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Effect of Squealer tip with Deep Scale Depth on the Aero-thermodynamic Characteristics of tip leakage flow

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Journal of Thermal Science 2022年第5期31卷 1773-1789页

作者： BI Shuai WANG Longfei WANG Feilong WANG Lei LI Ziqiang Jiangsu Province Key Laboratory of Aerospace Power System Nanjing University of Aeronautics and AstronauticsNanjing210016China

In this paper,the aero-thermal performance of squealer tips with deep-scale depth is numerically investigated in an axial flow turbine,which is compared with the squealer tip with traditional cavity *** methods were validated with experimental *** effect of cavity depth and tip clearance was *** numerical results show that for the squealer tip with conventional cavity depth,the size of the reflux vortex enlarges as the cavity depth *** velocity and uniformity of high entropy production rate(EPR)inside the cavity reduce obviously with the cavity developing into ***,the increase of depth 10%of the blade span(H)leads to enlargement of cavity volume,which increases the total entropy production *** the overall dimensionless entropy production rate(DEPR)of gap and cavity obtains a maximum increase of 43.54%in contrast to the case with 1%H depth *** a result,the relative leakage mass flow rate reduces by 20.6%as the cavity depth increases from 1%to 10%.Given the heat transfer,as the cavity significantly increases to 10%H,the enhanced cavity volume results in a more enormous cavity vortex with low velocity covering the floor,which weakens the convective heat transfer intensity and reduces the area of high heat *** normalized average heat transfer coefficient at the cavity bottom reduces by 40.26%compared to the cavity depth of 1%*** addition,the deep-scale cavity is more effective in inhibiting leakage flow at smaller tip *** reduction amplitude of normalized average heat transfer coefficient at the squealer floor decreases as tip clearance increases,which reduces at most by about 72.6%for the tip clearance of 1%H.

关键词： squealer tip turbine aerothermodynamics tip leakage flow deep-scale depth heat transfer numerical methods

Simplified Numerical Models of the Unsteady tip leakage flow in Compressor

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Journal of Thermal Science 2023年第6期32卷 2386-2399页

作者： SI Changxin WU Zihao LIU Xiaohua School of Aeronautics and Astronautics Shanghai Jiao Tong UniversityShanghai200240China China Three Gorges Investment Management Co. Ltd.Shanghai200124China Key Laboratory of Aerodynamic Noise Control China Aerodynamics Research and Development CenterMianyang621000China

tip leakage flow(TLF)in compressors,which can cause flow blockage in blade passage and induce efficiency loss,is also a potential threat to the unsteady flow stability of modern *** paper provides an overview of the significance of tip leakage flow research,and introduces relevant previous *** calculating by different methods,large eddy simulation(LES)is demonstrated again as a suitable compromise between accuracy and computational cost for the unsteady flow *** types of simplified tip leakage flow models using LES are adopted with a focus on the unsteady characteristics of shedding vortices in a cavity *** paper applies these models to study the unsteady tip leakage flow which triggers the onset of acoustic resonance in a multistage axial *** with the detected acoustic resonance frequency of 5.22 rotational frequency(RF)in the previous experiment,the computed combination frequency in the 2-D model is equal to 5.232RF,and the simplified 3-D unsteady tip leakage flow model results in a combination frequency of ***,based on the small relative error between model results and experimental results,the simplified numerical models are validated to be sufficiently accurate,and theoretically provide a useful basis for the subsequent research of unsteady tip leakage flow in turbomachinery.

关键词： turbomachinery compressor tip leakage flow unsteady flow

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

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Chinese Journal of Aeronautics 2023年第10期36卷 165-181页

作者： Xiaohua LIU Zihao WU Changxin SI Jun YANG Xiaofeng SUN School of Aeronautics and Astronautics Shanghai Jiao Tong UniversityShanghai 200240China Key Laboratory(Fluid Machinery and Engineering Research Base)of Sichuan Province Xihua UniversityChengdu 610039China China Three Gorges Investment Management Co.Ltd Shanghai 200124China School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China Research Institute of Aero-Engine Beihang UniversityBeijing 100191China

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 *** 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)*** 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 *** 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 *** 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 *** 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.

