the Detached-Eddy Simulation on a Transonic Rotor with Vortex Breakdown Phenomenon

Energies ◽

10.3390/en12050954 ◽

2019 ◽

Vol 12 (5) ◽

pp. 954 ◽

Cited By ~ 4

Author(s):

Xiangyu Su ◽

Xiaodong Ren ◽

Xuesong Li ◽

Chunwei Gu

Keyword(s):

Vortex Breakdown ◽

Leakage Flow ◽

Angle Distribution ◽

Detached Eddy Simulation ◽

Tip Leakage Flow ◽

Flow Angle ◽

Tip Leakage ◽

Transonic Compressor ◽

Eddy Simulation ◽

Compressor Rotor

Tip leakage vortex (TLV) in a transonic compressor rotor was investigated numerically using detached-eddy simulation (DES) method at different working conditions. Strong unsteadiness was found at the tip region, causing a considerable fluctuation in total pressure distribution and flow angle distribution above 80% span. The unsteadiness at near choke point and peak efficiency point is not obvious. DES method can resolve more detailed flow patterns than RANS (Reynolds-averaged Navier–Stokes) results, and detailed structures of the tip leakage flow were captured. A spiral-type breakdown structure of the TLV was successfully observed at the near stall point when the TLV passed through the bow shock. The breakdown of TLV contributed to the unsteadiness and the blockage effect at the tip region.

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Entropy Analysis of the Flat Tip Leakage Flow with Delayed Detached Eddy Simulation

Entropy ◽

10.3390/e21010021 ◽

2018 ◽

Vol 21 (1) ◽

pp. 21 ◽

Cited By ~ 2

Author(s):

Hui Li ◽

Xinrong Su ◽

Xin Yuan

Keyword(s):

Tip Clearance ◽

Flow Structures ◽

Leakage Flow ◽

Detached Eddy Simulation ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Eddy Simulation ◽

Delayed Detached Eddy Simulation ◽

Passage Vortex ◽

Unsteady Effects

In unshrouded turbine rotors, the tip leakage vortices develop and interact with the passage vortices. Such complex leakage flow causes the major loss in the turbine stage. Due to the complex turbulence characteristics of the tip leakage flow, the widely used Reynolds Averaged Navier–Stokes (RANS) approach may fail to accurately predict the multi-scale turbulent flow and the related loss. In order to effectively improve the turbine efficiency, more insights into the loss mechanism are required. In this work, a Delayed Detached Eddy Simulation (DDES) study is conducted to simulate the flow inside a high pressure turbine blade, with emphasis on the tip region. DDES results are in good agreement with the experiment, and the comparison with RANS results verifies the advantages of DDES in resolving detailed flow structures of leakage flow, and also in capturing the complex turbulence characteristics. The snapshot Proper Orthogonal Decomposition (POD) method is used to extract the dominant flow features. The flow structures and the distribution of turbulent kinetic energy reveal the development of leakage flow and its interaction with the secondary flow. Meanwhile, it is found that the separation bubble (SB) is formed in tip clearance. The strong interactions between tip leakage vortex (TLV) and the up passage vortex (UPV) are the main source of unsteady effects which significantly enhance the turbulence intensity. Based on the DDES results, loss analysis of tip leakage flow is conducted based on entropy generation rates. It is found that the viscous dissipation loss is much stronger than heat transfer loss. The largest local loss occurs in the tip clearance, and the interaction between the leakage vortex and up passage vortex promotes the loss generation. The tip leakage flow vortex weakens the strength of up passage vortex, and loss of up passage flow is reduced. Comparing steady and unsteady effects to flow field, we found that unsteady effects of tip leakage flow have a large influence on flow loss distribution which cannot be ignored. To sum up, the current DDES study about the tip leakage flow provides helpful information about the loss generation mechanism and may guide the design of low-loss blade tip.

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Detached Eddy Simulation: Recent Development and Application to Compressor Tip Leakage Flow

Journal of Turbomachinery ◽

10.1115/1.4052019 ◽

2021 ◽

pp. 1-400

Author(s):

Xiao He ◽

Fanzhou Zhao ◽

Mehdi Vahdati

Keyword(s):

Flow Field ◽

Model Development ◽

Main Flow ◽

Transition To Turbulence ◽

Leakage Flow ◽

Detached Eddy Simulation ◽

Grid Spacing ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Eddy Simulation

Abstract Detached Eddy Simulation (DES) and its variants are emerging tools for turbomachinery simulations. In this paper, the state-of-the-art upgrades of DES are reviewed, and their capabilities in predicting compressor tip leakage flow are discussed. The upgrade with the best potential is identified as the Delayed DES (DDES) method with the grid spacing FKHΔhyb, which unlocks the physics of the Kelvin-Helmholtz instability in compressor tip leakage flow. The upgraded grid spacing FKHΔhyb is compared against the widely used default one Δmax in a backward-facing step and a low-speed axial compressor rotor. Results show that the DDES method with FKHΔhyb predicts both the main flow field and the turbulence field with reasonably good accuracy. However, the original DDES method with Δmax predicts a delayed transition to turbulence, which leads to an inaccurate prediction of the main flow field when using a coarse mesh. The findings in this paper highlight the future opportunities for using the DDES-FKHΔhyb method to predict tip-driven compressor stall and generate a turbulence database for turbulence model development.

