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

Entropy ◽  
2018 ◽  
Vol 21 (1) ◽  
pp. 21 ◽  
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.

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

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.

Application of Detached Eddy Simulation to a Subsonic Compressor Rotor

2008 ◽  
Author(s):  
Chunwei Gu ◽  
Fan Feng ◽  
Xuesong Li ◽  
Meilan Chen
Keyword(s):  
Wake Flow ◽  
Leakage Flow ◽  
Separation Region ◽  
Detached Eddy Simulation ◽  
Tip Leakage Flow ◽  
Blade Loading ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Compressor Rotor ◽  
Des Model

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.

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

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.

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

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 954 ◽  
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.

Interaction Mechanisms Between Tip Leakage Flow and the Passage Vortex in a Linear Turbine Rotor Cascade

1988 ◽  
Vol 110 (3) ◽  
pp. 329-338 ◽  
Author(s):  
A. Yamamoto
Keyword(s):  
Three Dimensional ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Passage Vortex ◽  
Generation Mechanisms ◽  
Downstream Flow

In order to study the loss generation mechanisms due to the tip-leakage flow in turbine rotor passages, extensive traverse measurements were made of the three-dimensional flows in a low-speed linear cascade for various tip-clearance sizes and for various cascade inlet flow angles (or incidences). Effects of the leakage flow on the cascade downstream flow fields and interactions between the leakage flow and the passage vortices are discussed in detail based on the traverse measurements and flow-visualization tests in terms of secondary flows and the associated losses. Other traverses were also performed of the tip-casing endwall flows both inside and outside the tip-clearance gap using a micro five-hole pitot tube to reveal the axial development of the interaction throughout the cascade passage. Overall loss characteristics of the present high-turning cascade with blunt leading and trailing edges are obtained and compared with those predicted by the Ainley–Mathieson method.

Analysis of the relationship between turbulence characteristics and loss mechanism in the tip leakage flow of turbine blade

2021 ◽  
pp. 095765092110320
Author(s):  
Hui Li ◽  
Xinrong Su ◽  
Xin Yuan
Keyword(s):  
Tip Clearance ◽  
Flow Structures ◽  
Small Scale ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Loss Mechanism ◽  
Turbulence Characteristics ◽  
Tip Leakage ◽  
Viscous Loss ◽  
The Relationship

The tip leakage flow passed over the tip clearance makes the flow very complicated near the tip gap, and the interaction of the tip leakage vortex and endwall vortex enhances the instability of the flow. Accurately capturing detailed flow structures and investigating the relationship between the flow structures and loss are beneficial for understanding the flow physics and providing guidance on reducing the loss. Due to the conventional Reynolds Averaged Navier-Stokes (RANS) methods is limited to predict the complex turbulence structures of the tip clearance flow, high fidelity simulation approaches are needed. In this work, the hybrid RANS/Large Eddy Simulation (LES) is adopted to simulate the tip leakage flow in linear cascade and demonstrates its ability to capture the small-scale flow structures. With the POD method, the time-averaged flow field and the dominating modes are obtained. Based on the analysis of the POD modes, it is found that the induced vortex generated by the interaction between the leakage vortex and the endwall vortex has strong turbulence characteristics. Based on the entropy generation rates, viscous loss mechanism is further analyzed. It is found that the shear strain rates dominate the viscous dissipation losses, and the fluctuation dissipation has a strong local enhancement effect.

Vortex Structures Analysis and Loss Mechanisms in Axial Compressor Cascade With and Without Bleeding Slot Using Large Eddy Simulation

2020 ◽  
Author(s):  
Yun Gong ◽  
Shaowen Chen ◽  
Haipeng Zheng ◽  
Songtao Wang
Keyword(s):  
Large Eddy Simulation ◽  
Axial Compressor ◽  
Vortex Structures ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Passage Vortex ◽  
Large Eddy

Abstract Tip leakage flow is one of the main sources of flow losses in an axial compressor, and the understanding of the tip leakage flow helps to explore better flow control methods and design more advanced compressors. Therefore, the vortex structures and loss mechanisms were analyzed in a compressor cascade with tip clearance in the present paper. Large eddy simulation was used to better resolve the vortices with more accurate numerical results. The iso-surface of Q criterion in the compressor cascade is captured for recognizing and analyzing the vortex structures. The horse shoe vortices, tip leakage vortex, induced vortex, tip separation vortex and passage vortex were well captured and their interactions were interpreted. Fast Fourier Transformation was also applied to analyze the frequency signal in the flow field. Afterwards, the case with an upstream bleeding slot was also calculated and compared with the original case without a bleeding slot. The bleeding rate is 2.8% of the mass flow rate at inlet. The removal of the inlet boundary layer resulting from the bleeding leads a 42.4% reduction of the total pressure loss coefficient compared with that of the case without the bleeding slot. In the case with the bleeding slot, the size of the passage vortex is greatly reduced, and the mixing between the tip leakage vortex and passage vortex is postponed. Better performance is achieved with the bleeding slot accordingly.

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