关键词： Acoustic Resonance(AR) Jet flow Multistage compressor tip leakage flow Unsteady flow

Experimental and Numerical Investigation of the Unsteady tip leakage flow in Axial Compressor Cascade

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Journal of Thermal Science 2013年第2期22卷 103-110页

作者： Chengqing Li Tingfeng Ke Jingxuan Zhang Hongwu Zhang Weiguang Huang Shanghai Advanced Research Institute Chinese Academy of Sciences

For convenience of both measurement and adjusting the clearance size and incidence, the current research is mainly conducted by experiments on an axial compressor linear cascade. The characteristics and the condition under which the unsteadiness of tip leakage flow would occur were investigated by dynamic measuring in different clearances, inlet velocities and incidences. From the experiment it is found that increasing tip clearance size or reducing rotor tip incidence can affect the strength of the tip clearance flow. Then the experimental results also indicate the tip leakage shows instability in certain conditions, and the frequency of unsteadiness is great influenced by inflow angle. The condition of occurrence of tip leakage flow unsteadiness is when the leakage flow is strong enough to reach the pressure side of the adjacent blade. The main cause of tip leakage flow unsteadiness is the tip blade loading.

关键词： axial flow compressor linear cascade tip leakage flow unsteady

The Self-induced Unsteadiness of tip leakage flow in an Axial Low-Speed Compressor with Single Circumferential Casing Groove

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Journal of Thermal Science 2013年第6期22卷 565-572页

作者： DU Juan LI Jichao WANG Kai LIN Feng NIE Chaoqun Institute of Engineering Thermophysics Chinese Academy of Sciences Key Laboratory of Advanced Energy and Power Chinese Academy of Sciences

Numerical investigation on the self-induced unsteadiness of tip leakage flow(TLF) for an axial low-speed compressor with smooth wall and six single grooved casings are presented. A ten-passage numerical scheme is used to solve the unsteady Reynolds averaged Navier-Stokes(URANS) equations. It is found that the single grooves at various axial locations could have a large impact on the self-induced unsteadiness and the stall margin improvement(SMI) of compressor. The trend of SMI with groove center location demonstrates that the groove located near the mid of blade tip chord generates the best SMI. The worst groove is located about 20% Cax after the blade leading edge. The root-mean-squre of static pressure(RMSP) contours at 99.5% span and fast Fourier transform for the static pressure traces recorded in the tip clearance region for each casing are analyzed. The results demonstrate that the single groove location not only affects the oscillating strength but also the frequency of the unsteady tip leakage flow. At the near-stall point of smooth casing, the self-induced unsteadiness of TLF is enhanced most by the best grooved casing for SMI. While, the self-induced unsteadiness disappears when the worst groove for SMI is added. The characteristic frequency of TLF is about 0.55 blade passing frequency(BPF) with smooth casing. The frequency components become complicated as the single groove moves from the leading edge to the trailing edge of the blade.

关键词： tip leakage flow unsteadiness circumferential groove stall margin improvement

Calculation of the Energy Loss for tip leakage flow in Turbines

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Chinese Journal of Aeronautics 2004年第3期17卷 142-148页

作者： Mohsen Hassanvand 王松涛冯国泰王仲奇 School of Energy Engineering Harbin Institute of Technology Harbin 150001 China

A commercial N-S solver has been employed for simulation and investigation ofthe unsteady flow field inside the tip clearance of a turbine rotor. The main objective of thispaper is to introduce a new method of energy loss calculation for the flow field in tip clearanceregion of a turbine rotor blade. This method can be easily used in all kinds of flow fields. Regionsof high viscous effects have been found to be located near the shroud rather than the blade tip. Itis shown that the time-averaged loss of energy in tip leakage flow is dissimilar for differentrotor blades. This result is a helpful hint that can be taken by blade designers to designnon-uniform rotor blades with different geometric and aerodynamic loads to minimize the energy loss.