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Flow Mechanism and Loss Analysis of Tip Leakage Flow With Delayed Detached Eddy Simulation

Volume 2A: Turbomachinery ◽

10.1115/gt2019-90410 ◽

2019 ◽

Author(s):

Hui Li ◽

Xiutao Bian ◽

Xinrong Su ◽

Xin Yuan

Keyword(s):

Entropy Generation ◽

Flow Structures ◽

Leakage Flow ◽

Detached Eddy Simulation ◽

Tip Leakage Flow ◽

Turbulence Characteristics ◽

Tip Leakage ◽

Loss Analysis ◽

Eddy Simulation ◽

Delayed Detached Eddy Simulation

Abstract The complex leakage flow structure in the tip region of unshrouded rotor is a main source of turbine aerodynamic loss. Due to the complex turbulence characteristics of the tip leakage flow, the widely used Reynolds Averaged Navier-Stokes (RANS) approach may fail to accurately predict the multi-scale turbulent flow and the related loss. In order to effectively improve the turbine efficiency, more insights into the turbulence characteristics and the loss mechanism in the tip leakage flow are required. In this work, a Delayed Detached Eddy Simulation (DDES) study is conducted to simulate the flow inside a high pressure turbine blade, with emphasis on the tip region. DDES results are in good agreement with the experiment and the comparison with RANS results verifies the advantages of DDES in resolving finer flow structures of leakage flow, also in capturing the complex turbulence characteristics. The snapshot Proper Orthogonal Decomposition (POD) method is used to extract the dominant flow features. The flow structures and the distribution of Reynolds stress help to reveal the process of leakage flow and its interaction with the secondary flow. Meanwhile, it is found that the separation vortex (SV) forms from leading edge to trailing edge, and the strong interactions between tip leakage vortex (TLV) and passage secondary vortex (PSV) significantly enhance the turbulence intensity. Based on the DDES results, loss analysis of tip leakage flow is conducted based on entropy generation rates. For the leakage flow related loss, the largest local entropy generation rate occurs at 50 % of axial chord, and the interaction between the leakage vortex and up passage vortex promotes the loss generation. To sum up, the current DDES study about the tip leakage flow provides helpful information about the loss generation mechanism and may guide the design of low-loss blade tip.

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Detached Eddy Simulation: Recent Development and Application to Compressor Tip Leakage Flow

10.1115/gt2021-59077 ◽

2021 ◽

Author(s):

Xiao He ◽

Fanzhou Zhao ◽

Mehdi Vahdati

Keyword(s):

Flow Field ◽

Model Development ◽

Main Flow ◽

Transition To Turbulence ◽

Leakage Flow ◽

Detached Eddy Simulation ◽

Grid Spacing ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Eddy Simulation

Abstract Detached Eddy Simulation (DES) and its variants are emerging tools for turbomachinery simulations. In this paper, the state-of-the-art upgrades of DES are reviewed, and their capabilities in predicting compressor tip leakage flow are discussed. The upgrade with the best potential is identified as the Delayed DES (DDES) method with the grid spacing FKHΔhyb, which unlocks the physics of the Kelvin-Helmholtz instability in compressor tip leakage flow. The upgraded grid spacing FKHΔhyb is compared against the widely used default one Δmax in a backward-facing step and a low-speed axial compressor rotor. Results show that the DDES method with FKHΔhyb predicts both the main flow field and the turbulence field with reasonably good accuracy. However, the original DDES method with Δmax predicts a delayed transition to turbulence, which leads to an inaccurate prediction of the main flow field when using a coarse mesh. The findings in this paper highlight the future opportunities for using the DDES-FKHΔhyb method to predict tip-driven compressor stall and generate a turbulence database for turbulence model development.

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Improved Delayed Detached Eddy Simulation of Compressor Cascade Tip Leakage Flow

International Journal of Aeronautical and Space Sciences ◽

10.1007/s42405-020-00289-0 ◽

2020 ◽

Author(s):

Jingfeng Wu

Keyword(s):

Leakage Flow ◽

Detached Eddy Simulation ◽

Compressor Cascade ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Eddy Simulation ◽

Delayed Detached Eddy Simulation

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

International Journal of Turbo and Jet Engines ◽

10.1515/tjj-2015-0039 ◽

2016 ◽

Vol 33 (4) ◽

Cited By ~ 7

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.

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