关键词： tip leakage flow tip clearance unsteady flow energy loss

Experiment on Effect of tip Clearance leakage flow on Heat Transfer of Turbine Outer Ring

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Transactions of Nanjing University of Aeronautics and Astronautics 2021年第2期38卷 344-352页

作者： LIU Tianyi JIN Feng YANG Jiang WEI Xin College of Energy and Power Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016P.R.China

The cascade model was tested using transient liquid crystal temperature measurement *** effects of main flow Reynolds number,blowing ratio and tip clearance height on the convective heat transfer coefficient of the turbine outer ring were *** feature lines were marked on the turbine outer ring corresponding to the position of the *** conclusions are as follows:The tip clearance leakage flow has a great influence on the convective heat transfer coefficient of the turbine outer *** the clearance height and the blowing ratio are kept constant,gradually increasing the main flow Reynolds number will result in an increase in the convective heat transfer coefficient of the turbine outer *** the clearance height and the main flow Reynolds number are kept constant and the blowing ratio is gradually increased,the convective heat transfer coefficient of the turbine outer ring is almost *** heat transfer coefficient of the turbine outer ring surface is little affected by the blowing ratio;The clearance height has great influence on the heat transfer characteristics of the turbine outer *** the typical working condition in this paper,when the tip clearance height ratio is 1.6%,the convective heat transfer coefficient of the outer surface of the turbine is the highest.

关键词： tip leakage flow film cooling liquid crystal temperature measurement heat transfer characteristics

VR helicity density and its application in turbomachinery tip leakage flows

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Chinese Journal of Aeronautics 2022年第11期35卷 1-17页

作者： Yumeng TANG Yangwei LIU School of Energyand Power Engineering Beihang UniversityBeijing 100083China National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics Beihang UniversityBejing 100083China State Key Laboratory of Aerodynamics China Aerodynamics Research and Development CenterMianyang 621000China

Helicity is an important quantity that represents the topological interpretation of vortices;however,helicity is not a Galilean *** this study,VR helicity density(HVR)is derived via taking the dot product of vorticity with the unit real eigen vector of the velocity gradient tensor when the complex eigenvalues *** analytical solution of HVR is derived to resolve it in a local pointwise manner,and the Galilean invariance of HVR is *** leakage flow structures in a direct numerical simulation of a tip leakage flow model and a delayed detached eddy simulation of a low-speed large-scale axial compressor rotor are extracted using helicity,eigen helicity density and HVR *** show that the utilization of HVR permits the identification and accentuation of concentrated *** identified by HVR appear in more connective *** in the case of helicity,the sign of HVR distinguishes between primary and secondary vortices,while eigen helicity density *** normalized HVR is superior to the normalized helicity density in locating the vortex axis,especially for the induced vortex ***,HVR is a strong candidate to replace the helicity density,especially when Galilean invariance is required.

关键词： Compressor flow visualization Helicity tip leakage flow Vortex identification Vortical flow

Blade Lean and tip leakage flows in Highly Loaded Compressor Cascades

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Journal of Thermal Science 2021年第4期30卷 1388-1405页

作者： CAO Zhiyuan SONG Cheng ZHANG Xiang GAO Xi LIU Bo School of Power and Energy Northwestern Polytechnical UniversityXi’an 710072China

Blade lean has been intensively utilized in axial *** this study,three families of highly loaded compressor cascades featuring different aspect ratios(AR)with different levels of blade lean were designed and simulated with and without tip *** influences of blade lean on corner separation and tip leakage flow(TLF)were *** show that blade lean can exert spanwise pressure gradient confined to the fore part,spanwise mass flow rate re-distribution exhibiting differently at fore and rear part of blade,and stage reaction *** has a significant influence on blade *** the increase of AR,corner separation grows significantly and requires a higher lean level to be *** eliminates corner separation of linear cascades but also increases the loss of leaned cascades;blade lean introduces 22%higher tip leakage mass flow,but exhibits 43%(blade M)and 38%(blade E)lower tip leakage *** flow mechanism can be mainly accounted by the reduction of bulk flow velocity,tip leakage velocity and the velocity difference near leading edge(LE).High AR cascade induces re-distribution of TLF along blade chord and reduces leakage loss compared with low AR counterpart.

关键词： axial compressor leaned blade tip leakage flow aspect ratio corner separation